JP2000022460A - Audio power amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss inside a device and to permit remarkable miniaturization by amplifying the input voltage of a power amplifier part in an AB class push-pull output system having an amplified frequency band sufficiently higher than an audible frequency band at high speed with the signal of a frequency higher than double audible frequency bands. SOLUTION: An amplitude detecting circuit 21 performs working processing to an input voltage Vin into fully rectified waveform VA. A switching signal VF is the rectangular clock signal of a frequency sufficiently higher than the frequency band of the input voltage Vin more than double. An amplitude modulating signal VM is superimposed on the input voltage Vin by an adder circuit 24 and a synthetic signal VP for amplifying the input voltage Vin at high speed with the switching signal is generated. A speaker SP is driven by the valid output of a waveform similar to the input voltage Vin but an output voltage Vout of the power amplifier part 1 is amplified at high speed by the switching signal VF. Thus, the period for the output voltage Vout to stay near an intermediate potential (Vcc/2 or Vee) is remarkably shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio power amplifier and, more particularly, to a technology effective when applied to an audio power amplifier of an AB class push-pull output system. Amplifier) that is effective for the technology.

[0002]

2. Description of the Related Art In audio power amplifiers, especially power amplifiers for car audio, there is a strong demand for downsizing of devices in addition to high output specifications.

[0003] Therefore, conventionally, an AB class push-pull output system and a BTL drive system have been adopted for a high output specification.
(Semiconductor integrated circuits), respectively (for example, see “Basic Transistor Amplifier Design Method” published by Radio Engineering Co., Ltd., pp. 24-255: Class AB Audio Power Amplifier).

FIG. 13 shows a schematic configuration of an audio power amplifier of a class AB push-pull output system.

In the power amplifier shown in FIG. 1, a power transistor (npn) constituting a class AB push-pull output stage 11 is provided.
The power amplifier unit 1 is composed of bipolar transistors (Q1 and Q2) and a pre-stage driver circuit 12 for biasing and driving the power transistors Q1 and Q2.

The transistors Q1 and Q2 of the output stage 11 are connected in series between a positive power supply potential Vcc and a negative power supply potential Vee, and an intermediate connection point (a so-called node) is taken out as an output, and this output (Vout) is externally supplied. The speaker SP is connected to a load.

The transistor Q1 on the positive power supply potential Vcc side supplies an output current (sink current) Is from the positive power supply potential Vcc, and the transistor Q2 on the negative power supply potential Vee generates an output current (sink current) Id from the negative power supply potential Vee. Turn on electricity. The energizing operation of the two transistors Q1 and Q2 is complementarily linearly controlled according to the input voltage Vin, so that an output voltage Vout corresponding to the input voltage Vin is generated and applied to the speaker SP.

In this case, the power amplifier section 1 is operated in a constant voltage output mode by voltage negative feedback (not shown), and is constant with respect to the input voltage Vin regardless of the magnitude of the output current Io flowing through the speaker SP. Are output in a linear proportional relationship.

[0009]

However, it has been clarified by the present inventors that the above-described technology has the following problems.

That is, in the audio power amplifier of the class AB output system described above, the energizing operation of the two transistors Q1 and Q2 of the output stage 11 is linearly controlled in a complementary manner, so that the output voltage Vout according to the input voltage Vin. Is generated, the output voltage Vout and the power supply voltage Vcc
The difference from -0,0-Vee is consumed by transistors Q1 and Q2.

For example, in FIG. 13, the output voltage Vo
In a saturated state where ut swings to the positive or negative power supply potential Vcc or Vee side, the transistor Q1 or Q2
Is cut off, the internal loss in the transistors Q1 and Q2 can be reduced to almost zero. Further, the output voltage Vout is reduced to zero (ground potential: G
In the case of (ND), both the transistors Q1 and Q2 can be cut off, and in this case also, the internal loss in the transistors Q1 and Q2 can be made substantially zero.

