Voltage generation circuit and sound output circuit

Abstract

The voltage generation circuit includes: a voltage input terminal; a voltage output terminal; a first resistive element, a first terminal of which is electrically connected to the voltage input terminal; a second resistance element having a third terminal electrically connected to the second terminal and a fourth terminal electrically connected to a ground potential; a first capacitance element, a first capacitance terminal of which is electrically connected to the voltage input terminal; the fifth terminal of the third resistor element is electrically connected with the second capacitor terminal; a seventh terminal of the fourth resistor element is electrically connected with a sixth terminal of the fourth resistor element; a first inverting input terminal of the first operational amplifier is electrically connected with the sixth terminal, a first non-inverting input terminal of the first operational amplifier is electrically connected with the second terminal, and a first output terminal of the first operational amplifier is electrically connected with the voltage output terminal and the eighth terminal.

Description

Technical Field

[0001] The present disclosure relates to a voltage generating circuit and a sound output circuit. Background Art

[0002] Conventionally, as a voltage generating circuit for generating a predetermined voltage, there is known a preamplifier that performs amplification and level shifting. The preamplifier is a preamplifier that uses an operational amplifier to amplify and output an input signal input from a pair of input terminals, wherein a negative input terminal of the pair of input terminals is connected to an inverting input terminal of the operational amplifier via a negative input resistor, and the inverting input terminal of the operational amplifier is connected to the output via a feedback resistor, and a positive input terminal is connected to a non-inverting input terminal of the operational amplifier via a positive input resistor, and a voltage dividing point obtained by resistor-dividing a positive reference voltage is connected to the non-inverting input terminal of the operational amplifier (see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 11-168330 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] Conventional voltage generating circuits may generate voltage in a state where a fluctuation component superimposed on an input voltage is not sufficiently reduced, and further improvement is required.

[0008] The present disclosure provides a voltage generating circuit and a sound output circuit capable of generating a voltage in a manner that reduces a fluctuation component superimposed on an input voltage.

[0009] Solutions for solving problems

[0010] One embodiment of the present disclosure is a voltage generating circuit, which includes: a voltage input terminal, to which an input voltage is input; a voltage output terminal, which outputs an output voltage; a first resistor element, which has a first terminal and a second terminal, the first terminal being electrically connected to the voltage input terminal; a second resistor element, which has a third terminal and a fourth terminal, the third terminal being electrically connected to the second terminal, and the fourth terminal being electrically connected to a ground potential; a first capacitor element, which has a first capacitor terminal and a second capacitor terminal, the first capacitor terminal being electrically connected to the voltage input terminal; a third resistor element, which has a fifth terminal and a sixth terminal, the fifth terminal being electrically connected to the second capacitor terminal; a fourth resistor element, which has a seventh terminal and an eighth terminal, the seventh terminal being electrically connected to the sixth terminal; and a first operational amplifier, which has a first inverting input terminal, a first non-inverting input terminal, and a first output terminal, the first inverting input terminal being electrically connected to the sixth terminal, the first non-inverting input terminal being electrically connected to the second terminal, and the first output terminal being electrically connected to the voltage output terminal and the eighth terminal.

[0011] One embodiment of the present disclosure is a sound output circuit, which includes the above-mentioned voltage generating circuit and a fourth operational amplifier, wherein the fourth operational amplifier has a first input terminal, a second input terminal and a fourth output terminal, the output voltage output by the voltage generating circuit is input to the first input terminal of the fourth operational amplifier, a sound input signal is input to the second input terminal of the fourth operational amplifier, and a sound output signal based on the sound input signal is output from the fourth output terminal of the fourth operational amplifier.

[0012] Effects of the Invention

[0013] According to the present disclosure, it is possible to generate a voltage in a manner that reduces a fluctuation component superimposed on an input voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a circuit diagram showing an example of the sound output circuit according to the first embodiment.

[0015] Figure 2 : is a circuit diagram showing an example of the voltage generating circuit according to the first embodiment.

[0016] Figure 3 : is a circuit diagram showing an example of a voltage generating circuit according to the second embodiment.

[0017] Figure 4 : is a circuit diagram showing a voltage generating circuit according to a comparative example.

[0018] Figure 5It is a diagram showing input-output characteristics of variable components according to the second embodiment and a comparative example.

[0019] Figure 6 : is a circuit diagram showing an example of a voltage generating circuit according to the third embodiment.

[0020] Figure 7 : is a circuit diagram showing an example of a voltage generating circuit according to the fourth embodiment.

[0021] Figure 8 : is a circuit diagram showing an example of a voltage generating circuit according to the fifth embodiment.

[0022] Fig. 9 : is a circuit diagram showing an example of a voltage generating circuit according to the sixth embodiment.

[0023] Fig.10 1 is a diagram showing an example of the output voltage of the voltage generating circuit in the second embodiment and the output voltage of the voltage generating circuit in this embodiment.

[0024] Fig.11 : is a circuit diagram showing a voltage generating circuit according to a modification of the sixth embodiment.

[0025] Fig.12 : is a circuit diagram showing an example of a voltage generating circuit according to the seventh embodiment.

[0026] Fig.13 1 is a diagram showing an example of the output voltage of the voltage generating circuit in the sixth embodiment and the output voltage of the voltage generating circuit in this embodiment. DETAILED DESCRIPTION

[0027] (Insights that form the basis of this disclosure)

[0028] Conventional voltage generating circuits can operate as bias circuits that output bias voltages. The bias circuit outputs a bias voltage based on an input voltage, but if the input voltage fluctuates, the bias voltage is output in a state that includes the fluctuating component. In order to remove the fluctuating component, a method of absorbing the fluctuating component by adding an element such as a capacitor to the bias circuit can be considered. However, in this case, since the electrostatic capacitance of the capacitor needs to be increased, the capacitor is enlarged, resulting in an enlargement of the device including the bias circuit. Therefore, a technology for reducing the fluctuating component while suppressing the enlargement of the device is required.

[0029] Hereinafter, embodiments of a voltage generating circuit and a sound output circuit according to the present disclosure will be described with reference to the drawings.

[0030] [First embodiment]

[0031] (Structure of sound output circuit)

[0032] Figure 1 1 is a circuit diagram showing an example of a sound output circuit 100 according to the first embodiment. The sound output circuit 100 is a circuit for amplifying a sound signal. The sound output circuit 100 includes a sound input terminal Vi, a sound output terminal Vo, an operational amplifier OP10 and a voltage generating circuit 10 .

[0033] The operational amplifier OP10 includes an inverting input terminal op10-, a non-inverting input terminal op10+, and an output terminal Vop10. The inverting input terminal op10- is electrically connected to the sound input terminal Vi via a capacitor element C11 and a resistor element R13 connected in series. In addition, the inverting input terminal op10- is electrically connected to the output terminal Vop10 via a capacitor element C12 and a resistor element R14 connected in parallel. The non-inverting input terminal op10+ is electrically connected to the voltage output terminal (at the voltage generating circuit 10) of the voltage generating circuit 10. Figure 1 The bias voltage generated by the voltage generating circuit 10 is input to the non-inverting input terminal op10+. The output terminal Vop10 is electrically connected to the sound output terminal Vo via the capacitor element C13. The capacitor element C11, the capacitor element C12, and the capacitor element C13 are, for example, capacitors.

[0034] The audio output circuit 100 is a single power amplifier circuit electrically connected to a power supply voltage and a ground potential, i.e., a ground. The audio output circuit 100 amplifies the amplitude of an audio input signal by two times and outputs the amplified audio signal as an audio output signal. The audio output circuit 100 can be used in a car audio system, for example.

[0035] exist Figure 1 In FIG. 1 , the graph g1 shows the voltage amplitude waveform of the sound input signal at the sound input terminal Vi. In the graph g1, the solid line shows the waveform when the amplitude of the sound input signal is the maximum, and the dotted line shows an example of the waveform when the amplitude of the sound input signal is smaller than the maximum amplitude. Here, the amplitude when the amplitude of the sound input signal is the maximum amplitude is the maximum amplitude at which the operational amplifier OP10 can output the sound without distorting the sound input signal. The relationship between the waveform represented by the solid line and the waveform represented by the dotted line is the same in the graphs g2, g3, and g4.

[0036] Graph g2 is a graph showing the voltage amplitude waveform of the input signal between the capacitor element C11 and the resistor element R13. In the graph g2, in any waveform, a bias voltage is added to the signal from the sound input terminal Vi. The bias voltage is a voltage generated and output by the voltage generating circuit 10, for example, a voltage of half (1 / 2) of the power supply voltage.

[0037] Graph g3 is a graph showing a voltage amplitude waveform of an output signal at output terminal Vop10 of operational amplifier OP10. The waveform shown in graph g3 is a waveform obtained by inverting the phase of the waveform shown in graph g2 and amplifying the amplitude by a predetermined amplification factor. The amplification factor is, for example, 2 times.

[0038] Graph g4 is a graph showing a voltage amplitude waveform of a sound output signal at the sound output terminal Vo. In the sound output signal shown in graph g4, the bias voltage is removed by the action of the capacitive element C13.

[0039] Therefore, when a noise component is superimposed on the bias voltage outputted from the voltage generating circuit as the output voltage, the operational amplifier OP10 amplifies the input signal in a manner that adds the noise component. Therefore, it is preferable to obtain a constant voltage that does not contain a noise component as the bias voltage. Thus, the operational amplifier OP10 can amplify and output the input signal in a manner that does not superimpose a noise component. In this case, a signal with a large amplitude can be ensured by the amplification process of the operational amplifier OP10. The noise component is an AC component other than the DC component of the voltage, and is a variable component of the voltage.

[0040] In addition, the bias voltage may not be a value equal to half the power supply voltage. For example, the bias voltage may be adjusted to a voltage other than a value equal to half the power supply voltage depending on the IC constituting the operational amplifier OP10.

[0041] The voltage generating circuit 10 can have various circuit structures. Below, the circuit structure of the voltage generating circuit 10 is described according to each embodiment. The voltage generating circuit 10 of the first embodiment is a voltage generating circuit 10A. The voltage generating circuit 10 of the second embodiment is a voltage generating circuit 10B. The voltage generating circuit 10 of the third embodiment is a voltage generating circuit 10C. The voltage generating circuit 10 of the fourth embodiment is a voltage generating circuit 10D. The voltage generating circuit 10 of the fifth embodiment is a voltage generating circuit 10E. In addition, the structure of the sound output circuit 100 is the same in each embodiment.

[0042] (Structure of voltage generation circuit)

[0043] Figure 2 : is a circuit diagram showing an example of a voltage generating circuit 10A. The voltage generating circuit 10A includes a voltage input terminal Vin, a voltage output terminal Vout, a resistor element R1, a resistor element R2, a resistor element R6, a resistor element R7, a capacitor element C1, and an operational amplifier OP1.

