JPH0329512A - Semiconductor analog switch - Google Patents

Abstract

PURPOSE:To reduce a leakage current by arranging plural semiconductor analog switch components in series and leading out a connection terminal externally from the connecting point via another semiconductor analog switch component operated inversely from the semiconductor analog switch components. CONSTITUTION:Analog switch components 1a, 1b are arranged in series, switched simultaneously with a control signal 5 supplied externally to switch a signal current flowing between input and output terminals 4a, 4b. An analog switch component 2a is arranged between a connecting pint 8a of the analog switch components 1a, 1b and an auxiliary voltage terminal 6b provided externally and switched inversely to the analog switch components 1a, 1b by a signal conversion circuit 3. Thus, a voltage difference across the analog switch component 1b goes to zero and no leakage current does not flow to the analog switch component 1b and an input/output terminal 4b.

Description

[Detailed Description of the Invention] , No. 1 The present invention relates to a semiconductor analog switch circuit, and for example, in an electronic circuit of an electric measuring device or an electroacoustic device, switching of an analog electric signal or opening/closing operation is performed by a control signal given from the outside. Suitable for analog switch circuits.

For example, in a measuring instrument that automatically measures the electrical characteristics of a semiconductor device, there is a measurement range switching circuit, a voltage/current range switching circuit for the power supply applied to the device under test, etc.
In many cases, electromagnetic relays having mechanical contacts or analog switching elements using FETs are used for circuits that change circuit constants using control signals and switching circuits for measurement terminals.

u<' ” i The above electromagnetic relay uses a mechanical mechanism to open and close the contacts, so it has a short lifespan compared to other electronic components and semiconductor devices. This is a factor that reduces the reliability of the equipment used.

Further, compared to electromagnetic relays, analog switch elements using FETs have a problem in that they have a large leakage current when turned off, causing signal leakage and wraparound, and their range of use is limited.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor Analog Gusinchi circuit that solves the above-mentioned problems.

The technical means for achieving the above object of the present invention is to connect one switch terminal to each other and arrange them in series, and take out the other switch terminal as an input/output terminal for the electrical signal to be switched. , first and second analog switch elements that open and close simultaneously and in the same manner according to a control signal applied from the outside, and a terminal provided exclusively at the connection point between the first and second analog switches and externally. a third analog switch element disposed between the connection point and capable of applying any voltage from the outside to the connection point; The present invention is characterized in that an analog switch circuit is constructed with a signal conversion circuit that processes a control signal given from the outside so that the switch is turned on.

According to the above configuration, when the first and second analog switch elements are OFF, the third analog switch element is ON.
Then, a terminal provided exclusively outside and a connection point between the eleventh and second analog switches are electrically connected. At this time, if the dedicated terminal is grounded, the leakage current flowing to the first and second analog switch elements will flow from the connection point of the first and second analog switches to the third analog switch element. Since the analog switching element is grounded through a dedicated terminal provided externally, signal leakage due to leakage current of the first and second analog switch elements is eliminated. Furthermore, when a voltage equal to the voltage of the input/output terminal to the first analog switch element is applied to the dedicated terminal through, for example, a voltage follower using an operating amplifier, the first analog switch which is OFF is applied. The voltage between the switch terminals of the element is only the offset voltage of the voltage follower, and can be reduced to approximately zero volts. Therefore, the leakage current flowing through the first analog switch element is: Leakage current = Offset voltage = OFF resistance, so
An analog switch circuit with extremely low leakage current can be constructed.

In the above description, when the first analog switch is replaced with the second analog switch, the leakage current flowing through the second analog switch can be made extremely small by the same effect.

Embodiments of the semiconductor analog switch circuit according to the present invention will be described with reference to FIGS. 1, 2, and 3.

1 and 2 show semiconductor analog switch circuits showing respective embodiments according to the present invention, and FIG. 3 shows one example of an analog switch element that is one component of the semiconductor analog switch circuit according to the present invention. This is an example.

In FIG. 1, analog switch elements 1(a) and 1(
b) are arranged in series and open and close at the same time according to a control signal 5 given from the outside, and input/output terminals 4 (a)
4 (b) Opens and closes the signal current flowing between.

