Power amplifier

Abstract

To drive an acoustic transducer with flat frequency characteristics while reducing current magnetostriction.SOLUTION: A power amplifier 10A includes a first amplifier 110 that outputs an output sound signal Vout to a speaker 20 that converts Vout into sound, a voltage feedback circuit 100 that negatively feeds back the voltage of the output sound signal Vout to the input of the first amplifier 110, and a current feedback circuit 150 that negatively feeds back a voltage corresponding to the current flowing through the speaker 20 to the input of the first operational amplifier 110, and the voltage feedback circuit 100 includes a voltage feedback resistor 130 and a compensation circuit 140 connected in parallel with the voltage feedback resistor.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] This disclosure relates to a power amplifier device.

Background Art

[0002] Patent Document 1 discloses an amplifier device that connects a circuit having a frequency characteristic opposite to the impedance of a speaker in series with the speaker. According to this amplifier device, the speaker is driven with a relatively low impedance near the resonance frequency of the low frequency range and with a relatively high impedance in other frequency bands. The conventional amplifier device has an advantage that it can improve the electro-magnetic distortion of the speaker.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional technology, the input voltage of the speaker is affected by the circuit connected in series with the speaker. Therefore, the frequency characteristic of the input voltage of the speaker is not flat. On the other hand, when the frequency characteristic of the input voltage is flat, the frequency characteristic of the sound emitted by the speaker becomes flat. Therefore, the conventional amplifier device has a problem that it cannot flatten the frequency characteristic of the speaker.

[0005] In consideration of the above circumstances, one aspect of this disclosure aims to solve the problem of driving an acoustic transducer with a flat frequency characteristic while reducing electro-magnetic distortion.

Means for Solving the Problems

[0006] To solve the above problems, a power amplifier according to one aspect of the present disclosure generates an output sound signal by power amplified an input sound signal. The power amplifier includes an amplification circuit that amplifies the input sound signal and outputs the amplified signal as the output sound signal to an acoustic transducer that converts the output sound signal into sound; a voltage feedback circuit that negatively feeds back the voltage of the output sound signal to the input of the amplification circuit; and a current feedback circuit that negatively feeds back the current flowing through the acoustic transducer to the input of the amplification circuit. The voltage feedback circuit includes a voltage feedback resistor and a compensation circuit connected in parallel with the voltage feedback resistor. The voltage feedback circuit and the current feedback circuit virtually create a compensation impedance connected in parallel to the acoustic transducer, and the impedance of the parallel circuit of the acoustic transducer and the compensation impedance is flatter than the frequency characteristics of the impedance of the acoustic transducer. The voltage feedback circuit and the current feedback circuit virtually create an output resistance connected in series with the acoustic transducer, and the output resistance is greater than the resistance value of the acoustic transducer. [Brief explanation of the drawing]

[0007] [Figure 1] This is a block diagram showing an example configuration of the acoustic system 1 according to the first embodiment. [Figure 2] This is a circuit diagram showing the equivalent circuit of sound system 1. [Figure 3] This graph shows the frequency characteristics of the voltage at the first node N1 of the acoustic system 1. [Figure 4] This is an explanatory diagram showing the output impedance Zo of the power amplifier 10. [Figure 5] This is a circuit diagram showing an example of the power amplifier 10. [Figure 6] This is a circuit diagram showing an example circuit for examining the open-circuit output voltage V2. [Figure 7] This is a circuit diagram showing an example of a power amplifier 10. [Figure 8] This is a circuit diagram showing an example configuration of sound system 1. [Figure 9]Figure 8 is a circuit diagram showing an example of the values ​​for each element of the acoustic system 1. [Figure 10] This is a circuit diagram showing an example configuration of the sound system 1 according to the second embodiment. [Figure 11] This is a circuit diagram showing an example configuration of the sound system 1 according to the third embodiment. [Figure 12] This is a graph showing the frequency characteristics of distortion. [Modes for carrying out the invention]

[0008] 1. First Embodiment Figure 1 is a block diagram showing an example configuration of an acoustic system 1 according to the first embodiment. The acoustic system 1 comprises a power amplifier 10 and a speaker 20. The power amplifier 10 generates an output sound signal Vout by amplifying an input sound signal Vin. The power amplifier 10 outputs the output sound signal Vout to the speaker 20. The speaker 20 is an example of an acoustic transducer that converts the output sound signal Vout into sound. The speaker 20 is a dynamic speaker having a voice coil. The speaker 20 comprises a speaker unit and an enclosure that houses the speaker unit. The speaker 20 is connected to the power amplifier 10 via a first node N1.