[0044] An input voltage is input to the voltage input terminal Vin. An output voltage is output from the voltage output terminal Vout. The resistor element R6 has a terminal tr1 and a terminal tr2. Terminal tr1 is electrically connected to the voltage input terminal Vin. Here, "electrical connection" includes a case where two elements are directly connected, and a case where two elements are connected in a manner such that other conductive elements are interposed between them and current can flow from one side to the other side. The resistor element R7 has a terminal tr3 and a terminal tr4. Terminal tr3 is electrically connected to terminal tr2. Terminal tr4 is electrically connected to the ground potential, i.e., the ground. The capacitor element C1 has a capacitor terminal tc1 and a capacitor terminal tc2. Below, the terminals of the capacitor element are sometimes referred to as capacitor terminals. The capacitor terminal tc1 is electrically connected to the voltage input terminal Vin and the terminal tr1. The resistor element R1 has a terminal tr5 and a terminal tr6. Terminal tr5 is electrically connected to the capacitor terminal tc2. Terminal tr5 can also be directly connected to the capacitor terminal tc2. The resistor element R2 has a terminal tr7 and a terminal tr8. Terminal tr7 is electrically connected to terminal tr6.

[0045] The operational amplifier OP1 has an inverting input terminal op1-, a non-inverting input terminal op1+, and an output terminal Vop1. The inverting input terminal op1- is electrically connected to the terminal tr6 and the terminal tr7. The non-inverting input terminal op1+ is electrically connected to the terminal tr2 and the terminal tr3. The output terminal Vop1 is electrically connected to the voltage output terminal Vout and the terminal tr8. The operational amplifier OP1 also has a positive side power supply terminal and a negative side power supply terminal. The positive side power supply terminal is electrically connected to the power supply potential, and the negative side power supply terminal is electrically connected to the ground potential. In other words, the voltage generating circuit 10A is a single power supply circuit. For example, a voltage that is the same as the input voltage input to the voltage input terminal Vin is input to the positive side power supply terminal. The voltage input to the positive side power supply terminal may also be different from the input voltage input to the voltage input terminal Vin.

[0046] The resistance value of the resistor R6 is, for example, 10 kΩ. The resistance value of the resistor R7 is, for example, 10 kΩ. The capacitance value of the capacitor C1 is, for example, 1 μF. The resistance value of the resistor R1 is, for example, 30 kΩ. The resistance value of the resistor R2 is, for example, 30 kΩ. The capacitance value of each element is, for example, the value of electrostatic capacitance.

[0047] The input voltage input from the voltage input terminal Vin is divided by the resistor element R6 and the resistor element R7, and is input to the non-inverting input terminal op1+. The input voltage may contain a DC component as the original input voltage and a fluctuating component as noise. In the present embodiment, the resistance value of the resistor element R6 is equal to the resistance value of the resistor element R7. Therefore, the input voltage is input to the non-inverting input terminal op1+ as a voltage of approximately half the size. At this time, the DC component and the variable component contained in the input voltage are both input to the non-inverting input terminal op1+ in a manner of approximately half the size. The variable component input to the non-inverting input terminal op1+ is output to the output terminal Vop1 in a manner where the amplitude becomes (1+(resistance value of the resistor element R2) / (resistance value of the resistor element R1)) times. At this time, the phase is not reversed in the variable component input to the non-inverting input terminal op1+ and the variable component output to the output terminal Vop1. In the present embodiment, the resistance value of the resistor element R1 is equal to the resistance value of the resistor element R2. Thus, the variable component input to the non-inverting input terminal op1+ is output to the output terminal Vop1 in a manner that the amplitude is doubled and the phase remains unchanged. That is, the variable component having the same amplitude as the amplitude of the variable component contained in the input voltage is output to the output terminal Vop1. In addition, the input voltage input from the voltage input terminal Vin is input to the inverting input terminal op1- via the capacitor C1 and the resistor R1. The capacitor C1 extracts the variable component from the input voltage by blocking the DC component of the input voltage. The variable component input to the resistor R1 is output to the output terminal Vop1 in a manner that the phase is reversed and the amplitude is (the resistance value of the resistor R2) / (the resistance value of the resistor R1) times. In the present embodiment, the resistance value of the resistor R1 is equal to the resistance value of the resistor R2. Thus, the variable component input to the resistor R1 is output to the output terminal Vop1 in a manner that the phase is reversed and the amplitude is 1 times. Thus, the voltage generating circuit 10A can cancel the fluctuation component input to the non-inverting input terminal op1+, and thus can reduce the fluctuation component included in the output voltage output from the voltage output terminal Vout.

[0048] In addition, as for the noise as a variable component, for example, the following noises are considered. The noise may include noise generated by a microcomputer, DSP or other device electrically connected to the voltage input terminal Vin. The noise may include electrical noise generated by a drive system of a vehicle equipped with a voltage generating circuit 10 and a sound output circuit 100. For example, the noise may include noise such as an AC generator, a motor or an ignition noise of the vehicle. In addition, the noise may also include electrical noise originating from outside the vehicle. In addition, the noise may also include noise generated by the sound output circuit 100.

[0049] According to such a voltage generating circuit 10, the variable component that may be contained in the input voltage input to the voltage input terminal Vin is extracted by the capacitor element C1 and applied to the inverting input terminal op1-, and the signal output from the operational amplifier OP1 is fed back. Thus, the voltage generating circuit 10 can eliminate the variable component, and can output a constant voltage even if there is a change in the input voltage. In addition, compared with the case where the variable component is suppressed by a filter, the voltage generating circuit 10 can remove the variable component by a small component. In addition, the voltage generating circuit 10 does not use a diode such as a Zener diode to remove the variable component. Therefore, it is also possible to suppress the generation of noise caused by the elements in the voltage generating circuit 10, which may be caused, for example, when a diode is used. In addition, the ratio of the resistance value of the resistor element R6 to the resistance value of the resistor element R7 is equal to the ratio of the resistance value of the resistor element R1 to the resistance value of the resistor element R2. Thus, the output voltage of the operational amplifier OP1 is not easy to change.

[0050] Furthermore, compared with a case where a voltage generating circuit 10B of a second embodiment described later includes a capacitive element C2 , the voltage generating circuit 10A can remove fluctuation components in a wider frequency band.

[0051] In addition, the sound output circuit 100 having such a voltage generating circuit 10 can use a constant voltage with a suppressed variable component as a bias voltage. Therefore, the sound output circuit 100 can amplify and output the sound input signal without superimposing the variable component. Therefore, the sound output circuit 100 can output a sound output signal with suppressed noise.

[0052] [Second embodiment]

[0053] (Structure of voltage generation circuit)

[0054] Figure 3 1 is a circuit diagram showing an example of a voltage generating circuit 10B according to the second embodiment. The voltage generating circuit 10B is different from the voltage generating circuit 10A in that it includes a capacitor element C2. Regarding the voltage generating circuit 10B, the description of the same structure and operation as the voltage generating circuit 10A according to the first embodiment is omitted or simplified.

[0055] In addition to the structure of the voltage generating circuit 10A, the voltage generating circuit 10B further includes a capacitor element C2. The capacitor element C2 includes a capacitor terminal tc3 and a capacitor terminal tc4. The capacitor terminal tc3 is electrically connected to the terminal tr7. The capacitor terminal tc3 may also be directly connected to the terminal tr7. The capacitor terminal tc4 is electrically connected to the terminal tr8 and the output terminal Vop1 of the operational amplifier OP1. The capacitor terminal tc4 may also be directly connected to the terminal tr8 and the output terminal Vop1. The capacitor element C2 is connected in parallel with the resistor element R2.

[0056] The capacitance value of the capacitive element C2 is, for example, 0.47 pF.

[0057] Capacitor C2 adjusts the phase of the high frequency component passing through capacitor C2. Therefore, capacitor C2 can improve the phase delay in the feedback circuit that feeds back from output terminal Vop1 to inverting input terminal op1-, thereby helping to suppress oscillation of operational amplifier OP10 in the high frequency band.

[0058] (Relationship between input voltage and output voltage)

[0059] Next, the relationship between the input voltage input from the voltage input terminal Vin and the output voltage output from the voltage output terminal Vout will be described.

[0060] In addition, in the following description, the resistance value of each resistor element (R1, R2, ...) is sometimes described using the same reference numeral as the reference numeral annotated to the resistor element. Similarly, the capacitance value of each capacitor element (C1, C2, ...) is sometimes described using the same reference numeral as the reference numeral annotated to the capacitor element. In addition, the value of the input voltage input from the voltage input terminal Vin is sometimes described using the same reference numeral as the voltage input terminal Vin. Similarly, the value of the output voltage output from the voltage output terminal Vout is sometimes described using the same reference numeral as the voltage output terminal Vout.

[0061] like Figure 3 As shown, the capacitor element C1 and the resistor element R1 connected in series form an impedance Z1. In addition, the capacitor element C2 and the resistor element R2 connected in parallel form an impedance Z2. In the following, the impedance values ​​of the impedances (Z1, Z2) are sometimes described using the same reference numerals as those used for the impedances.

[0062] First, the voltage V1 at point p1 is expressed by the following equations (1) and (2). In addition, "·" represents a multiplication symbol. Point p1 is a node connecting terminal tr6, inverting input terminal op1-, and terminal tr7. Voltage V1 represents a voltage input to inverting input terminal op1-.

[0063] V1=Vin-I1·Z1…(1)

[0064] V1=Vout+I2·Z2…(2)

[0065] In addition, I1 is a current flowing from the resistance element R1 to the point p1, and I2 is a current flowing from the point p1 to the resistance element R2 and the capacitance element C2.

[0066] In addition, the voltage V2 at the point p2 is expressed by the following equation: The point p2 is a node connecting the terminal tr2, the terminal tr3, and the non-inverting input terminal op1+. The voltage V2 represents the voltage input to the non-inverting input terminal op1+.

[0067] [Number 1]

[0068]

[0069] Here, the operational amplifier OP1 operates so that the voltage V1 and the voltage V2 are the same voltage. Therefore, the following relational expression holds.

[0070] V1=V2…(4)

[0071] If the current I1 is solved based on equations (1) and (4), the following relationship holds.

[0072] [Number 2]

[0073]

[0074] In addition, according to Kirchhoff's Current Law, the current flowing to the point p1 becomes the following current.

[0075] I1=I2+I3

[0076] Furthermore, I3 is a current flowing from the point p1 to the inverting input terminal op1-.

[0077] The input impedance of the inverting input terminal op1- is very high. Therefore, the current I3 is a current amount that can be almost ignored. Therefore, the following relationship holds.

[0078] I1=I2…(6)

[0079] When the output voltage Vout is solved based on equations (2), (3), (4), (5), and (6), the following equation is obtained.

[0080] [Number 3]

[0081]

[0082] Next, the operation with respect to the DC component and the fluctuation component of the input voltage will be described.

