Constant voltage circuit and electronic device

Abstract

This constant voltage circuit (1) comprises: a DC feedback circuit (3); and an AC feedback circuit (4) which performs band selection on an AC component, which overlaps an output voltage Vout, amplifies the band-selected AC component, and then feeds back the amplified band-selected AC component to a control element Mpass. The AC feedback circuit (4) includes: a voltage detection circuit (41) which includes a capacitor Ccap of which one terminal is connected to an output terminal Po, and a gate-grounded transistor MN1 of which a source S is connected to the other terminal of the capacitor Ccap; and an amplification circuit (42) which amplifies an output signal from the voltage detection circuit (41) and outputs the amplified signal to the control element Mpass. The voltage detection circuit (41) includes a transistor MN2 that is serially connected to the transistor MN1, and connects a drain D of the transistor MN1 to a gate G of the transistor MN2 and the amplification circuit (42). The amplification circuit (42) includes transistors MP2, MP3 of a current mirror circuit, and source-grounded transistors MN3, MN4. Accordingly, a PSRR is enhanced to a wideband, while the performance of low power consumption of an LDO is maintained.

Description

[Technical field]

[0001] The present invention relates to a constant voltage circuit and an electronic device to which, for example, a low dropout voltage regulator LDO (Low Drop Out) is applied. [Background technology]

[0002] In recent years, with the spread of battery-powered applications (devices), there has been an increasing demand for long-term operation of LDOs used in constant-voltage circuits, and the development of low-power circuits is being considered. In addition, since some analog circuits that make up devices are sensitive to noise and are easily affected by noise generated in power supply parts such as switching converters, there is also a growing demand for LDOs with noise removal capabilities.

[0003] Incidentally, in an LDO that uses a differential amplifier, it is known that when the current consumption is reduced, the operating frequency shifts to a lower range, which degrades the ability to detect ripples (AC noise) generated by DC-DC converters and switching regulators, etc., making it difficult to fully utilize the power supply rejection ratio (PSRR).

[0004] Conventionally, in order to make the PSRR function effectively, a circuit has been proposed in which a feedback circuit for a direct current voltage (DC) and a feedback circuit for an alternating current voltage (AC) are provided, and feedback amplified signals from both feedback circuits are superimposed and fed back to a power supply control element, thereby maintaining the PSRR characteristics including AC noise (for example, Patent Document 1 and Non-Patent Document 1). FIG. 5 shows the constant voltage circuit described in Patent Document 1, and includes a DC feedback circuit having feedback resistors R1 and R2 connected in series to the output terminal of a control transistor Mp, a differential amplifier provided between the midpoint of R1 and R2 and a transistor M5 and made up of transistors M1B, M11, M12, M3, and M4, a differential amplifier provided between the output terminal of the control transistor Mp and the transistor M5 and made up of transistors M2B, M21, M22, M3, and M4, and a high-pass filter HPF (C F ,R F ) is connected in parallel. In the circuit described in Patent Document 1, when AC noise is superimposed on the output voltage Vo, the transistors M21 and M22 are operated via the high-pass filter HPF, so that the combined output resistance of the transistors (M11, M12 and M21, M22) is reduced to approximately half or less, and the current consumption increases by the amount of the transistor M2B, widening the PSRR bandwidth. In other words, the function of the PSRR is improved to a wide bandwidth by superimposing the feedback voltage obtained by the differential amplifier on the DC side and the feedback voltage amplified by the differential amplifier on the AC side.

