JPH04270512A - Switch circuit - Google Patents

Abstract

PURPOSE:To realize the switch circuit in which one input terminal is employed for logic signal input, one switching transistor(TR) is used so as to reduce number of circuit components and which is turned on/off with a sufficiently small base current. CONSTITUTION:The switch circuit is provided with a 1st differential amplifier circuit comprising a 1st TRQ2 and a 2nd TRQ3, a 2nd differential amplifier circuit comprising a 3rd TRQ21 and a 4th TRQ22, a 1st level shift circuit whose one terminal connects to a base of the 1st TRQ2 and whose other terminal connects to a base of the said 3rd TRQ21, a 2nd level shift circuit whose one terminal connects to a base of the 2nd TRQ3 and whose other terminal connects to a base of the said 4th TRQ22 and a circuit varying the base potential of the said 1st TRQ2 and the 3rd TRQ21.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides two
The present invention relates to an amplifier circuit having a switch function of selectively outputting a signal to only one of two output terminals, and is particularly used in an integrated circuit.

0002

2. Description of the Related Art A conventional example will be described below with reference to FIG.

In FIG. 4, transistors Q2 and Q3
is a switch circuit in which only one of them is turned on by a logic signal. Changes in the collector current of transistor Q1 are directly applied to transistor Q2 or transistor Q.
This is a change in the collector current of one of the transistors 3 that is ON.

In FIG. 4, when the A terminal is at high level and the A' terminal is at low level, transistors Q10 and Q
11 is on, and Q8 and Q9 are off. transistor Q
11 turns on, the voltage drop across resistor R9 increases, transistor Q5 turns off, and transistor Q7 also turns off. Further, by turning on the transistor Q10, the base potential of the transistor Q3 decreases, and Q3 turns off. In other words, when the A terminal is at high level and the A' terminal is at low level, the input signal is amplified,
Appears only at the output load resistance RL1.

On the other hand, when the A terminal is at a low level and the A' terminal is at a high level, transistors Q10 and Q11 are turned off and transistors Q8 and Q9 are turned on. When transistor Q8 turns on, the voltage drop across resistor R8 increases, transistor Q4 turns off, and transistor Q
6 is also off. Further, by turning on transistor Q9, the base potential of transistor Q2 decreases and Q2 turns off. In other words, when the A terminal is at low level and the A' terminal is at high level, the input signal is amplified and the output load RL
Appears only in 2.

Note that even if transistors Q2 and Q3 are not turned off, transistors Q4 and Q5 are turned off, thereby turning off transistors Q6 and Q7. However, if transistors Q2 and Q3 remain on, when transistors Q4 and Q5 turn off, Q2 and Q3
The transistors Q2 and Q3 are turned off because they reach saturation and have an adverse effect on other components.

The signal Vout appearing at resistor RL1 or resistor RL2 is expressed as Vout=(R2/R1)(R
L/R3) Vin (however, RL=RL1=RL2).

[0008]

A conventional switch circuit requires two logic control terminals: an A terminal and an A' terminal for inputting a signal complementary to the signal input to the A terminal. Furthermore, the number of transistors for the switch is 4.
transistors (transistors Q8 to Q1 in FIG. 4)
1) is required. Furthermore, the currents of transistors Q8 and Q11 that turn off transistors Q4 and Q5 must be relatively large in order to turn off transistors Q4 and Q5 on the emitter side. As a result, there is a problem in that wasteful current increases.

The present invention has been made in view of the above-mentioned circumstances, and has the same function as a conventional circuit with one logic control terminal and one switching transistor, and further performs on/off with a sufficiently small current. The purpose is to provide a switch circuit that can.

0010

Means for Solving the Problems A switch circuit according to a first aspect of the present invention includes a first differential circuit comprising first and second transistors whose emitters are connected to each other; a third transistor having a polarity opposite to that of the second transistor, whose emitters are connected to each other and whose collector is connected to the collector of the second transistor; and a fourth transistor whose collector is connected to the collector of the first transistor.
a second differential circuit consisting of a transistor; and a first level shift circuit having one terminal connected to the base of the first transistor and the other terminal connected to the base of the third transistor. , a second level shift circuit having one terminal connected to the base of the second transistor and the other terminal connected to the base of the fourth transistor, and the bases of the first and third transistors. It is equipped with a circuit that changes the potential in conjunction with each other.

