JP3223060B2 - Amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit, and more particularly, to an improvement of an amplifier circuit such as an audio amplifier with high power consumption efficiency.

[0002]

2. Description of the Related Art An audio amplifier according to a conventional example will be described below with reference to the drawings. In the audio amplifier according to the conventional example, it has been an issue to reduce power consumption and to achieve as high efficiency as possible. In a conventional audio amplifier, an amplifier circuit as shown in FIG. 6 has been proposed to improve the efficiency (hereinafter, this circuit is referred to as a first conventional circuit). This is to increase the efficiency of power consumption by supplying a power supply voltage that fluctuates so as to follow the fluctuation of the amplified signal.

That is, the first conventional circuit includes transistors (Q1, Q2) according to the state of an audio signal (hereinafter referred to as an amplified signal) amplified by a preamplifier (3) and transistors (Q1, Q2) in an output stage. ) Is a circuit for changing a power supply voltage (+ Vc, -Vc). The offset power supply (4) adds a constant offset voltage to an amplified signal, and inputs the amplified signal to an inverting input section of a comparator (7). By driving the chopper power supply circuit (8) with the output of (7), a power supply voltage in which a fixed offset voltage is added to the amplified signal can be supplied as shown in FIG.

Therefore, when a small level is input, the power supply voltage (+
Vc, -Vc), and the power supply voltage (+ Vc, -Vc) can be increased at the time of large-level input.
Last stage transistor (Q1, Q2) at the time of low level input
In this case, power loss can be suppressed, and efficiency can be improved. However, according to the first conventional circuit shown in FIG. 6, the audio signal rises sharply, and the limit value of the rising speed of the low-pass filter including the coil (L) and the capacitor (C) in the chopper power supply circuit is reduced. Fig. 8
As shown in FIG. 12, the power supply to the transistors (Q1, Q2) cannot follow, and the output of the amplifier is clipped. Therefore, in order to improve this, the amplification as shown in FIGS. A circuit (hereinafter referred to as a second conventional circuit) has been proposed.

A detailed circuit diagram of this amplifier circuit is shown in FIG.
As shown in FIG. 3, the description will be complicated, and therefore, this amplifier circuit will be described here with reference to FIG. 12 which is a block diagram schematically showing its functions. Also,
The switching circuit (SW) in FIG. 12 includes the transistors (TR151 and TR152) and the resistor (R151) in FIG.
And the MOSFET (TR153), and the capacitor (C151) and the coil (L151)
PF [Low Pass Filter: (14)
A).

According to a second conventional circuit as shown in FIG. 12, an amplified signal (Z) which is an output of a power amplifier (15B) is output.
S) is differentiated and output by the gradient detecting unit (11), a constant voltage is added to the amplified signal (ZS) by the offset voltage generating unit, and the differential and the constant voltage of the amplified signal (ZS) are added by the adding circuit (12). An offset voltage (Va) that is the sum of the added amplified signal (ZS) and the amplified signal (ZS) is generated. Then, the power supply voltage (+ V) output from the chopper power supply circuit (14) is output by the first comparator (13A).
c) and the offset voltage (Va) are compared.

According to the comparison processing, when the power supply voltage (+ Vc) is higher than the offset voltage (Va), the switching circuit (SW) is turned off, and when the power supply voltage (+ Vc) is lower than the offset voltage (Va), the switching circuit is switched. When the circuit (SW) is turned on, the second
Comparator (13A) and chopper power supply circuit (1
4) the power supply voltage (+ Vc) is the offset voltage (Va)
It works to follow.

As described above, the conventional circuit shown in FIG. 12 described above always generates the offset voltage (Va) which is the sum of the voltage obtained by adding a constant voltage to the amplified signal (ZS) and the differential of the amplified signal (ZS). The power amplifier (15B) operates so that the power supply voltage (+ Vc) applied to the collector of the last transistor (TR11) of the power amplifier (15B) follows. Considering the case where an amplified signal (ZS) having a steep rise as shown in FIG. 9 is generated in the circuit, a fixed value is added to the amplified signal (ZS), and an amplified signal (ZS) as shown in FIG. ZS) is differentiated, and the offset voltage (Va) as shown in FIG. 11 is generated by taking the sum of the amplified signal (ZS) added with a constant value and the differential of the amplified signal (ZS). The power supply voltage (+ Vc) generated by the chopper power supply circuit (14) is generated and supplied so as to always follow this offset voltage (Va).

