JPS5862932A - Analog switch circuit - Google Patents

Abstract

PURPOSE:To obtain a circuit of low distortion factor, by branching an analog input signal into a plurality of parallel paths and controlling an analog switch circuit inserted at the middle point of the paths. CONSTITUTION:An input signal (a) applied to an input terminal 1 is branched into parallel paths (a), (b) and (c) and analog switch circuits 2, 3 are inserted between resistors R1, R2, and R'1, R'2 of the paths (a), (b). A joining point (d) of the paths (a), (b) and (c) is connected to a - signal input terminal of an operational amplifier 7 and the output of the amplifier 7 is fed back to the - signal input terminal via a resistor R4. The circuits 2, 3 are controlled with a control signal from control terminals 5, 6 and 5', 6'. Through the combination of the applied time of the control signal, the synthesized value of the signal of the joining point (d) of the paths (a), (b), and (c) is changed to compensate the deterioration in distortion characteristics due to diodes and to decrease the distortion factor of the analog switch circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog switch circuit designed to reduce distortion.

Conventionally, analog switch circuits have often been used with a switch circuit inserted in series in a signal path and configured as shown in FIG. In the figure, 11 is a signal input terminal, 12 is a switch circuit, and has two pairs of diodes connected in opposite directions.

It consists of D2 and "3 e" 4. 14 is the output terminal, 1
621-. and 16 are the diode pair D1. D, and “3 e”
4, each control terminal 17 is an operational amplifier, "IL
*Rb is resistance.

FIG. 2 is a diagram showing the timing relationship of control signals to control terminals 16 and 16. The control signal is connected to the positive supply voltage (V+
) and the negative power supply voltage (V-)-, which are in opposite phase to each other. Therefore, during period 〒1, both diodes Dl#D are ON, and therefore the switch circuit 1
2 is also OR4! : and, conversely, becomes OFF during period T2.

The analog signals input to the input terminal 11 are sequentially switched ON and OFF according to the control signal, and an output is obtained at the output terminal 14. Generally diode DI “””
4, a switching current flows when it is ON, and its input/output characteristics have non-linearity, so the ON resistance also changes depending on the input signal level, fluctuations in diode characteristics, and other causes, and the distortion rate is -40 ! The reality is that we can only expect a grade of B. However, this value was insufficient when low strain rate characteristics were required.

The present invention eliminates the above-mentioned conventional problems, and will be described below along with one embodiment thereof.

FIGS. 3 to 6 show embodiments applied to a circuit that switches a sine wave voltage and outputs it as a staircase wave.
FIG. 3 is a circuit diagram thereof, FIG. 4 is a waveform diagram of input/output voltages, and FIG. 6 is an explanatory diagram showing the timing relationship of switching of the switch circuit. In FIG. 3, 2 is a first switch circuit, 3 is a second switch circuit having the same configuration as the first switch circuit, R1-R4,R(,' is a resistor, 4 is an output terminal,
6, 6°s/ and e/ are respectively the first. A control terminal 7 corresponding to the second switch circuits 2 and 3 is an operational amplifier.

In FIG. 4, the control terminals 6°6 and 2, respectively,
5' and 6' are the control voltage waveforms, E is the input analog signal waveform to the input terminal 1, and E is the output waveform from the output terminal 4. In the above embodiment, R3) Rζ+Rf>Horse+R2
・・・・・・・・・・・・・・・・・・(1) Rlg<
<R1, R2・・・・・・・・・・・・Nini...
・・・・・・・・・I will do more if I am chosen by love. However, Rs is the resistance value when the switch circuits 2 and 3 are turned on.

Next, the operation of the above embodiment will be explained. The input signal applied to the input terminal 1 is divided into three paths, a, b, and c, with a resistance R in the path a and a resistance R1' in the 2y path.

Hz In the path O, after turning on the resistor R3, the signal joins again to the point d, and is commonly input to the (-) signal terminal of the operational amplifier 7. Between the paths a and b, there is a first switch circuit 2 between the resistors R1 and R2, and between the resistors R, l and R2.
'A second switch circuit 3 is connected between each ground and the ground, and when these switch circuits are ON, the ON resistance R11! is a low value. will be inserted in parallel with signal paths a and b.

In the above configuration, for example, when the first switch circuit 2 is ON and the second switch circuit 3 is Oyy, the signal of the first switch circuit is (Rz/R1)(Rt+Chang/R* (Rt +Rz/
Rs)゛・・−・−・−・・(Attenuated by the barrel (/ represents parallel connection), as mentioned above (in the model, R2/Rs=Rg, so approximately Ra・
(Rt /R2)<< 1, and the signal will be greatly attenuated. Therefore, in this case, the signal added to point d is determined by the path c, and the resistance R1'+R
11! -, the output voltage is determined by the ratio of the parallel composite value of R3 and R4.

Next, when the 12 sets of switch circuits 2.3 are driven by different control signals as shown in FIG. If there is a relationship shown in equation (1) between the sum of the resistances in the time paths a and b, a staircase-like output pulse waveform as shown in FIG. 4 is obtained.

As mentioned above, the distortion characteristics of an analog switch deteriorate when the diode is ON, but in the above configuration, the switch circuit is inserted in parallel with the signal path, and for example, the inherent O distortion factor of the switch circuit is -40 ( IB1 (Assuming that the signal attenuation rate according to equation (2) is 16011B, the distortion factor of the diode in the OFF state is extremely low, so there is no problem, and the total distortion is -4◇+(-eo) =-1ooa. In the end, a distortion rate improvement of 60 (1B) was achieved.In the above configuration, if the degree of signal attenuation is increased, the output decreases, but this is because the amplification degree of the operational amplifier 7 is not sufficiently increased. All you have to do is take a larger value and compensate.In the above explanation, we have explained the case where a diode is used as the switching element, but the same applies to the case where other analog switching elements such as transistors and AWOS are used. Needless to say, the number of parallel-connected branches is not limited to the above-mentioned 3 ([), but various cases of 2 or more can be considered.

As explained above, according to the present invention, an analog input signal is branched into a plurality of parallel paths, and an analog switch circuit connected between the signal path and the ground is inserted at the intermediate point of each path. By controlling switching and inputting the output to an operational amplifier with resistive feedback,
An analog switch circuit with an extremely low distortion rate can be realized, and its industrial value is great.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram of a conventional analog switch circuit, Fig. 2 is a waveform diagram of its main parts, Fig. 3 is a wiring diagram of an analog switch circuit according to the actual male side of the present invention, and Fig. 4 is a diagram of its main parts. The signal waveform diagram in FIG. 6 is a diagram for explaining the operation. 1...Input terminal, 2.3...Switch circuit, 4...Output terminal, 5, 6.5', 6'.
...Control terminal, 7...Operation amplifier, R1
-R4, Rf, il/...river/resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person
4wA 81m1 0 Hatake 2 Figure Kite 3 Figure 3R3゜No. 51! I

Claims (1)

[Claims] a plurality of parallel resistance circuits each having one end commonly connected to a signal input terminal; and at least one parallel resistance circuit connected between an intermediate point of at least one of the parallel resistance circuits and ground, each having a control signal terminal. An analog switch circuit comprising a switch circuit and an operational amplifier circuit connected between the other commonly connected end of the parallel resistance circuit and an output terminal.