[0009] Figure 2 is a circuit diagram showing the equivalent circuit to be implemented in the sound system 1. As shown in Figure 2, the equivalent circuit of the power amplifier 10 comprises a voltage source 2, an output resistor 111, and a compensation impedance Zc. One terminal of the output resistor 111 is connected to the voltage source 2. The other terminal of the output resistor 111 is connected to the compensation impedance Zc. The compensation impedance Zc is a circuit in which a first capacitor 141, a first resistor 142, and a first coil (inductor) 143 are connected in series. The voltage source 2 is an equivalent circuit corresponding to the amplifier described later. The output impedance of the voltage source 2 is zero. The output voltage V1 output from the voltage source 2 is the amplified voltage of the input sound signal Vin and is proportional to the input sound signal Vin. The resistance value of the output resistor 111 is Ro, for example, 32Ω. The capacitance value of the first capacitor 141 is C, for example, 6μF. The inductance value of the first coil 143 is L, for example, 2.2mH.

[0010] Here, the output sound signal Vout of the equivalent circuit in Figure 2 when speaker 20 is not connected, that is, the open-circuit output voltage V2 of the power amplifier 10 as seen from speaker 20, is given by the following equation 1. V2=V1×(Zc / (Ro+Zc))…Formula 1

[0011] The impedance Zsp is the impedance of speaker 20. The equivalent circuit of speaker 20 comprises a coil 21, a resistor 22, a coil 23, a resistor 24, and a capacitor 25. One terminal of coil 21 is supplied with the output sound signal Vout from the power amplifier 10 via the first node N1. The other terminal of coil 21 is connected to one terminal of resistor 22. The other terminal of resistor 22 is connected to the intermediate node Nc. Coil 23, resistor 24, and capacitor 25 are connected in parallel between the intermediate node Nc and ground. The inductance value of coil 21 is L21, for example, 0.07mH. The resistance value of resistor 24 is R21, for example, 7.5Ω. The inductance value of coil 23 is L22, for example, 0.43mH. The resistance value of resistor 24 is R22, for example, 4.1Ω. The capacitance value of capacitor 25 is C22, for example, 30μF.

[0012] The inductance represented by coil 21 is mainly the inductance component of the voice coil of the speaker unit. The resistance represented by resistor 22 is mainly the resistance component of the voice coil. Coil 23, resistor 24, and capacitor 25 are the motional impedance of speaker 20. The motional impedance is determined according to the structure of the speaker unit and the structure of the enclosure.

[0013] Resonance occurs at low frequencies due to the motional impedance. This resonance frequency is the low-frequency resonance frequency F0 of speaker 20. FIG. 3 is a graph for explaining the low-frequency resonance frequency F0. Curve G1 in FIG. 3 is the frequency characteristic of the voltage at the first node N1 of the acoustic system 1, and the frequency characteristic of the motional impedance is compensated to be flat by the compensating impedance Zc connected in parallel. On the other hand, curve G2 shows the frequency characteristic of the voltage at the first node N1 when the compensating impedance Zc is removed from the acoustic system 1. As in this example, the resonance frequency and Q value of the compensating impedance Zc are adjusted to substantially match the resonance frequency and Q value of the motional impedance.