Therefore, in FIG. 9, when the change of the amplified signal (ZS) which is difficult to follow when supplying the power supply voltage (+ Vc) in the conventional circuit shown in FIG. Since the power supply voltage (+ Vc) is supplied so that the differential of the increased amplified signal (ZS) follows the added offset voltage (Va), the supply of the power supply voltage (+ Vc) changes with the change of the amplified signal (ZS). I can follow with plenty of time,
High efficiency has been realized while suppressing clipping of the output of the amplifier which has occurred in the first conventional circuit.

[0010]

However, FIG.
According to the second conventional circuit as shown in FIG. 13, when an audio signal is absent, there is a problem that switching noise occurs in the amplifier output due to the following reasons. That is, in the amplifier circuit shown in FIG. 12, the input signal (AS) and the amplified signal (Z
Even when S) has no signal, the MOSFET (TR153), which is a switching transistor, repeats the ON / OFF operation under the control of the second comparator (13B).

When the MOSFET (TR153) is turned on, the coil (L151) → capacitor (C151) → ground potential (G) is applied from the positive power supply (+ Vcc) as shown in FIG.
The current (i) flows through a path ND), and at this time, the capacitor (C151) is charged. Thereafter, when the MOS transistor (TR153) is turned off, the capacitor (C1) is turned off.
Since the charge charged in 51) is discharged, the potential at the point D in FIG. 14 constantly fluctuates as shown in FIG. 15 due to the charge and discharge.

FIG. 15 is a waveform showing a change in the potential at point D, where HK indicates a discharge period. This discharge period (HK) is relatively long, and the potential fluctuation at the point D falls in a so-called audible frequency band. Such a potential change at the point D leaks to the speaker (SP) when there is no signal, which causes a problem that noise is generated from the speaker (SP) when no audio signal is input.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional disadvantages. As shown in FIG. 1, a signal amplifying section for amplifying an input signal and outputting the amplified signal as an amplified signal is provided. A gradient detection unit that detects a gradient of the amplified signal and outputs it to an offset voltage generation unit, an offset voltage generation unit that generates an offset voltage based on the amplified signal and a gradient of the amplified signal, and outputs the offset voltage to a chopper power supply circuit. A switching element that operates to fluctuate a power supply voltage, and a filter circuit including a coil and a capacitor, the chopper power supply circuit that supplies a power supply voltage that follows the offset voltage to the signal amplification unit, and is connected to the switching element; A current adjusting resistor for reducing a current flowing through the switching element when the amplified signal is not output; A width circuit, a signal amplifier for amplifying an input signal as shown in FIG. 3 and outputting the amplified signal as an amplified signal, a gradient detector for detecting a gradient of the amplified signal and outputting it to an offset voltage generator, A power supply that generates an offset voltage based on a gradient of the amplified signal and outputs the offset voltage to a voltage supply unit, and a switching element that performs a switching operation to vary a power supply voltage, and that follows the offset voltage. A steep rise of an audio signal is provided by an amplifier circuit having a chopper power supply circuit for supplying a voltage to the signal amplification section and a switch circuit for forcibly turning off the switching element when the amplification signal is not output. Also, the power supply to the transistors (Q1, Q2) follows, the efficiency is improved, and the amplifier is turned off when there is no signal. There is provided an amplifier circuit makes it possible to suppress the switching noise occurs in the output.

[0014]

According to an amplifier circuit of the present invention, a signal amplifier for amplifying an input signal and outputting the amplified signal as an amplified signal, a gradient detector for detecting a gradient of the amplified signal and outputting the amplified signal to an offset voltage generator, An offset voltage generation section that generates an offset voltage based on the amplified signal and its gradient and outputs the offset voltage to a chopper power supply circuit, and a switching element that performs a switching operation to vary the power supply voltage. A chopper power supply circuit to be supplied to the amplifying unit, and a current adjusting resistor connected to the switching element for reducing a current flowing through the switching element when an amplified signal is not output.

Since the current flowing through the switching element and the coil when there is no signal is reduced by the current adjusting resistor, the point D does not rise to the potential at which switching is started, and the switching element is not switched. That is, when there is no signal, the switching element operates as a dropper. Therefore, it is possible to reduce noise when there is no signal, which has conventionally occurred due to the voltage fluctuation.

