JPS62160852A - Signal isolation circuit - Google Patents

Abstract

PURPOSE:To attain a stable operation by converting an input signal into a pulse width signal, detecting the leading/trailing of the pulse width signal and inputting the detected output to a photocoupling circuit so as to decode a desired signal thereby decreasing the power required for isolation. CONSTITUTION:A digital signal inputted from a digital circuit is fed to a digital/ pulse width conversion circuit 1 and a voltage signal inputted from an analog circuit is fed to a voltage/pulse width conversion circuit 2. The signal (a) subjected to pulse width conversion is inputted to a leading/trailing detection circuit 3 and a detected pulse signal (b) operates the photocoupling circuit 4. The circuit 4 generates an output pulse signal bb having the same waveform as that of the signal (b) and the isolation is applied in the circuit 4. A frequency division circuit 5 inputs the signal bb, a pulse width/digital conversion circuit 6 converts a frequency division output C1 or C2 into a digital signal or a pulse width/voltage conversion circuit 7 converts the signal into a voltage signal, and then the result is sent. Thus, the power required for isolation is decreased to attain the stable operation.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a signal isolation circuit.

[Conventional technology]

Conventionally common insulation methods of this type include those using photocouplers and transformers.

In particular, isolation using a photocoupler is very commonly used as an isolation method for digital signals.

[Problem that the invention seeks to solve]

However, since the photocoupler consumes a relatively large current of about several milliamperes, sufficient power cannot be obtained for two-wire transmitters, battery-powered instruments, etc., and there is a risk of malfunction.

[Means for solving problems]

The present invention includes a circuit that converts an input signal into a pulse width signal;
A circuit for detecting the rise and fall of the pulse width signal is provided, and the detection output is used as an input to a photocoupling circuit.

[Effect]

Power consumption of the shifted coupling circuit is suppressed by making the rising edge/falling edge detection output a narrow pulse signal. The output of the photocoupling circuit is restored to a desired signal by the output circuit.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a waveform diagram of each part for explaining its operation.

In Figure 1, 1 is a digital/pulse width conversion circuit that converts a digital signal input from a digital circuit into a pulse width signal, and 2 is a voltage that converts a voltage signal input from an analog circuit into a pulse width signal. /Pulse width conversion circuit. Although both of these are shown in the figure, it goes without saying that either one of these may be used.

The pulse width-converted signal a as shown in FIG. 2(&) is input to the rising/falling detection circuit 3, and the rising/falling circuit 3 detects the pulse width as shown in FIG. 2(b). A narrow pulse signal is generated at the rising and falling edges. This pulse should be as narrow as possible within the range that allows the photocoupler to operate.

The foot coupling circuit 4 generates an output pulse signal bb having the same waveform as this input pulse signal. Insulation takes place here.

The frequency dividing circuit 5 inputs the output pulse signal bb,
In this case, depending on the initial state, two types of output signals C1 or c2a as shown in FIG. 2 (eat or (d)) are possible. Therefore, The duty ratio of the pulse width signal a is O(D≦
By specifying 50chi or 50≦D (100%), the correct output can be selected. Fig. 3 shows an example of the configuration of such a selection circuit. 51 is an amplifier, and 52 is an exclusive logic. In the sum circuit, R is a resistor and C is a capacitor.

Thereafter, the frequency-divided output is converted into a digital signal by a pulse width/digital conversion circuit 6, or converted into a voltage signal by a pulse width/voltage conversion circuit 7, and sent to a digital circuit and an analog circuit, respectively.

If the lighting time of the photocoupler and the pulse width of the pulse signal b1 are about 1μ, then a normal pulse width signal, for example, a signal with an average on time of about 1m5ec, will be 100
It consumes about 1/0 of the power and is extremely effective, especially for two-wire transmitters that must operate at 4 mA or less. 'Furthermore, in the above-described embodiment, only the rising edge of the output pulse of the photocoupler is used, so that conversion errors are small and a stable output can be obtained. Also,
By configuring the photocoupler drive/control circuit and signal restoration circuit with CMO8 circuits, the effect of reducing power consumption can be made even more remarkable.

In the above embodiment, the duty ratio is O~50 (50~1
00)% pulse width signal could only be used, but by changing the configuration of the rise/fall υ detection circuit 3, photocoupling circuit 4, and frequency division circuit 5 as shown in FIG. Such restrictions can be eliminated.

In FIG. 4, 3A is a rising edge detection circuit which detects the rising edge υ of the pulse width signal a as shown in FIG. 5(&) and generates a signal b1 as shown in FIG. 5(b). Output. on the other hand,
3B is a fall detection circuit which detects the fall of the pulse width signal a and outputs a signal b2 as shown in FIG. 5(e).

As a result, Photokagura 4A and 4B each have bl
A signal bb2 having a waveform similar to that of signals bb1 and b2 having a similar waveform is output.

On the other hand, the set/reset circuit 5A sets its output to "1" upon input from the photocoupler 4A, and resets its output to "0" upon input from the photocoupler 4B. This output signal C is shown in FIG. 5(d).

In this way, by separately detecting the rising edge and falling edge of the pulse width signal a and turning on the respective photocouplers, regardless of the tutity ratio of the pulse width signal a,
It becomes possible to accurately restore the input signal.

〔Effect of the invention〕

As explained above, according to the present invention, the input signal is converted into a pulse width signal and the photocoupling circuit is operated by the rise and fall detection signals, thereby reducing the power required for insulation. This results in stable operation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining its operation, FIG. 3 is a circuit diagram showing an example of the configuration of the output section, and FIG. A block diagram showing another embodiment, and FIG. 5 is a waveform diagram thereof. 1...Digital/pulse width-conversion circuit, 2...
・Voltage/pulse width conversion circuit, 3...Rise/fall detection circuit, 3A...Rise detection circuit, 3B...-
Falling edge detection circuit, 4, 4A, 4B...II @ photo coupling circuit, 5... Frequency division circuit, 5A... Set/reset circuit, 6... Pulse width/digital conversion Circuit, 7φ...Pulse width/voltage conversion circuit.

Claims (1)

[Claims] A circuit that converts an input signal into a pulse width signal, a circuit that detects the rise and fall of the pulse width signal, a photocoupling circuit that receives this detection signal as input, and a desired output signal from the output signal of this photocoupling circuit. A signal isolation circuit comprising: a circuit for restoring a signal of