[0083] First, in order to simplify the above-mentioned formula (7), R6=R7 is set, and the formula (7) is transformed into the formula (8).

[0084] [Number 4]

[0085]

[0086] Impedance Z1 and impedance Z2 are expressed using complex numbers.

[0087] The impedance Z1 is the series combined resistance of the capacitance element C1 and the resistance element R1 , so the following relationship holds.

[0088] [Number 5]

[0089]

[0090] Here, if ω=2πf is substituted and transformed, the following relational expression holds: The frequency f is the frequency of the fluctuation component included in the input voltage.

[0091] [Number 6]

[0092]

[0093] Here, if the frequency f at which the real part and the imaginary part of equation (9) are equal is set as the cutoff frequency f low , then the following relationship holds.

[0094] [Number 7]

[0095]

[0096] At a frequency f lower than the cut-off frequency f low When f is low, the impedance Z1 becomes high. When f=0, that is, when the input voltage contains only a DC component, the impedance Z1 becomes infinite Ω. Regarding the DC component contained in the input voltage Vin, if an infinite number is substituted into the impedance Z1 in equation (8), the following relational expression holds.

[0097] [Number 8]

[0098]

[0099] Thus, the output voltage Vout becomes a value of 1 / 2 of the input voltage Vin.

[0100] In addition, the impedance Z2 is the parallel composite resistance of the capacitance element C2 and the resistance element R2, so the following relational expression holds.

[0101] [Number 9]

[0102]

[0103] Then, if ω=2πf is substituted and transformed, the following relational expression holds.

[0104] [Number 10]

[0105]

[0106] If the frequency f where the real part and imaginary part of equation (10) are equal is set as the cutoff frequency f high , then the following relationship holds.

[0107] [Number 11]

[0108]

[0109] At a frequency f lower than the cut-off frequency f high When f is high, the value (admittance) of the inverse of impedance Z2 (1 / Z2) becomes high. That is, when f=infinity, impedance Z2 becomes 0Ω. Regarding the high-frequency component included in the input voltage Vin, if 0 is substituted into impedance Z2 in equation (9), the following relational expression holds.

[0110] [Number 12]

[0111]

[0112] Thus, the output voltage Vout becomes a value of 1 / 2 of the input voltage Vin.

[0113] On the other hand, at frequency f, the cutoff frequency f low With the cut-off frequency f high When Z1=Z2, the value in the bracket of equation (8) is "0", and the output voltage Vout becomes 0. That is, in this case, the fluctuation component of the input voltage Vin is removed and is not output to the output voltage Vout.

[0114] When the frequency f at which Z1=Z2 is obtained, the following relational expression holds true based on equations (9) and (10).

[0115] [Number 13]

[0116]

[0117] If equation (11) is transformed, the following relational equation holds.

[0118] [Number 14]

[0119]

[0120] Here, if R2=R1 and C1>>C2, the first term on the left side can be approximated to "1" and the fourth term can be approximated to "0". Therefore, equation (12) becomes the following equation.

[0121] [Number 15]

[0122]

[0123] If equation (13) is solved with respect to frequency f, the following relational equation holds.

[0124] [Number 16]

[0125]

[0126] In the case of the frequency f shown in the equation (14), the voltage generating circuit 10B has the highest effect of removing the fluctuation component.

[0127] In addition, the above cutoff frequency f low For example, the cut-off frequency f is between 5 Hz and 10 Hz. high For example, the frequency may be 500 kHz or more and 10 MHz or less, or 10 MHz or more. In this case, the voltage generating circuit 10B can appropriately remove the fluctuation component of the input voltage in the frequency range of 20 Hz to 20 kHz and the frequency range of 20 Hz to 100 kHz.

[0128] Figure 4 2 is a circuit diagram showing a voltage generating circuit 10X according to a comparative example. The voltage generating circuit 10X includes a resistor element R8X, a resistor element R9X, a capacitor element C5X, an operational amplifier OPX, a voltage input terminal VinX, and a voltage output terminal VoutX.

[0129] One end of the resistor R8X is electrically connected to the voltage input terminal VinX. One end of the resistor R9X is electrically connected to the other end of the resistor R8X, and the other end of the resistor R9X is electrically connected to the ground potential. One end of the capacitor C5X is electrically connected to the other end of the resistor R8X and one end of the resistor R9X, and the other end of the capacitor C5X is electrically connected to the ground potential.

[0130] The inverting input terminal opX- of the operational amplifier OPX is electrically connected to the output terminal of the operational amplifier OPX. The non-inverting input terminal opX+ of the operational amplifier OPX is electrically connected to the other end of the resistor element R8X, one end of the resistor element R9X, and one end of the capacitor element C5X. The output terminal VopX of the operational amplifier OPX is electrically connected to the inverting input terminal opX- of the operational amplifier OPX and the voltage output terminal VoutX.

[0131] The resistance value of the resistor element R8X is, for example, 10 kΩ. The resistance value of the resistor element R9X is, for example, 10 kΩ. The capacitance value of the capacitor element C5X is, for example, 1 μF.

[0132] Figure 5 : is a diagram showing the input-output characteristics of the variable component as the noise component involved in the second embodiment and the comparative example. Specifically, Figure 5The figure shows the change in the magnitude of the variable component that appears at the voltage output terminal Vout when a sine wave as a variable component is applied to the voltage input terminal and the sine wave is swept in the range of 20 Hz to 20 kHz. 20 Hz to 20 kHz is equivalent to the general audible frequency range. Figure 5 In FIG. 1 , a noise signal SG1 representing a variable component of the present embodiment is shown by a solid line, and a noise signal SGX representing a variable component of the comparative example is shown by a dotted line. Figure 5 In FIG. 1 , the noise signal SG1 and the noise signal SGX are represented by relative values ​​(dB) representing the value of the output relative to the input, that is, relative values ​​representing the value of the variable component included in the output voltage relative to the value of the variable component included in the input voltage.

[0133] If the noise signal SG1 of the present embodiment is compared with the noise signal SGX of the comparative example in the audible frequency range, it can be seen that the noise signal SG1 is smaller than the noise signal SGX in the entire audible frequency range, and the noise is further reduced. For example, around 20 Hz, the present embodiment can further reduce the noise by about 10 dB compared with the comparative example.

[0134] Therefore, it can be understood that, in this embodiment, the noise on the input side is less likely to be transmitted to the output side than in the comparative example. In addition, in this embodiment, it can be understood that there is a frequency (e.g., about 8kHz) that greatly reduces the input noise. This frequency is equivalent to the frequency f derived using the above formula (14). In this embodiment, the variation component between the low frequency determined by the capacitor element C1 and the high frequency that depends on the operating performance of the operational amplifier OP1 can be reduced.

[0135] In addition, the voltage generating circuit 10B can adjust the capacitance value C1 and the resistance value R1. Figure 5 Therefore, in the voltage generating circuit 10B, the intensity and frequency range of the noise canceling function, which is the function of reducing the fluctuation component, can be adjusted.

[0136] In addition, in the first embodiment, the input-output characteristics of the fluctuation component are not particularly shown in the graph, but this is also the case in the first embodiment.

[0137] [First Modification of Second Embodiment]

[0138] In the second embodiment, the resistance value R1 is equal to the resistance value R2 and the resistance value R6 is equal to the resistance value R7, but the present invention is not limited thereto. In the first variant, as long as the resistance value R6: the resistance value R7 = the resistance value R1: the resistance value R2 is satisfied, the resistance value R1 is different from the resistance value R2 and the resistance value R6 is different from the resistance value R7. In this case, the output voltage Vout satisfies the following relationship.

[0139] [Number 17]

[0140]

[0141] By satisfying this relational expression, the voltage generating circuit 10B can arbitrarily change the output voltage output from the voltage output terminal Vout. In this case, the voltage generating circuit 10B can also reduce the variable component as a noise component. In addition, in this modification, as an example, the resistance value of the resistor element R6 is 16.667 kΩ, and the resistance value of the resistor element R7 is 10 kΩ. In addition, as an example, the resistance value of the resistor element R1 is 30 kΩ, and the resistance value of the resistor element R2 is 18 kΩ.

[0142] Here, a case where the output voltage Vout is set to an arbitrary voltage will be considered.

[0143] In the voltage generating circuit 10, the DC component of the output voltage Vout can be set to an arbitrary value other than 1 / 2 of the DC component of the input voltage Vin by changing the ratio of the resistance values ​​of the resistor element R6 and the resistor element R7. low ~f high To adjust the AC component between resistors R1 and R2, it is necessary to adjust the resistor values ​​R1 and R2.

[0144] When the input voltage Vin is only a DC component, the impedance Z1 is infinite Ω. Therefore, if impedance Z1=infinity is substituted into equation (7), the following relationship holds for the resistance values ​​R6 and R7.

[0145] [Number 18]

[0146]

[0147] By using equation (15), if the resistance value R7 and the output voltage Vout are determined, the resistance value R6 can be determined.

[0148] At this time, if the constants of impedance Z1 and impedance Z2 are determined so that the constants in the brackets of equation (7) are equal to "0", the cutoff frequency f low ~f high The AC component between them can be removed and will not be output to the output voltage Vout. That is, it is only necessary to find the relationship between the resistance value R6, the resistance value R7, the impedance Z1 and the impedance Z2 that becomes "0" in the brackets of formula (7). Specifically, it is sufficient to set the relationship to the following formula (16).

[0149] [Number 19]

[0150]

[0151] In addition, since the capacitance value C1 and the capacitance value C2 are small, they can be ignored. Therefore, approximation can be performed by setting the relationship as shown in Formula (17).

[0152] [Number 20]

[0153]

[0154] Thus, in the voltage generating circuit 10B, the generated bias voltage can be adjusted to an arbitrary value by adjusting the resistance value of each resistor element. In addition, in the voltage generating circuit 10B, by setting the resistance value R6: resistance value R7 = resistance value R1: resistance value R2, it is possible to output an arbitrary output voltage within the range in which the operational amplifier OP1 can operate while maintaining the noise elimination capability.

[0155] [Second Modification of Second Embodiment]

[0156] In the second embodiment, the case where the operational amplifier OP1 is a single power supply and the negative power supply terminal is connected to the ground potential in the voltage generating circuit 10B is mainly illustrated, but it is not limited to this. The voltage generating circuit 10B can operate even if it has an operational amplifier OP1 with a dual power supply. As an example, the sum of a DC component 8V and a variable component can be applied to the positive power supply terminal (Vin) of the operational amplifier OP1. In addition, a DC component -8V can be applied to the negative power supply terminal (-V) of the operational amplifier OP1.

[0157] [Third Modification of Second Embodiment]

[0158] In the second embodiment, the case where the operational amplifier OP1 is a single power supply and the negative power supply terminal is connected to the ground potential in the voltage generating circuit 10B is mainly illustrated, but the present invention is not limited thereto. Alternatively, the positive power supply terminal of the operational amplifier OP1 may be connected to the ground potential and the negative power supply terminal may be connected to a predetermined potential. In other words, the voltage generating circuit 10B can operate even if the operational amplifier OP1 has a positive single power supply, and can operate even if the operational amplifier OP1 has a negative single power supply.

