JP3439030B2 - 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 specifically, an object thereof is to reduce adverse effects due to switching noise of an amplifier circuit used in an audio amplifier or the like and provided with a switching power supply.

[0002]

2. Description of the Related Art An amplifier circuit mounted on an audio amplifier according to a conventional example will be described below. Conventionally, in an audio amplifier that uses a constant voltage as a power supply voltage, the amplifier is driven by using a high voltage that can always obtain the maximum output as a power supply voltage.

In such a circuit, even if the output is at a low level, the power supply voltage is high enough to always take out the maximum output, so that the power consumption in the amplifier becomes unnecessarily large. , The efficiency of the amplifier was low. Therefore, in order to improve the efficiency of the amplifier, the following amplifier circuit has been proposed. In this technique, a voltage obtained by multiplying the amplified signal (ZS) by a constant voltage is used as a power supply voltage, and the power supply voltage is changed while the power supply voltage is changed according to the increase or decrease of the amplified signal (ZS).

Specifically, this circuit is a circuit as shown in FIG. 17, and has an amplifier (1) and an auxiliary power supply section (2). A power source having the same configuration as the auxiliary power source unit (2) is connected to the negative side of the amplifier (1),
Since this is the same as the positive side, the description is omitted. According to the above circuit, when the power is turned on, a constant power supply voltage (± Vcc) is applied to the auxiliary power supply unit (2).

Next, the input signal (AS) is amplified by the amplifier (1) to generate an amplified signal (ZS), which is output to a speaker (not shown) and simultaneously output to the auxiliary power supply section (2). Then, a constant voltage is added to the amplified signal (ZS) by the offset voltage generation circuit (4), and the amplified signal (ZS) is input to the inverting input unit (-) of the comparator (7). On the other hand, the power supply voltage (+ Vc) output from the chopper power supply (8) is input to the non-inverting input portion (+) of the comparator (7), and the power supply voltage (+ Vc) and a constant voltage are always added. It is compared with the amplified signal (ZS).

The output of the comparator (7) is connected to the switching element (SW) of the chopper power supply (8),
The amplified signal (ZS) with a constant voltage added is used as the power supply voltage (+
When Vc) falls, the output of the comparator (7) becomes low level (hereinafter referred to as “L”), the switching element (SW) is turned on, the power supply voltage (+ Vc) rises, and on the contrary, the constant voltage rises. When the power supply voltage (+ Vc) exceeds the amplified signal (ZS) generated, the output of the comparator (7) becomes a high level (hereinafter referred to as “H”), the switching element (SW) is turned off, and the power supply voltage (+ Vc). Rises.

As a result of the above operation, the power supply voltage (+ Vc) changes while following the voltage obtained by multiplying the amplified signal (ZS) by a constant voltage as shown in FIG.
Is supplied to. The input signal (AS) is amplified by the amplifier (1) using this power supply voltage (+ Vc), and the amplified signal (ZS) is output to the speaker. By varying the power supply voltage (± Vc) according to the magnitude of the amplified signal (ZS) in this way, compared with the case where the amplifier is driven with a high voltage that can always obtain the maximum output as the power supply voltage, We were trying to improve efficiency by reducing the loss of power consumption when outputting at a small level.

[0008]

However, the above conventional amplifier circuit uses the chopper power source (8), and the switching frequency of this switching element (SW) is
It is about 200 kHz to 500 kHz. This is to obtain the frequency characteristic of the amplifier up to 20 kHz which is the upper limit of the audible band, and at the same time, to secure the followability of the output waveform and suppress the ripple component.

The frequency of noise of the switching element (SW) is 200 kHz of the fundamental frequency and the second to fifth harmonics, that is, 400 kHz to 1 MHz. This noise is A
Since it falls within the range of 200 kHz to 2 MHz which is the frequency band of the M radio, there is a problem that noise is output from the AM radio when the AM radio is located near this amplifier circuit.

Particularly for in-vehicle applications, since a radio tuner of AM or FM and an audio amplifier are used together, this problem has been a serious problem that cannot be ignored.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art. As shown in FIG. 1, a signal amplifier for amplifying an input signal and outputting the amplified signal, and the amplified signal. And a switching power supply including a switching element that generates a power supply voltage that follows the amplified signal, and the switching power supply is in operation while the radio is operating near the amplification circuit. The above problem is solved by an amplification circuit characterized by stopping the switching operation of the switching element and supplying a constant voltage to the signal amplification section.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION 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 the drawings.

Specifically, this amplifier circuit is a circuit as shown in FIG. 1, and is used as an audio amplifier having a built-in tuner, and is an example of a signal amplifier section (11).
And an auxiliary power supply section (12). The amplifier (1
A power source having the same configuration as the auxiliary power source unit (12) shown in FIG. 1 is connected to the negative side of 1), which is an auxiliary power source unit (12) that generates a positive power source voltage (+ Vc). The configuration is the same as that of the above, except that a negative power supply voltage (-Vc) is generated, and therefore it is not shown and the description is omitted.