[0005] FIG. 6 shows the constant voltage circuit described in Non-Patent Document 1, which includes a DC feedback circuit including feedback resistors R11 and R12 connected in series to the output terminal of a control transistor Mp, a differential amplifier (Error Amplifier) ​​whose midpoint is connected to the non-inverting input terminal and whose inverting input terminal is applied with a reference voltage Vref, and a high-pass filter HPF (C ff1 ,R ff1 ) and a differential amplifier H having an operational amplifier connected to its output side. ffThe circuit described in Non-Patent Document 1 includes an AC feedback circuit consisting of a feedforward amplifier (s) and a summing amplifier that is provided on the output side of the DC feedback circuit and the AC feedback circuit and sums both feedback signals and guides them to the gate of the control transistor Mp. ff By superimposing the signal amplified in (s) and increasing the load current, the PSRR function is improved in the high frequency range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4236586 [Non-patent literature]

[0007] [Non-Patent Document 1] M. El-Nozahi, A. Amer, J. Torres, K. Entesari and E. Sanchez-Sinencio, “High PSR Low Drop-Out Regulator With Feed-Forward Ripple Cancellation Technique,” ​​IEEE J. Solid-State Circuits, vol.: 45, Issue: 3, pp. 565 - 577, March 2010. Summary of the Invention [Problem to be solved by the invention]

[0008] By the way, the output resistance of the transistor used in the LDO is ro=1 / λI D (However, I D : drain current, λ: coefficient), and the output resistance ro and drain current I DIt is known that there is an inverse proportional relationship between the output current and the output resistance (RO) (see R. Jacob Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition: Wiley-IEEE Press, 2004 / 11 / 1, pp271-,280). In an LDO using a differential amplifier, if you try to reduce the current consumption in order to extend the operating time (reducing power consumption), the output resistance ro increases, making it difficult to fully utilize the PSRR characteristics. This shows that there is a trade-off between extending the operating time (reducing power consumption) and PSRR performance.

[0009] In the circuits described in Patent Document 1 and Non-Patent Document 1, in order to improve the PSRR over a wide band including high frequencies, it is necessary to lower the output impedance of the differential amplifier. However, since the output impedance of the differential amplifier is inversely proportional to the current consumption as described above, an issue remains as to the trade-off.

[0010] The present invention has been made in view of the above, and provides a constant voltage circuit and electronic device that improves the PSRR over a wide band including high frequencies while maintaining the low power consumption performance of an LDO. [Means for solving the problem]

[0011] The constant voltage circuit according to the present invention includes a DC feedback circuit that amplifies the error between an output voltage output to an output terminal side via a control element and a predetermined reference voltage using a differential amplifier and feeds the error back to the control element, and an AC feedback circuit that applies band selection to an AC component superimposed on the output voltage, amplifies the AC component, and feeds the AC component back to the control element. The AC feedback circuit includes a voltage detection circuit including a capacitor having one end connected to either the input terminal or the output terminal of the control element and a first transistor having a grounded gate and a source connected to the other end of the capacitor, and an amplifier circuit that amplifies an output signal from the voltage detection circuit and outputs the signal to the control element. The voltage detection circuit includes a second transistor connected in series to the first transistor, and the drain of the first transistor is connected to the gate of the second transistor and to the amplifier circuit, and the amplifier circuit includes a source-grounded transistor circuit.

[0012] According to the present invention, when the output voltage deviates from a predetermined reference voltage (an error occurs), a feedback signal corresponding to the error is generated and guided to a control element, thereby eliminating the error. On the other hand, when an AC component, which is an AC ripple, occurs in the output voltage, the AC component passes through a capacitor, is detected by a voltage detection circuit including a first transistor with a grounded gate, and is amplified and output. In this way, by coupling a coupling capacitor to a node of a source with low impedance and connecting the drain of the first transistor to the gate of a second transistor connected in series to reduce the output resistance to the capacitor, the AC component in the output voltage is amplified and detected in a wide band without using a differential amplifier. As a result, the output signal from the voltage detection circuit amplified in a wide band is further amplified and fed back to the control element, since a high voltage gain is obtained in the source-grounded transistor circuit of the amplifier circuit, and the AC component superimposed on the output voltage is eliminated. Therefore, a constant voltage circuit can be provided that improves PSRR in a wide band while maintaining low power consumption performance.

