JPH07118620B2 - Bidirectional amplifier - Google Patents

Description

The present invention relates to a bidirectional signal amplifier.

[Conventional technology]

As shown in FIG. 3, the conventional bidirectional signal amplifier has 2
It is composed of two signal amplifiers 1 and 2 and two switches 3 and 4, and when a signal is to be input from the terminal 10 and output from the terminal 11, the terminal 10 of the switch 3 and the input 6 of the signal amplifier 1 are short-circuited, Moreover, when it is desired to short the terminal 11 of the switch 4 and the output 7 of the signal amplifier 1 or to input a signal from the terminal 11 and output the signal from the terminal 10, the terminal 11 of the switch 4 and the input 7 of the signal amplifier 2 are short-circuited. In addition, the terminal 10 of the switch 3 and the output 8 of the signal amplifier 2 are short-circuited.

[Problems to be solved by the invention]

The above-described conventional bidirectional signal amplifier must use two switches in order to switch the direction of signal flow, and even if an electronic switch is used,
If it is going to be integrated into an IC, it is difficult to mount the switch part on the same IC, and it is necessary to bring out the input / output terminals of the amplifier to the outside, which has the disadvantage of increasing the number of pins.

In contrast to the conventional bidirectional signal amplifier described above, the present invention is
It has an original content that the directionality of a signal can be switched by giving a DC voltage from the outside.

[Means for solving problems]

The transistor circuit of the present invention includes a first transistor and a second transistor, the first load is connected to the collector of the first transistor, and the common emitters of the first and second transistors are grounded via the first impedance. , The common emitter includes a first differential circuit connected to the first input / output terminal via a second impedance, a third transistor and a fourth transistor, and a collector of the fourth transistor has a second load. And the common emitters of the third and fourth transistors are grounded via the third impedance, and the common emitter is connected to the second input / output terminal via the fourth impedance. A fifth transistor whose collector is connected to the base of the second transistor and whose emitter is grounded; and a collector which is connected to the base of the third transistor And a collector of the first transistor is connected to the base of the third transistor, and a collector of the fourth transistor is connected to the base of the second transistor, and At the base of each of the first, fourth, fifth, and sixth transistors, one set of the first and fifth transistors or the fourth and sixth transistors is responsive to the signal from the external input terminal. It is characterized in that a control circuit for supplying a control signal for exclusively turning on and off is provided.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.
Two transistors 107, 108, 109, 110, 111 and 112, and 6
Load 101, 102, 103, 104, 105 and 106, and control circuit 11
It consists of three.

The control circuit 113 turns on or off any two transistors of the transistors 107 and 111 and the transistors 110 and 112 according to a signal input to the external input terminal 116. Now, assuming that a signal is input to the external input terminal 116 so that the transistors 107 and 111 are turned on, the signal source 117 is connected to the terminal 114,
An input signal to the terminal 114 is amplified by an amplifier composed of loads 101, 102 and 104 and a transistor 107, and its gain is R ₁₀₂ / R ₁₀₁ , where R ₁₀₁ and R ₁₀₂ are resistance values of the loads 101 and _102.
Becomes

The signal amplified by this amplifier passes through the emitter follower formed by the transistor 109 and the load 105,
It is output from the emitter of the transistor 109 and is output to the terminal 115 through the load 106.

Since the transistors 107 and 111 are on and the transistors 110 and 112 are off, the base of the transistor 108 is at the saturation voltage level of the transistor 111, and the transistor 108 is off because it forms a differential circuit with the transistor 107. The transistor 109 is turned on because the transistor 110 is off.

Next, transistors 107 and 111 are off and transistor 11
It is assumed that a signal is input to the external input terminal 116 so that 0 and 112 are turned on. Remove signal source 117 from terminal 114 and
Connect to 5.

In this case, since the transistors 110 and 112 are turned on, the base of the transistor 109 is at the saturation voltage level of the transistor 112, and the transistor 109 is
Since the differential circuit is formed, the transistor 109 is turned off.

Therefore, the input signal input to the terminal 115 is the load 103, 10
It is amplified by the amplifier composed of 5,106 and the transistor 110, and input to the base of the transistor 108. Transistor 107
Is off, the transistor 108 is turned on. Therefore, the signal input to the base of the transistor 108 is output to the emitter of the transistor 108 through the emitter follower composed of the transistor 108 and the load 104, and the load 1
It is output to the terminal 104 through 01.

As described above, the signal is amplified in both directions from the terminal 114 to the terminal 115 and from the terminal 115 to the terminal 114 according to the signal input to the external input terminal 116.

FIG. 2 is a circuit diagram of a second embodiment of the present invention, which is a differential circuit 227,228,229, transistors 215,216, and a resistor 20.
1,202,203,204,205,206,207,208,209,210,229, capacitors 221,223, coil 222, constant current source 219, signal source 23
0, voltage source 220, terminals 224 and 225, and external input terminal 226.