However, the output voltage Vout is lower than the power supply potential Vc.
When the potential becomes an intermediate potential (for example, near Vcc / 2 or Vee / 2) apart from c or Vee and zero potential (GND), its output voltage Vout and power supply potential V
The difference between Vcc and Vee (Vcc-Vout or Vout-Vee) is consumed as the internal loss of transistors Q1 and Q2.

FIG. 14 is a graph showing the relationship between the output voltage (V) and the internal loss (W) of the class AB power amplifier. As shown in FIG. 14, the internal loss (W) of the power amplifier is shown. Means that the output voltage Vout is Vcc / 2 or Vee /
It becomes maximum (Wmax) where it becomes 2.

This internal loss finally appears as heat generation. Therefore, in this type of audio power amplifier, it is indispensable to take measures to dissipate heat generated by internal loss. In order to smoothly perform the heat radiation, a large heat sink having a sufficient heat absorption volume and heat radiation area is required, but this heat sink has prevented the audio power amplifier as a device from being downsized. In particular, in recent audio power amplifiers in the form of ICs, heat sinks occupy most of the devices. Therefore, miniaturization of the heat sink is indispensable for miniaturization of the device.

However, the heat radiation performance of the heat sink greatly depends on its size, and its miniaturization directly lowers the heat radiation performance. If the heat radiation performance cannot be secured, the only way to reduce the internal loss is to reduce the internal loss. However, in order to reduce the internal loss, the output rating of the power amplifier must be greatly reduced.

On the other hand, as a method of reducing the size of the heat sink, it is conceivable to use active cooling means such as a blower fan or a Peltier element, but in this case, power consumption for cooling is newly required. In addition, there is no need for a new measure to deal with the heat generated by the power consumption of the cooling means.

As described above, in the above-described conventional audio power amplifier, the internal loss in the power amplifier section has been a great obstacle to downsizing the device.

It is an object of the present invention to provide a technique capable of reducing the internal loss of an audio power amplifier and significantly reducing the size of the device without causing a significant decrease in output.

The above and other objects and features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0020]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, the first means is a class AB push-pull output type power amplifier having an amplification frequency band sufficiently higher than the audio frequency band, and an audio frequency within the amplification frequency band of the power amplifier. Signal processing means for causing the input voltage of the power amplifier to swing at high speed with a switching signal having a frequency twice or more the bandwidth (first invention).

The second means is provided with a signal processing means for causing the input voltage of the power amplifier to oscillate at a high speed with a rectangular-wave-like switching signal (second invention).

The third means is provided with a signal processing means for causing the input voltage of the power amplifier to oscillate at a high speed with a sine wave switching signal (third invention).

The fourth means is provided with a signal processing means for performing variable control such that the width of the high-speed amplitude increases as the output voltage of the power amplifier unit approaches the midpoint between the power supply potential and the reference potential ( 4th invention).

The fifth means is provided with signal processing means for performing variable control such that the width of the high-speed amplitude becomes smaller as the output voltage of the power amplifier section approaches both ends of the dynamic range (the fifth invention). ).

According to the above-described means, the maximum value of the internal loss caused by the output operation of the class AB audio power amplifier can be greatly reduced, and the heat generation due to the internal loss can also be greatly reduced. it can.

As a result, the object of reducing the internal loss of the audio power amplifier and enabling a significant reduction in the size of the device can be achieved without causing a significant reduction in output.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows a first embodiment of an audio power amplifier to which the technique of the present invention is applied.

The audio power amplifier shown in FIG. 1 has a power amplifier 1 which is a main part of power amplification, and has a frequency within the amplification frequency band of the power amplifier 1 and more than twice the audible frequency band. There is provided a signal processing circuit 2 for causing the input voltage Vin of the power amplifier section 1 to have a high-speed amplitude with the switching signal VF.

The power amplifier 1 comprises an output stage 11 and a preceding driver circuit 12. The output stage 11 includes a single-ended push-pull circuit including first and second npn power bipolar transistors Q1 and Q2 connected in series between a positive power supply potential Vcc and a negative power supply potential Vee.

