JPH08148948A - Power amplifier circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Generates a signal of the same phase and amplitude as the back electromotive voltage of the speaker, does not generate a potential difference between the two, and supplies only the signal component to the speaker. A power amplifier circuit of the present invention comprises first and second amplifier circuits having differential inputs and a buffer amplifier circuit 20, and the positive input terminal 11 of the first amplifier circuit 10 is a signal input terminal. 40, the output of the first amplifier circuit is connected to the positive input terminal 32 of the second amplifier circuit 30 and the positive input terminal of the buffer amplifier circuit 20, and the output of the second amplifier circuit 30 is It is connected to the negative input terminal 12 of the first amplifier circuit 10, and the output of the buffer amplifier circuit 20 is the negative input terminal 31 and the signal output terminal 41 of the second amplifier circuit 30.
Connected to.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speaker drive power amplifier circuit for audio, which is mainly used in AV equipment and information communication equipment.

[0002]

2. Description of the Related Art Conventionally, an audio speaker driving power amplifier circuit used in AV equipment or the like has been required to faithfully supply an input waveform to a speaker as a load. In particular, it is known that a dynamic speaker generates a counter electromotive voltage due to its inductance component. When such a dynamic speaker is driven by a non-feedback or voltage feedback amplifier circuit, a counter electromotive voltage flows through the amplifier's voice coil through the amplifier circuit, and a sound that is not originally the original sound is produced, resulting in a significant loss of hearing. Therefore, in order to reduce the sound due to the counter electromotive voltage, a current feedback amplifier circuit as shown in FIG. 5 has been conventionally used. Since the current feedback amplifier circuit detects the current waveform flowing through the voice coil L of the speaker by the small resistance r and performs feedback, a current faithful to the waveform of the input flows through the voice coil L of the speaker. Further, since the source of the counter electromotive voltage v generated in the voice coil L of the speaker is also included in the negative feedback loop of the current feedback amplifier circuit, there is an advantage that the counter electromotive voltage v is suppressed by the negative feedback action. there were. However, the current feedback amplifier circuit has the following drawbacks.

That is, since the impedance of the speaker fluctuates depending on the frequency, when the load impedance of the current feedback amplifier circuit increases, the amount of negative feedback decreases, the gain increases, and the sound pressure of the speaker increases. That is, there is a drawback that a sound pressure corresponding to the load impedance of the speaker is generated, which is out of the desired flat frequency (sound pressure) characteristic.
The voltage feedback amplifier circuit has a drawback that flat frequency characteristics cannot be suppressed but the counter electromotive voltage cannot be suppressed, and the current feedback amplifier circuit can suppress counter electromotive voltage but a flat frequency characteristic cannot be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention provides a power amplifier circuit that eliminates the influence of a back electromotive force generated by a speaker without depending on the impedance characteristic of the speaker and on voltage feedback or current feedback. The purpose is to

[0005]

In order to solve the above-mentioned conventional problems, a power amplifier circuit of the present invention comprises first and second amplifier circuits having differential inputs and a buffer amplifier circuit. The positive input terminal of the amplifier circuit is connected to the signal input terminal, the output of the first amplifier circuit is connected to the positive input terminal of the second amplifier circuit and the positive input terminal of the buffer amplifier circuit, The output of the second amplifier circuit is connected to the negative input terminal of the first amplifier circuit, and the output of the buffer amplifier circuit is connected to the negative input terminal and the signal output terminal of the second amplifier circuit. .

[0006]

With this configuration, the output of the power amplifier circuit is
Since the input signal multiplied by the gain of the power amplifier circuit and the voltage having the same phase and same amplitude as the counter electromotive voltage generated at the speaker terminals are generated, the potential difference due to the counter electromotive voltage of the speaker does not occur and only the input signal component is generated. It can flow to the speaker and the frequency characteristic can be flattened regardless of the impedance of the speaker.

[0007]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram for explaining the operating principle of the first embodiment of the present invention. In FIG. 1, 40 and 41 are signal input terminals and signal output terminals of the power amplifier circuit 1 of the present invention, and 11 and 12 are positive input terminals and negative input terminals of the first amplifier circuit 10 having a gain A, respectively. , 31 and 32 are the negative input terminal and the positive input terminal of the second amplifier circuit 30 having the gain B, respectively.
3 and 33 are output terminals of the first and second amplifier circuits, 20 is a buffer amplifier circuit, and 42 is a speaker connected to the signal output terminal 41 of the power amplifier circuit 1 of the present invention.

