JPS60155930A - Optical comparator - Google Patents

Abstract

PURPOSE:To provide an optical comparator reduced in the influence to the strong and weak variation in an optical signal, constituted so as to optically form a comparison reference signal from same light. CONSTITUTION:A sine wave detection signal corresponding to a light receiving amount is outputted through an amplifier 3, to which a first light detector 1 equipped with an optical diode D1 and a feed-back resistor R1 are connected, in correspondence to light receiving amount and supplied to a comparator 8. On the other hand, a reference signal, which is optically formed from same light by a second light detector 2 equipped with parallelly connected optical diodes D2, D3 matched with the diode D1 and outputting the same phase signal and a signal different in a phase by 180 deg., an amplifier 4 similar to the amplifier 3 and a voltage dividing circuit 7 for determining a duty ratio, is also supplied to the comparator 8. By this constitution wherein the reference signal based on a separate power source is not used and the reference signal optically formed from same light is used, an optical comparator reduced in the influence to the strong and weak variation in the optical signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical comparator used for detecting optical signals utilized in optical equipment such as rotary encoders.

[Background technology]

Conventionally, this type of optical comparator converts an optical signal photoelectrically, and detects the optical signal by comparing it with a reference voltage set by a separate power source. However, if there are fluctuations in the intensity of light and variations in the performance of the photoelectric conversion elements used, such as photodiodes, the reference voltage is absolute, which has the drawback of decreasing detection accuracy. .

[Purpose of the invention]

This invention optically generates a comparison signal for the first output signal obtained from the first optical signal using the second and third optical signals seen from the same light, thereby affecting the strength fluctuations of the optical signal. The purpose of the present invention is to provide an optical comparator with less.

[Disclosure of the invention]

The gist of the invention is to provide a first photodetector (1) that generates a first electrical signal in response to a first optical signal a;
and a second photodetector (2) which generates a second electrical signal for generating a comparison signal of the first electrical signal in response to a third optical signal S, clc; The first one is connected to each of the two photodetectors (3) and is used for feedback. a first amplifier (3) comprising second resistors R1 and R2 and generating a first output signal and a second output signal in response to the first electric signal and the second electric signal; an amplifier (4), a voltage dividing resistor R3°R4 connected to an output terminal of the second amplifier (4) having a terminal for generating a third WL signal obtained by dividing the second output signal; and the first amplifier. (3) and the output terminals of the voltage dividing resistors R3 and R4. It is an optical comparator comprising a comparator (8) for comparing two signals in response to each of the third air signals. The entire invention will be explained below based on an embodiment shown in FIGS. 1 and 2. FIG. 1 shows the configuration of an embodiment of the present invention. Here, for example, the first. The second optical signals a and b are in phase,
It is assumed that the third optical signal C has a phase difference of 180°. By irradiating these optical signals to the photodiodes D1 to D3, the first and second photodetectors +11 and +2
1 to 1st. A second acid signal is generated, respectively. It becomes one input of the second amplifiers +31 and +41. The other input is the voltage v1 applied to the cathodes of photodiodes DI to D3. 1st. Second amplifier (3), (4
) return culvert 1. The resistance values of the second resistors Rj#R2 are equal.

By arbitrarily selecting the ratio of the voltage dividing resistors R3 and R4, the data 1 ratio of the output signal of this optical comparator is determined.

The following discussion will be based on an example in which the resistor R3=R4e, first, i, and third optical signals are sinusoidal waves.

The second output signal of the second amplifier 4 is such that the optical signal 2.3 is 180
'Since there is a phase difference, the combination of the waveforms shown in FIG. 2 (1) and (2) results in the linear waveform shown in FIG. 2 (3). This second
The output signal of the amplifier (4) is divided by the voltage dividing resistors R3 and R4, and since the resistance values of the resistors R3 and R4 are equal, the second
As shown in Figure (4), it is a linear waveform that is half of the waveform in Figure 2 (3). This becomes the third output signal. v2 in Figure 2
is the resistance R1 (or R2) of the current generated by the optical signal
The magnitude of the voltage drop due to

Since the first optical signal is in phase with the second optical signal and the feedback resistance R] and R2 are equal, the first output signal of the first amplifier is
The waveform is shown in Figure (5).

The first output signal becomes an input signal to the inverting terminal of the comparator (8), and the third output signal becomes an input signal to the non-inverting terminal.

When the output of the comparator (8) can reach the potential of v3, the output signal becomes a rectangular wave shown in FIG. 2 (6).

Therefore, by matching the photodiodes DI to D3, the comparison reference voltage (third output signal) of the comparator (8) is optically generated. An optical comparator with an arbitrary duty ratio can be realized by following the fluctuation of the input signal and changing the ratio of the voltage dividing resistors R3 and R4 appropriately.

〔Effect of the invention〕

↓Contrary to the above, according to the optical comparator of the present invention, the comparison reference voltage follows the variation in the photoelectric conversion signal level to be compared due to the difference in the sensitivity of the photodiode and the variation in the optical signal. By appropriately selecting the ratio of the voltage dividing resistors that create the voltage, it is possible to obtain an arbitrary duty ratio that has little influence on fluctuations in the optical signal.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing an embodiment of the present invention, with Figure 1 being a circuit diagram and Figure 2 being a graph. ...Second photodetector, (3)...
First amplifier, (4)...second amplifier, (8)...comparator.

Claims (2)

[Claims] (1) a first photodetector (1) that generates a first electrical signal in response to the first optical signal a; and second and third optical signals;
a second photodetector (2) for generating a second electrical signal responsive to c and for generating a comparison signal of the first electrical signal;
The first... comprising second resistors R1 and R2;
a first amplifier (3) that generates a first output signal and a second output signal in response to the first electrical signal and the second electrical signal, respectively;
), the second amplifier (4) having a second amplification 6 (4) and a terminal for generating a third electric signal obtained by dividing the voltage of the second output signal.
) connected to the output terminals of the first amplifier (3), and the output terminals of the first amplifier (3) and the output terminals of the first amplifier (3). An optical comparator comprising a comparator (8) responsive to each of the third electrical signals to compare the two signals. (2) The first photodetector (1) and the second photodetector (2) are
It is composed of a photodiode, and the second optical signal and the third optical signal are
An optical comparator according to claim 1, wherein the first optical signal has a phase *t- of 1800 with respect to each other, and the first optical signal is in phase with either the second or the third optical signal.