The amplifier (11) is an example of a signal amplifier, and amplifies the input signal (AS) by using a power supply voltage (+ Vc) described later and outputs an amplified signal (ZS). Each of them has a voltage amplifying unit for amplifying the voltage of the input signal (AS) and a current amplifying unit for amplifying the output of the voltage amplifying unit by current, but they are not particularly shown. The auxiliary power supply unit (12) is a circuit having an offset voltage generation circuit (14), a comparator (17B), and a chopper power supply (18), and increases or decreases the amplification signal (ZS) of a constant DC voltage (+ Vcc). And is supplied to the amplifier (11). Specifically, for the amplified signal (ZS),
An offset voltage generated by the offset voltage generation circuit (14) is added, and a positive power supply voltage (+ Vc) that changes so as to follow this voltage is supplied.

The offset voltage generator (14) is for multiplying the amplified signal (ZS) by a constant voltage. The comparator (17B) is an example of a signal generator, and includes an amplified signal (ZS) on which a constant voltage is added and a positive power supply voltage (+ V).
c), and the comparison result is output to the switching element (SW).

The switching element (SW) has its gate connected to the output of the comparator (17B), its source connected to a constant DC voltage (+ Vcc), and its drain constituting a low-pass filter of the chopper power supply (18) ( D), MOS connected to choke coil (L)
It is composed of a FET, which is turned on / off according to the output of the comparator (17B), and supplies a constant DC voltage (+ Vcc) to the amplifier (11) while increasing or decreasing it.

The switching circuit (SC) is connected between the switching element (SW) and a constant voltage (Vz) and is turned on when the radio operation signal (AM) is input.
Then, the gate potential of the switching element (SW) is forcibly lowered to a constant voltage (Vz) which is a voltage at which the switching element (SW) is turned on, and is turned on.

The operation of the above amplifier circuit will be described below. First, a constant power supply voltage (±
Vcc) is applied. Next, the input signal (AS) is amplified by the amplifier (11) to generate an amplified signal (ZS), which is output to a speaker (not shown) and simultaneously output to the auxiliary power supply unit (12).

Then, a constant voltage is added to the amplified signal (ZS) by the offset voltage generation circuit (14), and the amplified signal (ZS) is input to the inverting input section (-) of the comparator (17B). On the other hand, the power supply voltage (+ V) output from the chopper power supply (18) is applied to the non-inverting input portion (+) of the comparator (17B).
c) is input, and the power supply voltage (+ Vc) is constantly compared with the amplified signal (ZS) on which a constant voltage is added.

The comparison result by the comparator (17B) is output to the switching element (SW). At this time, when the power supply voltage (+ Vc) exceeds the amplified signal (ZS) on which the constant voltage is added, the output of the comparator (17B) becomes a high level (hereinafter referred to as “H”), and the switching element (SW) becomes When the power supply voltage (+ Vc) is turned off and the amplified power supply voltage (+ Vc) falls below the amplified signal (ZS) on which a constant voltage is added, the output of the comparator (17B) is at a low level (hereinafter referred to as "L"). The switching element (SW) is turned on and the power supply voltage (+ Vc) rises.

In this way, the switching element (SW)
Repeats ON / OFF operation. The switching frequency at this time is 200 to 500 kHz. By the above operation, the power supply voltage (+ Vc) is supplied to the amplifier (11) while changing so as to follow the voltage obtained by adding a constant voltage to the amplified signal (ZS) as shown in FIG. The input signal (AS) is amplified by the amplifier (11) using this power supply voltage (+ Vc), and the amplified signal (ZS) is output to the speaker. Therefore, the efficiency is higher than that when a constant voltage is used as the power supply voltage. Will get better.

The operation that is a characteristic operation of this embodiment when the AM radio is ON will be described below. In this case, when the AM radio is turned on, at the same time, for example, the VH signal from the microcomputer is output to the switching circuit (SC)
To enter. Then, the switching circuit (SC) is turned on and the constant voltage (V) is applied to the gate of the switching element (SW).
z) is applied, the switching element (SW) continues to be turned ON and does not perform ON / OFF operation during the period when the VH signal is input from the microcomputer regardless of the operation of other circuits. Therefore, during this period, a constant power supply voltage (± Vcc) is applied to the amplifier (11), and the same operation as that of a normal class AB amplifier is performed.