[0014] FIG. 4 is an explanatory diagram showing the output impedance Zo of the power amplifier device 10. As shown in FIG. 4, the output impedance Zo of the equivalent circuit of FIG. 2 becomes the impedance of a circuit in which the output resistor 111 and the compensating impedance Zc are connected in parallel. The output impedance Zo is given by Equation 2 shown below. Zo = Ro / / Zc = Ro·Zc / (Ro + Zc)… Equation 2 Note that “ / / ” indicates the arithmetic expression for parallel impedance.

[0015] According to Thevenin's law, if the open-circuit output voltage V2 of the equivalent circuit shown in Equation 1 is equal to the open-circuit output voltage of a certain circuit as seen from the speaker 20, and the output impedance of the equivalent circuit shown in Equation 2 is equal to the output impedance of that circuit, then that circuit will operate electrically equivalent to the equivalent circuit of FIG. 2. In this embodiment, Thevenin's law is used to explain the implementation of the circuit of the power amplifier 10 as follows.

[0016] First, assume a circuit of a power amplifier that outputs the open-circuit output voltage V2 shown in Equation 1. FIG. 5 is an example of a circuit when the speaker 20 is removed from the equivalent circuit of FIG. 2. In FIG. 5, the power amplifier 10 includes a first amplifier 110, an input resistor 120, a voltage feedback resistor 130, an output resistor 111, and a compensation circuit 140. The first amplifier 110 is a differential amplifier that amplifies the voltage difference between the positive input terminal and the negative input terminal and outputs a voltage proportional to that voltage difference from the output terminal. In the circuit of FIG. 5, the impedance of the input resistor 120 is Rin. The impedances of the output resistor 111 and the voltage feedback resistor 130 are Ro. The impedance of the compensation circuit 140 is Zc.

[0017] An input audio signal Vin is supplied to one terminal of the input resistor 120. The negative input terminal of the first amplifier 110 is connected to the other terminal of the input resistor 120. A voltage feedback resistor 130 is provided between the output terminal and the negative input terminal of the first amplifier 110. One terminal of the output resistor 111 is connected to the output terminal of the first amplifier 110. The other terminal of the output resistor 111 is connected to the compensation circuit 140. The compensation circuit 140 is configured by connecting a first capacitor 141, a first resistor 142, and a first coil 143 in series.

[0018] In the power amplifier 10 of FIG. 5, the first amplifier 110 is a voltage source with an output impedance that is approximately zero. The output impedance Zo of the power amplifier 10 is the output impedance Zo shown in FIG. 4.

[0019] In the power amplifier 10 of FIG. 5, the output voltage V1 output from the first amplifier 110 is given by Equation 3 shown below. V1=Vin×Ro / Rin…Equation 3 Equation 4, which represents the open-circuit output voltage V2, is derived from Equation 3 and Equation 1. V2=(Vin×Ro / Rin)×(Zc / (Ro+Zc)) =Vin×Ro×Zc / (Rin×(Ro+Zc))…Formula 4

[0020] Now, let's consider the circuit in Figure 6, which has the same open-circuit output voltage V2. The transfer characteristics of this circuit are given by Equation 5 shown below. Vout = Vin × (Ro / / Zc) / Rin =Vin×Ro×Zc / ((Rin×(Ro+Zc))…Equation 5 In other words, the open-circuit output voltage of the assumed circuit in Figure 6 is the same as the open-circuit output voltage V2 of the power amplifier 10 in Figure 5. On the other hand, the output impedance of the assumed circuit in Figure 6 is zero, and is not the same as the output impedance of the power amplifier 10 in Figure 5. Therefore, if impedance Ro / / Zc is added to the output of the circuit in Figure 6, the same output impedance will be obtained. Figure 7 is the circuit in which impedance Ro / / Zc is added to the output of the circuit in Figure 6, and is equivalent to the circuit in Figure 2.

[0021] In the assumed circuit shown in Figure 7, the impedance Ro / / Zc is connected to the output terminal of the first amplifier 110.