[0013] Furthermore, the present invention is preferably an electronic device having a constant voltage circuit, and thus an electronic device having an integrated constant voltage circuit can be provided. Effect of the Invention

[0014] According to the present invention, it is possible to improve the PSRR over a wide bandwidth while maintaining the low power consumption performance of an LDO. [Brief description of the drawings]

[0015] [Figure 1] 1 is a circuit diagram showing a first embodiment of a constant voltage circuit according to the present invention. [Diagram 2] FIG. 13 shows the frequency characteristics of the PSRR obtained by simulating a constant voltage circuit. In the figure, (1) is an embodiment in which the circuit shown in FIG. 1 is applied, and (2) is a comparative example in which the circuit shown in FIG. 1 is applied without the AC feedback circuit. [Diagram 3] FIG. 11 is a circuit diagram showing another embodiment of the voltage detection circuit. [Figure 4] FIG. 11 is a circuit diagram showing another embodiment; (A) is an example in which a transistor MN11 is added as a cascode to an amplifier circuit, and (B) is an example in which a plurality of systems with capacitors of different sizes are connected in parallel. [Diagram 5] This is a conventional constant voltage circuit described in Patent Document 1. [Figure 6] This is a conventional constant voltage circuit described in Non-Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 1 is a circuit diagram showing a first embodiment of a constant voltage circuit according to the present invention. In this embodiment, the constant voltage circuit 1 is configured with an LDO, and includes a control circuit 2 having a transistor Mpass, which is a control element connected between a power supply Vdd line and an output terminal Po, a DC feedback circuit 3, and an AC feedback circuit 4. The AC feedback circuit 4 includes a voltage detection circuit 41, indicated by a thin dashed line frame, and an amplifier circuit 42 on the output side (next stage) of the voltage detection circuit 41.

[0017] The transistor Mpass of the control circuit 2 has its source S connected to the power supply Vdd line and its drain D connected to the output terminal Po. The transistor Mpass functions as a control element, and controls the output voltage Vout to be maintained at a predetermined constant voltage by controlling the load current Iload flowing from the source S to the drain D according to the level of a feedback voltage (described later) input to the gate G. As a result, even if the output voltage Vout deviates from the predetermined constant voltage and an error occurs, a feedback signal corresponding to the error is generated and the output voltage Vout is returned to the predetermined constant voltage. The output terminal Po of the transistor Mpass has a bypass capacitor Cout (including an electrical series resistance Re), and when a required load (device) is connected between the output terminal Po and the ground (common), a load current Iload at a constant voltage is supplied from the power supply Vdd.

[0018] The load (device) is mainly a wearable device, and may be a smartphone, a camera, a video camera with a video deck, a laptop PC, a CMOS image sensor, an RF module, an oscillator (VCO, PLL), an ADC, a DAC, wireless earphones, smart glasses, a wireless electroencephalogram instrument, an IoT edge device, a network camera, or other various devices. The constant voltage circuit 1 may be connected directly to a battery or to an application via a switching converter. Specifically, the power supply Vdd may be a battery power supply or an output power supply of a switching converter. The constant voltage circuit 1 may be detachably connected between the power supply and the device, or may be integrated with the device.

[0019] The DC feedback circuit 3 includes feedback resistors R1 and R2 connected in series between the output terminal Po and the ground (common), and an operational amplifier, for example, a differential amplifier OP, whose non-inverting input terminal is connected to the midpoint of the feedback resistors R1 and R2, whose inverting input terminal is applied with a predetermined reference voltage Vref, and whose output terminal is connected to the gate G of the transistor Mpass. The details of the differential amplifier OP are described in the dashed frame indicated by a lead line in the upper right margin of FIG. 1. The differential amplifier OP may have a known circuit configuration, and is composed of transistors MP4, MP5, MN5, and MN6 and a constant current source Ib1 in this example. The midpoint of the feedback resistors R1 and R2 is connected to the gate of the transistor MN5, and the reference voltage Vref is connected to the gate of the transistor MN6. The differential amplifier OP is designed so that when the divided voltage at the midpoint of the feedback resistors R1 and R2 coincides with the reference voltage Vref, the load current flowing through the transistor Mpass does not change and the output voltage Vout is stabilized at a predetermined constant voltage. In the above, MP denotes a P-type MOSFET and MN denotes an N-type MOSFET, and so on hereafter.