As described above, according to the amplifier circuit of this embodiment, the switching operation of the switching element (SW) is stopped when the AM radio is operating in the vicinity, so that the conventional switching operation occurs. The harmonic component of switching noise falls within the range of 200 kHz to 2 MHz, which is the frequency band of AM radio, and when AM radio is nearby, the problem that noise is output from this AM radio should be suppressed as much as possible. Will be possible.

This is especially effective for an audio amplifier equipped with an AM or FM radio tuner. In addition,
In the present embodiment, the amplifier circuit having the circuit configuration as shown in FIG. 1 has been described, but the present invention is not limited to this, and changes so as to follow the voltage obtained by adding a constant voltage to the amplified signal (ZS). The same effect can be obtained with any circuit as long as it is an amplifier circuit that operates with a power supply voltage and has a chopper power supply including a switching circuit.

(2) Second Embodiment Before describing the amplifier circuit according to the second embodiment of the present invention below, it will be briefly explained why the following configuration is adopted in the present embodiment. explain. In the amplifier circuit according to the circuit configuration of the first embodiment, when the amplified signal (ZS) having a sharp rise is generated as shown in FIG. 4, the auxiliary power supply unit cannot follow the abrupt change, and As shown in, the power supply voltage (+ Vc), which should originally be higher than the amplified signal (ZS), is lower than the amplified signal (ZS), and the amplified signal (ZS) is distorted. This problem is solved by the amplifier circuit according to the embodiment.

A second embodiment of the present invention will be described below with reference to the drawings. Note that description of items common to the first embodiment will be omitted to avoid duplication. The difference of this circuit from the first embodiment is not that the amplified signal (ZS) is simply superposed with a constant voltage and the power supply voltage follows it, but the slope detection section (7
1) The gradient of the amplified signal (ZS) is detected, and the sum of the detection result and the constant voltage is added to the amplified signal (ZS).

The amplifier circuit according to the present embodiment is used for an audio amplifier having a built-in tuner, and as shown in FIG. 3, a gradient detector (71) and an offset voltage generator (7).
2), a chopper power source (74), an auxiliary power source section (77) having a first and second comparator (73A, 73B) and a switching circuit (SC), a preamplifier (75A),
It is a circuit having an amplification section (75) including a power amplifier (75B).

The gradient detecting section (71) is a circuit that has a differentiating circuit and finds the differential of the amplified signal (ZS). The offset voltage generation unit (72) includes an offset unit (72A) for adding a constant voltage to the amplified signal (ZS) and an addition circuit (72B).
And a constant voltage and an offset voltage (Va) which is a result of addition of the amplified signal.

The first comparator (73A) and the second comparator (73B) constitute an example of a signal generator, and a voltage is applied to the gate electrode of the switching element (SW) to turn it on / off. It is a circuit that controls the state. The second comparator (73B) is provided for stabilizing the operation. The chopper power source (74) has a switching element (SW). The switching element (SW) has a source connected to a constant power supply voltage (+ Vcc), a drain connected to a diode (D150) and a capacitor (C151), and a gate connected to a second comparator (73B). And O
N / OFF is performed to step down a constant power supply voltage (+ Vcc) to generate a power supply voltage (+ Vc).

Further, the switching circuit (SC2) is connected between the switching element (SW) and a constant voltage (Vz), and is turned on when the radio operation signal (AM) is input.
It is a circuit for turning on the gate potential of the switching element (SW) by forcibly raising the gate potential. The operation of the amplifier circuit according to this embodiment will be described below.

First, the amplified signal (ZS) output from the power amplifier (75B) is a gradient detecting section (7) which is a differentiating circuit.
Differentiated by 1). On the other hand, a constant voltage is added to the amplified signal (ZS) by the offset voltage generator (72), and the addition result of the differential of the amplified signal (ZS) and the amplified signal (ZS) added with the constant voltage is added by the addition circuit. A voltage (hereinafter referred to as offset voltage (Va)) is generated.

Then, the first comparator (73A) outputs the power supply voltage (+) which is the output of the chopper power supply (74).
Vc) and the offset voltage (Va) are compared and output to the inverting input side of the second comparator (73B),
The output result compared with the reference voltage of the non-inverting input of the second comparator (73B) is output to the switching element (SW), and the switching element (SW) is turned on / off at the switching frequency of 200 to 500 kHz.

That is, when the power supply voltage (+ Vc) falls below the offset voltage (Va), the first comparator (73)
The output of A) becomes "L", and the second comparator (73
This "L" is input to the non-inverting input (-) of B). Then, the output of the second comparator (73B) becomes "H", and the switching element (SW) of the chopper power supply (74).
Turns on and the power supply voltage (+ Vc) rises.

On the contrary, when the power supply voltage (+ Vc) exceeds the offset voltage (Va), the output of the first comparator (73A) becomes "H" and the non-inverting input (-) of the second comparator (73B). This "H" is input. Then, the output of the second comparator (73B) becomes "L", and the switching element (SW) of the chopper power supply (74) becomes OF.
Then, the power source voltage (+ Vc) drops.