[0159] Compared with the first embodiment, the voltage generating circuit 10B of the second embodiment can suppress the oscillation of the operational amplifier OP1 by including the capacitor element C2. The effects other than this are the same as those of the first embodiment. Therefore, the relationship between the input voltage and the output voltage considered above is Figure 5 The comparison result can be said to be the same in the first embodiment.

[0160] [Third Embodiment]

[0161] Figure 6 1 is a circuit diagram showing an example of a voltage generating circuit 10C according to the third embodiment. The voltage generating circuit 10C is different from the voltage generating circuit 10B in that it includes a capacitor element C3. Regarding the voltage generating circuit 10C, the description of the same structure as the voltage generating circuit 10A according to the first embodiment or the voltage generating circuit 10B according to the second embodiment is omitted or simplified.

[0162] In addition to the structure of the voltage generating circuit 10B, the voltage generating circuit 10C also includes a capacitor element C3. The capacitor element C3 has a capacitor terminal tc5 and a capacitor terminal tc6. The capacitor terminal tc5 is electrically connected to the output terminal Vop1 and the voltage output terminal Vout. The capacitor terminal tc5 can also be directly connected to the output terminal Vop1 and the voltage output terminal Vout. The capacitor terminal tc6 is electrically connected to the ground potential. A resistor element R3 can be connected in series to the capacitor terminal tc6. The resistor element R3 is, for example, the equivalent series resistance of the capacitor element C3. The resistance value of the resistor element R3 can be appropriately set based on the characteristics of the capacitor element C3.

[0163] The capacitance value of the capacitance element C3 is, for example, 1 μF. The resistance value of the resistance element R3 is, for example, 1 Ω.

[0164] The capacitor element C3 can pass the variable components of the high frequency band of the signal output from the output terminal Vop1, but does not pass the DC component. Therefore, the capacitor element C3 acts as a noise filter at the output stage of the voltage generating circuit 10C. Therefore, the output voltage output from the voltage output terminal Vout is a voltage after the variable components of the high frequency band are reduced. In this way, the voltage generating circuit 10C can improve the output characteristics of the high frequency band by having the capacitor element C3 in the front stage of the voltage output terminal Vout. The voltage generating circuit 10C can, for example, reduce the variable components in the frequency band above 100kHz. As a result, it is easy to make the sound output circuit 100 equipped with the voltage generating circuit 10C comply with EMC (Electromagnetic Compatibility) which is an international standard.

[0165] [Fourth Embodiment]

[0166] Figure 7 1 is a circuit diagram showing an example of a voltage generating circuit 10D according to the fourth embodiment. Regarding the voltage generating circuit 10C, the description of the same structure as the voltage generating circuit 10A according to the first embodiment, the voltage generating circuit 10B according to the second embodiment, or the voltage generating circuit 10C according to the third embodiment is omitted or simplified.

[0167] The voltage generating circuit 10D includes a voltage follower circuit K1 and an LPF circuit K2 which is an RC type LPF (Low Pass Filter) circuit in addition to the configuration of the voltage generating circuit 10B. The voltage follower circuit K1 includes an operational amplifier OP2. The LPF circuit K2 includes a resistor R4 and a capacitor C4.

[0168] The resistor element R4 has a terminal tr9 and a terminal tr10. The terminal tr9 is electrically connected to the output terminal Vop1. The capacitor element C4 has a capacitor terminal tc7 and a capacitor terminal tc8. The capacitor terminal tc7 is electrically connected to the terminal tr10 of the resistor element R4. The capacitor terminal tc8 is electrically connected to the ground potential.

[0169] The operational amplifier OP2 has an inverting input terminal op2-, a non-inverting input terminal op2+, and an output terminal Vop2. The inverting input terminal op2- is electrically connected to the output terminal Vop2. The non-inverting input terminal op2+ is electrically connected to the terminal tr10 and the capacitor terminal tc7. The output terminal Vop2 is electrically connected to the voltage output terminal Vout.

[0170] The resistance value of the resistor element R4 is, for example, 10 kΩ, and the capacitance value of the capacitor element C4 is, for example, 10 μF.

[0171] The voltage generating circuit 10D of this embodiment has a higher noise elimination capability than the voltage generating circuit 10C of the third embodiment. As an example, the case where the resistance value of the resistor R4 is 10kΩ and the capacitance value of the capacitor C4 is 10μF is described. The variable component of the frequency higher than the cut-off frequency in the output voltage flowing into the LPF circuit K2 passes through the capacitor C4 and flows to the ground. In this embodiment, the cut-off frequency is calculated to be 1.59Hz. Therefore, the DC component and the variable component below 1.59Hz in the output voltage output from the operational amplifier OP1 and input to the LPF circuit K2 are output to the voltage follower circuit K1, and the AC component with a frequency higher than 1.59Hz is not output to the voltage follower circuit K1.

[0172] When a load change occurs, the current flowing through the resistor R4 changes, which may cause noise.

[0173] For example, when the output impedance of the circuit is large, if a load change occurs and the output current changes, a voltage drop may occur and the output voltage may change. On the other hand, even if a load change occurs, the operational amplifier OP2 can maintain the voltage of the output terminal Vop2 constant through feedback. Thus, the operational amplifier OP2 can operate in the same way as when the output impedance is small. For example, even when a load change occurs due to the flow of current to the resistor element R4, the voltage of the output terminal Vop2 can be maintained constant. Therefore, the voltage of the voltage output terminal Vout electrically connected to the output terminal Vop2 is also maintained constant. Therefore, the voltage follower circuit K1 can reduce the output impedance of the voltage generating circuit 10D. In the case where the voltage generating circuit 10D does not have the voltage follower circuit K1, the resistance value of the resistor element R4 is equivalent to the output impedance of the voltage generating circuit 10D. For example, in the case where the voltage follower circuit K1 is not provided, the output impedance of the voltage generating circuit 10D is 10kΩ. On the other hand, in the case Figure 7 When the voltage follower circuit K1 is provided as shown, the output impedance of the voltage generating circuit 10D is reduced to approximately several mΩ to 1Ω.

[0174] Thus, the voltage generating circuit 10D of this embodiment includes the voltage follower circuit K1 and the LPF circuit K2 at the subsequent stage of the operational amplifier OP1, thereby reducing the high-frequency component included in the output voltage of the voltage generating circuit 10D and improving the bias voltage generation performance.

[0175] [Fifth Embodiment]

[0176] Figure 8 1 is a circuit diagram showing an example of a voltage generating circuit 10E according to the fifth embodiment. The voltage generating circuit 10E is different from the voltage generating circuit 10B in that it includes a voltage follower circuit K3. Figure 8 The description of the voltage generating circuit 10D having the same structure as the voltage generating circuit 10A involved in the first embodiment, the voltage generating circuit 10B involved in the second embodiment, the voltage generating circuit 10C involved in the third embodiment, or the voltage generating circuit 10D involved in the fourth embodiment is omitted or simplified.

[0177] The voltage generating circuit 10E includes a voltage follower circuit K3 in addition to the configuration of the voltage generating circuit 10B. The voltage follower circuit K3 includes an operational amplifier OP3.

[0178] The operational amplifier OP3 has an inverting input terminal op3-, a non-inverting input terminal op3+, and an output terminal Vop3. The inverting input terminal op3- is electrically connected to the output terminal Vop3. The non-inverting input terminal op3+ is electrically connected to the terminal tr2 and the terminal tr3. The output terminal Vop3 is electrically connected to the inverting input terminal op3- and the non-inverting input terminal op1+.

[0179] By configuring in this way, the influence of the impedance between the connection point of the resistor element R6 and the resistor element R7 and the operational amplifier OP1 can be reduced. For example, it is assumed that the distance between the connection point of the resistor element R6 and the resistor element R7 and the operational amplifier OP1 is greater than a predetermined distance, or that a predetermined noise source exists near the connection point of the resistor element R6 and the resistor element R7 and the operational amplifier OP1. In this case, if noise enters the path connecting the connection point of the resistor element R6 and the resistor element R7 and the non-inverting input terminal op1+, the voltage input to the non-inverting input terminal op1+ changes. As the predetermined noise source, for example, a DCDC circuit is assumed to be provided near the voltage generating circuit 10E. In addition, even if the noise source is not physically connected to any part of the voltage generating circuit 10E, the noise source and the voltage generating circuit 10E are electrically interfered. Since the noise source is provided near the voltage generating circuit 10E, the voltage generating circuit 10E may be affected by the noise source.

[0180] On the other hand, in the voltage generating circuit 10E, by disposing the voltage follower circuit K3 at the preceding stage of the non-inverting input terminal op1+, the operation of the operational amplifier OP1 can be stabilized, and thus the noise canceling capability can be maintained.

[0181] In addition, it is possible to set a structure in which at least two structures of the structures of the voltage generating circuit 10 of each of the above-mentioned embodiments are combined. For example, the structures of at least two embodiments of the third embodiment, the fourth embodiment, and the fifth embodiment may be combined to form the voltage generating circuit 10. In addition, in the third embodiment, the fourth embodiment, and the fifth embodiment, the voltage generating circuit 10 may not include the capacitor element C2, similarly to the first embodiment.

[0182] In the above-mentioned embodiments, the amplifier circuit using the bias voltage generated by the voltage generating circuit 10 is not limited to the sound output circuit 100, but may be other circuits. For example, such an amplifier circuit can be widely applied to a circuit that performs amplification using a constant voltage, and may also be a motor drive circuit.

[0183] [Sixth Embodiment]

[0184] Fig. 91 is a circuit diagram showing an example of a voltage generating circuit 10F according to the sixth embodiment. The voltage generating circuit 10F is different from the voltage generating circuit 10B in that it includes a diode element D1 and a resistor element R5. Fig. 9 For the voltage generating circuit 10F having the same structure as the voltage generating circuit 10A involved in the first embodiment, the voltage generating circuit 10B involved in the second embodiment, the voltage generating circuit 10C involved in the third embodiment, the voltage generating circuit 10D involved in the fourth embodiment, or the voltage generating circuit 10E involved in the fifth embodiment, the description thereof is omitted or simplified.

[0185] The voltage generating circuit 10F includes a diode element D1 and a resistor element R5 in addition to the configuration of the voltage generating circuit 10B.

[0186] The diode element D1 has a diode terminal td1 and a diode terminal td2. Hereinafter, the terminals of the diode element are sometimes referred to as diode terminals. The diode terminal td1 is electrically connected to the capacitor terminal tc2 and the terminal tr5. The diode element D1 may be a rectifying diode element or a Schottky diode.