The output voltage Vout of the power amplifier 1
Is extracted from a node (intermediate connection point) of the transistors Q1 and Q2, and is applied to a speaker SP as a load. By applying the output voltage Vout, a drive current Io (Io = Is−) applied to the speaker SP through the transistor Q1 and / or Q2.
Id) flows.

The pre-stage driver circuit 12 has a bias and drive circuit for operating the transistors Q1 and Q2 of the output stage 11 in class AB operation. This power amplifier section 1
Although it is configured to have a frequency band (40 kHz or more) sufficiently higher than the audible frequency band (about 20 kHz), the frequency characteristics of this level are equal to those of a normal transistor (I
(Including those converted into C) can be easily obtained.

The signal processing circuit 2 includes an oscillation circuit 22 for generating a switching signal VF having a frequency of twice or more the audible frequency band, and an amplitude detection for linearly detecting (full-wave detection) the absolute value of the input voltage Vin of the audio power amplifier. A circuit 21, a VCA (variable gain amplifier) 23 for transmitting the switching signal VF with a gain corresponding to the output signal VA of the amplitude detection circuit 21, and an addition circuit 24 for adding and superimposing the output VM of the VCA 23 on the input voltage Vin. It consists of.

In this embodiment, a rectangular wave having a duty of 50% is used as the switching signal VF. The frequency of the switching signal VF is set to be twice or more the audio frequency in order to prevent a sideband generated around the frequency of the switching signal VF from covering the audio frequency band.

Next, the operation will be described.

FIG. 2 shows an operation waveform chart of a main part of the power amplifier shown in FIG. 1 and 2, first, an absolute value of an input signal Vin is linearly detected by an amplitude detection circuit 21 to obtain a full-wave rectified waveform (VA).
Is processed. The switching signal VF is a rectangular clock signal having a frequency sufficiently higher (twice or more) than the frequency band of the input signal Vin, and the output signal VA of the amplitude detection circuit 21 is set as an envelope by the VCA 23. Amplitude modulation is applied. This amplitude modulation signal V
By superimposing M on the input signal Vin by the adder circuit 24, it is possible to generate a composite signal VP in which the input signal Vin is made to have a high-speed amplitude by the switching signal VF. The synthesized signal VP is input to the power amplifier 1 and power-amplified.

As a result, the output voltage Vout of the power amplifier unit 1 has the high-speed amplitude waveform due to the switching signal VF as it is like the input voltage VP, but the speaker SP as the load has the output voltage Vout.
Is driven with an effective output voltage corresponding to the time average of the above. The waveform of the effective output voltage is a waveform in which the high-speed amplitude change due to the switching signal VF has been canceled out by time averaging due to the response characteristics of the speaker SP, and corresponds to the waveform of the original input voltage Vin.

It should be noted here that the speaker SP is driven by an effective output having a waveform similar to the input voltage Vin.
The output voltage Vout of the power amplifier unit 1 is caused to have a high-speed amplitude by the switching signal VF. As a result, the period during which the output voltage Vout stays near the intermediate potential (Vcc / 2 or Vee / 2) is significantly reduced.
As described above, this intermediate potential (Vcc / 2 or Vee / 2) has the maximum internal loss of the power amplifier unit 1 (Wm / 2).
ax), but the output voltage Vout
Changes in a waveform such that the period during which the internal loss is maximum is the shortest. Thereby, the internal loss in the power amplifier unit 1 is greatly reduced.

FIG. 3 is a graph showing the relationship between the effective output voltage (V) of the above-described audio power amplifier and the internal loss (W).

In this case, the effective output voltage Vmout has substantially the same load driving power as the output voltage Vout whose amplitude is changed at a high speed by the switching signal VF, as described above.

In the conventional power amplifier in which the output voltage Vout becomes the effective output voltage Vmout as it is, FIG.
, The effective output voltage Vmout (= Vou)
When t) becomes the intermediate potential (Vcc / 2 and Vee / 2), the internal loss reaches the maximum peak.