[0022] Incidentally, speaker 20 exhibits what is known as current magnetostriction. Current magnetostriction arises because the impedance Zsp of speaker 20 contains nonlinear elements. For example, the force generated in the voice coil is determined by the product of the effective magnetic flux density, the length of the voice coil, and the current flowing through the voice coil. That is, in order for electroacoustic conversion to be performed accurately in speaker 20, the effective magnetic flux density must be uniform regardless of the position of the voice coil. However, in actual speaker 20, the effective magnetic flux density tends to become non-uniform as the amplitude increases.

[0023] In other words, the impedance Zsp will fluctuate due to the influence of current-induced magnetic distortion. The fluctuating component of impedance Zsp is represented by ΔZsp. When speaker 20 is driven with a constant voltage, current-induced magnetic distortion of ΔZsp / Zsp is generated. Since speaker 20 in this embodiment employs a dynamic speaker unit, the driving force of the cone, which is the diaphragm, is proportional to the current. Therefore, current-induced magnetic distortion is converted into sound.

[0024] If a speaker 20 is driven using a power amplifier 10 having an output impedance n times the nominal impedance of the speaker unit, the current fluctuation will be ΔZsp / (Zsp+n×Zsp) compared to driving the speaker 20 using a circuit with an output impedance of the nominal impedance. As a result, the current magnetostriction will be 1 / (n+1) compared to constant voltage drive. The nominal impedance of the speaker unit is, for example, 8Ω.

[0025] Therefore, in order to reduce current-magnetic distortion, it is preferable to increase the resistance component of the output impedance. However, if the resistance component is realized by a physical resistive element, a large power loss occurs due to that resistive element.

[0026] Therefore, in this embodiment, by negative feedback of the current flowing through the speaker 20, an impedance Ro / / Zc as shown in Figure 7 is virtually generated, reducing current magnetic distortion without increasing power loss, and flattening its frequency characteristics.

[0027] Figure 8 is a circuit diagram showing an example configuration of the sound system 1, in which the assumed circuit of Figure 7 is used to virtually generate an output impedance Ro / / Zc using current feedback. The sound system 1 comprises a power amplifier 10A and a speaker 20. In other words, the circuit of the power amplifier 10A is equivalent to the circuit in Figure 2. The power amplifier 10A comprises a first amplifier 110, an input resistor 120, a voltage feedback circuit 100, and a current feedback circuit 150.

[0028] The first amplifier 110 has a first positive input terminal T1, a first negative input terminal T2, and a first output terminal T3. An input resistor 120 is connected to the first negative input terminal T2. The input sound signal Vin is input to the first negative input terminal T2 via the input resistor 120.

[0029] The voltage feedback circuit 100 negatively feeds back the output sound signal Vout to the input of the first amplifier 110. The voltage feedback circuit 100 includes a voltage feedback resistor 130 and a compensation circuit 140 connected in parallel with the voltage feedback resistor 130. The voltage feedback resistor 130 is connected between the first negative input terminal T2 and the first output terminal T3. The compensation circuit 140 is connected between the first negative input terminal T2 and the first output terminal T3. The compensation circuit 140 consists of a first capacitor 141, a first resistor 142, and a first coil (inductor) 143 connected in series. The connection order of the first capacitor 141, the first resistor 142, and the first coil 143 is arbitrary.

[0030] The current feedback circuit 150 includes a current feedback resistor 151 and a current sensing resistor 152. The current feedback resistor 151 is connected between the second node N2 and the first negative input terminal T2. The speaker 20 and the current sensing resistor 152 are connected to the second node N2. The current sensing resistor 152 is used to detect the current flowing through the speaker. The current sensing resistor 152 is connected between the speaker 20 and ground. The resistance value of the current feedback resistor 151 is Rfb. The resistance value of the current sensing resistor 152 is Rs.