Therefore, for example, when the configuration of this chopper power supply circuit is as shown in FIG. 14, the MOSFET (TR153) constituting the switching element
Gate-source voltage (Vgs) of the MOSF
The drain current (Id) of the ET (TR153) decreases. In this case, the MOSFET (TR153) is always in an energized state due to a decrease in the gate-source voltage (Vgs). As a result, the current component (i) of the path from the positive power supply (+ Vcc) to the coil (L151) → the capacitor (C151) → the ground potential (GND) flows. Of the potential at point D is so small as to be almost negligible.

As described above, a switching element such as a MOSFET (TR153) is always energized by a current adjusting resistor when there is no signal, and the current flowing through this switching element is reduced. This makes it possible to minimize the occurrence of noise when there is no signal, which is caused by potential fluctuations leaking to the amplifier output.

Further, according to the amplifier circuit of the present invention, a signal amplifier, a gradient detector, an offset voltage generator,
It has a chopper power supply circuit and a switch circuit for forcibly turning off a driver circuit of the switching element when an amplified signal is not output. For this reason, conventionally, a switching element such as a MOSFET performs a switching operation when an input signal is absent, and the potential at the point D in FIG. 14 fluctuates. According to this, the driver circuit of the switching element is forcibly turned off by the switch circuit when there is no signal, so the switching element does not perform the switching operation when there is no signal, and the above-described fluctuation of the potential does not occur.
This fluctuation is suppressed from leaking into the amplifier output (speaker) as in the related art.

As a result, it is possible to suppress the occurrence of noise which has conventionally occurred when there is no signal as much as possible. In the amplifier circuit according to the present invention, the switching element is MO
As shown in FIG. 4, the switch circuit has a resistor connected between the emitter and the base of an NPN-type transistor whose emitter is grounded, and has a collector connected to a MOSF.
A resistor and a diode are connected in series between the gate of the ET and between the base of the NPN transistor and the output of the signal amplifier.

According to such a switch circuit, when an amplified signal is being output from the signal amplifying section, this is input to the base of the NPN transistor via the diode and the resistor, and the NPN transistor is turned on. On the other hand, when the amplified signal is absent, no signal is input to the base of the NPN transistor via the diode and the resistor, so that the NPN transistor is turned off.

Therefore, when the amplified signal is a non-signal, it is OFF.
Then, the switching operation required for the amplifier circuit according to the present invention, which is turned on when the amplified signal is output, can be realized with a relatively simple circuit configuration. Also, the output voltage at which switching is started can be set arbitrarily by the division ratio of the resistance between the base and the emitter of the transistor and the resistance connected in series to the base.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment Hereinafter, an amplifier circuit according to a first embodiment of the present invention will be described with reference to FIGS. The power supply circuit according to the embodiment of the present invention is a part of the amplifier circuit according to the embodiment, and includes a power supply circuit (17) on the positive side and a power supply circuit (16) on the negative side.

The amplifier circuit according to the embodiment of the present invention is a high-efficiency audio amplifier. As shown in FIG. 3, a + side power supply circuit (17), a − side power supply circuit (16), a preamplifier (15A) and a power amplifier (15B). In the present embodiment, the power supply circuit (1
Only 7) will be described. -Side power supply circuit (16)
Is configured in the same manner as the + side, and is driven by the negative power supply (−Vcc), and its operation is symmetric with the + side.

As shown in FIG. 3, the power supply circuit (17) on the + side includes a constant voltage generation circuit (10), a gradient detection section (11),
An offset voltage generator (12), a first comparator (13A), a second comparator (13B), a current adjusting resistor (R141), and a chopper power supply circuit (14) constitute an embodiment of a signal amplifier. Power amplifier (1
5B) supplies the power supply voltage (+ Vc) related to the collector of the transistor (TR11) at the last stage.

The constant voltage generating circuit (10) is a circuit for generating a constant voltage required for the amplifier circuit.
A constant voltage is supplied to the non-inverting input portion of the comparator (13B), that is, the base of the transistor (TR142). The gradient detection unit (11) includes a capacitor (C11
0), differentiating circuit (11A) composed of resistor (R110)
And a transistor (TR110) and resistors (R111, R111).
112).

The function is to differentiate the amplified signal (ZS) output from the power amplifier (15B) by a differentiating circuit (11A), and based on the result of the differentiation, an offset voltage generator (12).
More specifically, the differentiation circuit (11
A) The base current of the transistor (TR110) fluctuates according to the output of A), and the collector current of the transistor (TR110) fluctuates. The base potential of the transistor (TR121) connected to the collector of the transistor (TR110) changes in accordance with the change. Let me.