Further, a switch circuit according to a second aspect of the present invention includes a first differential circuit including first and second transistors whose emitters are connected to each other, and the first and second transistors. are of opposite polarity and have emitters connected to each other and a collector connected to the collector of the first transistor, and a third transistor whose collector is connected to the collector of the second transistor.
a second differential circuit consisting of a fourth transistor connected to the collector of the first transistor;
a first level shift circuit having one terminal connected to the base of the second transistor and having another terminal connected to the base of the third transistor; The device includes a second level shift circuit whose terminal is connected to the base of the fourth transistor, and a circuit that changes the amount of level shift of the first level shift circuit.

0012

[Operation] In the switch circuit according to the first aspect of the present invention, the base potentials of the second and fourth transistors are constant. On the other hand, the base potentials of the first and third transistors are changed by a circuit that changes the base potentials of the first and third transistors in conjunction with each other. As a result, only one of the first and third transistors or the second and fourth transistors is turned on.

Furthermore, in the switch circuit according to the second aspect of the present invention, the level shift amount of the second level shift circuit is constant. On the other hand, the level shift amount of the first level shift circuit is changed by a circuit that changes the level shift amount of the first level shift circuit. As a result, only one of the first and third transistors or the second and fourth transistors is turned on.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amplifier circuit according to a first embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the emitter electrode of transistor Q1 is grounded. The base electrode of the transistor Q1 is connected to one end of the resistor R1 and the resistor R
Connected to one end of 2. The other end of resistor R1 is connected to one end of capacitor C1. An input signal Vin is supplied to the other end of the capacitor C1. The collector electrode of transistor Q1 is connected to the emitter electrodes of transistors Q2 and Q3.

The base electrode of transistor Q2 is connected to the anode of diode D3 and the cathode of diode D2. The cathode of diode D3 is connected to the anode of diode D4 and the collector electrode of transistor Q20. Diode D4 is cascaded to diode D5. The cathode of diode D5 is grounded. The base electrode of transistor Q20 is connected to the A terminal via a resistor, and the emitter electrode is grounded.

Diode D2 is cascaded to diode D1. The anode of diode D1 is connected to current source I2 and the base electrode of transistor Q21.

The collector electrode of transistor Q2 is connected to the collector electrode of transistor Q22 and the base electrode of transistor Q7. The base electrode of transistor Q22 is connected to current source I3 and the anode of diode D6. Diode D6 is connected in cascade with diode D7.

The base electrode of transistor Q3 is connected to the cathode of diode D7 and the anode of diode D8. Diode D8 is cascaded to diode D9. The cathode of diode D9 is grounded. The collector electrode of transistor Q3 is the collector electrode of transistor Q21 and the collector electrode of transistor Q6.
connected to the base electrode of.

The emitter electrode of transistor Q6 is connected to the emitter electrode of transistor Q7, and also to the other end of R2 and one end of R3, and the other end of R3 is grounded. The collector electrode of transistor Q6 is connected to one end of the current path of resistor RL1. A power supply voltage Vcc is supplied to the other end of the resistor RL1. A collector electrode of transistor Q7 is connected to one end of resistor RL2. A power supply voltage Vcc is supplied to the other end of the resistor RL2. In the above configuration, the configuration other than the switch circuit 1 is the same as the conventional circuit shown in FIG.

Note that the diode D1 and diode D2 shown in FIG. 1 constitute a first level shift circuit. Diodes D6 and D7 constitute a second level shift circuit. Transistors Q2 and Q3 and transistors Q22 and Q21 constitute a complementary differential switch circuit. Next, the operation of the amplifier circuit according to the first embodiment will be explained.

As shown in FIG. 1, an input signal to be amplified is applied to the base electrode of transistor Q1 via capacitor C1 and resistor R1. Either transistors Q2 and Q22 or transistors Q3 and Q21 are turned on. The turned-on transistor acts as a common-base circuit. The output signal output from the transistor that is turned on is input to the base electrode of the output transistor Q6 or Q7, and output to the output load. Assuming that the signal Vout appearing at the resistor RL1 or the resistor RL2 has an overall open-loop gain that is sufficiently larger than the closed-loop gain as in the conventional circuit shown in FIG. 4, then Vout=(
R2/R1) (RL/R3) Vin (RL=R
(L1=RL2).

