JPH0750858B2 - Bidirectional signal selection circuit - Google Patents

Description

The present invention relates to a bidirectional signal selection circuit.

[Conventional technology]

A conventional bidirectional signal selection circuit, as shown in FIG.
It consists of terminal 101, terminal 102, terminal 103, and switch 104.When transmitting a signal from terminal 101 to terminal 103, connect switch 104 to terminal 101 and transmit the signal from terminal 102 to terminal 103. When transmitting, the switch 104 is connected to the terminal 102. Also, the signal from the terminal 103 to the terminal 101, or
When transmitting to the terminal 102, the switch 104 is switched according to the terminal. Therefore, this bidirectional signal selection circuit transmits a signal from the terminal 101 or the terminal 102 to the terminal 103,
Further, the signal is transmitted by selecting either of the terminals 101 and 102 from the terminal 103.

[Problems to be solved by the invention]

Since the conventional bidirectional signal selection circuit described above has to transmit signals bidirectionally, a mechanical switch, a relay, or an electronic switch must be adopted as the switch 104. Therefore, mechanical switches, relays, etc. cannot be integrated into an IC, and electronic switches are unidirectional, so it is difficult to construct a bidirectional switch. Therefore, when trying to incorporate the bidirectional signal selection circuit inside the IC, conventionally, it is inevitable that only the switch portion is provided outside the IC.

[Means for solving problems]

The bidirectional signal selection circuit of the present invention includes a first, second, third,
The first input terminal is the first impedance in the common emitter of the first, second, third and fourth transistors of the first differential circuit composed of the fourth transistor and the first constant current source. Is connected via the first load impedance, the fifth and sixth transistors, and the second constant current source to the collector of the second transistor. A first switch connected to the base of the transistor and grounding the base of the fifth transistor by the first control signal is connected to the common emitters of the fifth and sixth transistors through the second load impedance. Is connected to the second input / output terminal, the collector of the sixth transistor is connected to the third load impedance and the base of the fourth transistor, and the base of the fourth transistor is connected. A second switch grounded by the second control signal is connected, and a collector of the first transistor has a third load impedance, a seventh and an eighth transistor, and a third constant current source. The base of the seventh transistor of the differential circuit is connected, the third switch that connects the base of the seventh transistor to the ground by the third control signal is connected, and the common emitters of the seventh and eighth transistors are The third input / output terminal is connected through the fifth load impedance, the collector of the eighth transistor is connected to the sixth load impedance and the base of the third transistor, and the base of the third transistor is connected. Is connected to a fourth switch which is grounded by a fourth control signal, and selectively supplies a base bias signal to the bases of the first, second, sixth and eighth transistors. Supplying, and the first, second, third, and generates a fourth control signal, and the first, characterized by comprising a control circuit having a second external input terminal.

〔Example〕

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

FIG. 1 is a circuit diagram of an embodiment of the present invention, and this bidirectional signal selection circuit is composed of three differential circuits and four switch circuits. The first differential circuit is a transistor
17 to 24, resistors 32 to 41, constant current source 45, bias voltage source 46, 47,
It is composed of a signal direction switching terminal 50 and a signal selection terminal 51, and is connected to a power supply 48. 1st signal from terminal 49 to terminal 52
(Or terminal 53), a control voltage V _D1 that turns on transistors 17 and 18 and turns off transistors 19 and 20 is applied to terminal 50, and the collector of transistor 17 receives the first output voltage. Appears, and further to terminal 52 (terminal 53
When a control voltage V _S1 (V _S2 ) that turns on the transistor 21 and turns off 22 (turns on 22 and turns off 21) is applied to the terminal 51 when the signal is output, the collector of the transistor 21 ( The second output voltage (third output voltage) appears at the collector of the transistor 22), and the fourth output appears at the connection point between the resistors 33 and 34 (connection point between the resistors 35 and 36). The voltage (fifth output voltage) appears.

Then send the second signal from terminal 52 (or terminal 53)
When outputting to 49, a control voltage V _D2 that turns on the transistors 19 and 20 and turns off the transistors 17 and 18 is given to the terminal 50, and the sixth output voltage appears at the collector of the transistor 20, Further, when inputting a signal from the terminal 52 (from the terminal 53), the control voltage V _S3 (V _S4 ) for turning on the transistor 24 and turning off 23 (turning on 23 and turning off 24) is applied to the terminal 5.
Is given, the seventh output voltage (eighth output voltage) appears at the collector of the transistor 24 (collector of the transistor 23), and the connection point between the resistor 39 and the resistor 40 (the resistor 37 and the resistor 38). A ninth output voltage (tenth output voltage) appears at the connection point).