[0031] The output impedance Zout virtually generated in the power amplifier 10A by current feedback through resistor Rfb is given by equation 6 shown below. Zout = Rs × (Ro / / Zc) / Rfb =(Rs / Rfb)×Ro×Zc / (Ro+Zc)…Equation 6 Here, if the resistance values ​​of the current feedback resistor 151 and the current sensing resistor 152 are set so that Rs / Rfb = 1, then equation 6 becomes equation 7 shown below. Zout = Ro × Zc / (Ro + Zc) ... Equation 7

[0032] By comparing Equation 2 and Equation 7, it can be understood that the output impedance Zo of the power amplifier 10 and the output impedance Zout of the power amplifier 10A are the same. Also, when the speaker 20 is disconnected from the first node N1, the voltage at the first node N1 is Vout, as shown by Equation 5. Therefore, from the perspective of Thevenin's Law, the acoustic system 1 in Figure 8 is equivalent to the equivalent circuit of the acoustic system 1 in Figure 2 (Figure 5) and the assumed circuit in Figure 7. In other words, the output of the power amplifier 10A of the acoustic system 1 in Figure 8 can be considered to have a virtual resistor 111 connected in series with the speaker 20 and a virtual impedance Zc connected in parallel with the speaker 20, similar to the equivalent circuit in Figure 2.

[0033] The acoustic system 1 in Figure 9 is a circuit diagram showing an example of the values ​​of each element in the acoustic system 1 in Figure 8. If the impedance of the compensation circuit 140 is matched to the impedance of the speaker 20 as in Figure 5, it becomes too small for the voltage feedback circuit 100 of the first amplifier 110. Therefore, in the acoustic system 1 in Figure 9, the transmission characteristics are the same as those of the acoustic system 1 in Figure 8, and the impedance of the voltage feedback circuit 100 and the current feedback resistor 151 is designed to be 1250 times that of the case in Figure 5.

[0034] As described above, according to this embodiment, the power amplifier 10A that generates an output sound signal Vout by power amplified an input sound signal Vin includes a first amplifier 110 that outputs to a speaker 20 that converts the output sound signal Vout into sound, a voltage feedback circuit 100 that negatively feeds back the voltage of the output sound signal Vout to the input of the first amplifier 110, and a current feedback circuit 150 that negatively feeds back a voltage corresponding to the current flowing through the speaker 20 to the input of the first amplifier 110. Furthermore, the voltage feedback circuit 100 includes a voltage feedback resistor 130 and a compensation circuit 140 connected in parallel with the voltage feedback resistor 130.

[0035] As described above, the output of the power amplifier 10A in Figure 8 can be virtually considered to have the same impedance Zc as the compensation impedance Zc in the equivalent circuit of Figure 2 connected in parallel with the speaker 20, and the flat frequency characteristics of the impedance of that parallel circuit realize the curve G1 in Figure 3. Therefore, the frequency characteristics of the impedance of that parallel circuit are flatter compared to the frequency characteristics G2 of the impedance of the speaker 20. Thus, the power amplifier 10A can drive the speaker 20 with a voltage that has a flat frequency characteristics compared to the case where there is no impedance Zc in Figure 2 and the speaker 20 is driven only by the output resistor 111.

[0036] Furthermore, as described above, the output of the power amplifier 10A is virtually connected in series with the speaker 20 to the same resistance as the output resistor 111 in Figure 2. Here, the circuit is designed so that the resistance value Ro of the output resistor 111 is sufficiently larger than the sum of the resistance values ​​R21 and R22 of the speaker 20. In the example shown in Figure 2, Ro is 32Ω, and the sum of R21 and R22 is 11.6Ω. In this case, the current magnetic distortion is reduced to approximately 1 / 4.

[0037] In other words, the power amplifier 10A virtually drives a series circuit consisting of a parallel circuit of the impedance Zsp of the speaker 20 and a virtual impedance Zc for compensation, and a virtual output resistor 111, with an output voltage V1 proportional to the input sound signal Vin. As a result, when the speaker 20 is connected, the voltage at the first node N1 is a voltage with a flat frequency response, obtained by dividing the output voltage V1 by the impedance of the output resistor 111 and the parallel circuit. On the other hand, when the speaker 20 is not connected, the voltage at the first node N1 is a voltage (open-circuit output voltage V2) obtained by dividing the output voltage V1 by the output resistor 111 and the compensation impedance Zc.