The offset voltage generator (12) includes transistors (TR121, TR122) and resistors (R121 to R121).
R124). Its function is to add a fixed voltage to the amplified signal (ZS) which is the output of the power amplifier (15B), and to add the amplified signal (ZS),
The differential result, which is the output from the gradient detector (11), is added and output to the non-inverting input of the first comparator (13A). To be more specific, the resistors (R123, R124)
Is connected to the base of the transistor (TR122) and the resistor (R123) is connected to the collector to add a constant voltage to the amplified signal (ZS), thereby causing a change in the collector current of the transistor (TR110). The potential at the point A in FIG. 3 (hereinafter referred to as an offset voltage (Va)) to which the variation of the base potential of the transistor (TR121) and the amplified signal (ZS) added with a constant voltage are added as the first potential. Comparator (13
Transistor (TR132) which is a non-inverting input part of A)
Output to the base.

The first comparator (13A) and the second comparator (13B) constitute an example of the drive control section (13). First comparator (13A)
Is a circuit including transistors (TR131 to TR133), resistors (R131 to R133), and a capacitor (C130).

Its function is to compare the power supply voltage (+ Vc) output from the chopper power supply circuit (14) with the offset voltage (Va) from the offset voltage generator (12), The operation is controlled. More specifically, when the offset voltage (Va) is lower than the power supply voltage (+ Vc), the transistor (TR1)
31), a constant current from a constant current generating circuit composed of resistors (R131, R132) and a capacitor (C130) flows through the transistor (TR132), and conversely, the power supply voltage (+ V
When the offset voltage (Va) is higher than c), most of the constant current flows to the transistor (TR133), and the base voltage of the transistor (TR141) is controlled by the collector current of the transistor (TR133). Drive control of the second comparator (13B).

The second comparator (13B) includes a transistor (TR141, TR142) and a resistor (R142).
Circuit. Its function is to compare the output signal of the first comparator (13A) with the constant voltage generated by the constant voltage generation circuit (10) and control the operation of the chopper power supply circuit (14) according to the state. Specifically, when the collector voltage of the transistor (TR133) corresponding to the output signal of the first comparator (13A) is input to the base of the transistor (TR141), the transistor (TR141) operates and its collector current This controls the operation state of the transistors (TR151, TR152) that drive the chopper power supply circuit (14).

The chopper power supply circuit (14) includes a transistor (TR151, TR152) and a MOSFET (TR1).
53), a switching element (SW) including a resistor (R151), a capacitor (C151), and a coil (L15).
1) LPF (Low Pass Filter) (14A) and flywheel diode (D1)
50).

This is because the switching element (SW) is turned on based on the drive control of the second comparator (13B).
/ OFF operation enables power amplifier (15B)
Is a circuit for supplying the power supply voltage (+ Vc) to the collector of the transistor (TR11) at the last stage. The current adjustment resistor (R141) supplies a bias necessary for the operation of the second comparator (13B), and at the same time, the gate of the MOSFET (TR153) connected via the transistors (TR151, TR152). This is a resistor that reduces the source-to-source voltage (Vgs).

Actually, in the second conventional circuit, the current adjusting resistor (R141) is connected to the second comparator (13B) as shown in FIG. 13, but in the amplifier circuit according to the present embodiment, The point that the resistance value of the current adjustment resistor (R141) is lower than that of the related art is different from the related art. Specifically, the resistance value is about half of the conventional resistance value. The operation of the circuit will be described below in two cases: (A) when the amplified signal (ZS) is output, and (B) when there is no amplified signal (ZS). In any case, the constant voltage generator (10), the gradient detector (11), the offset voltage generator (12), the first comparator (13A), and the second comparator (13B).
It is assumed that the positive power supply (+ Vcc) for driving the chopper power supply circuit (14) has already been applied.

(A) When an amplified signal (ZS) is output First, an audio signal (AS) is input to a preamplifier (15A), amplified by a power amplifier (15B), and then output by transistors (TR11, TR12) at the final stage. The amplified signal (ZS) is output to the speaker (SP). The amplified signal (ZS) is also input to the differentiating circuit (11A) of the gradient detecting unit (11), and is also input to the base of the transistor (TR122) of the offset voltage generating unit (12) via the resistor (R124). .