It is preferable that both the first and second amplifier circuits have differential inputs and have the same input / output linearity. The buffer amplifier circuit 20 is a non-inverting amplifier circuit having a gain of 1, and for example, a complementary emitter follower circuit can be used.

The input signal E _{I that} has just entered from the signal input terminal 40 is supplied to the positive input terminal 11 of the first amplifier circuit 10. The output voltage E _O appearing at the output terminal 13 of the first amplifier circuit 10 is supplied to the input of the buffer amplifier circuit 20, while being supplied to the positive input terminal 32 of the second amplifier circuit 30. The output of the buffer amplifier circuit 20 is supplied to the negative input terminal 31 of the second amplifier circuit 30, and at the same time the signal output terminal 41 is supplied.
Is also supplied.

A speaker 42 is connected to the signal output terminal 41, and when the output voltage E _O appearing at the output terminal 13 of the first amplifying circuit is supplied to a buffer amplifying circuit which is a non-inverting amplifying circuit having a gain of 1. The output becomes E _O , but the counter electromotive voltage E _{B of the} speaker is generated as described above, and the signal output terminal 4
Appears E _O 'shown in the following formula to 1.

E _O '= E _O + E _B (Equation 1) E _O ' is the second is supplied to the negative input terminal 31 of the amplifier circuit 30, the output voltage -E B _B of the formula shown below by the differential input and the gain B of the E _O of the positive input terminal 32 appears at the output terminal 33.

{E _O − (E _O + E _B )} B = −E _B B (Equation 2) This output voltage is the negative input terminal 12 of the first amplifier circuit 10.
The input signal E supplied to the signal input terminal 40
An output that is differentially input together with _I and has a gain of A times appears at the output terminal 13. That is, E _O is derived by the following equation.

E _O = {E _I − (− E _B B)} A = AE _I + ABE _B (Equation 3) In the second amplifier circuit where AB = 1 now When the gain B is obtained, B = 1 / A, and (Equation 3) is expressed as (Equation 4).

E _O = AE _I + E _B ... (Equation 4) The voltage of (Equation 4) is buffered. The same voltage appears in the output voltage of the amplifier circuit 20.

Since the E _B appearing in the buffer amplifier circuit 20 and the counter electromotive voltage E _B generated in the speaker have the same phase and the same amplitude, no voltage difference occurs due to the E _B there, and eventually the input signal E _I AE _I amplified by A times in the first amplifier circuit flows to the speaker.

Although the above description has been made assuming that the input / output linearity of the buffer amplifier circuit 20 is an ideal straight line, it actually has a certain degree of non-linearity. Therefore, another buffer amplifier circuit having the same input / output linearity is inserted between the output terminal 13 of the first amplifier circuit and the positive input terminal 32 of the second amplifier circuit (not shown). It is preferable that the common mode removal be performed by the second amplifier circuit 30.

FIG. 3 is an actual circuit diagram showing the explanatory diagram of FIG. In FIG. 3, the attached numbers are the same as those in FIG.
The configuration of the input / output resistance that determines the gain and its resistance value are described. The configuration and resistance value of the input / output resistors that determine the gain of a general differential input amplifier circuit are already known, and in order to obtain the gain A, the input resistors R from the respective input terminals 11 and 12 and the feedback It is composed of a resistor AR and a divided resistor AR. On the other hand, since the gain B of the second amplifier circuit 30 is B = 1 / A as described above, the feedback resistance is R / A with respect to the input resistance R, as in the first amplifier circuit. The dividing resistor can be composed of R / A.

Although the buffer amplifier circuit 20 is described as an operational amplifier having a non-inversion and a gain of 1 in FIG. 1 for convenience, it is possible to use a complementary emitter follower circuit as shown in FIG. 3 without paying attention to this. It goes without saying that you can do it.