[0038] Furthermore, the current feedback circuit 150 negatively feeds back the voltage across the current sensing resistor 152, which is connected between the speaker 20 and ground, to the first amplifier 110 via a current feedback resistor 151 connected between the second node N2, to which the speaker 20 and the current sensing resistor 152 are connected, and the first negative input terminal T2. In other words, the current flowing through the speaker 20 is negatively fed back to the first amplifier 110 via the current feedback resistor 151.

[0039] Furthermore, the compensation circuit 140 includes a first capacitor 141, a first coil (inductor) 143, and a first resistor 142, which are connected in series in any order between the first negative input terminal T2 and the first output terminal T3. The first coil may be a simulated inductor. At the low-frequency resonant frequency F0 of the speaker 20, the value of the motional impedance of the speaker 20 increases. Due to current feedback, a compensation impedance with a frequency characteristic similar to that of the compensation circuit 140 is virtually generated in parallel with the speaker 20 at the output of the power amplifier 10A, canceling out the effect of the motional impedance of the speaker 20.

[0040] 2. Second Embodiment The compensation circuit 140 of the power amplifier 10A according to the first embodiment is configured by connecting a first capacitor 141, a first resistor 142, and a first coil 143 in series. Both terminals of the first coil 143 are floating. In contrast, the power amplifier 10A of the second embodiment differs from the power amplifier 10A of the first embodiment in that it uses a coil with one terminal grounded.

[0041] Figure 10 shows an example of the configuration of the sound system 1 according to the second embodiment. The sound system 1 according to the second embodiment is configured similarly to the sound system 1 according to the first embodiment in Figure 9, except that a compensation circuit 160A with the same characteristics as the compensation circuit 140 of the power amplifier 10A is used instead. The compensation circuit 160A will be described below.

[0042] The compensation circuit 160A in Figure 10 comprises a second amplifier 161, a second resistor 162, a second capacitor 163, a second coil 164, and a third resistor 165. The second amplifier 161 has a second positive input terminal T4, a second negative input terminal T5, and a second output terminal T6. The second output terminal T6 is connected to the second negative input terminal T5. The second amplifier 161 functions as a voltage follower.

[0043] The second resistor 162 is provided between the first output terminal T3 and the second positive input terminal T4 of the first amplifier 110. The resistance value of the second resistor 162 is, for example, 9.1kΩ. The second capacitor 163 is provided between the second positive input terminal T4 and ground. Each of the second resistor 162 and the second capacitor 163 is connected to the third node N3. The capacitance value of the second capacitor 163 is, for example, 10nF. The second coil 164 is provided between the second positive input terminal T4 and ground. The inductance value of the second coil 164 is, for example, 1.4H. The third resistor 165 is provided between the second output terminal T6 and the first negative input terminal T2 of the first amplifier 110. The resistance value of the third resistor 165 is, for example, 27.5kΩ.

[0044] 3. Third Embodiment The compensation circuit 160A according to the second embodiment includes a second coil 164. In contrast, the acoustic system 1 according to the third embodiment differs in that the second coil 164 is a simulated inductor. The grounded second coil 164 has a simpler corresponding simulated inductor than the floating first coil 143 of the first embodiment.

[0045] Figure 11 shows an example of the configuration of the sound system 1 according to the third embodiment. The sound system 1 according to the third embodiment is configured similarly to the sound system 1 according to the second embodiment in Figure 10, except that a compensation circuit 160B is used instead of the compensation circuit 160A of the power amplifier 10A. The compensation circuit 160B will be described below.

[0046] The compensation circuit 160B in Figure 10 is connected between the first negative input terminal T2 and the first output terminal T3 of the first amplifier 110. The compensation circuit 160B includes a simulated inductor using the second amplifier 161.