The second differential circuit consists of transistors 1 to 4, resistors 25, 26, 29,
It consists of a constant current source 42 and a terminal 49. When transmitting the first signal from the terminal 49 to the terminal 52 (or terminal 53),
A second output voltage (third output voltage) is applied to the base of the transistor 1 (base of the transistor 2), and first and second switch circuits are connected to the bases of the transistors 3 and 4, The switch circuit includes transistors 9 and 1.
The first output voltage is applied to the bases of the transistors 9 and 10. Therefore, the transistors 9 and 10 are turned on, the bases of the transistors 3 and 4 become a voltage close to the ground potential, and the first signal is input to the terminal 49 and input to the emitter of the transistor 1 (emitter of the transistor 2) via the resistor 29. Is output to the collector of the transistor 1 (collector of the transistor 2), and if the resistors 25, 26, 29 are made equal, a signal having a level substantially equal to the first signal is obtained,
It is input to the base of the transistor 7 (base of the transistor 5). The third differential circuit includes transistors 5 to 8
And resistors 27, 28, 30, 31 and constant current sources 43, 44, and the third and fourth switch circuits are connected to the bases of the transistors 5 and 7, and the switch circuits are It is composed of transistors 11, 12, 15 and 16, and since the transistor 20 is off at the bases of the transistors 11 and 12, no voltage is applied, so the transistors 11 and 12 are off. Since the transistors 23 and 24 are off, no voltage is applied to the bases of the transistors 6 and 8, and the transistors 6 and 8 are off. Therefore, the signal input to the base of the transistor 7 (base of the transistor 5) passes through the emitter of the transistor 7 (transistor 5) through the resistor 31 (resistor 30) when the transistor 16 (transistor 15) is off. Output to terminal 52 (terminal 53).

Next, when outputting the second signal from the terminal 52 (terminal 53) to the terminal 49, the second signal is input to the terminal 52 (terminal 53) and the transistors 5 and 7 are off (transistor 11, 12
Since the sixth output voltage is applied to the base of, the transistors 11 and 12 are turned on, and the base potentials of the transistors 5 and 7 are close to the ground potential. ) It is input to the emitter of the transistor 8 (transistor 6) through the resistor 31 (resistor 30) and output from the collector of the transistor 8 (transistor 6). If the resistors 27, 28, 30, 31 are made equal, the second When the signals are at almost the same level as the output signal and the transistors 9 and 10 are off (the control voltage V _D2 that turns on the transistors 19 and 20 is applied to the terminal 50, the transistors 17 and 18 are off). Therefore, since no voltage is applied to the bases of the transistors 9 and 10,
9,10 will be off. ) And when the transistor 13 (transistor 14) is off, it is input to the base of the transistor 3 (transistor 4), and when the transistors 1 and 2 are off (transistor 18 is off, transistors 21 and 22
Turns off, no voltage is applied to the bases of the transistors 1 and 2, and the transistors 1 and 2 turn off. ),
Resistance from the emitter of transistor 3 (transistor 4)
It is output to the terminal 49 via 29.

〔The invention's effect〕

As described above, according to the present invention, since the bidirectional signal selection circuit can be configured by combining three differential circuits, it is suitable for an IC, and a signal is input from the terminal of the IC.
ICs with separate I / O pins can be provided by incorporating this circuit as a part of the IC in that it can selectively supply signals inside the IC and output the signals selected inside the IC to the terminals. However, the number of pins is also reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
It is a circuit diagram of a prior art example. 1-24 …… Transistor, 25-41 …… Resistance, 42-45 ……
Constant current source, 50 …… Signal direction switching terminal, 51 …… Signal selection terminal.

Claims (1)

[Claims] 1. The first, second, third and fourth transistors of a first differential circuit comprising first, second, third and fourth transistors and a first constant current source. The first input terminal is connected to the common emitter of the second transistor through the first impedance, and the collector of the second transistor has the first load impedance, the fifth and sixth transistors, and the second constant current source. A fifth switch connected to the base of the fifth transistor of the second differential circuit, which connects the base of the fifth transistor to the ground by the first control signal. The common emitter of the transistor is connected to the second input / output terminal via the second load impedance, the collector of the sixth transistor is connected to the third load impedance and the base of the fourth transistor, Previous Second switch for the base of the fourth transistor grounded by the second control signal is connected,
The collector of the first transistor is connected to the base of the seventh transistor of the third differential circuit composed of the fourth load impedance, the seventh and eighth transistors, and the third constant current source. A third switch that connects the base of the seventh transistor to the ground by the third control signal is connected, and the common emitters of the seventh and eighth transistors are connected to the third input / output terminal via the fifth load impedance. The collector of the eighth transistor is connected to the sixth load impedance and the base of the third transistor, and the fourth switch grounds the base of the third transistor by the fourth control signal. Connected, first,
A base bias signal is selectively supplied to the bases of the second, sixth, and eighth transistors, and the first, second, third, and fourth control signals are generated, and the first and second A bidirectional signal selection circuit comprising a control circuit having an external input terminal.