As is clear from the above description, according to this configuration, the output of the power amplifier circuit has the gain of the first amplifier circuit, that is, the input signal multiplied by A, and the same amplitude as the back electromotive force of the speaker. , The potential difference due to the back electromotive force of the speaker does not occur, and only the input signal component flows through the speaker and a waveform faithful to the original sound is reproduced. Further, since it is different from the method using current feedback, there is an effect that the frequency characteristic can be flattened regardless of the impedance of the speaker.

(Embodiment 2) FIG. 2 shows an explanatory view for explaining a second embodiment of the present invention.

In FIG. 2, the same elements as those of FIG. 1 are denoted by the same reference numerals, and therefore the repetitive description will be omitted. 1 and 2
1 is that the positive input terminal 32 of the second amplifier circuit 30 is connected to the output terminal 13 of the first amplifier circuit 10 in FIG. 1, whereas the second amplifier circuit 30 of FIG. That is, the positive input terminal 32 is connected to the signal input terminal 40.

Since the buffer amplifier circuit 20 is not particularly necessary, it is omitted here and the output terminal 13 of the first amplifier circuit 10 is directly connected to the signal output terminal 41.

The input signal E _{I, which} has just entered from the signal input terminal 40, is supplied to the positive input terminal 11 of the first amplifier circuit 10 and is supplied to the positive input terminal 32 of the second amplifier circuit 30. . The output voltage E _O appearing at the output terminal 13 of the first amplifier circuit 10 is supplied to the negative input terminal 31 of the second amplifier circuit 30 and simultaneously to the signal output terminal 41.

A speaker 42 is connected to the signal output terminal 41, and the output voltage E _O appearing at the output terminal 13 of the first amplifier circuit and the counter electromotive voltage E _{B of the} speaker as described above are output to the signal output terminal. 41, and becomes E _O 'shown in the following equation.

E _O '= E _O + E _B (Equation 5) E _O ' is the second The output voltage of the formula shown below appears at the output terminal 33, which is supplied to the negative input terminal 31 of the amplifier circuit 30 and is differentially input with E _I of the positive input terminal 32 and the gain B.

{E _I − (E _O + E _B )} B (Equation 6) This output voltage is the output voltage of the first amplifier circuit 10. Negative input terminal 12
The input signal E supplied to the signal input terminal 40
An output that is differentially input together with _I and has a gain of A times appears at the output terminal 13. That is, E _O is derived by the following equation.

E _O = {E _I − (E _I −E _O −E _B ) B} A E _O = (A−AB) E _I + ABE _O + ABE _B (1-AB) E _O = (A−AB) E _I + ABE _B E _O = (A-AB) E _I / (1-AB) + ABE _B /(1-AB).....(Equation 7) Now AB / (1-AB) ) = 1, the gain B of the second amplifier circuit is obtained, and B = 1 / 2A, and (Equation 7) is expressed as (Equation 8).

[0029] _{E O = (2A-1)} E I + E B ·················· ( Equation 8) voltage first amplifier circuit (8) 10 It appears at the output terminal 13 of, for the counter-electromotive voltage E _B generated in the speaker in phase the same amplitude, because the potential difference due to the counter electromotive voltage of the speaker does not occur, after all, the input signal E _I (2A-1) times The amplified (2A-1) E _I will flow to the speaker.

Although the above description has been made assuming that the input / output linearity of the first amplifier circuit 10 is an ideal straight line,
In reality, it has some non-linearity. To this end, a third amplifier circuit having the same input / output linearity as the first amplifier circuit, non-inverted, and having a gain A is connected to the signal input terminal 40 and the positive input terminal 32 of the second amplifier circuit. (Not shown) between the second amplification circuit 3 and the non-linear common-mode removal.
It is preferable to carry out at 0.

At this time, since the voltage condition and the gain condition obtained above are different, the following will be shown. Since the voltage of the positive input terminal 32 of the second amplifier circuit changes from E _I to AE _I , the output voltage appearing at the output terminal of the second amplifier circuit, that is, (Equation 6) is as shown in (Equation 9).

{AE_I-(E_O+ E_B)} B ···· (Equation 9) This voltage is supplied to the negative input terminal of the first amplifier circuit,
E of signal input terminal 40 _IAmplifies with A times. Follow
Output voltage of the first amplifier circuit, that is, E_OIn (Equation 10)
It is derived as shown.

