JPS6133703Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier device used as, for example, an audio power amplifier.

Generally, when a power amplification stage composed of power transistors, power FETs, etc. is operated in class B or class AB, large distortion occurs. For this reason, recent audio amplifiers apply a large amount of negative feedback in order to reduce distortion. However, in order to stabilize the negative feedback, a phase compensation circuit is used to reduce the amount of feedback in the high frequency range. For this reason, distortion in the high frequency range of the amplifier increases as the amount of feedback decreases.

However, feed forward technology is known as a technology for canceling such distortion. FIG. 1 is a block diagram showing an example of an amplifying device using conventional feed forward technology. In the figure, 1 is the input terminal to which the signal to be amplified is given, and 2 is the input terminal to which the signal to be amplified is given from input terminal 1 to the non-inverting input, and the amplification degree in the high range is reduced so that negative feedback can be stably applied. This is a preamplifier that is phase compensated so that the Reference numeral 3 denotes a large power amplifier that amplifies the output of the preamplifier 2 and has relatively high distortion, for example, poor linearity. Furthermore, numeral 4 is a small power amplifier that amplifies the output of the preamplifier 2 and has relatively little distortion, for example, good linearity. A negative feedback circuit 5 is interposed between the output of the high power amplifier 3 and the inverting input of the preamplifier 2. The output of the large power amplifier 3 is supplied via the impedance element 6, and the output of the small power amplifier 4 is directly supplied to the load 7. Alternatively, there have been cases where a simple resistor is used instead of the small power amplifier 4. In such a configuration, the mutual composition at the output point is
It is limited to a ratio of 6dB/OCT. On the other hand, in actual equipment, in many cases, the transfer characteristic of amplifier 3 includes not only the first-order characteristic (6 dB/OCT) but also the second-order high-frequency attenuation characteristic (equivalent to 12 dB/OCT). In such cases, preamplifier 2
Even if phase compensation of 6 dB/OCT is performed, the overall characteristics including amplifier 3 will actually be 6 dB/OCT in the high frequency range due to the influence of stray capacitance and input capacitance of other elements.
It is well known that the above phase compensation results. Therefore, by adding the output of the amplifier 4 to the output as a signal that increases by 6 dB/OCT in the high frequency range using the impedance element 6, the effect of feed forward on the signal frequency is only at one frequency point. Therefore, almost no distortion improvement effect can be obtained, especially in high frequencies.

The present invention was developed in view of the above circumstances, and aims to provide an amplifier device that can reduce the increase in distortion in the high frequency range of a negative feedback amplifier and also reduce distortion in a wide frequency band. It is something.

That is, the distortion canceling effect by the feed forward system will be explained with reference to the block diagram shown in FIG. 2 which is an embodiment of the present invention. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. Considering the conditions under which the distortion and noise components generated in the large power amplifier 3 do not appear at the load end using a calculation formula, the following is obtained. In order to make the explanation easier to understand, the amplification degree of each amplifier 3 and 4 in the figure is assumed to be 1.
Even if this amplification degree is other than 1 and the amplification degrees are different from each other, the distortion canceling effect due to the feedforward can be explained by the following calculation formula.
In this case, it goes without saying that the conditional expression for canceling distortion by feed forward is also different.

First, in FIG. 2, the following equation (1) holds true in the preamplifier 2 and high power amplifier 3.

ei = eg + be ₀ ... (1) where ei is the input signal voltage eg is the voltage between the input terminals of the preamplifier b is the gain of the negative feedback circuit e ₀ is the output voltage of the high power amplifier From equation (1) above, the following ( 2) Equation is obtained.

eg=ei−be ₀ ……(2) Also, the following equation (3) is obtained.

e ₀ = n + Aeg ... (3) where n is the distortion and noise component in the high power amplifier A is the amplification factor of the preamplifier From the above equations (2) and (3), the following equation (4) can be obtained.

_e0 =n+A(ei- _be0 )...(4) From this equation (4), the following equations (5) and (6) are obtained.

(1+Ab)e ₀ =n+Aei...(5) e ₀ =n+Aei/1+Ab...(6) Here, the distortion and noise component n included in the output voltage _e0
Letting e ₀ n, the following equation (7) can be obtained.

e ₀ n=n/1+Ab (7) On the other hand, no distortion or noise occurs in the small power amplifier 4, and if its output voltage is e ₁ , the following equation (8) is obtained.

e ₁ = e ₀ −n ... (8) From these equations (7) and (8), the following equations (9) and (10) are obtained.

e ₁ = n + Aei / 1 + Ab - n ... (9) = -Abn + Aei / 1 + Ab ... (10) Therefore, if the distortion and noise component n included in the output voltage e ₁ is e ₁ n, the following (11 ) formula is obtained.

e ₁ n=−Abn/1+Ab (11) Here, the output voltages e ₀ n and e ₁ n of the large power amplifier 3 and the small power amplifier 4 have opposite phases and different magnitudes. Therefore, the above output voltage e ₀ n, e ₁ n
are added to the load 7 of impedance Z _L via each output impedance Z ₁ and Z ₂ , mutual distortion,
The condition under which the noise component n is canceled out and does not appear in the inter-terminal voltage eL is given by the following equation (12).

n/1+Ab×Z ₁ Z _L /Z ₂ +Z ₁ Z _L +−Abn/1+Ab×Z ₂ Z _L /Z ₁ +Z ₂ Z
_L = 0...(12) However, Z ₁ Z _L is Z ₁ ×Z _L /Z ₁ +Z _L Z ₂ Z _L is Z ₂ ×Z _L /Z ₂ +Z _L Therefore, from this equation (12), the following ( Equations 13) and (14) are obtained.