[0187] The resistor element R5 has a terminal tr11 and a terminal tr12. The terminal tr11 is electrically connected to the diode terminal td2. The terminal tr12 is electrically connected to the capacitor terminal tc4, the terminal tr8, the output terminal Vop1, and the voltage output terminal Vout. The resistor element R5 limits the current flowing to the diode element D1.

[0188] The voltage generating circuit 10F may not include the resistor element R5. For example, when the current flowing through the diode element D1 is small, that is, when the current flowing through the diode element D1 is smaller than a predetermined current, the resistor element R5 may be omitted.

[0189] Next, the circuit operation of the voltage generating circuit 10F will be described.

[0190] When the power supply is started, i.e., when the input voltage Vin is applied to the voltage generating circuit 10F, the voltage at the point noise1 between the capacitor element C1 and the resistor element R1 becomes the power supply voltage, i.e., the input voltage Vin. The capacitor element C1 does not allow the DC component to pass when it is stable, but allows the AC component to pass when the power supply is started, i.e., when the voltage changes from 0V to 8V. The amount of current passing through the capacitor element C1 changes according to the time from the power supply startup. The voltage at the point noise1 is actually lower than the power supply voltage.

[0191] The operational amplifier OP1 controls the output voltage Vop1 to eliminate the potential difference between the voltage input to the inverting input terminal op1- and the voltage at the point Vhalf input to the non-inverting input terminal op1+. Specifically, since the voltage of the inverting input terminal op1- is higher than 4V, the operational amplifier OP1 outputs a voltage from the output terminal Vop1 that is reduced by the difference between the potential of the inverting input terminal op1- (about 8V) and the potential of the non-inverting input terminal op1+ (4V) relative to 4V. In this example, 4V-4V=0V is output. Therefore, as the output voltage Vout of the voltage generating circuit 10F, 0V equal to the output voltage Vop1 is output. In addition, the output voltage Vop1 is the voltage of the output terminal Vop1.

[0192] When the output voltage Vout is 0V, a potential difference equal to or greater than the forward voltage Vf is generated in the forward direction of the diode element D1. Therefore, the diode element D1 is turned on, and current flows. The forward voltage Vf is, for example, 0.7V.

[0193] The voltage of point noise1 is generated by the charge QC1 of the capacitor element C1, and the charge is not replenished afterwards. Therefore, the charge QC1 flows to the voltage output terminal Vout via the diode element D1, and as a result, the voltage of point noise1 decreases. In addition, the voltage input to the inverting input terminal op1- decreases by the amount of the voltage drop of point noise1, and the voltage of the output terminal Vop1 of the operational amplifier OP1 increases.

[0194] When the potential difference between the voltage at point noise1 and the output voltage Vout becomes less than 0.7V, the diode element D1 is turned off, and the charge QC1 accumulated in the capacitor element C1 stops moving. Therefore, the voltage generating circuit 10F can rapidly increase the output voltage Vout before the output voltage Vout reaches (the voltage at point Vhalf - 0.7V). In addition, by reducing the resistance value of the resistor R5, the charge QC1 can flow more rapidly. Therefore, the voltage generating circuit 10F can rapidly increase the output voltage Vout.

[0195] In addition, as the diode element D1, a Schottky barrier diode with a low forward voltage Vf may be used. In this case, compared with the case of using a normal diode element D1, the voltage generating circuit 10F can rapidly increase the output voltage Vout, that is, can rapidly improve it. The forward voltage Vf of the Schottky barrier diode is, for example, about 0.4V or 0.5V.

[0196] Next, characteristics that the voltage generating circuit 10F should satisfy will be described.

[0197] For example, the resistance value of the resistor R5 as a constant is determined based on at least one of the time required to discharge the charge QC1 accumulated in the capacitor C1 and the upper limit of the operating current of the operational amplifier OP1. For example, the smaller the resistance value of the resistor R5, the earlier the rise time of the output voltage Vout, but the operating current of the operational amplifier OP1 increases. Therefore, the rise time of the output voltage Vout is set in consideration of the maximum operating current of the operational amplifier OP1. For example, when the resistance value of the resistor R5 is small, the current flows early, so the charge QC1 flows early, and discharges early.

[0198] Based on the constants of the voltage generating circuit 10F, the coefficient A is calculated by the following equation (19).

[0199] [Number 21]

[0200]

[0201] As an example, regarding the constants in equation (19), the resistance value of the resistor R1 is 30 (kΩ), the resistance value of the resistor R2 is 30 (kΩ), and the resistance value of the resistor R5 is 400 (Ω). In this case, the coefficient A is 0.00503.

[0202] Use coefficient A to calculate the operating current of operational amplifier OP1. The maximum operating current of operational amplifier OP1 is equal to Fig. 9 The maximum value of the current I10 at the point noise1 shown is expressed by the following equation (20).

[0203] [Number 22]

[0204]

[0205] As an example of the constants of formula (20), the voltage Vc at the point noise1 is 8 V, the voltage Vp at the connection point between the terminal tr2 and the terminal tr3 is 4 V, and the forward voltage Vf of the diode element D1 is 0.7 V. In this case, the current I10 is 18.38 (mA). In addition, the voltage Vp is the voltage at the point Vhalf, which becomes the reference of the desired output voltage Vout.

[0206] A portion of the current I10 flows to the operational amplifier OP1. Therefore, the current I needs to be less than the allowable current of the operational amplifier OP1. When the current I10 is allowed to be the maximum current of the operational amplifier OP1, the time constant is calculated. If the time when the value of the output voltage Vout becomes 63.2% of the set value of the output voltage Vout is set as the time constant τ (s), the time constant τ is calculated by the following formula (21). In addition, the set value is, for example, 4V.

[0207] [Number 23]

[0208]

[0209] As an example, regarding each constant in the formula (21), the capacitance value of the capacitor C1 is 10 (μF). In this case, the time constant τ is 2.18 (ms).

[0210] In the voltage generating circuit 10B of the second embodiment in which the diode element D1 and the resistor element R5 of the present embodiment are not inserted, the time constant τ′ is calculated by the following equation (22).

[0211] τ'=C1·R1…(22)

[0212] As an example, if the constants in the formula (22) are set to the same values ​​as the capacitance value C1 and the resistance value R1 of the present embodiment, the time constant τ′ is 300 (ms).

[0213] Therefore, the voltage generating circuit 10F rises approximately 137 times earlier than the voltage generating circuit 10B.

[0214] In addition, the voltage Vc varies between 0V and the upper limit of the voltage Vc. The maximum value of the upper limit of the voltage Vc is the input voltage Vin. The later the rise time of the output voltage Vout is, the smaller the upper limit of the voltage Vc is. In addition, the forward voltage Vf of the diode element D1 may actually change over time according to the current flowing in the diode element D1. In this example, the forward voltage Vf is assumed to be a constant value to calculate the various equations.

[0215] Next, the forward allowable current of the diode element D1 will be described.

[0216] The forward allowable current of the diode element D1 is the upper limit value allowed as the current flowing in the forward direction of the diode element D1. For example, the diode element D1 is selected by considering at least one of the following situations: the current value flowing in the resistor element R5 is less than the forward allowable current of the diode element D1, the forward voltage Vf is smaller than the potential difference between the input voltage Vin and the output voltage Vout, and the reverse current is small.

[0217] The maximum current I13 flowing through the diode element D1 and the resistor element R5 is calculated by the following equation (23). Then, the calculation result is compared with the forward allowable current of the diode element D1.

[0218] [Number 24]

[0219]

[0220] That is, the current I13 is calculated based on the voltage Vc passing through the capacitor element C1 and the voltage Vp expected to be output as the output voltage Vout. As for the constants of formula (23), as an example, the voltage Vc at the point noise1 is 8V, the output voltage Vout is 4V, the forward voltage Vf of the diode element D1 is 0.7V, the resistance value of the resistor element R1 is 30 (kΩ), the resistance value of the resistor element R2 is 30 (kΩ), the resistance value of the resistor element R5 is 400 (Ω), and the capacitance value of the capacitor element C1 is 10 (μF). In this case, the maximum current I13 is 18.25 (mA). Therefore, as the diode element D1, a diode with a forward allowable current greater than 18.25 (mA) is selected.

[0221] As the diode element D1, a diode whose forward voltage Vf is smaller than the potential difference of (Vc-Vout) is selected. In addition, the smaller the forward voltage Vf of the diode element D1, the earlier the rise time of the output voltage Vout can be made. For example, the forward voltage Vf of a PN junction diode formed by a silicon semiconductor is about 0.7V. In contrast, the forward voltage Vf of a Schottky barrier diode is about 0.5V, so compared with a PN junction diode formed by a silicon semiconductor, the forward voltage Vf can be reduced, and the rise time of the output voltage Vout can be made earlier. In addition, as the diode element D1, a PN junction diode or other diodes using a germanium semiconductor instead of a silicon semiconductor can also be used. Such a forward voltage Vf can be considered in the selection of the diode element D1.

[0222] In the diode element D1, there is a phenomenon that current flows in the reverse direction. This current is called reverse current. When the value of the reverse current is large, the noise removal performance of the diode element D1 and the resistor element R5 may deteriorate. For example, the reverse current of a PN junction diode formed by a silicon semiconductor is about 140nA, and the noise removal performance is hardly deteriorated. The noise removal performance is, for example, a PSRR (Power Supply Rejection Ratio) characteristic. On the other hand, the reverse current of a Schottky barrier diode or the like is about 50uA, and sometimes the noise removal performance deteriorates. Such a reverse current can be considered in the selection of the diode element D1.

[0223] Fig.10 is a diagram showing an example of the output voltage Vout of the voltage generating circuit 10B in the second embodiment and the output voltage Vout of the voltage generating circuit 10F in this embodiment. Fig.10 10B and the voltage at the point noise1 in the voltage generating circuit 10F are also shown. Fig.10In the figure, the voltage at point noise is simply represented as "noise", and the voltage at point noise1 is simply represented as "noise1".

[0224] In the voltage generating circuit, if the capacitance value of the capacitor C1 and the value of the resistor R1 are increased, the noise removal capability is improved, but the time taken for the output voltage Vout to rise tends to be longer. The resistance value of the resistor R1 is equal to the resistance value of the resistor R2.

[0225] For example, if the constant of the capacitor C1 is increased, the noise removal capability in the audio band is improved, but the time taken for the output voltage Vout to rise is increased. Therefore, the time taken to start the audio output circuit 100 is also increased. In contrast, the voltage generating circuit 10F of this embodiment can shorten the time taken for the output voltage Vout to rise.

