JPS62270Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a push-pull amplifier circuit that eliminates distortion and reduces power loss.

Generally, distortion in amplifier circuits is removed by applying negative feedback, but in order to do this, generally many amplifier circuits for negative feedback are connected and a large amount of negative feedback is applied, so the frequency characteristics and the time of the negative feedback signal are Delays may cause the circuit to oscillate or cause transient distortion.

Therefore, this invention allows distortion to be removed without using a negative feedback configuration.

FIG. 1 is a diagram of its basic principle. 1 is an input terminal, 2 is an amplifying transistor, and a signal obtained on the emitter side of the transistor is supplied to a load resistor 7 via an emitter resistor 4. Since the amplification characteristics of the transistor 2 are non-linear characteristics, the output signal is distorted.

Therefore, an operational amplifier 3 is provided to detect this distortion component. In this example, a differential amplifier 3 is used, the input signal is supplied to the non-inverting input terminal,
The output signal obtained on the emitter side is supplied to the inverting input terminal. The output of operational amplifier 3 is connected to summing resistor 6
is combined into the above-mentioned output signal.

According to this configuration, since only the distortion component is output from the operational amplifier 3, its reverse phase output is added to the output signal, so that the distortion component is canceled out.
This can be explained quantitatively as follows.

That is, in this circuit, the voltage at input terminal 1 is
e ₁ is the amplified voltage obtained at the emitter of transistor 2, e ₂ is the voltage across the load resistor 7, e ₃ is the output voltage of operational amplifier ₃ , and e is the amplified voltage obtained at the emitter of transistor 2. The amplification degree is Av,
If the amplification degree of the operational amplifier 3 is A', the following equation holds true.

e ₂ = Ave ₁ ………(1) e ₄ = (e ₁ − e ₂ ) A′ = (1 − Av) A′ e ₁ …(2) And the current i flowing through the summing resistors 4 and 6 ₄ or
i ₆ is the value of summing resistor 4 and R ₄ is the value of summing resistor 6.
If R ₆ , it is expressed by the following formula.

i ₄ = e ₂ - _{e 3} /R ₄ (3) i ₆ = e ₄ - e ₃ / R ₆ (4) Therefore, the output voltage e ₃ is e ₃ = (i ₄ + i ₆ ) _R7 = ( _e2 - _e3 / _R4 + _e4 - _e3 / _R6 ) _R7 ={Av/ _R4 +(1-Av)A _' / _R6 } _e1R7- (1/ _R4 +1/ _R6 ) _e3R7 =( _R6 - _R4A ' _{/ R4R6} ) _{Ave1R7 +} A _' /
R ₆ e ₁ R ₇ − (1/R ₄ + 1/R ₆ ) e ₃ R ₇ ………(5) Since the amplification degree Av is nonlinear, the distortion component at the output voltage e ₃ is removed from equation (5). To do this, R ₆ −R ₄ A′/
The term R ₄ R ₆ ×Ave ₁ R ₇ may be set to zero.

In other words, in order to obtain an output signal without distortion, the amplification degree must be
A' should be selected as A'=R ₆ /R ₄ (6).

By selecting the amplification degree A' of the operational amplifier 3 as R ₆ /R ₄ in this way, a distortion-free output can be obtained regardless of the amplification degree Av of the amplifier circuit. Therefore, since distortion can be reliably removed without using a negative feedback configuration, there is no drawback caused by the negative feedback configuration.

By the way, the basic circuit described above can also be applied to a push-pull amplifier. Figure 2 is an example.

In this figure, 2 and 14 are amplification transistors, 13 and 16 are emitter resistors, and the midpoint of their connection connects to a load resistor 7 via a summing resistor 4, which will be described later.
connected to. Then, as described above, the output signal obtained from the midpoint of the connection between the emitter resistors 13 and 16 and the input signal are differentially amplified and the distortion component is detected. Even in this configuration, the push-pull amplifier PA
As in FIG. 1, the distortion components caused by the above are canceled out.

Now, in this circuit, the push-pull amplifier PA
In order to synthesize the output of and the output of operational amplifier 3,
A pair of summing resistors 4 and 6 are required as shown. In this case, although the value of the summing resistor 4 is small, since the summing resistor 4 is inserted into the output current supply path, the power loss due to the summing resistor 4 becomes considerably large.

Therefore, in the present invention, the power loss caused by the summing resistor 4 can be reduced in a push-pull amplifier circuit having a distortion removal function as shown in FIG.

