JPH0444846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an analog switch for cutting and cutting signals.

(Prior art) Conventional analog switches include those that use bipolar transistors, unipolar transistors, and even thyristors, but with the exception of those that use bipolar transistors, they can be incorporated into inexpensive integrated circuits. It was not suitable for

However, even with an analog switch using bipolar transistors, if the transistor Q1 is connected in parallel between the signal line a and the ground as shown in FIG. When turning on to short-circuit output terminal 1 to ground, it is necessary to insert resistor R1 in signal line a to prevent short-circuiting between input terminal 2 and ground. There is a problem that losses occur. 3
4 is a drive signal input terminal for driving an analog switch, 4 is a signal source, and 5 is a load.

Furthermore, as shown in Fig. 4, when an analog switch is constructed by inserting a transistor Q2 in series on the signal line a, the transistor Q
A drive signal source 6 for driving 2 must be inserted in series with the signal source 4, and a transistor Q
There is a problem in that the on/off state of signal source 4 is affected by the impedance of signal source 4. 7 is a power supply for transistor Q2.

In addition, two transistors have their collectors and emitters connected in antiparallel, one collector-emitter common connection part connected to the input terminal, the other collector-emitter common connection part connected to the output terminal, and the bases commonly connected. An analog switch consisting of (For example, Utility Model Application Publication No. 57-100333,
(Japanese Patent Application Laid-open No. 109362/1983).

However, in this analog switch, the base current that controls it flows through the collector and emitter.
There is a problem in that an error occurs in the signal current obtained at the output terminal side.

(Object of the invention) The present invention was made in view of the above situation,
To provide an analog switch that reduces transmission loss of a signal as a controlled object, is not affected by signal source impedance in on/off control, and does not cause errors in the obtained signal current.

(Structure of the Invention) For this purpose, the analog switch of the present invention connects the collector and emitter in antiparallel, connects one collector-emitter common connection to the input terminal, and connects the other collector-emitter common connection to the output terminal. In an analog switch consisting of two transistors whose bases are connected to a A drive circuit in which first and second current sources are connected, and a third current source having a current value equal to the current value obtained by adding the currents of the first and second current sources to the base is connected, and operation of the drive circuit. The device is configured to include means for turning on and off.

(Example) Hereinafter, an example of the analog switch of the present invention will be described. FIG. 1 shows the principle equivalent circuit. In this embodiment, a transistor serving as a switching element is configured as a bidirectional PNP transistor in which an emitter and a collector are formed to have the same shape and area. In terms of an explanatory equivalent circuit, this bidirectional transistor is 2
pnp transistors Q3 and Q4. The bases of these transistors Q3 and Q4 are commonly connected, and the collectors of one of them are commonly connected to the emitter of the other, that is, they are connected in antiparallel. One of the collector-emitter common connection portions is connected to the input terminal 2, and the other is connected to the output terminal 1. Further, these transistors Q3 and Q4 have constant current sources 8 and 9 at their emitters.
A constant current I is supplied from the base, and a constant current 2I is sucked out from the base by another constant current source 10. These constant current sources 8 to 10 constitute a drive circuit independent from the input terminal 2 and the output terminal.

Therefore, in this bidirectional transistor, the constant current I from the constant current source 8 is applied to one transistor Q3.
The constant current I from the constant current source 9 flows from the emitter to the base of the other transistor Q4 and flows into the constant current source 10, thereby turning on the transistor Q3. It can be treated as if the other transistor Q4 is turned on by the current flowing into the current.

In this on state, the signal applied to the input terminal 2 is transmitted to the output terminal 1. In this transmission,
The loss in the transistors Q3 and Q4 is an emitter-collector loss (several ohms), but this is negligible. In addition, constant current sources 8 to 10
There is no possibility that this current will leak into the transmitted signal.

Note that the transistors Q3 and Q4 can be turned on and off by turning on and off the constant current sources 8 to 10 using a control signal applied to the control terminal 11.

FIG. 2 shows a circuit embodying the constant current circuit portion of the circuit described above. The constant current sources 8 and 9 are each composed of transistors Q5 and Q6, and these transistors Q5 and Q6 are connected to a diode-connected multi-emitter transistor Q7 which acts as a reference side.
and constitute a pseudo current mirror. That is,
A current that is half the collector current of transistor Q7 flows through the collector of each transistor Q5, Q6. Further, the constant current source 10 is composed of a transistor Q8, and constitutes a current mirror with a diode-connected transistor Q9 functioning as a reference side. Note that the transistor Q7 on the reference side is connected to a transistor Q10, and this transistor Q10 forms a current mirror with the transistor Q9. B1 and B2 are ±V
It is a power source that generates a voltage of . The positive side of one power supply B2 is connected to the collector of a transistor Q9 via a switch 12 and a resistor R4.

Now, set the value of resistor R4 appropriately and set V/R4.
If the current is set so that =2I flows through the collector of transistor Q9, transistors Q8 and Q1
A constant current of 2I flows through each collector of 0. Also, for this reason, the collector of transistor Q7 also has 2
Since a constant current I flows through each emitter (a constant current I flows through each emitter), the transistors Q5 and Q
A constant current I flows through 6.

The on/off states of the transistors Q5 to Q10 follow the on/off state of the switch 12. As a result, the operation of the bidirectional transistor equivalently made up of transistors Q3 and Q4 is turned on and off by turning on and off the switch 12, and the transmission of the signal from the input terminal 2 to the output terminal 1 is interrupted. .

(Effects of the Invention) As explained above, according to the analog switch of the present invention, since the on-resistance is low, there is little signal loss, and since the drive circuit is independent from the input terminal and output terminal, the signal source impedance The drive current does not affect the signal current flowing through the output terminal. Furthermore, it is possible to handle large current signals, and the drive circuit can be easily configured, making it easy to integrate the circuit.

[Brief explanation of drawings]

Fig. 1 is a theoretical equivalent circuit diagram of an analog switch according to an embodiment of the present invention, Fig. 2 is a circuit diagram of an analog switch embodying the drive circuit part in Fig. 1, and Figs. 3 and 4 are conventional circuit diagrams. FIG. 2 is a circuit diagram of an analog switch.

Claims (1)

[Claims] 1. The collector and emitter are connected in antiparallel, one collector-emitter common connection part is connected to the input terminal, the other collector-emitter common connection part is connected to the output terminal, and the base is commonly connected. In an analog switch consisting of two transistors, the emitters and collectors of the two transistors are formed to have the same shape and the same area, and first and second current sources of the same current are connected to the common connection between the collectors and emitters. a third current source having a current value equal to the sum of the currents of the first and second current sources connected to the base;
An analog switch comprising means for turning on and off the operation of the drive circuit.