JPS60148229A - Analog-digital converting circuit - Google Patents

Abstract

PURPOSE:To prevent damage to a digital circuit due to an excessive input signal by coupling a double integration circuit outputting a pulse width signal proportional to the amplitude of an analog input signal and a pulse width counter circuit by means of a photocoupler. CONSTITUTION:After the analog signal A from a terminal 1 is integrated for a prescribed time at an integration device, a switch 4 is thrown to the position of a terminal 3, a prescribed voltage B of opposite polarity to the signal A is inputted to the integration device 5, a comparator 6 is operated at the same time so as to compare the output C of the integration device 5 with a prescribed voltage level D. The comparator 6 consitute the double integration circuit which outputs a signal E for the time when it is detected that the signal C reaches the voltage level D. A light emitting doide 12 of a photocoupler 11 is lighted by the signal E, the light of the diode 12 is received by a phototransistor (TR)13, and its output is inputted to a counter circuit 8. The time width of the signal E is proportional to the amplitude of the signal A, the width is counted by the circuit 8 by using the clock pulse and the result is outputted as a digital signal F. Since the coupler 11 isolates an excess input signal, the damage of the circuit 8 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an analog-to-digital conversion circuit for converting an analog input signal to a digital signal, and particularly to a double-integration type analog-to-digital conversion circuit using a double-integration circuit.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, (l) is an input terminal to which analog signal input voltage A is applied between common terminal (2), and (3) is a predetermined input terminal with opposite polarity to input voltage A between common terminal (2). (4) is an analog switch that switches terminals 11+(31), (5) is an integrator consisting of an operational amplifier, and (6) is a terminal to which a constant voltage B of integrator (5) is applied. A comparator detects when a predetermined voltage level D is reached, and these input terminals (1) + 2) + 31 and analog switch (4)
)l/integrator a (5) and the comparator (6) constitute a double integration circuit (7). (8) is a counting circuit that counts the pulse width of the output voltage E from the comparator (6) using clock pulses, and 191QI is a digital signal F output terminal. Figure 2 shows the output voltage C of the integrator (5) and comparator (6).
and E, T1 is an analog signal measurement period when the analog switch (4) in FIG. 1 is switched to the terminal (1) side, and T2 is a period when the analog switch (4) is switched to the terminal (3)
) side is the pulse conversion period "al" is the analog signal measurement period fitl T when the analog input signal is at a low voltage A.

The change in the output voltage C of the operational amplifier (5) at C1
1 is the change in voltage C during the pulse conversion period T2 for the same voltage tag e r Ca2 is the analog input signal being high (,
Change in voltage C during period T when N voltage A2 'e
e Cb2 is the voltage C in period T2 with respect to voltage A2
E represents the output voltage Ek of the comparator (6) with respect to the input signal A, and E2 represents the voltage E with respect to A2.

Next, its operation will be explained. When the contact on the terminal [11 side] of the analog switch (4) is closed, the analog signal input voltage A is input to the integrator (5) via the switch (4). The input voltage A is applied during the analog signal measurement period T1 in FIG.
) side, the voltage decreases at a slope proportional to the magnitude of the analog input voltage A. For example, A with low input voltage,
When the voltage is high, it falls like Ca1, and when the voltage A2 is high, it falls like Ca2, and at the end of T, the output voltage C of the integrator (5) decreases by a voltage proportional to the input voltage A, and the voltage level It is lower than D. Next, the analog switch (4) is switched to the terminal (3) side.

Entering the pulse conversion period T2, the comparator (6) starts operating at the same time to generate a positive output voltage. When entering the pulse conversion period T2, the integrator (5) integrates a constant voltage B with the opposite polarity to the input voltage A, and the output voltage C has the same slope whether the input voltage is A1 or A2. Cbl”
It rises like b2. This integrator output voltage C (Cbl
, Cb2) reaches a predetermined voltage level D1, for example Ov, the comparator (6) polarizes it and makes its output zero. That is, from the comparator (6), the pulse width W (Wl, W2) Nohals voltage E is proportional to the integration time in the two period T2.
(gE) is obtained. This pulse 121@W will be proportional to the magnitude of the analog signal input voltage A. This pulse width W is counted by a clock pulse in a counting circuit (8) and outputted as a digital output signal F to an output terminal +9+ fil.

Conventional double-integration type analog-to-digital conversion circuits are configured as described above, so when an excessive voltage or current is input to the analog signal input voltage, one circuit is destroyed and the entire circuit including the digital output circuit is destroyed. In order to prevent this, it is necessary to add an insulating circuit, which has the disadvantage that the entire device becomes expensive.

[Summary of the invention]

This invention was made to eliminate the above-mentioned drawbacks of the conventional circuit, and by coupling the output circuit of the double integration circuit and the input circuit of the counting circuit with a photocoupler, insulation was achieved at low cost. The purpose is to provide analog-to-digital conversion circuits.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, (l) to 0I indicate the same parts as the same reference numerals in FIG.

That is, the configuration differs from that in FIG. 1 only in that the output circuit of the comparator (6) is coupled to the input circuit of the counting circuit (8) via the photopower 1 or αυ. Therefore, in normal operation, it is no different from that in FIG. 1, but with the analog circuit of the double integration circuit (7).

The digital circuit below the counting circuit (8) is a photocoupler aη
Since it is optically insulated by , the digital side is not affected by any abnormal voltage generated on the analog circuit side. Furthermore, even if the analog circuit is destroyed due to excessive input voltage, the damage will not be transmitted to the digital side, and the influence on the entire circuit can be suppressed.

[Effects of the Invention] As described above, according to the present invention, optical isolation between the analog side and the digital side is achieved by simply adding a photocoupler, so it is possible to achieve optical isolation between the analog side and the digital side by simply adding a photocoupler. This has the effect of preventing expensive damage to digital circuits.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional double integral type analog-to-digital exchange circuit, Fig. 2 is an explanatory diagram of its operation, and Fig. 3 is a circuit diagram showing an embodiment of the present invention. 11+ +21 is an analog input signal input terminal. +31 +21 is a constant voltage application terminal, (4) is an analog switch. (5) is an integrator, (6) is a comparator, and (7) is (1) to (
6) is a double integrating circuit, (8) is a counting circuit, +9+fIQ is a digital output terminal, fill is a photocoupler, 0 is its detection diode, and H is a phototransistor. The same reference numerals in the drawings indicate the same or corresponding parts. Agent Masuo Oiwa (and 2 others) Figure 2 Figure 3

Claims (1)

[Claims] After integrating the analog input signal for a predetermined time, a constant voltage of opposite polarity to this analog input signal is integrated until the integrated voltage reaches a predetermined level, and an output signal with a pulse width proportional to the magnitude of the analog input signal is generated. In an analog-to-digital converter circuit having a double integrating circuit to obtain a pulse width, and a counting circuit to count the pulse width of an output signal from this circuit, the output circuit of the double integrating circuit and the input circuit of the counting circuit are connected by a photocoupler. An analog-to-digital conversion circuit characterized by a combination of