JPH0389620A - Analog switching circuit - Google Patents

Abstract

PURPOSE:To realize an analog switch which is economical and requires less space by inputting an analog signal to the inverted input terminal of an operational amplifier, and connecting a DC voltage and the output of a control switch to the non-inverted input terminal. CONSTITUTION:When 0V is inputted as the turn-off signal to a control signal terminal 15, a transistor TR 12 is turned off and the output to a non-inverted input terminal 11b of an operational amplifier 11 is stopped, and therefore, +5V of a DC voltage 14 is inputted to the non-inverted input terminal 11b. Then, the operational amplifier 11 does not output the signal inputted to an inverted input terminal 11a. Consequently, the analog output signal is not supplied to an output terminal 16. That is, this analog switch circuit turns on/off the analog signal by the control signal inputted to the control signal terminal 15. Since this analog switch circuit is inexpensively constituted and the required mounting space is small, it is suitable for miniaturization of a device.

Description

[Detailed Description of the Invention] [Summary] Regarding an analog switch circuit that turns on/off an analog signal, the purpose is to realize an analog switch circuit that is economical and requires less space. A control switch that turns on or off earth air and outputs it by controlling a signal, and outputs an input signal of an inverting input terminal when earth air is connected to a non-inverting input terminal, and a DC voltage is applied to the non-inverting input terminal. An operational amplifier is provided that does not output a human input signal from the inverting input terminal when connected, and an analog signal from the signal input terminal is input to the inverting input terminal of the operational amplifier, and a direct current from the control voltage terminal is input to the non-inverting input terminal. The voltage is connected to the output of the control switch, and by controlling the control switch, the potential of the non-inverting input terminal of the operational amplifier is controlled to turn on/off the analog signal input to the inverting input terminal. do.

[Industrial application field]

The present invention relates to an analog switch circuit that turns on/off analog signals.

Analog switches that turn on/off analog signal transmission paths are often used in communication equipment. FIG. 3 shows an example of a circuit in which such an analog switch is used.

FIG. 3(a) shows a joint termination separation circuit in a joint subscriber circuit of a digital exchange. In the subscriber circuit of a digital exchange, a 2-wire subscriber line is converted to a 4-wire system and connected to the digital communication network, but if the impedance seen from the subscriber line side becomes high impedance, the 2-wire subscriber line is A termination circuit is inserted into the bridge to match the impedance of the subscriber line including the terminal in the communication line of the line portion to ensure good communication characteristics. Reference numeral 22 in FIG. 3(a) is the above-mentioned termination circuit, and 23 is an analog switch that connects or disconnects the termination circuit 22 from the communication line under the control of the control section 24. In the case of two joint participants,
Two subscribers, A and B, are accommodated in one subscriber line, but when either subscriber makes a call alone to a party other than the joint subscriber, the termination circuit 22 is connected. The analog switch 23 is normally in the on state because good communication characteristics can be obtained in this state. However, when A and B communicate, two telephones are connected to the subscriber line, so if the termination circuit 22 remains connected, the communication characteristics will deteriorate. In mutual calls between joint subscribers, the telephones of the other parties serve as termination circuits. Therefore, in the joint subscriber circuit 21, in the case of mutual calls between joint subscribers, the termination circuit 22 is separated from the communication line, thereby achieving the above-mentioned situation. be able to solve problems. Specifically, when the control unit 24 identifies a mutual call between the joint subscribers by a method not shown, the analog switch 23 is turned off to separate the termination circuit 22 from the communication line.

FIG. 3(b) shows a balanced network switching circuit in a subscriber circuit of a digital exchange. In the subscriber circuit of a digital exchange, a 2-wire subscriber line is converted to a 4-wire system and connected to the digital communication network, but in order to prevent noise, etc., a balanced circuit network is installed in the 4-wire section. has been established. However, because the standards for subscriber lines differ from country to country, the balanced circuit networks created to suit the characteristics of subscriber lines also differ from country to country. Furthermore, even within the same country, different balanced circuit networks may be used depending on the line type and line length. For this reason, a method is often used in which a plurality of balanced circuit networks are provided in the subscriber circuit, and the optimal one is selected from among them and connected to the communication line, 32a in FIG. 3(b).
, 32b is a plurality of balanced circuit networks, and 33 is a control unit 3.
4, the plurality of balance circuits 1132a, 32b
This is an analog switch circuit for connecting either of the two to the telephone line. 33a and 33b in the analog switch circuit 33 are analog switches corresponding to the balanced circuit networks 32a and 32b, respectively.

The control unit 34 controls the analog switch circuits 33 of each subscriber circuit according to information inputted in advance, and connects each optimum balanced circuit network to the communication line.