However, in the above-described power amplifier of the present invention, as shown in FIG. 3B, the period during which the output voltage Vout of the power amplifier stays at the intermediate potential where internal loss is large is shortened, so that the effective output voltage is reduced. In the vicinity of the point where Vmout becomes the intermediate potential Vcc / 2 or Vee / 2, the loss decreases rather, and theoretically drops to almost zero. At least, the peak of the internal loss which is maximum at the intermediate potential Vcc / 2 or Vee / 2 is eliminated.

As a result, it is possible to greatly reduce the internal loss caused by the output operation of the class AB audio power amplifier. Accordingly, heat generation due to the internal loss can be significantly reduced. Due to this reduction in heat generation, heat radiation design becomes easy, and a large heat sink becomes unnecessary. As a result, the internal loss of the audio power amplifier can be reduced and the size of the device can be significantly reduced without causing a significant decrease in output.

In the embodiment described above, the input voltage Vin of the power amplifier 1 is made to have a high-speed amplitude by the rectangular-wave switching signal VF. However, the input voltage Vin of the power amplifier is made to have a high-speed amplitude by the sine-wave switching signal. It may be a configuration.

In this case, as shown in FIG. 3C, the effective output voltage Vmout is changed to the intermediate potential Vcc / 2 or Ve.
Although the effect of reducing the internal loss near e / 2 is slightly reduced, the effect of significantly breaking the maximum peak of the internal loss is sufficient, and at least compared to the conventional case shown in FIG. A significant effect of reducing internal loss can be obtained.

Further, the sine-wave-like switching signal does not theoretically involve harmonics, thereby providing an advantage that generation of broadband noise due to harmonics can be suppressed.

FIG. 4 shows a main part of an audio power amplifier according to a second embodiment of the present invention. The power amplifier shown in FIG. 1 includes a buffer circuit 13 that divides an input signal Vin into a positive phase and a negative phase, and first and second power amplifier units 1A and 1B that drive a speaker SP, which is a load, by BTL. The input voltage Vin of the power amplifier unit 1 is supplied by a switching signal VF having a frequency within the amplification frequency band of the power amplifier units 1A and 1B and more than twice the audible frequency band.
Is provided at a high speed.

The signal processing circuit 2 used here comprises an amplitude detection circuit 21, an oscillation circuit 22, a VCA 23, first and second addition circuits 24A and 24B, a level detection circuit 25, and a subtraction circuit 26.

The amplitude detection circuit 21 linearly detects the absolute value of the input voltage Vin of the audio power amplifier. The oscillating circuit 22 generates a switching signal VF having a frequency of twice or more the audible frequency band. The VCA 23 converts the switching signal VF into an output signal VA of the amplitude detection circuit 21.
Is transmitted with a gain according to. The adders 24A and 24B respectively output the output VM of the VCA 23 to the input voltages + Vin and -Vin.
It is superimposed on Vin. The level detection circuit 25 is a circuit that linearly detects a voltage equal to or higher than a predetermined threshold Vh, and cuts out a voltage waveform (VE) equal to or higher than the predetermined threshold Vh from the absolute value waveform (VA) of the input voltage Vin.

FIG. 5 shows the characteristics of the detection circuits (21, 25) used in the amplifier of FIG.

In the figure, (A) shows an amplitude detection circuit 21.
And outputs a voltage linearly proportional to the absolute value of the input voltage. (B) shows the input / output characteristics of the level detection circuit 25. When the input voltage exceeds a predetermined threshold value Vh, the input voltage is linearly proportional to the input voltage not less than the threshold value Vh. Output voltage.

In this case, the threshold value Vh is set so as to correspond to an input voltage at which the output voltage Vout of the power amplifier units 1A and 1B becomes an intermediate potential of Vcc / 2 or Vee / 2.

FIG. 6 shows an operation waveform chart of a main part of the circuit shown in FIGS.

4 to 6, first, the amplitude detection circuit 21 detects an absolute value waveform of the input signal Vin, that is, a so-called full-wave rectified waveform (VA). At the same time, the level detection circuit 25 linearly detects a voltage waveform (VE) that is equal to or greater than a predetermined threshold value Vh from the input signal Vin.