[0226] When referring to Fig.10 It can be seen that the voltage at point noise1 of the voltage generating circuit 10F rises sharply from 0V to near the input voltage Vin, drops sharply from near the input voltage Vin to near (4+0.7V), and then smoothly converges to near 4V. The period of smooth convergence is the same behavior as when the diode element D1 and the resistor element R5 are not present. In addition, it can be seen that the output voltage Vout of the voltage generating circuit 10F rises sharply from 0V and converges to near 4V corresponding to the voltage at point noise1. The voltage at point noise of the voltage generating circuit 10B and the output voltage Vout are also the same. However, the rise time of the output voltage Vout of the voltage generating circuit 10F, that is, the time constant τ, is 0.022 seconds, and the rise time of the output voltage Vout of the voltage generating circuit 10B, that is, the time constant τ, is 0.907 seconds. In the voltage generating circuit 10F here, as an example, the resistance value of the resistor element R5 is 200Ω. In this case as well, the voltage generating circuit 10F can significantly shorten the rise time compared to the voltage generating circuit 10B.

[0227] (Variation 1 of the Sixth Embodiment)

[0228] The voltage generating circuit 10F may also include a transistor instead of the diode element D1. The transistor is a bipolar transistor having a base terminal, a collector terminal, and an emitter terminal. The base terminal and the collector terminal are electrically connected to the capacitor terminal tc2 and the terminal tr5. The emitter terminal of the transistor is electrically connected to the terminal tr11. Even if such a voltage generating circuit 10F is a structure including a transistor instead of the diode element D1, the same effect as the case where the voltage generating circuit 10F includes the diode element D1 can be obtained.

[0229] (Variation 2 of the Sixth Embodiment)

[0230] Fig.11 1 is a circuit diagram showing an example of a voltage generating circuit 10F1 as a modified example of the voltage generating circuit 10F. The voltage generating circuit 10F1 has the following differences compared to the voltage generating circuit 10F. Specifically, the operational amplifier OP1 is not an operational amplifier of a positive single power supply, but an operational amplifier of a negative single power supply. In addition, the direction of the diode element D1 of the voltage generating circuit 10F1 is opposite to the direction of the diode element D1 of the voltage generating circuit 10F. In other words, the forward direction of the diode element D1 is not the direction from the diode element D1 toward the resistor element R5, but the direction from the resistor element R5 toward the diode element D1. Even with such a structure of the voltage generating circuit 10F1, the same effect as the voltage generating circuit 10F can be obtained.

[0231] Furthermore, Modification 1 and Modification 2 of the present embodiment may be combined.

[0232] In addition, in this embodiment, the voltage generating circuit 10F has a structure obtained by adding a diode element D1 and a resistor element R5 to the voltage generating circuit 10B, but the present invention is not limited to this. For example, the voltage generating circuit 10F may have a structure obtained by adding a diode element D1 and a resistor element R5 to the voltage generating circuit 10A of the first embodiment, the voltage generating circuit 10C of the third embodiment, the voltage generating circuit 10D of the fourth embodiment, or the voltage generating circuit 10E of the fifth embodiment. Even with such a structure, the same effect as that of the voltage generating circuit 10F can be obtained.

[0233] (Seventh Embodiment)

[0234] Fig.12 1 is a circuit diagram showing an example of a voltage generating circuit 10G according to the seventh embodiment. The voltage generating circuit 10G is different from the voltage generating circuit 10A in that it includes an additional circuit 50. Fig.12 Regarding the voltage generating circuit 10G, the description of the same structure as the voltage generating circuit 10A involved in the first embodiment, the voltage generating circuit 10B involved in the second embodiment, the voltage generating circuit 10C involved in the third embodiment, the voltage generating circuit 10D involved in the fourth embodiment, and the voltage generating circuit 10E involved in the fifth embodiment is omitted or simplified.

[0235] The voltage generating circuit 10G has the structure of the voltage generating circuit 10A and further includes an additional circuit 50. The additional circuit 50 includes a transistor Q1, a capacitor C5, a resistor R11, and a resistor R12. The capacitor C5 has a capacitor terminal tc9 and a capacitor terminal tc10. The resistor R11 has a terminal tr13 and a terminal tr14. The resistor R12 has a terminal tr15 and a terminal tr16.

[0236] The transistor Q1 is a bipolar transistor having a base terminal q1b, a collector terminal q1c, and an emitter terminal q1e. The base terminal q1b is electrically connected to the terminal tr14 and the capacitor terminal tc10. The collector terminal q1c is electrically connected to the capacitor terminal tc2, the terminal tr5, and the capacitor terminal tc9. The emitter terminal q1e is electrically connected to the terminal tr15.

[0237] In the resistor element R11, the terminal tr13 is electrically connected to the terminal tr2, the terminal tr3, and the non-inverting input terminal op1+. In the resistor element R12, the terminal tr16 is electrically connected to the terminal tr8, the output terminal Vop1, and the voltage output terminal Vout.

[0238] The capacitor element C5 is used to stop the operational amplifier OP1 from oscillating. The capacitance value of the capacitor element C5 can be any value in the range of 1 pF to 100 pF, but is preferably the minimum capacitance value that stops the operational amplifier OP1 from oscillating. In addition, the voltage generating circuit 10G may not include the capacitor element C5. The resistor element R11 limits the base current of the transistor Q1. In addition, the voltage generating circuit 10G may not include the resistor element R11.

[0239] In addition, the combination of the resistance values ​​of the resistor element R6, the resistor element R7, the resistor element R11, and the resistor element R12 is selected so that the output voltage Vout of the voltage generating circuit 10G in a stable state becomes a predetermined value. The output voltage Vout is, for example, 4 V. For example, the resistance value of the resistor element R6 is set to 10 kΩ, the resistance value of the resistor element R7 is set to 10 kΩ, the resistance value of the resistor element R11 is set to 0Ω, and the resistance value of the resistor element R6 is set to 20Ω. In addition, the resistance value of each resistor element can also be determined according to the amplification factor of the transistor Q1.

[0240] Next, the circuit operation of the voltage generating circuit 10G will be described.

[0241] When the power supply is started, that is, when the input voltage Vin is applied to the voltage generating circuit 10G, the voltage at the point noise2 between the capacitor element C1 and the resistor element R1 becomes the power supply voltage, that is, the input voltage Vin. The capacitor element C1 does not allow the DC component to pass when it is stable, but allows the AC component to pass when the power supply is started, that is, when it changes from 0 V to 8 V. The amount of current passing through the capacitor element C1 changes according to the change time, and the voltage at the point noise2 is actually lower than the power supply voltage.

[0242] The operational amplifier OP1 controls the voltage of the output voltage Vop1 so as to eliminate the potential difference between the voltage input to the inverting input terminal op1- and the voltage of the point Vhalf2 input to the non-inverting input terminal op1+. Therefore, the output voltage Vout of the voltage generating circuit 10G, which is equal to the voltage of the output voltage Vop1, outputs 0V. Specifically, due to the current flowing from the point Vhalf2 to the transistor Q1, the voltage of the point Vhalf2 becomes lower than the voltage obtained by dividing the input voltage Vin by the resistor element R3 and the resistor element R4. Therefore, the voltage of the point Vhalf2 becomes about 2V relative to 4V, which is the set value of the output voltage Vout, and a voltage lower than 0V is output for the output voltage Vout. However, since the negative side of the power supply terminal of the operational amplifier OP1 is electrically connected to 0V, the actual output voltage Vout is 0V.

[0243] When the output voltage Vout is 0 V, a current is supplied from the point Vhalf2 to the transistor Q1 connected to the point noise2. Therefore, a current obtained by multiplying the base current by the current amplification factor hfe flows from the point noise2 to the voltage output terminal Vout via the resistor element R12.

[0244] The voltage of point noise2 is generated by the charge QC1 of the capacitor C1, and the charge is not replenished afterwards. Therefore, the charge QC1 flows to the voltage output terminal Vout via the transistor Q1, and as a result, the voltage of point noise2 decreases. In addition, the voltage input to the inverting input terminal op1- of the operational amplifier OP1 decreases by the amount of the voltage drop of point noise2, and the voltage of the output terminal Vop1 increases.

[0245] When the voltage at point noise2 becomes 4V, which is the set value of the output voltage Vout, the voltages of the inverting input terminal op1- and the non-inverting input terminal op1+ are reversed, and the voltage of the voltage output terminal Vout is output as a positive voltage. In other words, the voltage at point noise2 decreases, and the voltage at point noise2 and the output voltage Vout are divided by the resistor element R1 and the resistor element R2 to become a voltage near 2V. Moreover, at the moment when the voltage at point noise2 is lower than 4V, the voltage at the inverting input terminal op1- becomes smaller than 2V, which is the voltage at point Vhalf2. As a result, the voltage at the voltage output terminal Vout becomes a positive voltage.

[0246] When the voltage at the voltage output terminal Vout increases, the emitter current of the transistor Q1 decreases, thereby reducing the base current, and the voltage at the point Vhalf2 increases, and the voltage at the voltage output terminal Vout further increases.

[0247] When the voltage at point noise2 becomes the same as the output voltage Vout, the emitter current of transistor Q1 no longer flows. Therefore, the charge QC1 of capacitor C1 no longer flows to the voltage output terminal Vout via transistor Q1. Therefore, the voltage at point noise2 no longer decreases, and at the same time, the voltage at point Vhalf2 becomes 4V, which is the voltage obtained by dividing the input voltage Vin by resistor R3 and resistor R4, and the output voltage of the voltage output terminal Vout becomes 4V.

[0248] Fig.13 1 is a diagram showing an example of the output voltage Vout of the voltage generating circuit 10F in the sixth embodiment and the output voltage Vout of the voltage generating circuit 10G in the present embodiment.

[0249] In the voltage generating circuit, if the capacitance value of the capacitance element C1, the resistance value of the resistance element R1, and the resistance value of the resistance element R2 are increased, the noise removal capability is improved, but the rise time of the output voltage Vout tends to be prolonged.

[0250] Both the voltage generating circuit 10F and the voltage generating circuit 10G can quickly shorten the rise time of the output voltage Vout. In addition, the voltage generating circuit 10G can improve the noise removal performance at a low frequency of less than 1 kHz. Fig.13As shown, the rise time of the output voltage Vout in the voltage generating circuit 10G is 0.001 (ms), and the rise time of the output voltage Vout in the voltage generating circuit 10F is 0.023 (ms). That is, the voltage generating circuit 10G can shorten the rise time of the output voltage Vout more quickly than the voltage generating circuit 10F. On the other hand, according to the voltage generating circuit 10F, when the diode element D1 is used instead of the transistor, the voltage generating circuit 10F does not produce the manufacturing deviation of the current amplification factor hfe of the transistor. Therefore, the voltage generating circuit 10F can shorten the rise time of the output voltage Vout without relying on the individual diode element D1. In addition, the voltage generating circuit 10F can improve the noise removal performance at low frequencies less than 1kHz and medium and high frequencies above 1kHz.