Analog switch circuits are used as described above, but because the resistance value when the switch is turned on must be low, conventionally a semiconductor switch, CMOS switch, or
Relay contacts are used. However, both CMOS switches and relays are relatively expensive and require a large mounting space, and the use of relays in particular is a bottleneck in downsizing devices.

Therefore, there is a need for an analog switch circuit that is economical and requires less mounting space.

[Conventional technology]

FIG. 4 is a circuit diagram in which a conventional analog switch is used. FIG. 4(a) is an example of a CMOS switch, and FIG. 4(a) is an example of a relay switch.

In FIG. 4(a), 41 is a CMOS switch, and the CMOS switch 41 is turned on/off by a control signal, and analog signals are accordingly turned on/off.

When the control signal is turned on and the CMOS switch 41 is turned on, the analog signal is passed through the amplifier C1 resistor R3 to the operational amplifier (OP) 42 and the resistor R.
The signal is input to an amplifier circuit consisting of 2, amplified, and output. When the control signal is turned off, the CMOS switch 41 is turned off and output of the analog signal is stopped.

In Fig. 4 (0)), the CMOS in Fig. 4 (a)
A relay contact (ri) 43b is used instead of the switch 41. Components other than the relay are the same as in FIG. 4(a), and the same symbols are used for the same parts. Figure 4 (
In b), the relay (
RL ) 43a operates or restores, and accordingly, the relay contact (r l ) 43b turns on/off, and the fourth
Analog signals are output or stopped in the same way as in FIG.

The CMOS switch and relay switch shown in Figure 4 above are both suitable as analog switches because of their low resistance when turned on, but both CMOS switches and relays are relatively expensive and require a small amount of space. Relays in particular are a bottleneck in downsizing devices.

[Problem to be solved by the invention]

As described above, CMOS switches and relay switches used as analog switches in the prior art have disadvantages in that they are expensive and require a large amount of space for mounting.

The present invention aims to realize an analog switch circuit that is economical and requires less space.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

In the figure, 1 is an operational amplifier, 1a is an inverting input terminal of the operational amplifier 1, and 1b is a non-inverting input terminal. When the ground is connected to the non-inverting input terminal 1b, the analog signal input to the inverting input terminal 1a is output, and a DC voltage that is approximately the same voltage as the power supply voltage of the operational amplifier l is applied to the non-inverting input terminal 1b. In this case, the analog signal input to the inverting input terminal 1a is not output. Reference numeral 2 is a control switch that is turned on and off by a control signal. By connecting one side of the switch to the ground, when it is turned on, it outputs the ground air, and when it is off, it turns off the output (potential-free). state). In addition, 3 is an input signal terminal,
4 is a control voltage terminal, 5 is a control signal terminal, and 6 is an output terminal.

In FIG. 1, an analog signal from a human input signal terminal 3 is input to an inverting input terminal 1a of an operational amplifier l.

In addition, the DC voltage from the control voltage terminal 4 and the output of the control switch 2 are connected to the non-inverting input terminal 1b, and depending on whether the control switch 2 is turned on or off, the non-inverting input terminal 1b is connected to the earth or from the control voltage terminal 4. is configured to be connected to one of the DC voltages.

[For production]

Although not shown in the figure, the operational amplifier l in FIG.
is connected. In this case, the input voltage range of the operational amplifier 1 is approximately 15 to +5 V, as is well known. Furthermore, since the output voltage of the analog signal input to the inverting input terminal 1a is sent out using the voltage applied to the non-inverting input terminal 1b as a reference level, the potential of the non-inverting input terminal 1b is set to QV,
In other words, if it is at the ground level, the output voltage range is approximately 15%.
~+5v. Therefore, if the same voltage as the operation tB of the operational amplifier 1, for example +5V, is connected to the non-inverting input terminal 1b, the analog signal input to the inverting input terminal 1a will be output as +5V@14 quasi-level. However, as mentioned above, since the range of the output voltage is 15 to +5V, an output with +5V as the reference level means that no output is sent out as a result. That is, if the input level of the analog input signal is sufficiently small compared to the operating iis voltage of the operational amplifier 1, by connecting the same voltage as the operating power supply of the operational amplifier 1 to the non-inverting input terminal 1b, the output from the operational amplifier 1 is reduced. can be stopped.

In FIG. 1, the non-inverting input terminal 1b of the operational amplifier 1 is connected to the DC voltage from the control voltage terminal 4 and the output of the control switch 2. When turned on, non-inverting input terminal 1
The potential of b is at the earth level, therefore, the potential of input signal terminal 3
The analog signal inputted to the inverting input terminal 1a via the operational amplifier l is outputted from the output terminal 6.

