JPH0520010Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> This invention relates to a multiple feedback amplifier for high frequency signals, and in particular aims to increase the amplitude of the output of the multiple feedback amplifier with a limited power supply voltage.

<Description of Prior Art> FIG. 3 shows a circuit diagram of a conventional multiple feedback amplifier. The power supply voltage _Vcc from the power supply terminal 13 is applied to the collector of the first transistor 14 and the base of the second transistor 15 through the resistor 16, and the resistor 18
It is supplied to the collector of the second transistor 15 through. A signal on the collector side of the second transistor 15 is fed back to the emitter of the first transistor 14 through a resistor 17.
The signal on the emitter side of transistor 5 is fed back to the base of first transistor 14 through resistor 19. Further, the emitter of the first transistor 14 and the emitter of the second transistor 15 are connected to resistors 20 and 2, respectively.
It is grounded through 1. and input terminal 11
A high frequency signal inputted from the circuit is amplified by this circuit and outputted from the output terminal 12.

Now, consider a case where an external load having a resistance value of 50Ω is connected to the output terminal 12, for example. In a state where current is drawn from the external load to the amplifier side, that is, in a state where the current of the second transistor 15 increases, the output drive capability is large. On the other hand, when current flows to the external load side, the current of the second transistor 15 decreases, and the absolute current is insufficient to drive the external load sufficiently, causing distortion in the waveform. In order to increase this output drive capability, the resistance values of the resistors that make up the amplifier can be reduced to increase the current flowing through each part, but as a result, the input and output impedance of the amplifier becomes smaller. , the resistance value will no longer match the external resistance of 50Ω. Therefore, the above circuit has the disadvantage that the amplitude of the output signal cannot be increased unless the power supply voltage is changed.

Further, FIG. 4 shows a circuit diagram of another conventional multiple feedback amplifier. This uses a PNP type second transistor 24 instead of the NPN type second transistor 15 shown in _FIG . Collector and second transistor 24
is supplied through a resistor 21 to the emitter of a second transistor 24. The signal on the collector side of the second transistor 24 is fed back to the emitter of the first transistor 14 via the resistor 17, and the signal on the emitter side of the second transistor 24 is fed back to the base of the first transistor 14 via the resistor 19. There is. The emitter of the first transistor 14 is grounded through a resistor 20.

In this case as well, when the current flows to the external load side, the current of the second transistor 24 increases and the output drive capability becomes large, but on the other hand, when the current flows from the external load to the amplifier side,
The current of the second transistor 24 is reduced, the current flowing through the external load is reduced, and the output drive capability is reduced. Therefore, this circuit also has the disadvantage that the amplitude of the output signal cannot be increased.

<Purpose of the invention> The object of this invention is to provide a multiple feedback amplifier that can output a high-amplitude, high-frequency signal with a limited power supply voltage.

<Summary of the invention> As shown in FIG. 4, the multiple feedback amplifier according to this invention includes a first transistor, the base of which is connected to the collector of the first transistor, a second transistor of opposite polarity to the first transistor, and a second transistor whose base is connected to the collector of the first transistor. a first feedback circuit connected between the collector of the first transistor and the emitter of the first transistor; and a second feedback circuit connected between the emitter of the second transistor and the base of the first transistor;
The second amplifying means has the same structure as the first amplifying means, but has transistors and power supply terminals of opposite polarity.

<Embodiment of the invention> FIG. 1 shows a circuit diagram of a multiple feedback amplifier which is an embodiment of the invention. In the figure, the same parts as in FIG. 4 are indicated by the same symbols. In this circuit, the emitter of the first transistor 14 is connected to a negative voltage -
It is connected to the power supply terminal 25 to which _Vee is supplied. This amplifier consists of a positive power supply terminal 13, a negative power supply terminal 25, a first transistor 14 of NPN type, a second transistor 24 of PNP type, and resistors 16, 17, 19, 20, 21. means and a first transistor 14' of PNP type;
NPN type second transistor 24', negative power supply terminal 13', positive power supply terminal 25', and resistor 1
6', 17', 19', 20', and 21', and the bases of transistors 14 and 14' are connected to capacitors 22 and 2, respectively.
2' to the input terminal 11, and the collectors of the transistors 24 and 24' are connected to the capacitor 23.
It is connected to the output terminal 12 through.

In the above configuration, when a current is pulled from the external load connected to the output terminal 12 to the amplifier side, the transistor 24' is in a state where the current is pulled. Conversely, when the current starts to flow to the external load side, the current starts to flow from the transistor 24. Therefore, in comparison with the circuits of FIGS. 3 and 4, this circuit can increase the maximum amplitude of the output voltage for the same power supply voltage without changing the input/output impedance. For example, in the circuit shown in Figure 3, when the power supply voltage is 10V, the maximum amplitude of the output signal is
2V _pp , whereas in the circuit shown in Figure 1, when the power supply voltage is ±5V, the maximum amplitude of the output signal is
It is possible to obtain up to 5V _pp , and the maximum amplitude is about 2.5 times that of conventional circuits.

In addition, as shown in FIG.
The signal on the collector side of the second transistor 24' is fed back to the emitter of the first transistor 14 through the third transistor 26' and the resistor 17, and at the same time, the signal on the collector side of the second transistor 24' is also fed back to the emitter of the first transistor 14 through the third transistor 26' and the resistor 17'. It may be configured to feed back to the emitter of the transistor 14'.

<Effects of the invention> As explained above, the multiple feedback amplifier according to this invention is composed of two amplifying means having transistors and power supply terminals with different polarities, so it is possible to output high-amplitude output signals with a small power supply voltage. Obtainable.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a multiple feedback amplifier according to this invention, and FIGS. 3 and 4 are circuit diagrams of a conventional multiple feedback amplifier. 11...Input terminal, 12...Output terminal, 13,
13', 25, 25'... Power supply terminal, 14, 1
4'...first transistor, 15, 24, 24'...
...Second transistor, 16, 16', 17, 1
7', 18, 19, 19', 20, 20', 21,
21'...Resistor, 22, 22', 23...Capacitor, 26, 26'...Third transistor.

Claims (1)

[Scope of utility model registration request] A positive power supply terminal, a negative power supply terminal, a collector is connected to the above positive power supply terminal via a resistor, an emitter is connected to the above negative power supply terminal via a resistor, and an input terminal is connected to the collector via a resistor. a first NPN transistor whose base is connected to the terminal via a capacitor; the base is connected to the collector of the first transistor; the emitter is connected to the positive power supply terminal via a resistor; and an output terminal. a PNP type second transistor whose collector is connected to the collector via a capacitor, a first feedback circuit connected between the collector of the second transistor and the emitter of the first transistor, and the emitter of the second transistor and the A first amplifying means consisting of a second feedback circuit connected between the bases of the first transistor and a second amplifying means having the same configuration as the first amplifying means but having opposite characteristics of the transistor and the power supply terminal, respectively. The input side is connected via a capacitor,
The output side is a multiple feedback amplifier characterized by a configuration in which the collectors are directly connected to each other.