[0020] The voltage detection circuit 41 of the AC feedback circuit 4 detects and amplifies AC ripple noise superimposed on the output voltage Vout at the output terminal Po. The voltage detection circuit 41 has a transistor MP1 acting as a constant current source according to a bias voltage Vbiasp, a transistor MN1 as a current source according to a bias voltage Vbiasn1, and a transistor MN2 connected in series between a power supply Vdd and the ground.

[0021] The source S of the transistor MP1 is connected to the power supply Vdd, and the drain D is connected to the drain D of the transistor MN1. The source S of the transistor MN1 is connected to the drain D of the transistor MN2. The capacitor Ccap is interposed between the output terminal Po of the transistor Mpass and the source S of the transistor MN1. By connecting the capacitor Ccap to the source S of the transistor MN1, the output resistances of the node of the source S of the transistor MN1 and the node of the drain D of the transistor MN2 are connected in parallel, and an AC component corresponding to a band-pass filter frequency (band selection) determined by the high-pass filter frequency determined by the parallel combined output resistance value and the capacitance value of the capacitor Ccap, and the low-pass filter frequency determined by the output resistance of the voltage detection circuit 41 and the input capacitance of the amplifier circuit 42 can be detected. That is, an HPF that passes high frequency components according to the MOS characteristics of the transistor MN2 according to the current value of the constant current source of the transistor MP1 can be configured. Furthermore, the drain D of the transistor MN1 is connected to the gate G of the transistor MN2, that is, the drain voltage of the transistor MN1 is fed back to the gate G of the transistor MN2. This can reduce the output resistance of the drain D of the transistor MN2. Therefore, the parallel combined resistance value on the output side of the capacitor Ccap becomes smaller. The output impedance of the voltage detection circuit 41 will be described later.

[0022] The drain D of the transistor MP1 functions as the output terminal of the voltage detection circuit 41 and is connected to the gate G of the transistor MN3 of the amplifier circuit 42. A voltage corresponding to the difference between the current from the constant current source, which is the transistor MP1, and the current flowing through the transistor MN1 is output from the output terminal of the voltage detection circuit 41 as a detection voltage.

[0023] In the amplifier circuit 42, the transistors MN3 and MN4 form a common-source amplifier circuit, and the transistors MP2 and MP3 form a current mirror circuit, thereby providing a high output impedance and a high voltage gain.

[0024] The transistor MN3 converts the detection voltage input to the gate G into a current and passes it to the transistor MP2. The transistor MP2 shares a gate voltage with the transistor MP3, so that the current flowing through the transistor MP2 is copied to the transistor MP3, and the current is added to the output resistance of the transistor MN4, which is fixed to the gate voltage Vbiasn2, thereby amplifying it as the voltage of the drain D of the transistor MN4. The amplified voltage signal is then input to the gate G of the transistor Mpass.

[0025] As a result, a voltage corresponding to both the currents fed back from the DC feedback circuit 3 and the AC feedback circuit 4 is superimposed and input to the gate G of the transistor Mpass, and the transistor Mpass passes a load current corresponding to this input voltage, making the output voltage Vout a predetermined constant voltage and suppressing AC ripples. As described above, the AC feedback circuit 4 is configured not to use the reference voltage Vref, so that fluctuations in the reference voltage Vref do not affect the accuracy of the AC feedback operation.

[0026] Here, the output impedance of the voltage detection circuit 41 will be considered. The output impedance of the voltage detection circuit 41 is calculated as about 1 / gm when approximated by the transconductance gm of the transistor, and is known to be proportional to 1 / √Id (see R. Jacob Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition: Wiley-IEEE Press, 2004 / 11 / 1, pp271-,280). Comparing the output impedance 1 / gm with the output resistance ro of the differential amplifier in the circuits shown in Figs. 5 and 6, it is known that when 20 μA flows through the MOSFET, 1 / gm=6.7 kΩ, while ro=about 5 MΩ (see R. Jacob Baker, CMOS Circuit Design, Layout, and Simulation, Second Edition: Wiley-IEEE Press, 2004 / 11 / 1, pp283,289). According to the above, 1 / gm is approximately 1000 times smaller than ro, and the signal amplification factor has characteristics (e.g., 40 dB) similar to those of the differential amplifiers in FIGS. 5 and 6. In addition, the increase in output impedance when the drain current decreases is effective at 1 / √Id (i.e., the square root) and is not as high as that of a general differential amplifier. Therefore, there is no trade-off problem as in the past, and excellent high-frequency characteristics can be exhibited relative to PSRR under low power consumption.