The analog switch element 2 (a) is arranged between the connection point 8 (a) between the analog switch elements Ha) Hb) and an externally provided auxiliary voltage terminal 6 (b), and is connected to the signal conversion circuit 3.
Accordingly, analog switch elements 1(a) 1(b)
Perform the opening/closing operation in the opposite direction.

In addition, the voltage follower 7(a) has an input/output terminal 4(
It is provided to receive the voltage (b) with a high input impedance and supply the same voltage to the auxiliary input terminal 6(b) with a low output impedance.

According to the configuration in the diagram, an analog switch element! (a) 1
When (b) is OFF, analog switch element 2
(a) is ONL, so analog switch element 1
A voltage equal to that of the input/output terminal 4(b) is applied to the connection point 8(a) of (a) 1(b) by the voltage follower 7(a) and the analog switch element 2(a). Therefore, the voltage difference between both ends of the analog switch element 1(b) becomes zero volts, and no leakage current flows through the analog switch element 1(b) and the input/output terminal 4(b).

Also, simply analog switch 1 (a) 1 (b)
When it is desired to eliminate signal leakage between input/output terminals 4(a) and 4(b) when OFF, voltage follower 7(a)
) is not necessary, and the auxiliary voltage terminal 6(b) can be grounded.

At this time, the signal current flowing through the analog switch Ha) Hb) as a leakage current and flowing into the connection point 8(a) is all connected to the analog switch element 2(a) and the auxiliary voltage terminal 6(
Since it flows into the ground through input/output terminal 4 (a
) 4 (b) No signal leakage occurs between them.

FIG. 2 shows another embodiment, in which, in addition to the circuit configuration of FIG. 1, the connection point 8(a) and the analog switch element 1 (
a) Between 1 and (b), the analog switch element l
(a) 1 shows an example in which another analog switch element 1 (C) that performs the same opening/closing operation as in (b) is arranged in series. This analog switch circuit further includes a connection point 8 (b) between analog switch elements 1 (a) and 1 (c).
) is connected to one terminal of yet another analog switch element 2 (b) which has the same opening/closing operation as analog switch element 2 (a), and the other terminal is connected to another auxiliary voltage terminal 6 (a). The circuit is the same as the circuit in Figure 1 except that it is taken out to the outside, so the same parts are given the same reference numerals.
The explanation will be omitted. According to the embodiment shown in FIG. 2, the input/output terminal 4 (a) 4 has the same effect as the embodiment shown in FIG.
The leakage current flowing into both terminals in (b) can be eliminated. Also, simply analog switch 1
(a) 1 (b) 1 (c) is OFF, when it is necessary to eliminate signal leakage between input/output terminals 4 (a) and 4 (b), voltage follower 7 (a) and auxiliary voltage terminal 6 ( 7(b) provided at A> is unnecessary, and the auxiliary voltage terminal 6(
a) Either one or both of E3 (b) may be grounded.

FIG. 3 shows an example of the analog switch element, which is one component of the semiconductor analog switch circuit according to the present invention.

In the figure, the light emitting element 9 emits light in response to a control signal, and the emitted light generates an electromotive voltage in the photovoltaic elements 10(a) and 10(b). This voltage is MOSFET switch 1
(acts as a gate bias voltage for alH (bl),
Turn them on.

According to the present invention, it is possible to easily configure an analog switch circuit that is made of semiconductor elements and has low leakage current, and by replacing a conventional electromagnetic relay with mechanical contacts, high reliability of the device can be achieved. It can be sexualized.

Figure 1

[Brief Description of the Drawings] Figures 1 and 2 are configuration diagrams showing each embodiment of a semiconductor analog switch circuit according to the present invention, and Figure 3 is a configuration diagram of a semiconductor analog switch circuit according to the present invention. FIG. 2 is a configuration diagram showing a specific example of an analog switch element that is an element. 1(a) 1(b) 1(c) 2(a) 2(b)
...Analog switch circuit, 3...Signal conversion circuit, 7(a) 7(b)...Voltage follower,
@2 Figure

Claims (1)

[Claims] In a semiconductor analog switch circuit that opens and closes analog electrical signals in response to externally applied control signals, a plurality of semiconductor analog switch elements are arranged in series,
A semiconductor analog switch circuit characterized in that a connection terminal is taken out from the connection point to the outside via another semiconductor analog switch element that opens and closes in the opposite direction to that of the semiconductor analog switch element.