E _O = {E _I − (AE _I −E _O −E _B ) B} A (1-AB) E _O = (1−AB) AE _I + ABE _B E _O = AE _I + ABE _B / (1 -AB) (Equation 10) Now, when the gain B of the second amplifier circuit with AB / (1-AB) = 1 is obtained, B = 1 / 2A, Formula 10) is expressed as Formula 11.

E _O = AE _I + E _B ... (Equation 11) The voltage of (Equation 11) is the first Output terminal 13 of one amplifier circuit 10
Appeared, for the counter-electromotive voltage E _B generated in the speaker in phase the same amplitude, because the potential difference due to the counter electromotive voltage of the speaker does not occur, after all, the input signal E _I was amplified A times AE _I
Will flow into the speaker.

FIG. 4 is an actual circuit diagram showing the explanatory diagram of FIG. In FIG. 4, the attached numbers are the same as in FIG.
The configuration of the input / output resistance that determines the gain and its resistance value are described. The configuration and resistance value of the input / output resistance that determines the gain of a general differential input amplifier circuit are already known, and in order to obtain the gain A, the input resistance R from each of the input terminals 11 and 12 and the feedback It is composed of a resistor AR and a divided resistor AR. On the other hand, since the gain B of the second amplifier circuit 30 is B = 1 / 2A as described above, the feedback resistance is R / 2A with respect to the input resistance R as in the first amplifier circuit. The dividing resistor can be composed of R / 2A.

In Embodiments 1 and 2 of the present invention, FIG.
Further, although the circuit diagram of FIG. 4 is described as an operational amplifier circuit for convenience, the present invention is not limited to this.

As is apparent from the above description, the output of the power amplifier circuit is (2A
-1) times the input signal and a voltage with the same amplitude as the back electromotive force of the speaker are generated, so there is no potential difference due to the back electromotive force of the speaker, so only the input signal component flows to the speaker and the original sound is faithful. The waveform is played. Further, since it is different from the method using current feedback, there is an effect that the frequency characteristic can be flattened regardless of the impedance of the speaker.

[0038]

As described above, the present invention detects a back electromotive force generated by a speaker, generates a signal having the same phase and the same amplitude as that of the back electromotive force, does not generate a potential difference between the two signals, and outputs only the signal component to the speaker. To convey, a waveform faithful to the original sound is reproduced.

Further, since the counter electromotive voltage is not suppressed by the current feedback, the frequency characteristic is independent of the impedance of the speaker, and the flatness equivalent to the frequency characteristic of the first amplifier circuit 10 can be obtained. is there. Further, in the low sound range where the amplitude of the speaker becomes large, the influence of the back electromotive force becomes large, but by preventing this influence, a large amount of electric power can be supplied and a good bass can be extended. That is, there is an effect that the reproduced sound is made clear and delicate, and a good sound with extended low tone is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining an operation principle of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation principle of the second embodiment of the present invention.

FIG. 3 is a circuit diagram of a power amplifier circuit according to a first embodiment of the present invention.

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

FIG. 5 is a configuration diagram of a current feedback amplifier circuit in a conventional example.

[Explanation of symbols]

 1 Power Amplifier Circuit 10 First Amplifier Circuit 20 Buffer Amplifier Circuit 30 Second Amplifier Circuit 42 Speaker

Claims (2)

[Claims] 1. A first and second amplification circuit having differential inputs and a buffer amplification circuit, wherein a positive input terminal of the first amplification circuit is connected to a signal input terminal, and the first amplification circuit is connected. The output of the circuit is connected to the positive input terminal of the second amplifier circuit and the positive input terminal of the buffer amplifier circuit, and the output of the second amplifier circuit is connected to the negative input terminal of the first amplifier circuit. A power amplifier circuit in which an output of the buffer amplifier circuit is connected to a negative input terminal and a signal output terminal of the second amplifier circuit. 2. A first and a second amplifier circuit having a differential input, wherein a positive input terminal of the first amplifier circuit and a positive input terminal of the second amplifier circuit are connected to a signal input terminal. The output of the second amplifier circuit is connected to the negative input terminal of the first amplifier circuit, and the output of the first amplifier circuit is connected to the negative input terminal and the signal output terminal of the second amplifier circuit. Power amplifier circuit connected to.