The transistor (TR) of the gradient detector (11)
When there is no amplified signal (ZS) at the base of 110), the base is only biased by D102 (10), and since the emitter potential is 0, no collector current flows. When the amplified signal (ZS) is input,
The signal waveform is differentiated by a differentiating circuit (11A),
The base potential of the transistor (TR110) fluctuates according to the differentiated waveform, and its collector current changes.

At this time, the diode (D1) whose base potential of the transistor (TR110) becomes its operation reference value.
In a portion lower than the anode potential of (02), the transistor (TR110) performs a cutoff operation. When the rising gradient of the amplified signal (ZS) is steep, the output of the differentiating circuit (11A) largely swings to the positive side, so that the collector current of the transistor (TR110) also shows a large value accordingly.

On the other hand, when the amplified signal (ZS) has a falling slope, the output of the differentiating circuit (11A) swings to the negative side, but no collector current flows. Transistor (TR11
When the collector current of (0) flows, the base potential of the transistor (TR121) which has been flowing a constant DC current to the collector until the base potential is kept constant by the constant voltage generating circuit (10) is increased by the transistor ( T
The collector current of the transistor (TR121) increases by the amount corresponding to the decrease in the collector current of the transistor R110), and as a result, the potential of the point A, which is the collector potential, increases.

On the other hand, the amplified signal (ZS) is simultaneously input to the base of the transistor (TR122) of the offset voltage generator (12) via the resistor (R124). The transistor (TR122) performs an emitter follower operation in response to the amplified signal (ZS). However, since the collector saturates at a portion where the amplified signal (ZS) swings to the negative side, the amplified signal (ZS) is applied to the base and the emitter. A waveform with the negative side clipped appears.

The emitter of the transistor (TR122) is connected to the transistor (TR1) via a resistor (R122).
The current generated in 21) flows in. Transistor (TR
122) does not depend on this current, but since the resistor (R122) produces a potential difference according to the current,
The potential at the point A is a value obtained by adding the potential difference generated by the resistor (R122) to the emitter potential of the transistor (TR122).

Since the collector current of the transistor (TR121) is originally a DC current from the DC voltage generated by the constant voltage generating circuit (10), the waveform of the potential at the point A is applied to the emitter of the transistor (TR122). The appearing clip waveform is a waveform shifted to a constant voltage. However, if the amplified signal (ZS) has a steep rising gradient, the collector voltage of the transistor (TR121) increases due to the operation of the gradient detection unit (11). As a result, the potential at the point A, that is, the offset voltage (Va) has a waveform in which 1) an amplified signal (ZS) 2) a constant DC voltage 3) an output voltage from a differentiating circuit (11A) is added. The offset voltage (Va) thus generated is applied to the base of the transistor (TR132), which is the non-inverting input of the first comparator (13A).

The output potential of the chopper power supply circuit (14), that is, the power supply voltage (+ Vc) is input to the base of the transistor (TR133), which is the inverting input section of the first comparator (13A). Accordingly, the offset voltage (Va) and the power supply voltage (+ V) output from the chopper power supply circuit (14) are output by the first comparator (13A).
c) is performed, but the following operations are performed. (i) When the offset voltage (Va) is higher than the power supply voltage (+ Vc), (ii) When the offset voltage (Va) is higher than the power supply voltage Since the operation is different in the two cases of (less than (+ Vc)), each case will be described below.

(I) When the offset voltage (Va) is higher than the power supply voltage (+ Vc) In this case, the base potential of the transistor (TR132) is higher than the base potential of the transistor (TR133). Is turned off, and the transistor (TR133) is turned on. Then, the base potential of the transistor (TR141) rises due to the collector current of the transistor (TR133), turning on the transistor (TR141), and turning on the transistor (TR1).
42) is turned off.

When the transistor (TR141) is turned on and the collector current flows, the transistor (TR15) constituting the driver of the chopper power supply circuit (14)
1, TR152), the base potential drops, and the MOSFET
A low-level voltage is output to the gate of (TR153). Since the MOSFET (TR153) is a p-channel, it is turned on by a low level, and the power supply voltage (+ Vc), which is the output of the LPF (14A), is offset voltage (V
It begins to rise to follow a), and eventually reaches a level exceeding the offset voltage (Va).

(Ii) When the offset voltage (Va) is smaller than the power supply voltage (+ Vc) which is the output of the chopper power supply circuit (14) In this case, the base potential of the transistor (TR132) is set to the base potential of the transistor (TR133). Since the potential is lower than the potential, the transistor (TR132) is turned on and the transistor (TR133) is turned off.