When the output signal VA of the amplitude detection circuit 21 and the output signal VE of the level detection circuit 25 are subtracted and synthesized (VA-VE) by the subtraction circuit 26, the input signal Vin is positive with respect to the reference potential 0 (GND). Side intermediate potential (+ Vh)
, Or the negative potential (-Vh)
, A level detection output signal VH that takes the maximum voltage is obtained.

With this level detection output signal VH, VCA 23
The switching signal VF is variably controlled so that the switching signal VF becomes the output voltage Vo of the power amplifier units 1A and 1B.
When ut becomes the intermediate potential (Vcc / 2 or Vee / 2), the amplitude is modulated (VM) so as to have the maximum amplitude.

The amplitude modulation signal VM is supplied to an adder 24
A and 24B add and superimpose on the phase division output (+ Vin, -Vin) of the buffer circuit 13, respectively. Then, the added and superimposed synthesized signals + VP and -VP are power-amplified by the power amplifiers 1A and 1B, respectively, and applied to the speaker SP.

As a result, the output voltages + Vout, -Vout of the power amplifier sections 1A, 1B change as follows with respect to the input voltage Vin.

First, the output voltages + Vout and -Vout of the power amplifiers 1A and 1B are made to have a high-speed amplitude by the switching signal VF. The width of the high-speed amplitude is determined by the effective output voltage Vmout of the power amplifiers 1A and 1B. Maximum internal loss point (Vcc) of power amplifier sections 1A and 1B
/ 2 or Vee / 2). As a result, the period during which the output voltage Vout stays near the intermediate potential (Vcc / 2 or Vee / 2) is significantly reduced,
The internal loss in the power amplifier units 1A and 1B is greatly reduced.

At the same time, the power amplifier units 1A, 2B
Is effective output voltage Vmout of the power amplifier 1
The width of the high-speed amplitude becomes smaller as it approaches both ends (Vcc side or Vee side) of the output dynamic ranges of A and 1B. Thus, the effective output voltage Vmout of the power amplifier units 1A and 1B can be expanded to the full output dynamic range of the power amplifier units 1A and 1B. That is, the effective output can be increased while the internal loss of the power amplifier units 1A and 1B is kept low.

FIG. 7 shows the relationship between the output voltage waveform at the time of small amplitude output and the internal loss.

In the figure, first, the internal loss Pd1 (W) of the conventional class AB audio power amplifier is given by the following equation (1) when the impedance of the load (speaker) is RL.
Is required.

Pd1 (W) = amplifier remaining voltage (V) × output current (A) = (Vcc−x1) × x1 / RL (1) Next, the inside of the class AB audio power amplifier of the present invention. If the switching signal VF is a rectangular wave with a duty ratio of 50%, the output voltage is 2 × 1
Since (V) and 0 (V) are alternately repeated for the same time, the following is obtained.

Pd2 (W) = Internal loss at output voltage 2 × 1/2 + Internal loss at output voltage 0/2 Here, the internal loss at output voltage 2 × 1 is (Vcc−2x
1) × 2 × 1 / RL, the internal loss when the output voltage is 0 is (Vc
c−0) × 0 / RL, the internal loss Pd2 (W) is
It is given by the following equation (2).

Pd 2 (W) = (Vcc−2 × 1) × 2 × 1/2 RL (2) FIG. 8 shows the relationship between the output voltage waveform at the time of large amplitude output and the internal loss.

In the figure, first, the internal loss Pd1 (W) of the conventional class AB audio power amplifier is given by the above equation (1) as in the case of the small amplitude described above.

The internal loss Pd3 (W) of the class AB audio power amplifier of the present invention is such that the output voltage is 2 when the switching signal VF is a rectangular wave having a duty ratio of 50%.
Since x2-Vcc (V) and Vcc (V) are alternately repeated for the same time, the following is obtained.

Pd3 (W) = Internal loss at 2 × 2-Vcc / 2 + Internal loss at Vcc / 2 where the internal loss at output voltage 2 × 2-Vcc is ΔVc
c− (2 × 2-Vcc)｝ × (2 × 2-Vcc) / R
L, internal loss at output voltage Vcc is (Vcc-Vcc)
Since it is × Vcc / RL, the internal loss Pd3 (W) is given by the following equation (3).