When the control switch 2 is turned off by the control signal, the DC voltage connected to the control voltage terminal 4 is applied to the non-inverting input terminal 1b, so that the analog signal from the input signal terminal 3 is output from the operational amplifier 1 as described above. Therefore, no analog signal is sent out from the output terminal 6.

As described above, in the circuit shown in FIG.
By turning on/off the control switch 2 using a control signal connected to the input signal terminal, it is possible to turn on/off the analog signal input to the input signal terminal. Furthermore, since both the operational amplifier 1 and the control switch 2 shown in FIG. Can be constructed economically.

〔Example〕

FIG. 2 is a circuit diagram of one embodiment of the present invention.

In FIG. 2, 11 is an operational amplifier (OP) used as an analog switch, lla is an inverting input terminal (indicated by -) of the operational amplifier 11, llb is also a non-inverting input terminal (indicated by +), 12 is a transistor (Q
), 13 is the input signal terminal, 14 is the DC voltage (+5V)
, 15 is a control signal terminal of the transistor 12, 16 is an output terminal, and 17 is an operational amplifier (OP) used as an amplifier.
l), 17a is the inverting input terminal of the operational amplifier 17, 17
Similarly, b is a non-inverting input terminal, R1-R3 are resistors, and C is a capacitor. In addition, the operational amplifier 11 and the resistor R3
, the operational amplifier 17 and the resistor R1 each constitute an amplifier circuit.

Now, when +5■ is input as an on signal to the control signal terminal 15, the transistor 12 is turned on, and the operational amplifier 1
The ground air is connected to the non-inverting input terminal 11b of No. 1. When the ground air is connected to the non-inverting input terminal 11b, the operational amplifier 11 passes an analog signal input from the input signal terminal 13 to the inverting input terminal 11a via the resistor R3, and performs an operation through the capacitor C and the resistor R4. It is input to the inverting input terminal 17a of the amplifier 17. The analog signal input to the inverting input terminal 17a of the operational amplifier 17 is amplified by an amplification circuit constituted by the operational amplifier 17 and the resistor Rs, and is output from the output terminal 16.

Next, when Ov is input as an off signal to the control signal terminal 15, the transistor 12 is turned off, and the operational amplifier 11
Since no output is made to the non-inverting input terminal 11b, +5V of the DC voltage 14 is input to the non-inverting input terminal 11b. Operational amplifier 11 has +5V as an operating power supply.
is supplied (not shown), but the non-inverting input terminal 11
When +5V, which is the same voltage as the operating power supply, is input to b, the operational amplifier 11 no longer outputs the signal input to the inverting input terminal 11a, as described above. Therefore, no analog output signal is sent to the output terminal 16.

That is, the circuit shown in FIG. 2 is an analog switch circuit that turns on/off an analog signal by a control signal input to the control signal terminal 15, and can be applied to the analog switch circuit shown in FIG. 3, etc. In addition, since the operational amplifier U, transistor 12, and resistors R0 to R8 in Fig. 2 are extremely common components, an analog switch circuit consisting of these components can be constructed at low cost, and the required mounting space is small. , it is also suitable for downsizing the device.

〔Effect of the invention〕

As explained above, according to the present invention, an analog switch circuit can be constructed from inexpensive and small-sized components, which greatly contributes to economicalization and miniaturization of such analog switches.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a circuit diagram of an embodiment of the present invention, FIG. 3 is an example of use of an analog switch, and FIG. 4 is a circuit diagram of a conventional technique. In the figure, ■・−−−−−−−・−・・−・−・−・−・−・
・Operation amplifier 2−・−・・−1−−−・・−・ 3 ・−・−・−・・−1−−・−・ 4−・−・−・・−・ 5−・・・・・−−１−−・−・−・ ６ −−−−−−１・・・ It is. Control switch input signal terminal Control voltage terminal Control signal terminal Output terminal Example of analog switch usage Figure

Claims (1)

[Claims] A control switch (2) that turns on or off the earth air and outputs it under the control of a control signal input to a control signal terminal (5).
and outputs the input signal of the inverting input terminal (1a) when earth air is connected to the non-inverting input terminal (1b), and outputs the input signal of the inverting input terminal (1a) when a DC voltage is connected to the non-inverting input terminal (1b). An operational amplifier (1) that does not output the input signal of the input terminal (1a)
), the analog signal from the signal input terminal (3) is input to the inverting input terminal (1a) of the operational amplifier (1), and the DC voltage from the control voltage terminal (4) is input to the non-inverting input terminal (1b). and the output of the control switch (2), and by controlling the control switch (2), the potential of the non-inverting input terminal (1b) of the operational amplifier (1) is controlled, and the potential of the non-inverting input terminal (1b) is controlled.
1a) An analog switch circuit characterized in that it turns on/off an analog signal input to the circuit.