When the voltage of the voltage source 220 is set to V1 and a voltage V2 of V1 <V2 is applied to the external input terminal 226, the transistor 218 turns off and the transistor 217 turns on. Therefore, the transistors 211 and 215 are turned on.
A bias voltage is applied to each of the bases of the transistors, while the transistor 218 is turned off.
No voltage is applied to the base of 216, so transistor 2
11 and 215 are on and transistors 214 and 216 are off.

At this time, when the signal source 230 is connected to the terminal 224,
The input signal input to 4 is the transistor 211 and the resistor.
It is amplified by an amplifier composed of 201, 202, 204, a capacitor 221, and a coil 222, and the output of this amplifier is input to the base of the transistor 213.

Since the transistor 214 is off, the transistor 213 and the resistor 203 operate as an emitter follower, and the output point of this emitter follower is output to the terminal 225 via the resistor 206. At this time, the respective resistance values of the resistors ₂₀₁ , ₂₀₄ are R ₂₀₁ , R _204, and the respective values of the capacitor 221, coil 222 are C ₂₂₁ , L ₂₂₂ ,
If the voltage v _{i of the} input signal input to the terminal 224 is
The output voltage v _{i of} 25 is (Ω = 2π, is the frequency of the input signal), and an equalizing characteristic can be given to the input signal.

Next, when a voltage V3 of V1> V3 is applied to the external input terminal 226, the transistor 218 turns on and the transistor 217 turns off, so that a bias voltage is applied to the bases of the transistors 214 and 216, while the transistor 217 is Since it is off, no bias voltage is applied to the bases of the transistors 211 and 215, so that the transistors 214 and 216 are on and the transistors 211 and 215 are off.

At this time, when the signal source 230 is connected to the terminal 225,
The input signal input to is the transistor 214 and the resistor 2
It is amplified by the amplifier composed of 06, 203, 205 and the capacitor 223, and the output point of this amplifier is input to the base of the transistor 212.

Since the transistor 211 is off, the transistor 212 and the resistor 202 operate as an emitter follower, and the output point of this emitter follower is output to the terminal 224 via the resistor 201. At this time, assuming that the resistance values of the resistors ₂₀₆ and ₂₀₅ are R ₂₀₆ and R ₂₀₅ , the value of the capacitor 223 is C _223, and the voltage of the input signal input to the terminal 225 is v _in , the output voltage of the terminal 224 is
v _o ′ is (Ω = 2π, is the frequency of the input signal), and the input signal can have equalization characteristics different from those of the previous input signal. That is, different equalizing characteristics can be provided only by changing the direction of the external input signal.

〔The invention's effect〕

As described above, according to the present invention, since the direction of the signal flow can be switched by applying the DC voltage from the outside, it is possible to reduce the number of parts without the need to attach a mechanical switch to the outside. Since the circuit is suitable for IC and the input / output terminals of the amplifier are shared, the number of pins can be reduced. Furthermore, by changing the load impedance, not only the voltage gain of the amplifier but also the frequency characteristic can be changed, and different frequency characteristics can be given in the signal direction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a circuit diagram showing a conventional example. 1,2 …… Signal amplifier, 3,4 …… Switch, 107,108,109,11
0,111,112,211,212,213,214,215,216,217,218 …… transistor, 101,102,103,104,105,106,201,202,203,204,
205,206,207,208,209,210,229 …… Resistors, 221,223 ……
Capacitor, 222 ... Coil, 219 ... Constant current source, 220 ...
… Voltage source, 117,230 …… Signal source, 113 …… Control circuit, 10,1
1,114,115,224,225 …… terminal, 5,7 …… input, 4,6 …… output, 116,226 …… external input terminal.

Claims (1)

[Claims] 1. A first transistor and a second transistor are included, a first load is connected to a collector of the first transistor, and a common emitter of the first and second transistors is grounded via a first impedance. The common emitter is the second
A first differential circuit connected to the first input / output terminal via the impedance of, a third transistor and a fourth transistor, and a second load connected to the collector of the fourth transistor, ,
The common emitter of the fourth transistor is grounded via the third impedance, and the common emitter is connected to the second input / output terminal via the fourth impedance; The collector is connected to the base,
A fifth transistor having an emitter grounded; and a sixth transistor having a collector connected to the base of the third transistor and an emitter grounded, the collector of the first transistor being the third transistor
An external input terminal is connected to the base of the transistor, the collector of the fourth transistor is connected to the base of the second transistor, and the base of each of the first, fourth, fifth, and sixth transistors is connected to the external input terminal. First and fifth in response to the signal of
2. A bidirectional amplifier circuit comprising a control circuit for supplying a control signal for exclusively turning on and off each transistor or one set of each of the fourth and sixth transistors.