[0251] In addition, in this embodiment, the voltage generating circuit 10G is exemplified as having a structure obtained by adding the additional circuit 50 to the voltage generating circuit 10A, but the present invention is not limited to this. For example, the voltage generating circuit 10F may also have a structure obtained by adding the additional circuit 50 to the voltage generating circuit 10B of the second embodiment, the voltage generating circuit 10C of the third embodiment, the voltage generating circuit 10D of the fourth embodiment, or the voltage generating circuit 10E of the fifth embodiment. Even with such a structure, the same effect as the voltage generating circuit 10F can be obtained. However, the voltage generating circuit 10G is not suitable for the case where the operational amplifier OP1 is set as a negative single power supply.

[0252] [Note]

[0253] According to the description of the above embodiments, the following technology is disclosed.

[0254] (Technology 1)

[0255] A voltage generating circuit comprising:

[0256] a voltage input terminal to which an input voltage is input;

[0257] a voltage output terminal, which outputs an output voltage;

[0258] a first resistance element having a first terminal and a second terminal, the first terminal being electrically connected to the voltage input terminal;

[0259] a second resistance element having a third terminal and a fourth terminal, the third terminal being electrically connected to the second terminal, and the fourth terminal being electrically connected to a ground potential;

[0260] a first capacitor element having a first capacitor terminal and a second capacitor terminal, wherein the first capacitor terminal is electrically connected to the voltage input terminal;

[0261] a third resistor element having a fifth terminal and a sixth terminal, wherein the fifth terminal is electrically connected to the second capacitor terminal;

[0262] a fourth resistance element having a seventh terminal and an eighth terminal, the seventh terminal being electrically connected to the sixth terminal; and

[0263] A first operational amplifier has a first inverting input terminal, a first non-inverting input terminal and a first output terminal, wherein the first inverting input terminal is electrically connected to the sixth terminal, the first non-inverting input terminal is electrically connected to the second terminal, and the first output terminal is electrically connected to the voltage output terminal and the eighth terminal.

[0264] The voltage generating circuit is, for example, the voltage generating circuit 10. The voltage input terminal is, for example, the voltage input terminal Vin. The voltage output terminal is, for example, the voltage output terminal Vout. The first terminal is, for example, the terminal tr1. The second terminal is, for example, the terminal tr2. The first resistor is, for example, the resistor R6. The third terminal is, for example, the terminal tr3. The fourth terminal is, for example, the terminal tr4. The second resistor is, for example, the resistor R7. The first capacitor terminal is, for example, the capacitor terminal tc1. The second capacitor terminal is, for example, the capacitor terminal tc2. The first capacitor is, for example, the capacitor C1. The fifth terminal is, for example, the terminal tr5. The sixth terminal is, for example, the terminal tr6. The third resistor is, for example, the resistor R1. The seventh terminal is, for example, the terminal tr7. The eighth terminal is, for example, the terminal tr8. The fourth resistor is, for example, the resistor R2. The first output terminal is, for example, the output terminal Vop1. The first operational amplifier is, for example, the operational amplifier OP1.

[0265] According to this structure, the voltage generating circuit extracts the power supply variation component of the input voltage input from the voltage input terminal through the first capacitor element and applies it to the inverting input terminal of the first operational amplifier, and feeds back the signal output from the first operational amplifier OP. Thus, the voltage generating circuit can eliminate the variation component of the point obtained by voltage division using the first resistor element and the second resistor element. In addition, the voltage generating circuit does not need to be provided with a large capacitor element in order to remove noise. Therefore, the voltage generating circuit can suppress the enlargement of the device including the voltage generating circuit, and can suppress the variation component of the input voltage from being output to the output voltage. Therefore, it is possible to eliminate noise to improve the voltage generating circuit that generates the midpoint bias voltage.

[0266] (Technique 2)

[0267] The voltage generating circuit according to technique 1, wherein:

[0268] The ratio of the first resistance value of the first resistor element to the second resistance value of the second resistor element is equal to the ratio of the third resistance value of the third resistor element to the fourth resistance value of the fourth resistor element.

[0269] According to this configuration, the voltage generating circuit can generate an output voltage outputted from the voltage generating circuit in a manner that maintains the ratio of the voltages obtained by dividing the first resistor element and the second resistor element and maintains the noise canceling capability. In addition, the voltage generating circuit can adjust the bias voltage according to the above voltage ratio.

[0270] (Technique 3)

[0271] The voltage generating circuit according to technique 2, wherein:

[0272] The first resistance value is equal to the second resistance value,

[0273] The third resistance value is equal to the fourth resistance value.

[0274] According to this configuration, the voltage generating circuit obtains a voltage that is half of the input voltage to the voltage generating circuit by dividing the voltage using the first resistor and the second resistor, thereby being able to generate an output voltage from the voltage generating circuit while maintaining noise canceling capability.

[0275] (Technique 4)

[0276] The voltage generating circuit according to technique 2, wherein:

[0277] The first resistance value is different from the second resistance value,

[0278] The third resistance value is different from the fourth resistance value.

[0279] According to this configuration, the voltage generating circuit divides the voltage using the first resistor element and the second resistor element to obtain a voltage that is offset by a specified value relative to half of the input voltage input to the voltage generating circuit, thereby being able to generate an output voltage output from the voltage generating circuit in a manner that maintains noise elimination capability.

[0280] (Technique 5)

[0281] The voltage generating circuit according to any one of Techniques 1 to 4, wherein:

[0282] The third resistance value is greater than the first resistance value,

[0283] The fourth resistance value is greater than the second resistance value.

[0284] (Technique 6)

[0285] The voltage generating circuit according to any one of Techniques 1 to 5, wherein:

[0286] A second capacitor element is further provided. The second capacitor element has a third capacitor terminal and a fourth capacitor terminal. The third capacitor terminal is electrically connected to the seventh terminal, and the fourth capacitor terminal is electrically connected to the first output terminal.

[0287] The third capacitor terminal is, for example, a capacitor terminal tc3. The fourth capacitor terminal is, for example, a capacitor terminal tc4. The second capacitor element is, for example, a capacitor element C2.

[0288] According to this configuration, the voltage generating circuit can suppress the first operational amplifier from oscillating in the high frequency band, and can stably maintain the noise canceling capability.

[0289] (Technique 7)

[0290] The voltage generating circuit according to technique 6, wherein:

[0291] A first capacitance value, which is a capacitance value of the first capacitance element, is larger than a second capacitance value, which is a capacitance value of the second capacitance element.

[0292] (Technology 8)

[0293] The voltage generating circuit according to any one of Techniques 1 to 7, wherein:

[0294] A third capacitor element is further provided. The third capacitor element has a fifth capacitor terminal and a sixth capacitor terminal. The fifth capacitor terminal is electrically connected to the first output terminal and the voltage output terminal of the first operational amplifier. The sixth capacitor terminal is electrically connected to a ground potential.

[0295] The fifth capacitor terminal is, for example, the capacitor terminal tc5. The fifth capacitor terminal is, for example, the capacitor terminal tc5. The third capacitor element is, for example, the capacitor element C3.

[0296] According to this structure, the third capacitor element can pass the AC component of the high frequency band of the signal output from the first output terminal of the first operational amplifier, and does not pass the DC component. Therefore, the voltage generating circuit can reduce the AC component of the high frequency band, and thus can reduce the noise component superimposed in the high frequency band of the output voltage.

[0297] (Technique 9)

[0298] The voltage generating circuit according to any one of Techniques 1 to 7, further comprising:

[0299] a fifth resistance element having a ninth terminal and a tenth terminal, wherein the ninth terminal is connected to the first output terminal of the first operational amplifier;

[0300] a fourth capacitor element having a seventh capacitor terminal and an eighth capacitor terminal, the seventh capacitor terminal being connected to the tenth terminal, and the eighth capacitor terminal being electrically connected to a ground potential; and

[0301] A second operational amplifier has a second inverting input terminal, a second non-inverting input terminal and a second output terminal, wherein the second inverting input terminal is electrically connected to the second output terminal, the second non-inverting input terminal is electrically connected to the tenth terminal, and the second output terminal is electrically connected to the voltage output terminal.

[0302] The ninth terminal is, for example, terminal tr9. The tenth terminal is, for example, terminal tr10. The fifth resistor is, for example, resistor R4. The seventh capacitor is, for example, capacitor terminal tc7. The eighth capacitor is, for example, capacitor terminal tc8. The fourth capacitor is, for example, capacitor C4. The second output terminal is, for example, output terminal Vop2. The second operational amplifier is, for example, operational amplifier OP2.

[0303] According to this structure, the second operational amplifier of the voltage generating circuit operates as a voltage follower circuit, and the fifth resistor element and the fourth capacitor element operate as an RC type LPF circuit. Therefore, the voltage generating circuit can further reduce the high frequency band component included in the output voltage. In addition, the voltage generating circuit can reduce the output impedance, so it can output a constant output voltage without depending on the load of the device connected to the voltage generating circuit.

[0304] (Technology 10)

[0305] The voltage generating circuit according to any one of Techniques 1 to 7, wherein:

[0306] It also includes a third operational amplifier, which has a third inverting input terminal, a third non-inverting input terminal and a third output terminal, the third inverting input terminal is electrically connected to the third output terminal, the third non-inverting input terminal is electrically connected to the second terminal, and the third output terminal is electrically connected to the first non-inverting input terminal of the first operational amplifier.

[0307] The third output terminal is, for example, the output terminal Vop3. The third operational amplifier is, for example, the operational amplifier OP3.

[0308] According to this structure, the third operational amplifier of the voltage generating circuit disposed in the front stage of the first operational amplifier operates as a voltage follower circuit. Therefore, the voltage generating circuit can maintain a constant voltage input to the non-inverting input terminal of the first operational amplifier. Therefore, the voltage generating circuit can stabilize the operation of the operational amplifier OP1 and can generate a bias voltage while maintaining the noise elimination capability.

[0309] (Technology 11)

[0310] The voltage generating circuit according to any one of Techniques 1 to 10, wherein:

[0311] A diode element is further provided. The diode element has a first diode terminal and a second diode terminal. The first diode terminal is electrically connected to the second capacitor terminal, and the second diode terminal is electrically connected to the first output terminal.

[0312] The first diode terminal is, for example, a diode terminal td1 , and the second diode terminal is, for example, a diode terminal td2 .

[0313] According to this configuration, the voltage generating circuit can shorten the rise time of the output voltage while maintaining the noise removal capability in the entire audio frequency band. The entire audio frequency band here is, for example, 20 Hz to 20 kHz.

[0314] (Technology 12)

[0315] The voltage generating circuit according to technique 11, wherein:

[0316] A sixth resistor element is further provided. The sixth resistor element has an eleventh terminal and a twelfth terminal. The eleventh terminal is electrically connected to the second diode terminal, and the twelfth terminal is electrically connected to the first output terminal.

[0317] The eleventh terminal is, for example, the terminal tr11. The twelfth terminal is, for example, the terminal tr12. The sixth resistance element is, for example, the resistance element R5.

[0318] According to this configuration, the voltage generating circuit can suppress an excessive current from flowing through the diode element.