[0027] Furthermore, the voltage detection circuit 41 is capable of amplifying the AC signal superimposed on Vout in a wide band by coupling the capacitor Ccap to the source S of the transistor MN1, which has low impedance. The AC signal input to the source S of the transistor MN1 is amplified by the gate-grounded transistor MN1, and is output to the next stage (transistor MN3) through the low output resistance realized by the connection with the transistor MN2.

[0028] Next, the operation of the constant voltage circuit 1 will be described. Now, if a fluctuation occurs in the ripple component superimposed on the output voltage Vout of the output terminal Po, this fluctuation is detected as a voltage of the same phase fluctuation through the capacitor Ccap, and the detected voltage is amplified by the transistor MN1. The amplified signal can be extracted up to the high frequency range components by receiving the PSRR performance. The extracted signal is output to the next stage transistor MN3. Next, it is amplified by the amplifier circuit 42 equipped with a source ground amplifier circuit and a current mirror circuit, and output from the drain D of the transistor MP3. The output fluctuation voltage signal is input to the gate G of the transistor Mpass to drive the transistor Mpass. The transistor Mpass cancels out the AC component of the output voltage Vout by acting on the fluctuation component on the output Vout, and the ripple is suppressed. As for the fluctuation of the DC component, the output Vout is maintained at a predetermined constant voltage through the DC feedback circuit 3.

[0029] FIG. 2 shows the frequency characteristics of PSRR by simulation of a constant voltage circuit, where (1) is an embodiment in which the circuit shown in FIG. 1 is applied, and (2) is a comparative example in which the circuit shown in FIG. 1 is applied without the AC feedback circuit. Each is a simulation result for a fluctuating signal of the same level during light load operation. In the embodiment, the tail current Ib1 of the differential amplifier of the DC feedback circuit 3 is set to 50 nA, and the total current consumption is set to 720 nA. On the other hand, in the comparative example, the tail current Ib1 of the differential amplifier of the DC feedback circuit 3 is set to 250 nA, resulting in a total current consumption of 710 nA, which is almost the same as that of the embodiment.

[0030] In the comparative example, the ripple voltage generated by the front-stage switching converter drops along with the cutoff frequency of the differential amplifier, while in the example, the PSRR is stable at about 40 dB in a wide range from 100 Hz to about 4 KHz in the high frequency range. Therefore, it was found that in this frequency range, the example can exhibit a more stable PSRR performance. In addition, the PSRR in the frequency range of 10 KHz or more is a characteristic determined by the dominant parameters Cout and Re in FIG. 1, and the difference between the example and the comparative example was small. On the other hand, in the frequency range of 1 KHz or less, the example has a lower PSRR than the comparative example, but the switching frequency of the front-stage switching converter at a light load generally does not fall below 1 KHz, so this is not a problem. Thus, it was confirmed that the example has a stable or improved PSRR in a wide frequency range including a high frequency range of several hundred Hz to 10 KHz, compared to the comparative example.

