JPS6029246B2 - Feedback amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses the base of a first-stage transistor as an input, the collector of this first-stage transistor is connected to the base of a second-stage transistor, and the collector of this second-stage transistor is connected to a complementary circuit consisting of a group of transistors of different polarities. In addition, regarding a feedback amplifier circuit configured to connect the output end of the complementary circuit to the emitter of the first-stage transistor via a feedback resistor to apply DC feedback, especially when inserted between the emitter of the first-stage transistor and ground. The purpose of this invention is to be able to obtain good frequency characteristics even if the capacitor used is 4 mm in capacity, and to improve the asymmetry of the output waveform that is clipped when a large input signal is received.

Generally, a feedback amplifier circuit having a configuration as shown in FIG. 1 is known.

In FIG. 1, C is a DC blocking capacitor, R,, R2 are base bias resistors, R3 is a collector resistor of transistor Q, D is a diode that determines the bias emitter current of output transistors Q4 and Q5, Also serves as temperature compensation. R6 is the load resistance of transistor Q2, C3, R
A capacitor and a resistor 7 constitute a bootstrap circuit, and have the function of equivalently increasing the AC impedance of the load resistor R6. R8 is a protection resistor for output transistors Q4 and Q5, and these output transistors Q and Q are transistors with different polarities and constitute a complementary circuit. C4 is a DC blocking capacitor, R4 is a DC feedback resistor, R5 and R9 are AC feedback resistors, C2 is a DC blocking capacitor, and G is a Takagi stabilizing capacitor. Next, the operation of the above circuit will be explained.

First, to explain DC operation, the base voltage V of the first stage transistor Q is a voltage V. which is obtained by dividing the power supply voltage V by resistors R and R2. = branch house V, and the emitter current 1 of the first stage transistor Q is 1≠Jin (VBE: the base-emitter voltage of the transistor is approximately 0.6 V), so the DC voltage V2 of the output stage is V2 :V. -VBE-IR4;R; Harmful V-V Team (・Towashi).

Then, the resistances R, , R2 are determined so that normally V2=V. Next, the AC operation will be explained.

First, in terms of AC, if resistances R4 and R9 are R4<<R9, then
The signal from the external output R of the first stage transistor Q is fed back. In the circuit shown in FIG. 1, the gain without AC feedback is very large, and the gain with AC feedback is almost zero. In order to improve the distortion, the resistor R5, which serves as the AC emitter resistance of the first stage transistor Q, must have a small resistance value. Therefore, in order to improve the frequency characteristics in the low range, the capacitor C2 needs to have a large capacity. Now, consider a case where a large signal Va is input to input device a. When the waveform of the output stage, which is the emitter of the transistor Q, clips, the feedback voltage v clips, so that although the base input of the first stage transistor Q becomes large, the signal v fed back to the emitter of the first stage transistor Q does not become large. Therefore, in the positive half cycle, a current of 2 times flows through the capacitor C2, and the capacitor C2 is charged. Next, in the negative half cycle, when clipping occurs, the first stage transistor Q is turned off, so that the charge stored in the capacitor C2 is discharged through the resistor R4 with a current of 2. Here, resistance R4
, R5, since R5<<R4, the charging current is much larger. Therefore, the DC voltage across capacitor C2 increases. That is, the emitter DC voltage of the first stage transistor Q increases, and the output stage DC voltage y2 decreases. Therefore, the output clipped waveform becomes vertically asymmetrical as shown in FIG. In this way, in the following feedback type amplifier circuit, the capacitor C2 inserted between the emitter of the first stage transistor Q and the ground needs to have a large capacity in order to obtain good frequency characteristics, and furthermore, the input signal becomes large. When the output waveform clips, there is a drawback that the output waveform becomes vertically asymmetrical due to the difference in the time constant of charging and discharging the capacitor C2. The present invention eliminates such conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments. FIG. 3 shows an example of the configuration of a feedback amplifier circuit according to the present invention, which differs from that of FIG. 1 in that the emitter of the first stage transistor Q is connected to a resistor R of a relatively small value.

is connected to the emitter of the transistor Q3, which has a different polarity from the first stage transistor Q, through the
Connect the collector of transistor Q3 to ground, and connect the collector of transistor Q3 to the ground.
The reason is that a feedback resistor R4 and a capacitor C2 are connected to the base of the circuit. Next, the operation of the above circuit will be explained.