[0319] (Technology 13)

[0320] The voltage generating circuit according to any one of techniques 1 to 10, further comprising:

[0321] a transistor having a base terminal, a collector terminal, and an emitter terminal, the base terminal being electrically connected to the second terminal, the collector terminal being electrically connected to the second capacitor terminal; and

[0322] The seventh resistance element has a thirteenth terminal and a fourteenth terminal, the thirteenth terminal is electrically connected to the emitter terminal, and the fourteenth terminal is electrically connected to the first output terminal.

[0323] The base terminal is, for example, the base terminal q1b. The collector terminal is, for example, the collector terminal q1c. The emitter terminal is, for example, the emitter terminal q1e. The transistor is, for example, the transistor Q1. The thirteenth terminal is, for example, the terminal tr15. The fourteenth terminal is, for example, the terminal tr16. The seventh resistance element is, for example, the resistance element R12.

[0324] According to this configuration, the voltage generating circuit can significantly shorten the rise time of the output voltage while maintaining the noise removal performance at the low frequency of the sound band. The low frequency of the sound band here is, for example, less than 1 kHz.

[0325] (Technology 14)

[0326] The voltage generating circuit according to technique 13 further comprises:

[0327] A fifth capacitor element, the fifth capacitor element having a ninth capacitor terminal and a tenth capacitor terminal, the ninth capacitor terminal being electrically connected to the collector terminal and the second capacitor terminal, and the tenth capacitor terminal being electrically connected to the base terminal and the second terminal.

[0328] The ninth capacitor terminal is, for example, the capacitor terminal tc9. The tenth capacitor terminal is, for example, the capacitor terminal tc10. The fifth capacitor element is, for example, the capacitor element C5.

[0329] According to this configuration, even when the voltage generating circuit includes a transistor, it is possible to suppress the first operational amplifier from oscillating in a high frequency band, and to stably maintain the noise removal performance.

[0330] (Technology 15)

[0331] The voltage generating circuit according to technique 13, wherein:

[0332] An eighth resistor element is further provided. The eighth resistor element has a fifteenth terminal and a sixteenth terminal. The fifteenth terminal is electrically connected to the second terminal, and the sixteenth terminal is electrically connected to the base terminal and the tenth capacitor terminal.

[0333] The fifteenth terminal is, for example, the terminal tr13. The sixteenth terminal is, for example, the terminal tr14. The eighth resistance element is, for example, the resistance element R11.

[0334] According to this configuration, the voltage generating circuit can suppress an excessive base current from flowing into the transistor.

[0335] (Technology 16)

[0336] A sound output circuit, comprising:

[0337] The voltage generating circuit according to any one of Technique 1 to Technique 15; and

[0338] The fourth operational amplifier,

[0339] The fourth operational amplifier has a first input terminal, a second input terminal and a fourth output terminal.

[0340] inputting the output voltage output by the voltage generating circuit to the first input terminal of the fourth operational amplifier,

[0341] inputting a sound input signal to the second input terminal of the fourth operational amplifier,

[0342] A sound output signal based on the sound input signal is output from the fourth output terminal of the fourth operational amplifier.

[0343] The fourth operational amplifier is, for example, an operational amplifier OP10. The first input terminal is, for example, an inverting input terminal of the fourth operational amplifier. The second input terminal is, for example, a non-inverting input terminal of the fourth operational amplifier. The fourth output terminal is an output terminal Vop10. The sound output circuit is, for example, a sound output circuit 100.

[0344] According to this structure, the sound output circuit can input the output voltage generated by the voltage generating circuit to the fourth operational amplifier and use it as a bias voltage. Therefore, even if the sound input signal is amplified, the sound output circuit can converge the voltage of the signal within the range that the fourth operational amplifier can handle, and can appropriately implement the amplification processing of the sound signal.

[0345] In the above, various embodiments are described with reference to the accompanying drawings, but it is self-evident that the present invention is not limited to this example. It is obvious to those skilled in the art that various variations or modifications can be conceived within the scope described in the claims, and these variations or modifications certainly also belong to the technical scope of the present invention. In addition, the constituent elements in the above embodiments can be arbitrarily combined within the scope of the gist of the invention.

[0346] In addition, the present disclosure is based on Japanese patent application (Japanese Patent Application No. 2022-158437) filed on September 30, 2022, and the contents thereof are incorporated herein by reference.

[0347] Industrial Applicability

[0348] The present disclosure is useful for a voltage generation circuit, a sound output circuit, and the like that can generate a voltage in a manner that reduces a fluctuation component superimposed on an input voltage.

[0349] Description of Reference Numerals

[0350] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10F1, 10G: voltage generation circuit; 100: sound output circuit; C1, C2, C3, C4: capacitor elements; OP1, OP2, OP3, OP10: operational amplifier; R1, R2, R3, R4, R5, R6, R7, R11, R12: resistor elements; tc1, tc2, tc3, tc4, tc5, tc6, tc7, tc8, tc9, tc10: capacitor terminals; tr1, tr2, tr3, tr4, tr5, tr6, tr7, tr8, tr9, tr10, tr11, tr12, tr13, tr14, tr15, tr16: terminals; Vin: voltage input terminal; Vout: voltage output terminal; Vop1, Vop2, Vop3, Vop10: output terminals.

Claims

1. A voltage generating circuit, comprising: a voltage input terminal to which an input voltage is input; a voltage output terminal, which outputs an output voltage; a first resistance element having a first terminal and a second terminal, the first terminal being electrically connected to the voltage input terminal; a second resistance element having a third terminal and a fourth terminal, the third terminal being electrically connected to the second terminal, and the fourth terminal being electrically connected to a ground potential; a first capacitor element having a first capacitor terminal and a second capacitor terminal, wherein the first capacitor terminal is electrically connected to the voltage input terminal; a third resistor element having a fifth terminal and a sixth terminal, wherein the fifth terminal is electrically connected to the second capacitor terminal; a fourth resistance element having a seventh terminal and an eighth terminal, wherein the seventh terminal is electrically connected to the sixth terminal; as well as A first operational amplifier has a first inverting input terminal, a first non-inverting input terminal and a first output terminal, wherein the first inverting input terminal is electrically connected to the sixth terminal, the first non-inverting input terminal is electrically connected to the second terminal, and the first output terminal is electrically connected to the voltage output terminal and the eighth terminal.

2. The voltage generating circuit according to claim 1, wherein: The ratio of the first resistance value of the first resistor element to the second resistance value of the second resistor element is equal to the ratio of the third resistance value of the third resistor element to the fourth resistance value of the fourth resistor element.

3. The voltage generating circuit according to claim 2, wherein: The first resistance value is equal to the second resistance value, The third resistance value is equal to the fourth resistance value.

4. The voltage generating circuit according to claim 2, wherein: The first resistance value is different from the second resistance value, The third resistance value is different from the fourth resistance value.

5. The voltage generating circuit according to claim 2, wherein: The third resistance value is greater than the first resistance value, The fourth resistance value is greater than the second resistance value.

6. The voltage generating circuit according to claim 1, wherein: A second capacitor element is further provided. The second capacitor element has a third capacitor terminal and a fourth capacitor terminal. The third capacitor terminal is electrically connected to the seventh terminal, and the fourth capacitor terminal is electrically connected to the first output terminal.

7. The voltage generating circuit according to claim 6, wherein: A first capacitance value, which is a capacitance value of the first capacitance element, is larger than a second capacitance value, which is a capacitance value of the second capacitance element.

8. The voltage generating circuit according to claim 1 or 6, wherein: A third capacitor element is further provided. The third capacitor element has a fifth capacitor terminal and a sixth capacitor terminal. The fifth capacitor terminal is connected to the first output terminal and the voltage output terminal of the first operational amplifier. The sixth capacitor terminal is electrically connected to a ground potential.

9. The voltage generating circuit according to claim 1 or 6, wherein: Also available: a fifth resistance element having a ninth terminal and a tenth terminal, wherein the ninth terminal is connected to the first output terminal of the first operational amplifier; a fourth capacitor element having a seventh capacitor terminal and an eighth capacitor terminal, wherein the seventh capacitor terminal is connected to the tenth terminal, and the eighth capacitor terminal is electrically connected to a ground potential; as well as A second operational amplifier has a second inverting input terminal, a second non-inverting input terminal and a second output terminal, wherein the second inverting input terminal is electrically connected to the second output terminal, the second non-inverting input terminal is electrically connected to the tenth terminal, and the second output terminal is electrically connected to the voltage output terminal.

10. The voltage generating circuit according to claim 1 or 6, wherein: It also has a third operational amplifier, which has a third inverting input terminal, a third non-inverting input terminal and a third output terminal, the third inverting input terminal is electrically connected to the third output terminal, the third non-inverting input terminal is electrically connected to the second terminal, and the third output terminal is electrically connected to the voltage output terminal.

11. The voltage generating circuit according to claim 1 or 6, wherein: A diode element is further provided. The diode element has a first diode terminal and a second diode terminal. The first diode terminal is electrically connected to the second capacitor terminal, and the second diode terminal is electrically connected to the first output terminal.

12. The voltage generating circuit according to claim 11, wherein: A sixth resistor element is further provided. The sixth resistor element has an eleventh terminal and a twelfth terminal. The eleventh terminal is electrically connected to the second diode terminal, and the twelfth terminal is electrically connected to the first output terminal.

13. The voltage generating circuit according to claim 1 or 6, wherein: Also available: a transistor having a base terminal, a collector terminal, and an emitter terminal, the base terminal being electrically connected to the second terminal, the collector terminal being electrically connected to the second capacitor terminal; as well as The seventh resistance element has a thirteenth terminal and a fourteenth terminal, the thirteenth terminal is electrically connected to the emitter terminal, and the fourteenth terminal is electrically connected to the first output terminal.

14. The voltage generating circuit according to claim 13, wherein: Also available: A fifth capacitor element, the fifth capacitor element having a ninth capacitor terminal and a tenth capacitor terminal, the ninth capacitor terminal being electrically connected to the collector terminal and the second capacitor terminal, and the tenth capacitor terminal being electrically connected to the base terminal and the second terminal.

15. The voltage generating circuit according to claim 14, wherein: An eighth resistor element is further provided. The eighth resistor element has a fifteenth terminal and a sixteenth terminal. The fifteenth terminal is electrically connected to the second terminal, and the sixteenth terminal is electrically connected to the base terminal and the tenth capacitor terminal.

16. A sound output circuit, comprising: The voltage generating circuit according to claim 1 or 6; and The fourth operational amplifier, The fourth operational amplifier has a first input terminal, a second input terminal and a fourth output terminal. inputting the output voltage output by the voltage generating circuit to the first input terminal of the fourth operational amplifier, inputting a sound input signal to the second input terminal of the fourth operational amplifier, A sound output signal based on the sound input signal is output from the fourth output terminal of the fourth operational amplifier.

Images