[0047] The compensation circuit 160B comprises a second amplifier 161, a second resistor 162, a second capacitor 163, a third resistor 165, a fourth resistor 166, a third capacitor 167, and a fifth resistor 168. The second resistor 162 is provided between the first output terminal T3 of the first amplifier 110 and the third node N3. The third resistor 165 is provided between the second output terminal T6 and the first negative input terminal T2 of the first amplifier 110. The second capacitor 163 is provided between the third node N3 and ground. The third capacitor 167 is provided between the third node N3 and the second positive input terminal T4. The capacitance value of the third capacitor 167 is, for example, 13nF. The fourth resistor 166 is provided between the third node N3 and the second negative input terminal T5. The resistance value of the fourth resistor 166 is, for example, 330Ω. The fifth resistor 168 is provided between the second positive input terminal T4 and ground.

[0048] According to the compensation circuit 160B described above, a simulated inductor is formed by the second amplifier 161, the fourth resistor 166, the third capacitor 167, and the fifth resistor 168. The inductance value of the simulated inductor is equal to the inductance value of the second coil 164 in Figure 10. Since the compensation circuit 160B replaces the large second coil 164 with a simulated inductor, the circuit size can be reduced compared to the compensation circuit 160A.

[0049] Figure 12 is a graph showing the frequency characteristics of distortion. In this figure, curve Ca shows the distortion of the current flowing through speaker 20 when speaker 20 is driven by power amplifier 10A as in Figure 11, and curve Cb shows the distortion of the same current when speaker 20 is driven by a constant voltage power amplifier (with the current feedback resistor 151 and compensation circuit 160B removed from Figure 11). Comparing curves Ca and Cb, an improvement of approximately 6dB to 10dB in distortion of power amplifier 10A can be observed in the frequency band of 1kHz and above.

[0050] 4. Variations This disclosure is not limited to the embodiments described above, and various modifications are possible as described below. Furthermore, each embodiment and each modification may be combined as appropriate.

[0051] (1) Variation 1 In each of the embodiments described above, the power amplifier 10A was located outside the speaker 20, but the disclosure is not limited thereto. For example, a powered speaker may have the power amplifier 10A located inside the speaker 20. The compensation circuits 140, 160A, and 160B described above are designed according to the impedance Zsp of a particular speaker 20. Therefore, the power amplifier 10A is not suitable for speakers with a different impedance than that speaker. In a powered speaker, a power amplifier 10A suitable for a particular speaker 20 can be incorporated into the enclosure.

[0052] (2) Modification example 2 The first amplifier 110 in Figures 5 to 11 was designed as an inverting amplifier with the input voltage Vin input to the negative input terminal, but it is easy to redesign each of them as a non-inverting amplifier with the input voltage Vin input to the positive input terminal.

[0053] (3) Modification example 3 Each of the embodiments described above uses speaker 20 as an example of an acoustic transducer. An acoustic transducer is a device that converts electrical energy into sound. In this disclosure, the acoustic transducer converts the output sound signal Vout into sound. That is, this disclosure is not limited to speakers. The acoustic transducer may be a compression driver or an earphone driver. It also includes acoustic transducers that vibrate walls or the like using electrical energy.

[0054] (4) Modification 4 In each of the embodiments described above, the impedance Zc of the compensation circuit 140, 160A, or 160B is designed such that the frequency response of the impedance of the parallel circuit becomes flat in accordance with the impedance Zsp of the speaker 20. However, it does not need to be perfectly flat; it is sufficient that the frequency response of the impedance of the parallel circuit approaches flatness compared to the frequency response of the impedance of the speaker 20 alone. [Explanation of symbols]

[0055] 1…Sound system, 10, 10A…Power amplifier, 20…Speaker, 100…Voltage feedback circuit, 110…First amplifier, 111…Output resistor, 120…Input resistor, 130…Voltage feedback resistor, 140, 160A, 160B…Compensation circuit, 141…First capacitor, 142…First resistor, 143…First coil, 150…Current feedback circuit, 151…Current feedback resistor, 152…Current sensing resistor, 161…Second amplifier, 162…Second Resistor, 163...2nd capacitor, 164...2nd coil, 165...3rd resistor, 166...4th resistor, 167...3rd capacitor, 168...5th resistor, N1...1st node, N2...2nd node, N3...3rd node, T1...1st positive input terminal, T2...1st negative input terminal, T3...1st output terminal, T4...2nd positive input terminal, T5...2nd negative input terminal, T6...2nd output terminal, V1...output voltage, Vin...input sound signal, Vout...output sound signal.