Then, since the collector current of the transistor (TR133) stops flowing, the transistor (TR1)
41), the base potential of the transistor (TR14) decreases.
1) is turned off and the transistor (TR142) is turned on
Is done. Since the transistor (TR141) is turned off and its collector current is cut off, the transistor (TR) constituting the driver of the chopper power supply circuit (14)
151, TR152) rises and MOSF
A high-level voltage is output to the gate of ET (TR153).

A high level voltage is applied to the MOSFET (TR1
53) The MOSFET is output to the gate of
(TR153) is turned off, and as a result, the LPF (14
The power supply voltage (+ Vc) which is the output of A) starts to decrease.
In this case, the power supply voltage (+ Vc) decreases to the ground potential over time, but the first comparator (13A) constantly compares the power supply voltage (+ Vc) with the offset voltage (Va). , Power supply voltage (+ V
When c) falls below the offset voltage (Va), the above (i)
, The MOSFET (TR153) is turned on again, and the power supply voltage (+ Vc) starts to rise.

That is, the circuit is composed of the above (i) and (ii)
Is always repeated, the power supply voltage (+ V
c) operates so as to follow the offset voltage (Va). As described above, when the input signal (AS) is input, the circuit always performs the offset voltage (Va) which is the sum of the voltage obtained by adding a constant voltage to the amplified signal (ZS) and the differential of the amplified signal (ZS). Power amplifier (15
The operation is performed so that the power supply voltage (+ Vc) applied to the collector of the transistor (TR11) at the last stage of B) follows.

For example, considering an amplified signal (ZS) having a steep rise as shown in FIG. 9, a constant value is added to the amplified signal (ZS), and at the same time, the amplified signal (ZS) shown in FIG. The chopper power supply circuit obtains an offset voltage (Va) as shown in FIG. 11 by taking a differentiation and taking the sum of the amplification signal (ZS) with a fixed value added and the differentiation of the amplification signal (ZS). The power supply voltage (+ Vc) generated by (14) is generated and supplied so as to always follow this offset voltage (Va).

Therefore, when the change of the amplified signal (ZS) is steep, its differentiation is increased, and the increased amplified signal (ZS) is increased.
The power supply voltage (+ Vc) is supplied so as to follow the offset voltage (Va) in which the differential of the power supply voltage is added, so that the supply of the power supply voltage (+ Vc) can follow the change of the amplified signal (ZS) with a margin, and the conventional method can be used. It is possible to achieve high efficiency while suppressing clipping of the output of the amplifier that has been performed.

(B) When the Amplified Signal (ZS) is No Signal The operation described below is a major feature of the amplifier circuit of this embodiment. In this case, since the current adjusting resistor (R141) is connected to the gate of the MOS transistor (TR153) via the transistors (TR151 and TR152) constituting the switching element (SW) in this circuit, this MOS transistor (TR15
The gate-source voltage (VGS) of 3) is lower than that of the conventional circuit.

FIG. 2 shows a MOS transistor (TR153).
Gate-source voltage (Vgs) and drain current (I
d). In FIG. 2, V is Vgs in the conventional circuit, and V 'is Vgs in the circuit of the present embodiment.
It is. As shown in FIG. 2, the Id I2 at Vgs V 'of the present embodiment is extremely small compared to the Id I1 at Vgs V of the prior art. I understand.

According to the circuit, when there is no signal, first the first
In addition, since the current adjusting resistor (R141) having a lower resistance than the conventional one is connected to the gate side of the MOSFET (TR153), Vgs falls.
T (TR153) turns on. Current adjustment resistor (R14
According to 1), in order to reduce the current flowing through the switching element and the coil, the point D does not rise to a voltage at which switching is started, and the switching element is not switched. That is, when there is no signal, the switching element operates as a dropper.

Therefore, the MOS transistor (TR15
3) is turned on and the positive power supply (+ Vcc) → coil (L15
1) → Capacitor (C151) → Current component (i) flows through a path of ground potential (GND). As a result, in the second conventional circuit as shown in FIGS. 12 and 13, the fluctuation of the potential at the point D enters the so-called audible band and leaks to the speaker (SP), which occurs when there is no signal. It is possible to easily suppress the generation of noise as much as possible.