Pd3 (W) = (Vcc−x2) × (2 × 2−Vcc) / RL (3) FIG. 9 shows a main part of an audio power amplifier according to the third embodiment of the present invention. The power amplifier shown in FIG.
And an oscillating circuit 22 for generating a rectangular-wave switching signal VF having a frequency of twice or more the audible frequency band, and the switching signal VF. Input voltage Vin
And a switching circuit 27 for interrupting the switching.

FIG. 10 shows an operation waveform chart of a main part of the circuit shown in FIG.

In FIGS. 9 and 10, the input voltage Vi
When n is intermittently switched by the rectangular-wave switching signal VF, a synthesized signal VP equivalent to the case where the input voltage Vin of the power amplifier unit 1 is rapidly amplitude-tuned by the rectangular-wave switching signal VF is obtained in the same manner as shown in FIG. Obtainable.

FIG. 11 shows a main part of an audio power amplifier according to a third embodiment of the present invention. The power amplifier shown in the figure has an oscillation circuit 22 for generating a sine-wave-like switching signal VF having a frequency of twice or more the audible frequency band, and the entire waveform portion of the switching signal VF is on the plus side (or minus side). DC bias circuit 221 that performs an appropriate level shift, and a multiplying circuit 28 that multiplies the input signal Vin by a sine wave switching signal VF that is level shifted to the plus side, and a synthesized signal that can be quickly amplified by the sine wave switching signal VF. VP is input to the power amplifier 1.

FIG. 12 shows an operation waveform chart of a main part of the circuit shown in FIG.

In FIGS. 11 and 12, when the input voltage Vin is multiplied by the sine wave switching signal VF biased to the plus side, the input voltage Vin of the power amplifier section is made to have a high-speed amplitude by the sine wave switching signal VF. Can be obtained.

As described above, the first invention of the present invention is a class AB push-pull output type power amplifier unit (1, 1A, 1) having an amplification frequency band sufficiently higher than the audible frequency band (up to 20 kHz). 1B) and 2 of the audible frequency band within the amplification frequency band of the power amplifier section.
Signal processing means (2) for causing the input voltage (Vin) of the power amplifier section to swing at a high speed with a switching signal (VF) having a frequency (40 kHz or more) which is twice or more times. The internal loss of the audio power amplifier can be reduced and the device can be significantly reduced in size without inducing.

According to a second aspect, in the first aspect, the signal processing means (2) for causing the input voltage (Vin) of the power amplifier section (1, 1A, 1B) to have a high-speed amplitude by the rectangular-wave-like switching signal (VF). This makes it possible to effectively reduce the internal loss of the power amplifier.

According to a third aspect, in the first or second aspect, the signal processing means for causing the input voltage (Vin) of the power amplifier section (1, 1A, 1B) to have a high-speed amplitude with a sine-wave-like switching signal (VF). (2)
As a result, it is possible to suppress the occurrence of broadband noise due to harmonics.

In a fourth aspect based on any one of the first to third aspects, the output voltage (Vout) of the power amplifier section (1, 1A, 1B) is equal to the power supply potential (Vcc or Vee).
And the intermediate point (Vcc / 2 or Ve) between the reference potential (GND)
e / 2), a signal processing means (2) for performing variable control such that the width of the high-speed amplitude becomes larger as it approaches (e / 2), whereby the internal loss when the output voltage reaches the intermediate point is reduced. Peaks can be significantly reduced.

According to a fifth aspect, in any one of the first to fourth aspects, the output voltage (Vout) of the power amplifier section (1, 1A, 1B) approaches both ends (Vcc, Vee) of the dynamic range. The signal processing means (2) for performing variable control such that the width of the high-speed amplitude becomes smaller as the power amplifier section becomes smaller can be provided.

As described above, the invention made by the inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

For example, the switching processing of the input voltage can be performed by digital signal processing means by a microprocessor. The power amplifier unit 1 may use a MOS transistor as an output element.