As a result of the above operation, the power supply voltage (+ Vc) operates so as to follow the offset voltage (Va). In this way, the above-mentioned amplifier circuit always produces an offset voltage (Va) that is the sum of the differential of the amplified signal (ZS) and the voltage obtained by adding a constant voltage to the amplified signal (ZS),
The final stage transistor (TR of the power amplifier (75B)
The power supply voltage (+ Vc) applied to the collector of 11) operates so as to follow.

Here, considering an amplified signal (ZS) having a steep rise as shown in FIG. 4 in which distortion has occurred in the amplifier circuit of the first embodiment, the amplified signal (ZS).
Is added with a constant value (FIG. 5), at the same time, the differential of the amplified signal (ZS) as shown in FIG. 6 is taken, and the sum of the amplified signal with the fixed value added and the differential of the amplified signal (ZS) is taken. The offset voltage (Va) as shown in FIG. 7 is generated, and the power supply voltage (+ Vc) is changed and generated so as to follow the offset voltage (Va).

Therefore, when the change of the amplified signal (ZS) is steep, the differential increases, and the increased amplified signal (ZS)
Since the power supply voltage (+ Vc) is supplied so as to follow the offset voltage (Va) added with the differential of, the power supply voltage is always an amplified signal as shown in FIG. 7 even when there is a sharp signal change. Since it does not fall below, the amplified signal (Z
The power supply voltage (+ Vc) can follow the change in (S) with a margin, and it is possible to suppress the distortion of the output of the amplifier, which has occurred in the amplifier circuit of the first embodiment.

The operation when the AM radio which is a feature of the present invention is operating will be described below. in this case,
When the AM radio is turned on, a VH signal is simultaneously input to the switching circuit (SC2) from the microcomputer. Then, a constant voltage (V
z) is applied, the switching element (SW) stops the ON / OFF operation regardless of the operation of other circuits, and keeps ON while the VH signal is input from the microcomputer.
Therefore, during this period, a constant power supply voltage (± Vcc) is applied to the collector of the transistor (TR11) at the final stage of the power amplifier (75B), and the same operation as a normal class AB amplifier is performed.

As described above, according to the amplifier circuit of this embodiment, the switching operation of the switching element (SW) is stopped when the AM radio is operating in the vicinity, so that the conventional switching operation occurs. Switching noise is 200k, which is the frequency band of AM radio
It becomes possible to suppress the problem that noise is output from this AM radio when it is in the range of Hz to 2 MHz and there is an AM radio nearby.

Particularly, a radio tuner of AM or FM and an audio amplifier mounted together have a great effect. Although the amplifier circuit having the circuit configuration as shown in FIG. 3 has been described in the present embodiment, the present invention is not limited to this, and the addition result of the differential of the amplified signal (ZS) and the amplified signal (ZS) is further fixed. As long as the circuit operates with a power supply voltage that changes following the voltage generated by multiplying by, the same effect can be obtained with almost any circuit configuration.

An application example of the above circuit will be described below with reference to FIG. FIG. 8 is a circuit showing an example in which the above circuit is applied to an actual hybrid IC.
As shown in FIG. 8, this circuit includes an L channel amplifier (81), an R channel amplifier (82), and a control IC.
(83), positive side comparator (84), negative side comparator (85), noise cut circuit (86), positive side pre-driver (87), negative side pre-driver (88), positive side switching element (M1), a switching element (M2) on the negative side, and is provided with an audio amplifier for both L and R channels, and a power supply circuit for supplying a power supply voltage thereto.

Since this circuit is one of the application examples of the circuit shown in FIG. 8, description of the points common to the circuit of FIG. 8 will be omitted. The L channel amplifier (81) and the R channel amplifier (82) are preamplifiers (75
A), an amplifier corresponding to the power amplifier (75B), which includes the output transistors (Q3, Q4, Q) at the final stage of FIG.
7, Q8) are the transistors (TR11, TR1) of FIG.
It corresponds to 2).

The control IC (83) includes a gradient detecting section (71), an adding section (72) and a first comparator (73) shown in FIG.
It is an IC equipped with A). The positive side and negative side comparators (84, 85) are the second comparators (73B) in FIG.
Is a circuit corresponding to. The noise cut circuit (86) is a circuit including transistors (Q61, Q62),
When a radio operation signal (AM) is input from the external terminal No. 1 in FIG. 8, these transistors (Q61, Q6
2) are turned on at the same time, and the positive side and negative side pre-drivers (8
7,88) via the positive side switching element (M1),
It is a circuit that simultaneously turns on the negative side switching element (M2). In the circuit of FIG. 3, a switching circuit (SC2)
Corresponds to.