(2) Second Embodiment Hereinafter, an amplifier circuit according to a second embodiment of the present invention will be described. Description of items common to the first embodiment will be omitted to avoid duplication. The amplifier circuit according to the second embodiment is different from the amplifier circuit according to the first embodiment in that a switching circuit (MS) is connected between the ground potential (GND) and the collector of the transistor (TR152) as shown in FIG. Unlike the example, the subsequent configuration and operation are almost the same as in the first embodiment.

First, a switching circuit newly added in this embodiment will be described. When the amplified signal (ZS) has no signal, the switching circuit (MS)
F, and a circuit that performs a switching operation while monitoring the amplified signal (ZS), such as turning on when the amplified signal (ZS) is output. The specific configuration is shown in FIG. That is, the NPN transistor (tr
1) A resistor (r1) is connected between the emitter and the base,
The emitter is grounded, the collector is connected to the collector of the transistor (TR152) constituting the switching element (SW) of FIG. 3, and the base is connected with a resistor (r2) and a rectifying diode (d1) connected in series. It is connected.

The output of the power amplifier (15B) in FIG. 3 is connected to the diode (d1), from which the amplified signal (ZS) is input to the switching circuit (MS). According to the switch circuit (MS), when the amplified signal (ZS) is output from the power amplifier (15B), it is input to the base of the transistor (tr1) via the diode (d1) and the resistor (r2). So
When the base potential exceeds VBE, the output voltage VOUT when this switch circuit is turned on is VOUT = (VBE (r
1 + r2) / r1) + Vd, and can be arbitrarily set by r1 and r2.

On the other hand, when the amplified signal (ZS) is absent, it is not input to the base of the transistor (tr1) via the diode (d1) and the resistor (r2), so that the base-emitter voltage of the transistor (tr1) is low. That is, the transistor (tr1) is off. Therefore, the switch circuit (MS) outputs the amplified signal (Z
S) is turned off when there is no signal, and turned on when the amplified signal (ZS) is output.

In the following, the operation of the circuit will be described in the same manner as in the first embodiment: (A) when the amplified signal (ZS) is output, and (B) when the amplified signal (ZS) is absent. 2
The description is divided into two cases. (A) When the amplified signal (ZS) is output When the amplified signal (ZS) is output, the switch circuit (MS) is turned on by the above operation. In other respects, the operation is the same as that of the amplifier circuit of the first embodiment, and the same effect is obtained. Therefore, the description is omitted to avoid duplication. (B) When the Amplified Signal (ZS) is No Signal In addition, when there is no signal, the switch circuit (MS) is turned off. When this is turned off, the second comparator (13B)
Whatever the operation of the transistors (TR151, TR15) involved in driving the MOSFET (TR153),
2) The MOS transistor (TR153) does not operate as a driver transistor, and the gate of the MOSFET can be driven only at a few milliamps. Therefore MOSFET
Starts dropper operation because switching cannot be performed.

For this reason, conventionally, when the input signal is no signal, M
The OS transistor (TR153) performs a switching operation, and the potential at point D in FIG. 5 fluctuates.
P), noise was generated due to the leakage. However, according to the present invention, the driver circuit of the MOSFET (TR153) is forcibly turned off by the switch circuit (MS) when there is no signal. Since the operation is not performed, the dropper operates and the above-described fluctuation of the potential does not occur, the fluctuation is prevented from leaking into the speaker (SP) as in the related art.

As a result, it is possible to minimize the generation of noise which has conventionally occurred when there is no signal. Further, in the case of the amplifier circuit of the first embodiment, noise can be easily reduced, but even if the resistance value of the current adjustment resistor (R141) is set to an appropriate value, the MOS transistor (TR153) ) Has characteristic variations, so in some cases, noise could not be reduced.
According to the amplifier circuit of the present embodiment, the MOS transistor (TR153) is forcibly turned off when there is no signal, so that generation of noise can be suppressed regardless of the characteristics of the MOS transistor (TR153). it can.

[0061]

As described above, the power supply circuit according to the present invention has a signal amplifier, a gradient detector, an offset voltage generator, a chopper power supply circuit, and a current adjustment resistor. For this reason, the current flowing through the switching element is reduced by the current adjusting resistor, so that the current flowing from the switching element to the filter circuit of the chopper power supply circuit when there is no signal is reduced, and the switching element operates as a dropper without switching. It is possible to reduce noise generated at the time of signal.