Claims

1. A power amplifier that generates an output sound signal by power amplified an input sound signal, An amplification circuit that amplifies the input sound signal and outputs the amplified signal as the output sound signal to an acoustic transducer that converts the output sound signal into sound, A voltage feedback circuit that negatively feeds back the voltage of the output sound signal to the input of the amplification circuit, A power amplifier comprising a current feedback circuit that negatively feeds back the current flowing through the acoustic transducer to the input of the amplification circuit, The voltage feedback circuit comprises a voltage feedback resistor and a compensation circuit connected in parallel with the voltage feedback resistor. The voltage feedback circuit and the current feedback circuit virtually create a compensating impedance connected in parallel to the acoustic transducer, and the impedance of the parallel circuit between the acoustic transducer and the compensating impedance is flatter compared to the frequency characteristics of the impedance of the acoustic transducer. The voltage feedback circuit and the current feedback circuit virtually generate an output resistance connected in series with the acoustic transducer, and the output resistance is greater than the resistance value of the acoustic transducer. Power amplifier.

2. The power amplifier virtually drives a series circuit, in which the impedance of the parallel circuit and the output resistor are connected, with an output voltage proportional to the input sound signal. The power amplifier according to claim 1.

3. The acoustic transducer is connected to the output of the amplification circuit via the first node. When the acoustic transducer is not connected to the first node, the voltage at the first node is the voltage obtained by dividing the output voltage by the output resistor and the compensating impedance. The power amplifier according to claim 2.

4. The amplification circuit is a first amplifier having a first positive input terminal, a first negative input terminal, and a first output terminal. The current feedback circuit is, A current sensing resistor for current detection is connected between the acoustic transducer and ground, The system comprises a second node to which the acoustic transducer and the current sensing resistor are connected, and a current feedback resistor connected between the second node and the first negative input terminal. A power amplifier according to any one of claims 1 to 3.

5. The amplification circuit is a first amplifier having a first positive input terminal, a first negative input terminal, and a first output terminal. The voltage feedback resistor is connected between the first negative input terminal and the first output terminal. The aforementioned compensation circuit is The device comprises a first capacitor, a first inductor, and a first resistor, which are connected in series in any order between the first negative input terminal and the first output terminal. A power amplifier according to any one of claims 1 to 4.

6. The amplification circuit is a first amplifier having a first positive input terminal, a first negative input terminal, and a first output terminal. The voltage feedback resistor is connected between the first negative input terminal and the first output terminal. The aforementioned compensation circuit is A second amplifier having a second positive input terminal, a second negative input terminal, and a second output terminal connected to the second negative input terminal, A second resistor is provided between the first output terminal and the second positive input terminal, A second capacitance is provided between the second positive input terminal and ground, A second coil is provided between the second positive input terminal and ground, The device comprises a third resistor provided between the second output terminal and the first negative input terminal. A power amplifier according to any one of claims 1 to 4.

7. The amplification circuit is a first amplifier having a first positive input terminal, a first negative input terminal, and a first output terminal. The voltage feedback resistor is connected between the first negative input terminal and the first output terminal. The aforementioned compensation circuit is Connected between the first negative input terminal and the first output terminal, It features a simulated inductor using a second amplifier, A power amplifier according to any one of claims 1 to 4.

8. The second amplifier has a second positive input terminal, a second negative input terminal, and a second output terminal. The aforementioned compensation circuit is A second resistor is provided between the first output terminal and the third node, A third resistor is provided between the second output terminal and the first negative input terminal. A second capacitance is provided between the third node and ground, A third capacitance is provided between the third node and the second positive input terminal, A fourth resistor is provided between the third node and the second negative input terminal, The device comprises a fifth resistor provided between the second positive input terminal and ground, The power amplifier according to claim 7.

Images