According to this circuit, the input signals (AS1, AS2) of the L channel and the R channel are respectively 18
Nos. 1 and 22 are input to the external terminals and amplified by the L and R channel amplifiers (81, 82), respectively, and the 13th and 1st
The amplified signals (ZL, ZR) of the L and R channels are output to the speaker (not shown) from the fourth terminal. The amplified signals (ZL, ZR) are respectively supplied to the control IC (83).
And the power supply voltage (± Vc) is fed back at the same time.
The power supply voltage (± Vc) is generated by lowering the constant voltage (+ Vcc, −Vcc) applied from the second and ninth external terminals by the positive and negative switching elements (M1, M2). .

In this circuit, when the AM radio is operating, the radio operating signal (AM) is input from the first external terminal, and the transistors (Q61, Q62) of the noise cut circuit (86) are turned on at the same time. , The positive side switching element (M1) and the negative side switching element (M2) are simultaneously turned on via the positive side and negative side pre-drivers (87, 88). Then, these switching elements (M1, M2) that had been switching until then are turned on.
Since it continues, the same operation as a normal class AB amplifier is performed, and even if the AM radio is operating nearby, the switching noise does not adversely affect the AM radio.

(3) Third Embodiment A third embodiment of the present invention will be described below with reference to the drawings. The first and second
An amplifier that reduces power consumption by a method different from that of the above embodiment has been proposed (Japanese Patent Application No. 5-167864). This amplifier is a circuit using a BTL (Balanced Transformerless) circuit. Normally, this BTL requires four transistors and four switching regulators for driving the same, but the inventors of the present invention realized that the number of switching regulators could be reduced to one. A method for reducing noise using this method will be described below.

FIG. 9 is a circuit diagram showing an embodiment of the present invention. (17) shows two input terminals (18) and (19) of positive and negative, and a common terminal () for setting the DC level of the output signal. 70) and two positive and negative output terminals (21) and (22). Input signals from one input terminal are connected to resistors R1 and R2.
This is a first differential amplifier that amplifies with a gain determined by the ratio of 2.

Numerals (23) and (24) are bias circuits to which two output signals of the first differential amplifier (17) having mutually opposite phases are applied, and numeral (25) is the first SEPP OCL (sil).
ngle-ended push-pull output capacitor less) (26)
And the second SEPP OCL (27)
It is a BTL amplifier that drives (28). Also, (29)
Is a non-linear adder circuit that performs an adding operation when the levels of two output signals generated at both ends of the load (28) are below a predetermined value and performs a clamping operation between the input and output terminals when the level is above the predetermined value. ) Is an adder circuit for adding two output signals generated at both ends of the load (28). (31)
Is the output signal of the non-linear adder circuit (29) and the reference power source.
The second differential amplifier applies a comparison output signal according to the difference from the reference voltage of (32) to the common terminal (20) of the first differential amplifier (17), and (33) is The adder circuit (3
0) is a switching power supply for applying a power supply voltage whose bell changes according to the output signal level of 0) to the BTL amplifier (25).

A switching transistor (SC3) is added to the circuit having such a structure as shown in FIG. This switching transistor (SC3) is a feature of the present invention, and the transistor switch (5
0) When connected to the base of AM radio and the AM radio is operating in this vicinity, the radio operation signal (AM) inputs
N is a switching transistor that keeps the transistor switch (50) ON during the period when the radio operation signal (AM) is input.

The operation of the above circuit will be described below (A) A
If the M radio is not operating near the amplifier circuit,
(B) The case where the AM radio operates near the amplifier circuit will be described separately in two cases. (A) When the AM radio is not operating near the amplifying circuit Since the AM radio is not operating in this case, the radio operating signal (AM) is the switching transistor (AM).
Is not input to, and therefore this also does not turn on. Therefore, it may be treated as having no switching transistor (AM).

The input signal from the signal source (34) in FIG. 9 is applied to the inverting input terminal (19) of the first differential amplifier (17), and two amplified output signals having opposite phases are output terminals. (2
It occurs in 1) and (22). Then, the two output signals are respectively supplied to the first via the bias circuits (23) and (24).
And a second SEPP OCL (26) and (27).

The first and second SEPP OCLs (26)
The operation of the transistors forming (27) and (27) is such that when both the first and second transistors (35) and (36) are on, both the third and fourth transistors (37) and (38) are on. To do. Conversely, when the third and fourth transistors (37) and (38) are both turned on, the first and second transistors are turned on.
Both (26) and (27) are turned off.

FIG. 15 shows the first differential amplifier (17) of FIG.
And bias circuits (23) and (24) and BTL amplifier (25)
FIG. 15, the same circuit elements as those in FIG. 9 are designated by the same reference numerals. Next, how to determine the DC voltage of the terminals (39) and (40) will be described. The DC voltage at the terminals (39) and (40) is determined by the feedback loop of the non-linear adder circuit (29) and the second differential amplifier (31).