According to the amplifier circuit of the present invention, the signal amplifying section, the gradient detecting section, the offset voltage generating section,
A chopper power supply circuit having a switching element and a switch circuit are provided. For this reason, the driver circuit of the switching element is forcibly turned off by the switch circuit when there is no signal, so that the switching element does not perform the switching operation but the dropper operation when there is no signal, so that the above-described fluctuation of the potential does not occur. Therefore, it is possible to prevent the fluctuation from leaking into the speaker as in the related art, and it is possible to minimize the occurrence of noise that has conventionally occurred when there is no signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is an operation characteristic diagram of the MOS transistor according to the first example of the present invention.

FIG. 3 is a circuit diagram of an amplifier circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a switching circuit in an amplifier circuit according to a second embodiment of the present invention.

FIG. 5 is a diagram illustrating an operation of the amplifier circuit according to the second example of the present invention.

FIG. 6 is a circuit diagram illustrating a first conventional circuit.

FIG. 7 is a first graph illustrating the operation of the first conventional circuit.

FIG. 8 is a second graph illustrating the operation of the first conventional circuit.

FIG. 9 is a first graph illustrating an operation of a second conventional circuit.

FIG. 10 is a second graph illustrating the operation of the second conventional circuit.

FIG. 11 is a third graph illustrating the operation of the second conventional circuit.

FIG. 12 is a block diagram illustrating functions of a second conventional circuit.

FIG. 13 is a circuit diagram of a second conventional circuit.

FIG. 14 is a first graph illustrating a problem of the second conventional circuit.

FIG. 15 is a second graph illustrating a problem of the second conventional circuit.

[Explanation of symbols]

 (10) Constant voltage generation circuit (11) Gradient detection section (11A) Differentiation circuit (12) Offset voltage generation section (13) Drive control section (13A) First comparator (13B) Second comparator (14) Chopper power supply Circuit (14A) LPF (15) Signal amplifier (15A) Preamplifier (15B) Power amplifier (16) Negative power supply circuit (17) Positive power supply circuit (18) Voltage supply part (20) Support substrate (R141) Current adjustment resistor (SW) Switching element (SP) Speaker (Va) Offset voltage (+ Vcc) Positive power supply (+ Vc) Power supply voltage (AS) Audio signal [input signal] (ZS) Amplified signal (MS) Switching circuit

Continuation of front page (72) Inventor Yukio Sakuma 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Hiroyuki Kataoka 2-5-5-1 Keihanhondori, Moriguchi-shi, Osaka Sanyo JP-A-6-314936 (JP, A) JP-A-7-74548 (JP, A) JP-A-7-221559 (JP, A) JP-A-7-221556 (JP) JP-A-7-221557 (JP, A) JP-A-7-221558 (JP, A) JP-A-8-330853 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H03F 1/00-1/56 H03F 3/00-3/36

Claims (3)

(57) [Claims] A signal amplification unit that amplifies an input signal and outputs the amplified signal as an amplified signal; a gradient detection unit that detects a gradient of the amplified signal and outputs it to an offset voltage generation unit; An offset voltage generation unit that generates an offset voltage based on the gradient and outputs the offset voltage to a chopper power supply circuit, a filter circuit including a coil and a capacitor, and a switching element that performs a switching operation to vary the power supply voltage; A chopper power supply circuit for supplying a power supply voltage that follows the power supply voltage to the signal amplifying section, and the switching element when the amplified signal is not output.
Set the current adjustment resistor connected to the
The switching element is operated by dropping the switching element.
The current flowing through the
Characterized by suppressing the occurrence of switching noise
Width circuit. 2. A signal amplifying section for amplifying an input signal and outputting the amplified signal as an amplified signal; a gradient detecting section for detecting a gradient of the amplified signal and outputting it to an offset voltage generating section; An offset voltage generation unit that generates an offset voltage based on the gradient of the offset voltage and outputs the offset voltage to a voltage supply unit; and a switching element that performs a switching operation to vary a power supply voltage, and amplifies the power supply voltage that follows the offset voltage by the signal amplification. And a switch circuit for forcibly turning off the switching element when the amplified signal is not output. 3. The switching element has a MOSFET. The switch circuit has a resistor connected between an emitter and a base of an NPN-type transistor whose emitter is grounded.
3. The device according to claim 2, wherein a collector is connected to a gate side of said MOSFET, and a resistor and a diode are connected in series between a base of said NPN transistor and an output of said signal amplifier. Amplifier circuit.