Z ₁ Z _L /Z ₂ +Z ₁ Z _L =Ab・Z ₂ Z _L /Z ₁ +Z ₂ Z _L ...(13) Ab=Z ₁ Z _L /Z ₂ +Z ₁ Z _L・Z ₁ +Z ₂ Z _L /Z ₂ Z _L ...(14) In other words, if the loop gain Ab and impedances Z ₁ , Z ₂ , and Z _L are adjusted to satisfy equation (14), distortion-free output can be obtained as the load end voltage e _L Can be done. In the actual circuit, the impedance element 6 for the output of the large power amplifier 3 is a coil or a series circuit of a coil and a resistor, and the impedance element 8 for the output of the small power amplifier 4 is a resistor including a capacitor, or a series or series-parallel series of capacitors. It is necessary to accurately adjust the voltage and phase as a circuit.

With this configuration, due to the effect of negative feedback at the output of the high power amplifier 3, the distortion generated in the high power amplifier 3 is improved by the amount of feedback, and the output has a characteristic of increasing distortion toward the high frequency range. can get. Further, due to this negative feedback, a signal containing distortion having a phase opposite to that generated by the amplifier 3 is input to the input of the amplifier 3.
The input signal of this amplifier 3 is amplified by a small power amplifier 4 and added to the output via an impedance element 8.
In this way, if the frequency band is subjected to negative feedback, the distortions will cancel each other out, and a distortion-free signal can be supplied to the load 7.

As explained above, according to the present invention, even if a high power amplification element with a large amount of distortion is used, characteristics of low distortion can be obtained over a wide frequency band. In particular, it has been difficult to eliminate distortion in high frequency components such as switching distortion peculiar to bipolar transistors using the conventional feed-forward method, but according to the above embodiment, such distortion can be reliably eliminated. Can be done. That is, in the above embodiment, the addition of the distortion correction signal from the small power amplifier 4 does not simply increase at 6 dB/OCT toward the higher frequencies, but instead increases from 6 dB/OCT to 12 dB/OCT.
By being able to adjust the voltage and phase characteristics to match up to the OCT, a significant effect can be obtained in improving distortion of high frequency components such as switching distortion.

It should be noted that the present invention is not limited to the above-mentioned embodiment. For example, as shown in FIG. The output 9 may be disconnected to simply operate as a negative feedback amplifier circuit using the high power amplifier 3. In this case, the impedance 6 of the output of the high power amplifier 3
The coil used as the impedance 6 may be Q-dumped by inserting a resistor 10 in parallel with the impedance 6.

Further, as shown in FIG. 4, a parallel resonant circuit 10 consisting of a coil and a capacitor may be inserted in series with the impedance element 8 of the output of the small power amplifier 4 to reduce the distortion correction signal at a desired frequency. Furthermore, the voltage and phase of the distortion correction signal may be adjusted not only by the impedance elements 6 and 8 inserted into the outputs of the amplifiers 3 and 4, but also by the characteristics of the small power amplifier 4, for example. Of course.

Furthermore, FIGS. 5 and 6 are diagrams showing different specific embodiments of the present invention. In such a case, the small power amplifier 4
High voltage ± from a separate power supply from high power amplifier 3
Supplying V ₂ and operating with low distortion is extremely effective for improving overall characteristics.

As detailed above, the present invention provides negative feedback to the preamplifier and high power amplifier, and the small power amplifier that amplifies the output of the preamplifier cancels out the distortion generated in the high power amplifier. This is what I did. For this purpose, the outputs of the large power amplifier and the small power amplifier are supplied to the load via an impedance element having a predetermined constant. Therefore, it is possible to provide an amplifier device that can reduce distortion over a wide frequency band.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a block diagram explaining the principle of the present invention, and FIGS. 3 to 6 are block diagrams showing different embodiments of the present invention. 1... Input terminal, 2... Preamplifier, 3... Large power amplifier, 4... Small power amplifier, 5... Negative feedback circuit, 6, 8... Impedance element, 7... Load.

Claims (1)

[Scope of utility model registration request] a preamplifier that amplifies a signal applied from the outside; a first amplifier that amplifies the output of the preamplifier and has a transfer characteristic that has relatively poor linearity and includes a second-order high-frequency attenuation characteristic; a second amplifier with relatively good linearity to which the input of the first amplifier is applied; and a first amplifier including a reactance inserted between each output terminal of the first and second amplifiers and the load. and a second impedance element,
a negative feedback circuit that feeds back the output of the first amplifier to the input of the preamplifier;
and a second impedance element selected such that distortion occurring in the first amplifier is canceled out in the load by the output of the second amplifier.