[0031] Next, FIG. 3 shows a voltage detection circuit 41' showing another embodiment of the voltage detection circuit 41 shown in FIG. 1. In FIG. 1, the drain voltage of the drain D of the transistor MN1 is fed back to the gate G of the transistor MN2, but in the voltage detection circuit 41', a part of the drain voltage is fed back. Compared to the voltage detection circuit 41, the voltage detection circuit 41' is provided with transistors MN7 and MN8 connected in series. The transistor MN7 is used as a constant current source by applying a fixed bias to the gate-source voltage. The transistor MN8 connects the drain D of the transistor MN1 and the gate G of the transistor MN2 through the gate-source. The transistor MN8 acts as a source follower, lowering the potential by Vth (between the gate and source) and outputting it to the gate G of the transistor MN2. Meanwhile, while each transistor achieves the desired operation by being used in the saturation region, the input range of the voltage of the gate G of the transistor MN1 is limited by the power supply Vdd. In that case, it would be necessary to use transistors with high voltage resistance for the entire circuit, but in Figure 3, it would be possible to increase the power supply Vdd at which the circuit including the LDO part operates. Also, in the circuit of Figure 1, it would be difficult to design the bias within the circuit, but in the circuit of Figure 3, a higher power supply Vdd can be used, making circuit design easier. In this way, even if the power supply Vdd is increased by using circuit components with high voltage resistance, it is possible to design the same operation as in Figure 1 with a higher degree of freedom.

[0032] 4A and 4B are circuit diagrams showing other embodiments, in which (A) is an example in which a transistor MN11 is added as a cascode to an amplifier circuit 42', and (B) is an example in which multiple systems with capacitors of different sizes are connected in parallel.

[0033] In another embodiment shown in (A), a transistor MN11 is added in series with the transistor MN4 in cascode connection. This increases the output resistance of the amplifier circuit and synergistically improves the gain. It is believed that the gain of the circuit in FIG. 3(A) is approximately several hundred times higher than that of the circuit in FIG. 1.

[0034] In yet another embodiment shown in (B), a plurality of AC feedback circuits 4-1, 4-2, ... 4-N (N: 2 or more) with different capacitor capacitances are connected in parallel, and the outputs of the AC feedback circuits 4-1, 4-2, ... 4-N are superimposed by an adder circuit 5 and output to the gate G of the transistor Mpass. The capacitance values ​​of the capacitors Ccap1, Ccap2, ... CcapN set the respective filter frequencies. By arranging the AC feedback circuits 4-1, 4-2, ... 4-N in parallel, it is possible to expand the frequency band for improving the PSRR characteristics.

[0035] The voltage detection circuit 41 in the above embodiment is not limited to the circuit of Fig. 1, and may be another type of amplifier circuit designed to lower the impedance on the output side of the capacitor Ccap to which the output voltage Vout is input. The input of the AC feedback circuit 4, i.e., the capacitor Ccap, may be connected to the input end (source S) of the transistor Mpass functioning as a control element, in addition to being connected to the output end (drain D) Po. Furthermore, the amplifier circuit 42 is not limited to the circuit of Fig. 1, and may be a source-grounded amplifier circuit configuration connected to another known current source without a current mirror circuit.

[0036] Furthermore, the present invention is not limited to MOS type transistors, but may also be applied to other types of transistors.

[0037] As described above, the constant voltage circuit according to the present invention preferably includes a DC feedback circuit that amplifies the error between the output voltage output to the output terminal side via a control element and a predetermined reference voltage using a differential amplifier and feeds it back to the control element, and an AC feedback circuit that applies band selection to the AC component superimposed on the output voltage, amplifies it, and feeds it back to the control element. The AC feedback circuit includes a voltage detection circuit including a capacitor having one end connected to either the input terminal or the output terminal of the control element, and a first transistor with a grounded gate having a source connected to the other end of the capacitor, and an amplifier circuit that amplifies the output signal of the voltage detection circuit and outputs it to the control element. The voltage detection circuit includes a second transistor connected in series to the first transistor, and the drain of the first transistor is connected to the gate of the second transistor and to the amplifier circuit, and the amplifier circuit includes a source-grounded transistor circuit.