FIG. 16 shows a specific circuit of the nonlinear adder circuit (29). The output signal of the second differential amplifier (31) in FIG. 16 controls the current value of the variable current source (41) in FIG. When the current value of the variable current source (41) is changed, the direct current flowing through the emitter-collector paths of the transistors (42) and (43) is changed, and the bias circuits (23) and (2
The base voltages of the transistors (44) and (45) incorporated in 4) change. As a result, the base voltages of the first to fourth transistors (35) to (38) change, and the terminals (39)
And the DC voltage of (40) changes equally.

Since the second differential amplifier (31) of FIG. 16 performs the feedback operation so that the levels of the two input signals become equal to each other, the voltage Vc becomes equal to the voltage VBC, and at the same time the voltage Vc becomes equal.
ol and Vo2 are also equal to the voltage VBC. 16 resistance (46)
By the actions of (47) and (47), the above-described feedback operation is achieved. The diodes (48) and (49) in FIG.
It serves to prevent the voltages Vol and Vo2 in 9) and (40) from dropping below the voltage VBC below the forward voltage VF of the diode. The input / output characteristics of the circuit of FIG. 16 are shown in FIG. Figure 1
As is clear from 0, the circuit of FIG. 16 operates as an adder when the voltages Vol and Vo2 are close to each other (2 VF or less), but when the voltage is more than that, it functions as a clamp circuit.

Therefore, the DC voltage at the terminals (39) and (40) in FIG. 9 can be arbitrarily determined according to the reference power source (32). The invention is characterized in that the load (28) is driven by a half-wave signal. Therefore, the value of the reference power source (32) is
As shown in (a) and (b) of FIG. 11, it is set to a low value close to the earth level. In this state, as described above, the first and second
It is assumed that the transistors (35) and (36) are both turned on.
Then, the current flows from the terminal (39) to the terminal (40),
The voltage of (39) rises from the DC voltage VBC,
The voltage of 0) drops from the DC voltage VBC. However, the voltage of the terminal (40) does not drop below the voltage (VBCc-VF) according to the clamping operation of the nonlinear adder circuit (29).

The voltage of the terminal (39) rises according to the signal level. The situation is shown in the period t of FIGS. 11 (a) and 11 (b).
Shown in 1. FIG. 11A shows the voltage level of the terminal 39, and a half cycle of the signal is generated in the period t1. or,
FIG. 11B shows the voltage level of the terminal (40) during the period t.
In the case of 1, the voltage is clamped and dropped from the voltage VBC by the voltage VF during the period in which the negative half cycle originally occurs, and becomes a bell.

As is apparent from the period t1 in FIGS. 11A and 11B, the load is driven by the first and second transistors (35) and (36) performing class B operation. Next, FIG.
If the period t2 of 1 is reached, then the third and fourth transistors (37) and (38) are both turned on, and the terminal (40) is turned on.
Current flows from the terminal to the terminal (39). The operation in this case is also the same as that described above, and a clamped voltage is generated in FIG. 11A and a signal is generated in FIG. 11B.

It is therefore clear that the load (28) is driven with a half-he signal from both ends rather than a sinusoidal signal. The output signal generated in the load (28) is an AC component generated between both ends of the terminal (39) and the terminal (40), and therefore the AC signal of FIG. 11C obtained by subtracting the voltage Vo2 from the voltage Vol. Is the output. The circuit of FIG. 16 will be described in more detail.

It is assumed that sine waves of opposite polarities as shown in FIGS. 14 (a) and 14 (b) are generated at the terminals (39) and (40) in FIG. The AC component shown by the solid line in FIG. 14 is canceled by the action of the resistors (46) and (47) in FIG.
The DC component shown by the alternate long and short dash line 4 is added to obtain the state shown in FIG. 14C, and the voltage shown in FIG. 14C becomes equal to the DC voltage VBC. At this time, the diodes 48 and 49 of FIG. 9 do not operate.

Next, the diodes (48) and (49) shown in FIG.
Is not present, and in that state, the signal whose DC level is deviated as shown in FIGS. 11 (a) and 11 (b) is the terminal (39) of FIG.
And (40). Then, the diode (4
Assuming that 8) and (49) do not exist, a voltage such as the voltage Vx in FIG. 11 (e) is applied to the second differential amplifier (31) in FIG.

However, since the second differential amplifier (31) controls the voltage Vx to be equal to the DC voltage VBC, the output DC voltage of the first differential amplifier (17) can be stably determined. It's gone. Therefore, in the present invention, FIG.
6 diodes (48) and (49) are provided
The DC voltage is determined by using the clipping action of (48) and (49).