When a high level signal is input to the A terminal, transistor Q20 is turned on. As a result, the cathode of the diode D3 is grounded, and the base potential of the transistor Q2 becomes the forward voltage VF of the diode D3 (however, VCE(sat) of the transistor Q20 is set to 0). The base potential of the transistor Q21 becomes 3VF, which is higher by the forward voltage of 2VF of the diodes D1 and D2. On the other hand, the base potential of the transistor Q3 is always the forward voltage 2VF of the diodes D8 and D9 regardless of the signal state of the A terminal, and the potential of the base of the transistor Q22 is always the forward voltage 2VF of the diodes D8 and D9.
The base potential of is higher than that by the forward voltage of 2VF of diodes D6 and D7, and becomes 4VF.

Therefore, the base potential of transistor Q3 is higher than the base potential of transistor Q2. on the other hand,
transistor Q than the base potential of transistor Q22.
The potential of No. 21 is lower. Therefore, transistors Q2 and Q22 are turned off, and transistors Q3 and Q21 are turned on. As a result, transistor Q6 is turned on and transistor Q7 is turned off. The input signal Vout is amplified and appears at the output load RL1.

On the other hand, when a low level signal is input to the A terminal, the transistor Q20 is off, so the base potential of the transistor Q2 becomes the forward voltage of 3VF from the diodes D3 to D5, and the base potential of the transistor Q21 becomes 5VF. . On the other hand, the base potentials of the transistor Q3 and the base potential of the transistor Q22 are 2VF and 4VF as described above, so when the base potentials of the transistors Q2 and Q3 are compared, the base potential of the transistor Q2 is higher. Comparing the base potentials of transistors Q22 and Q21, transistor Q22 has a lower base potential. Therefore, transistors Q2 and Q22 are turned on, and transistors Q3 and Q2 are turned on.
1 is off. As a result, transistor Q6 is turned off, transistor Q7 is turned on, and the amplified signal appears at output load RL2. That is, when the A terminal is at a high level, the output signal appears only at the output load RL1, and when the A terminal is at a low level, the output signal appears only at the output load RL2.

As shown in FIG. 1, there is only one logic control terminal and only one switching transistor, Q20. Further, the current required for the switch operation is only a small base current for driving the transistor Q20, and the current is almost negligible. Next, a second embodiment is shown in FIG.

The circuit of the second embodiment shown in FIG.
The current sources I2 and I3 and the diodes D1 to D9 are replaced with resistors R10 to R15. Resistance R10
The resistance value of R16 is set such that when transistor Q20 is on, the base potential of transistors Q21 and Q2 is higher than the base potential of transistors Q22 and Q3, and when transistor Q20 is on, transistor Q2 is set.
The base potential of transistors Q22 and Q3 is
Set it so that it is lower than the base potential of. Furthermore, Figure 2
As shown in FIG. 1, the configuration other than the switch circuit 1 is the same as that shown in FIG. Next, the operation of the circuit according to the second embodiment will be explained.

In FIG. 2, input signal Vin is applied to the base electrode of transistor Q1 via capacitor C1 and resistor R1. When a high level signal is input to the A terminal, the transistor Q20 is turned on, and the resistors R12 and R16 are connected in parallel. Since the resistance values of the resistors R10 to R16 are set as described above, the transistor Q
The base potentials of transistors Q22 and Q3 are higher than those of transistors Q21 and Q2. As a result, transistor Q6 turns on, and a voltage signal appears at output load RL1.

On the other hand, when a low level signal is input to the A terminal, the transistor Q20 is turned off, and since the resistors R10 to R15 are set as described above, the base potential of the transistors Q21 and Q2 is changed to the base potential of the transistors Q22 and Q3. becomes higher than the base potential of As a result, transistor Q7 is turned on and a voltage signal is output to output load RL2. In other words, transistors Q6 and Q7 are selectively turned on/off depending on whether the signal input to the A terminal is at high level or low level.

As shown in FIG. 2, there is one logic control terminal, and there is only one switching transistor, transistor Q20. Further, the current required for the switch operation is only a small base current for driving the transistor Q20, and the current is almost negligible. Further, a third embodiment is shown in FIG.

As shown in FIG. 3, the emitter electrode of the transistor Q1 is grounded, and the base electrode is connected to the capacitor C1.
An input signal is applied via the resistor R1. Transistors Q2 and Q3 and transistors Q22 and Q21 constitute a complementary differential switch circuit. Furthermore, Figure 3
As shown in FIG. 1, the configuration other than the switch circuit 1 is the same as that shown in FIG. Next, the operation of the circuit according to the third embodiment will be explained.