In the above description, the case where the invention made by the present inventor is applied to an audio power amplifier for car audio, which is the field of application as the background, has been described. However, the present invention is not limited to this. It can also be applied to general stationary audio equipment.

[0085]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, there is obtained an effect that the internal loss of the audio power amplifier is reduced and the size of the device can be significantly reduced without causing a great decrease in output.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an audio power amplifier to which the technique of the present invention is applied.

FIG. 2 is an operation waveform chart of a main part of the power amplifier shown in FIG.

FIG. 3 is a graph showing a relationship between an effective output voltage of an audio power amplifier and an internal loss.

FIG. 4 is a circuit diagram showing a main part of an audio power amplifier according to a second embodiment of the present invention.

FIG. 5 is a characteristic diagram of a detection circuit used in the amplifier of FIG. 4;

FIG. 6 is an operation waveform chart of a main part of the power amplifier shown in FIGS. 4 and 5;

FIG. 7 is a diagram showing a relationship between an output voltage waveform at the time of small amplitude output and internal loss.

FIG. 8 is a diagram showing a relationship between an output voltage waveform at the time of large amplitude output and internal loss.

FIG. 9 is a circuit diagram showing a main part of an audio power amplifier according to a third embodiment of the present invention.

FIG. 10 is an operation waveform chart of a main part of the circuit shown in FIG. 9;

FIG. 11 is a circuit diagram showing a main part of an audio power amplifier according to a third embodiment of the present invention.

12 is an operation waveform chart of a main part of the power amplifier shown in FIG. 11;

FIG. 13 is a circuit diagram showing a schematic configuration of a conventional audio power amplifier.

FIG. 14 is a graph showing the relationship between the output voltage of a class AB power amplifier and internal loss.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power amplifier part 1A, 1B Power amplifier part 11 AB class output stage 12 Pre-stage driver circuit 13 Phase division circuit Vcc Positive power supply potential Vee Negative power supply potential Vin Input voltage Vout Output voltage Vmout Effective output voltage Q1, Q2 Power transistor SP load Speaker VF Switching signal 2 Signal processing circuit 21 Amplitude detection circuit 22 Oscillation circuit 221 DC bias circuit 23 VCA (variable gain amplifier) 24 Addition circuit 24A, 24B Addition circuit 25 Level detection circuit 26 Subtraction circuit 27 Switching circuit 28 Multiplication circuit

Continuing on the front page (72) Inventor Toshihiko Takanashi 15 Asahidai, Moroyama-cho, Iruma-gun, Saitama, Japan Intra-East Semiconductor Co., Ltd. F-term in the Semiconductor Division of Hitachi, Ltd. (Reference) 5J092 AA02 AA17 AA26 AA41 AA63 CA36 CA92 FA03 HA02 HA39 KA01 KA17 KA26 KA32 KA48 KA53 KA55 KA62 MA20 MA23 SA05 TA01 TA02 TA06 UM00 VM07 VM19

Claims (5)

[Claims] 1. A class AB push-pull output type power amplifier having an amplification frequency band sufficiently higher than an audio frequency band, and a power amplifier within the amplification frequency band of the power amplifier and having at least twice the audio frequency band. An audio power amplifier, comprising: signal processing means for causing the input voltage of the power amplifier section to swing at a high speed with a switching signal of a frequency. 2. The audio power amplifier according to claim 1, further comprising: signal processing means for causing the input voltage of the power amplifier to swing at a high speed with a rectangular-wave switching signal. 3. The audio power amplifier according to claim 1, further comprising signal processing means for causing the input voltage of the power amplifier to oscillate at a high speed with a sine wave switching signal. 4. A signal processing means for performing variable control such that the width of the high-speed amplitude increases as the output voltage of the power amplifier unit approaches an intermediate point between the power supply potential and the reference potential. 4. The audio power amplifier according to any one of items 1 to 3. 5. The apparatus according to claim 1, further comprising a signal processing unit for performing variable control such that the width of the high-speed amplitude decreases as the output voltage of the power amplifier unit approaches both ends of the dynamic range. Audio power amplifier as described in any.