Diode (48) in the embodiment of FIG.
In (49), the cathode and the anode may be reversed. However, in that case, the no-signal level VBC shown in FIGS. 11A and 11B is close to the power supply voltage (+ Vcc) level. The functions of the diodes (48) and (49) in FIG. 16 are the same as those of the first and second differential amplifiers (17) and (3) in FIG.
It is effective for 1), and the power supply in that case does not need to be a switching power supply.

To reduce power consumption in the circuit of FIG.
It suffices to apply a similar power supply voltage to the input signal to the collector-emitter path of the transistor in which the voltage VCE greatly changes according to the input signal. Therefore, in the present invention, the load
The voltages Vo1 and Vo2 generated at both ends of (28) are detected and added by the adder circuit (30), and the added signal (Vo1 + Vo) is added.
2) Transistor switch of switching power supply (33)
Turn on (50). Then the switching power supply
The voltage Vx shown in FIG. 11D is generated at the output terminal of (33).
Since the voltage Vx of FIG. 11 (d) is created based on the voltage generated across the load (28), it is possible to reliably generate the power supply voltage value that is responsive to the output signal level and to stabilize the voltage. It leads to reduction of power consumption. The Zener diode (51) is for level shifting. As is apparent from FIG. 11D, the voltage Vx that is similar to the signal voltage Vo1 is the first
The collector loss of the first transistor (35) will be added to the collector of the transistor (35) (Vx-V
It is clear that it is o1).

FIG. 11 (e) shows changes in the power supply voltage with respect to the signal in FIG. 11 (b), and it is clear that all the changes in the power supply voltage Vx are effectively used. Therefore, according to the circuit of FIG. 9, a power amplifier with a single power source and low power consumption can be obtained. In general, the switching power supply does not necessarily have high responsiveness and may not be able to follow a rapidly changing signal (on / off signal). In such a case, the first and third transistors (35) and ( 37) may be saturated. Therefore, in the present invention, the transistor
(52) is provided, and the first and third transistors (35) and
This prevents the collector voltage of (37) from decreasing.

FIG. 12 shows a specific circuit example of the adder circuit (30). Among the signals applied to the input terminals (53) and (54), the positive signal is added to the output terminal (55). Obtained. By the way, as a method of driving the load (28) of FIG. 9, a method of FIG. 13 may be used in addition to the BTL drive of FIG. In FIG. 13, assuming that a positive half-wave signal is applied to the input terminal (56), the first switch
(57) is turned off and the second switch (58) is turned on. Then, a current flows from the emitter of the first transistor 59 to the second switch 58. On the contrary, when a positive half-wave signal is applied to the input terminal (60), the first switch (57) is turned on and the second switch (58) is turned off to turn on the second transistor.
A current in the opposite direction is passed from (61) to the load (62). In this way, the load (62) may be driven with a half-wave signal.

(B) When the AM radio is operating near the amplifier circuit The operation in this case is a characteristic operation of the present invention. In this case, since the AM radio is operating, the radio operating signal (AM) is input to the switching transistor (SC3) in FIG. 9, and the switching transistor (SC3) is turned on. Then, the switching transistor (SC) turns on and the transistor switch (50)
Since the base potential of is reduced to the ground potential (GND), the transistor switch (50) is turned on only during the period when the radio operation signal (AM) is input regardless of the operation of other circuit parts, and the switching operation is performed. do not do.

Therefore, when the AM radio is operating nearby, the transistor switch (50) does not perform the switching operation, so that this switching noise jumps into the AM radio and is output as noise from the radio. Can be suppressed as much as possible.

[0069]

As described above, according to the amplifier circuit of the present invention, since the switching operation of the switching power supply is stopped only while the AM radio is operating nearby, this switching noise causes the AM radio. It is possible to prevent adverse effects such as jumping in.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating an operation of the amplifier circuit according to the first embodiment 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 diagram illustrating advantages of the amplifier circuit according to the second embodiment of the present invention.

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

FIG. 6 is a second diagram illustrating the operation of the amplifier circuit according to the second embodiment of the present invention.

FIG. 7 is a third diagram illustrating the operation of the amplifier circuit according to the second embodiment of the present invention.

FIG. 8 is a circuit diagram showing an application example of an amplifier circuit according to a second embodiment of the present invention.

FIG. 9 is a circuit diagram illustrating an amplifier circuit according to a third embodiment of the present invention.

FIG. 10 is a diagram showing input / output characteristics of a nonlinear adder circuit according to a third embodiment of the present invention.

FIG. 11 is a waveform diagram of the voltage supplied to the load of the amplifier circuit according to the third embodiment of the present invention.

FIG. 12 is a circuit diagram of an adder circuit according to a third embodiment of the present invention.