As shown in FIG. 3, transistor Q2
and Q21, or transistors Q3 and Q22 are turned on, and the turned-on transistor functions as a common base circuit. The output signal of the switch circuit 1 is output to the base electrodes of the output transistors Q6 and Q7, and the output load R of the transistor Q6 or Q7 that is turned on is output to the base electrodes of the output transistors Q6 and Q7.
A voltage signal appears on L1 or RL2. Similar to the conventional example, the signal Vout appearing on the resistor RL1 or the resistor RL2 is as follows: Vout=(R2/R1)(RL/R3)Vin (where RL=RL1 =RL2).

When a high level signal is input to the A terminal, transistor Q20 is turned on. As a result, the cathode of diode D3 is connected to the base electrode of transistor Q2, the amount of level shift changes, and a forward voltage of 3V from diode D1 to diode D3 is generated between the base electrode of transistor Q2 and the base electrode of transistor Q21.
F occurs. (However, VCE of transistor Q20
(sat)=0).

On the other hand, a forward voltage of 4 V is always applied between the base of the transistor Q3 and the base of the transistor Q22 from the diode D6 to the diode D9, regardless of the state of the A terminal.
F is occurring. Here, from resistor R10 to resistor R13
If the resistance values up to (The current must be sufficiently smaller than the forward current flowing from diode D1 to diode D3). Then, transistor Q6 turns on, transistor Q7 turns off, and the amplified signal appears at output load RL1.

On the other hand, when a low level signal is input to the A terminal, the transistor Q20 is turned off. As a result, a forward voltage of 5VF from the diode D1 to the diode D5 is generated between the base electrode of the transistor Q2 and the base electrode of the transistor Q21. On the other hand, transistor Q3
Since the voltage between the base electrode of the transistor Q22 and the base electrode of the transistor Q22 is 4VF as before, it can be seen that the transistors Q2 and Q21 are turned off and the transistors Q3 and Q22 are turned on. Then, transistor Q6 is turned off, transistor Q7 is turned on, and the amplified signal is output to output load RL2.

That is, when a high level signal is input to the A terminal, the voltage signal is output only to the output load RL1, and when a low level signal is input to the A terminal, the voltage signal is output to the output load RL1. Outputted only to RL2.

As shown in the circuit of the third embodiment,
There is only one input terminal for the logic control signal, and there is only one switching transistor, transistor Q20. Further, the current required for the switch operation is only a small base current for driving the transistor Q20, and the current is almost negligible. Note that the present invention is not limited to the above embodiments, and various modifications are possible. For example, although a diode is used as an element for changing the level shift amount in FIG. 3, a resistor may be used instead.

[0037]

Effects of the Invention According to the above configuration, only one terminal to which a logic control signal is input is required, and only one switching transistor is required. can be realized. In addition, the current required for switch operation is only a small base current, which can be ignored.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a switch circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a switch circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a switch circuit according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional switch circuit.

[Explanation of symbols]

1...Switch circuit, Q1, Q2, Q3, Q6, Q7, Q
20, Q21, Q22...Transistor, R1, R2, R
3, R10 to R16...Resistor, RL1, RL2...Load resistance, D1 to D9...Diode, C1...Capacitor.

Claims (2)

[Claims] 1. A first differential circuit comprising first and second transistors whose emitters are connected to each other; and the first and second transistors have opposite polarities, whose emitters are connected to each other, and whose collectors are opposite to each other. a second differential circuit including a third transistor connected to the collector of the second transistor, a fourth transistor whose collector is connected to the collector of the first transistor, and one terminal of which is connected to the collector of the first transistor; a first level shifting means connected to the base of the first transistor and having another terminal connected to the base of the third transistor; one terminal connected to the base of the second transistor; a switch circuit comprising: second level shift means having a terminal connected to the base of the fourth transistor; and means for changing base potentials of the first and third transistors in conjunction with each other. . 2. A first differential circuit including first and second transistors whose emitters are connected to each other; and the first and second transistors have opposite polarities, whose emitters are connected to each other, and whose collectors are opposite to each other. a second differential circuit including a third transistor connected to the collector of the first transistor, a fourth transistor whose collector is connected to the collector of the second transistor, and one terminal of which is connected to the collector of the second transistor; a first level shifting means connected to the base of the first transistor and having another terminal connected to the base of the third transistor; one terminal connected to the base of the second transistor; A switch circuit comprising: second level shift means whose terminal is connected to the base of the fourth transistor; and means for changing the amount of level shift of the first level shift means.