[0038] According to the present invention, when the output voltage deviates from a predetermined reference voltage (an error occurs), a feedback signal corresponding to the error is generated and guided to a control element, thereby eliminating the error. On the other hand, when an AC component, which is an AC ripple, occurs in the output voltage, the AC component passes through a capacitor, is detected by a voltage detection circuit including a first transistor with a grounded gate, and is amplified and output. In this way, a coupling capacitor is coupled to a node of a source with low impedance, and the drain of the first transistor is connected to the gate of a second transistor connected in series to reduce the output resistance to the capacitor, so that the AC component in the output voltage is amplified and detected in a wide band without using a differential amplifier. As a result, the output signal from the voltage detection circuit amplified in a wide band is further amplified and fed back to the control element, since a high voltage gain is obtained in the source-grounded transistor circuit of the amplifier circuit, and the AC component superimposed on the output voltage is eliminated. Therefore, a constant voltage circuit that improves PSRR in a wide band while maintaining low power consumption performance can be provided.

[0039] It is also preferable that the voltage detection circuit has a source follower circuit between the drain of the first transistor and the gate of the second transistor, which makes it possible to adopt a higher power supply voltage while taking into consideration the withstand voltage of the transistors used.

[0040] It is also preferable that the amplifier circuit includes a current mirror circuit serving as a current source. With this configuration, a desired current source can be secured.

[0041] It is also preferable that the amplifier circuit includes a circuit in which the common-source transistor circuits are cascode-connected in a plurality of stages, thereby increasing the output resistance of the amplifier circuit and synergistically improving the gain.

[0042] In addition, the present invention preferably includes an adder circuit, the AC feedback circuit being provided in parallel with first and second AC feedback circuits having the capacitors with different capacitance values, and the adder circuit superimposes the output signals of the first and second AC feedback circuits and outputs the superimposed signal to the control element. With this configuration, it is possible to expand the frequency band for improving the PSRR characteristics by arranging multiple AC feedback circuits in parallel, each having a capacitor with a different capacitance value.

[0043] Furthermore, according to the present invention, it is possible to provide an electronic device that is integrally equipped with the constant voltage circuit of the present invention, thereby increasing the versatility of the constant voltage circuit. [Explanation of symbols]

[0044] 1 Constant voltage circuit 2. Control circuit Mpass transistor (control element) 3 DC feedback circuit (direct current feedback circuit) OP Differential amplifier (operational amplifier) 4. AC feedback circuit 41,41' Voltage detection circuit 42,42' Amplification circuit MN1 transistor (first transistor) MN2 transistor (second transistor) MP1~MP5,MP21,MN3~MN8,MN11,MN21 Transistors Ccap, Ccap1, Ccap2, CcapN capacitors

Claims

1. a DC feedback circuit that amplifies an error between an output voltage output to an output terminal side via a control element and a predetermined reference voltage using a differential amplifier and feeds the error back to the control element; an AC feedback circuit that applies band selection to the AC component superimposed on the output voltage, amplifies the AC component, and feeds the amplified AC component back to the control element; The AC feedback circuit includes: a voltage detection circuit including a capacitor having one end connected to either the input end or the output end of the control element, and a first transistor having a grounded gate and a source connected to the other end of the capacitor; an amplifier circuit that amplifies an output signal of the voltage detection circuit and outputs the amplified signal to the control element; the voltage detection circuit includes a second transistor connected in series to the first transistor, the drain of the first transistor being connected to the gate of the second transistor and to the amplifier circuit; The amplifier circuit is a constant voltage circuit including a common-source transistor circuit.

2. 2. The constant voltage circuit according to claim 1, wherein the voltage detection circuit includes a source follower circuit between the drain of the first transistor and the gate of the second transistor.

3. 2. The constant voltage circuit according to claim 1, wherein the amplifier circuit includes a current mirror circuit serving as a current source.

4. 2. The constant voltage circuit according to claim 1, wherein the amplifier circuit includes a circuit in which a plurality of common-source transistor circuits are cascode-connected.

5. A summing circuit is provided, the AC feedback circuit is provided in parallel with first and second AC feedback circuits having the capacitors with different capacitance values, 2. The constant voltage circuit according to claim 1, wherein the adder circuit superimposes the output signals of the first and second AC feedback circuits and outputs the superimposed output signal to the control element.

6. 6. An electronic device comprising the constant voltage circuit according to claim 1.

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