FIG. 13 is a configuration diagram illustrating another method of the amplifier circuit according to the third embodiment of the present invention.

FIG. 14 is a waveform diagram illustrating the operation of the amplifier circuit according to the third embodiment of the present invention.

FIG. 15 is a circuit diagram showing an example of a differential amplifier circuit, a bias circuit, and a BTL amplifier according to a third embodiment of the present invention.

FIG. 16 is a circuit diagram showing an example of a nonlinear addition circuit according to a third embodiment of the present invention.

FIG. 17 is a circuit diagram of an amplifier circuit according to a conventional example.

FIG. 18 is a diagram illustrating an operation of an amplifier circuit according to a conventional example.

[Explanation of symbols] (11) Amplifier (Signal amplifier) (12) Auxiliary power supply (14) Offset voltage generation circuit (17B) Comparator (18) Chopper power supply (19) Signal generator (AM) Radio operation signal (AS) Input signal (ZS) Amplified signal (SW) Switching element (SC) Switching circuit (71) Gradient detector (72) Offset voltage generator (73A) First comparator (73B) Second comparator (74) Chopper power supply circuit (75) Signal amplifier (75A) Preamplifier (75B) Power amplifier (77) Auxiliary power supply (Va) Offset voltage (Vb) constant voltage (SC2) Switching circuit (81) L channel amplifier (82) R channel amplifier (83) Control IC (84) Positive side comparator (85) Negative side comparator (86) Noise cut circuit (87) Positive side pre-driver (88) Negative side pre-driver (M1) Positive side switching element, (M2) Negative side switching element (17) First differential amplifier (25) BTL amplifier (28) Non-linear addition circuit (30) Adder circuit (31) Second differential amplifier (50) Transistor switch (SC3) Switching transistor

Continuation of the front page (56) Reference JP-A-7-221558 (JP, A) JP-A-7-221557 (JP, A) JP-A-7-15248 (JP, A) JP-B-62-8973 (JP , B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H03F 1/26 H02M 3/155

Claims (4)

(57) [Claims] 1. A signal amplifier for amplifying an input signal and outputting the amplified signal as an amplified signal, an amplified signal amplified by the signal amplifier, and the signal amplifier.
Compared with the power supply voltage supplied to
Having a switching power supply having a switching element that generates a power supply voltage that follows the amplified signal, during a period when the radio is operating near the signal amplification unit,
The signal generated by operating the AM radio is described above.
In addition to the switching element, the switching element
An amplifier circuit characterized in that the teaching operation is forcibly stopped and a constant voltage is supplied to the signal amplifier section. 2. The switching power supply includes: an offset voltage generation unit that adds a constant voltage to the amplified signal to generate an offset voltage; and a power supply supplied to the offset voltage and the signal amplification unit.
A signal generation unit that compares a voltage and generates a drive signal having a predetermined switching frequency, and a switching element that performs a switching operation at the switching frequency, and supplies a voltage that follows the offset voltage to the signal amplification unit as a power supply voltage. The amplifier circuit according to claim 1, further comprising: 3. The switching power supply detects a gradient of the amplified signal and outputs it to an offset voltage generating section, a gradient detection section that generates an offset voltage based on the amplified signal and a gradient of the amplified signal. , An offset voltage generator for outputting to the chopper power supply, and an amplification signal detected by the offset voltage and slope detector.
Signal to which the gradient signal of the No. signal is added and the signal amplification unit is supplied.
And a switching element that performs a switching operation at the switching frequency, and supplies a voltage that follows the offset voltage to the signal amplification section. 2. The amplifier circuit according to claim 1, further comprising a chopper portion that supplies the voltage as a voltage. 4. The first and second input terminals, and the first and second input terminals.
A first differential amplifier having an output terminal and a common input terminal for defining a direct current level of the first and second output terminals for amplifying an input signal from one of the input terminals; A BTL amplifier that amplifies a load according to two output signals; and a BTL amplifier having the same size between the first input terminal and the first output terminal and between the second input terminal and the second output terminal. A negative feedback circuit that performs negative feedback, an adder that adds two output signals generated at the two output terminals, and a non-linear that clamps the levels of the two output terminals with reference to the added output level of the adder. An adder circuit; a second differential amplifier that applies a comparison output signal corresponding to a difference between an output signal of the nonlinear adder circuit and a reference voltage of a reference power source to the common terminal of the first differential amplifier; Two generated at both ends of load An adder circuit for adding the output signal, the power supply voltage the level of which changes according to the output signal level of the summing circuit and a switching power supply to be applied to the BTL amplifier, AM radio operates near the BTL amplifier Period
Signal generated by operating AM radio all the time
In addition to the switching element,
An amplifying circuit characterized in that a switching operation is forcibly stopped and a constant voltage is supplied to the BTL amplifier.