FIG. 3 is an example of this, in which a pair of emitter resistors 13 and 16 are connected in series, and first and second resistors 17 and 18 are connected in parallel. and,
The midpoint of the connection is connected to the inverting input terminal of an operational amplifier 3, which is constituted by a differential amplifier in this example, and the input terminal 1 is connected to the non-inverting input terminal of the operational amplifier 3. In addition, 19 is the input terminal 1 and the transistor 2,
This is a bias circuit inserted between the bases of each of the 14 bases.

Here, the push-pull amplifier PA can be operated in class B or class A operation by setting the bias. Note that the emitter resistors 13 and 16 are selected to have a resistance of 1Ω or less, and the first and second resistors 17 and 18
is selected to be smaller than the input impedance of the operational amplifier 3, but as large as possible, for example, on the order of several kΩ. First, in class B operation, transistors 2 and 14 are turned on alternately, so for example, when transistor 2 is on, transistor 14 is off, so the series circuit of resistors 17 and 18 is connected in parallel to emitter resistor 13. Almost equal to .
Therefore, in this case, the operational amplifier 3 in FIG.
This is substantially equivalent to the case where the inverting input terminal of is connected to the midpoint of the emitter resistor 4. Therefore, to remove distortion, the amplification degree A' of the operational amplifier 3 should be 2R ₆ /R ₁₃ (=2R
₆ /R ₁₆ ), a distortion-free output can be obtained regardless of the amplification degree Av of the push-pull amplifier PA.

Also, when the push-pull amplifier PA performs class A operation, transistors 2 and 14 are always on, so the combined resistance of both emitter resistors 13 and 16 replaces resistor 4 in the basic circuit of Figure 1. Therefore, the amplification degree A' of the operational amplifier 3 is 2R ₆ /R _1
3 (= 2R ₆ /R ₁₆ ), the push-pull amplifier PA
Distortion-free output can be obtained regardless of the amplification degree Av.

In the case of the configuration as shown in FIG.
Therefore, it is not necessary to provide the adding resistor 4 as shown in FIG. 2. Note that the values of the emitter resistors 13 and 16 are set to predetermined values as constants of the push-pull amplifier PA, so the amplification degree A' for removing distortion can be set by appropriately setting the value of the summing resistor 6. .

Furthermore, the values of the first and second resistors 17 and 18 are selected to be as large as possible after considering the input impedance of the operational amplifier 3 as described above. Vessels 17, 18
The effect of is negligible.

As described above, according to the configuration of the present invention, distortion can be removed without using the negative feedback configuration, so that the drawbacks (oscillation, transient distortion generation, etc.) caused by the negative feedback configuration can be eliminated. That is, in the present invention, by differentially amplifying the input signal and the output signal amplified by the push-pull amplifier PA, the opposite phase component of the distortion component generated by the push-pull amplifier PA is extracted, and this is used as the original output signal. First and second resistors 17 provided separately from the emitter resistors 13 and 16 can cancel out the distortion components as well as add the output signal of the push-pull amplifier PA to the operational amplifier 3. , 18, the emitter resistors 13, 16
Since the midpoint of the connection can be directly connected to the output terminal 5, and the pair of emitter resistors 13 and 16 can also be used as a summing resistor, power loss can be significantly reduced.

[Brief explanation of drawings]

Figure 1 is a basic circuit diagram of a distortion removal circuit, Figure 2 is a basic circuit diagram in which Figure 1 is applied to a push-pull amplifier circuit, and Figure 3 is a circuit diagram of an embodiment of a push-pull amplifier circuit according to the present invention. . 1 is an input terminal, 2 and 14 are transistors, 3 is a differential amplifier, 5 is an output terminal, 13 and 16 are emitter resistors, 17 and 18 are first and second resistors,
PA is a push-pull amplifier.

Claims (1)

[Scope of utility model registration request] The output terminal of the push-pull amplifier is led out from the connection midpoint of the emitter resistors of each transistor constituting the push-pull amplifier, and a resistor voltage divider circuit is connected in parallel with the pair of emitter resistors, and the resistor voltage divider circuit A push-pull amplifier circuit configured such that the divided voltage output point of and the input terminal of the push-pull amplifier are connected to the input terminal of a differential amplifier, and the output terminal of the differential amplifier is connected to the output terminal of the push-pull amplifier. .