First, DC operation will be explained. Resistance R, o is resistance R
3, the resistance R is caused by the emitter current of the first stage transistor Q. The voltage drop can be ignored. Furthermore, since the base current of transistor Q is very small, the voltage drop across resistor R4 can also be ignored. Therefore, if voltage drops across these resistors R, o, and R4 are ignored, V2=V, -2VB8. Next, AC operation will be explained.

If the current amplification factor of transistor Q is hfe, the impedance seen from the emitter side of transistor Q3 is R8.
=Island, the resistance value of the parallel sum of RB female resistors R4 and R5. If a transistor with a large hfe, for example hfe=100, is used as the transistor Q, then RB
= IKQ, R8 = 100, and transistor Q
The AC emitter resistance of , is approximately the resistance R,. It is determined by
Now, consider a case where the signal Va input to the input terminal a becomes large and the output waveform clips. Considering the positive half cycle, the difference between the input signal Va and the feedback voltage V causes the resistance R
, o, an alternating current iE force flows through the capacitor C2 (R5 <<R4). However, transistor Q
hfe becomes a small and small current, and the difference in charging and discharging the capacitor C2 becomes small. Therefore, there is no change in the DC bias, and there is little change in the output voltage V2. Therefore, the output clipped waveform is vertically symmetrical. or,
Since the resistors R5 and R4 can be made larger than those shown in Fig. 1,
Capacitor C2 can be made smaller.

Incidentally, in the above embodiment, the combinary circuit is composed of transistors Q4 and Q having different polarities, but in addition to this, as shown in FIG. It can also be constructed using Q7 to achieve high power.

In FIG. 4, D2 is a temperature compensation diode for the emitter bias of the first stage transistor Q. There is no problem in applying the present invention even if the complementary portions are Darlington connected in this way. In other words, by connecting the emitter of a transistor Q3 with a different polarity to the emitter side of the first-stage transistor Q, and connecting a feedback circuit to the base of the transistor Q, the difference between charging and discharging the capacitor C2 is reduced and a clipped waveform is created. It can be vertically symmetrical. As described above, according to the present invention, the emitter of the first stage transistor is connected to the emitter of the feedback transistor having a different polarity from the first stage transistor through a resistor, and the complementary circuit is connected to the base of the feedback transistor through the feedback circuit. Since the circuit is configured to add an output of Moreover, even if the input signal becomes large and the output waveform is clipped, the output waveform can be vertically symmetrical and no distortion will occur.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a secondary feedback type amplifier circuit, Fig. 2 is a clipped waveform diagram of its output, Fig. 3 is a circuit diagram showing an example of the configuration of the feedback type amplifier circuit of the present invention, and Fig. 4 is a circuit diagram showing a configuration example of the feedback type amplifier circuit of the present invention. FIG. 3 is a circuit diagram showing another configuration example of the feedback amplifier circuit of the present invention. Q. , Q2, Q3, Q4, Q5, Q, Q7...transistor, R, o, R4, R5, R9......resistance, C
2... Capacitor. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. The collector of the first-stage transistor whose base is input is connected to the base of the second-stage transistor, and the collector of the second-stage transistor is added to a complementary circuit consisting of a group of transistors with different polarities, while the emitter of the first-stage transistor is connected to the emitter of a feedback transistor whose polarity is different from that of the first-stage transistor through a resistor, and the base of this feedback transistor is connected to ground through a series circuit of a capacitor and a resistor, and the output of the complementary circuit is connected to the emitter of the feedback transistor whose polarity is different from that of the first stage transistor. A feedback amplifier circuit characterized in that the feedback amplifier circuit is configured such that feedback resistors are applied to a base and a connection point between a capacitor and a resistor forming the series circuit, respectively. 2. The feedback amplifier circuit according to claim 1, wherein a Darlington-connected transistor circuit is used as the complementary circuit.