JPH04337933A - Photodetecting amplifier - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving and amplifying device including a compensation circuit.

0002

2. Description of the Related Art In a conventional compensation circuit in a light-receiving amplifier, as shown in FIG. flows, the voltage drop is amplified by the amplifier 4, and an output signal is taken out. Here, when no optical signal enters the light receiving element 2, the analog switch 7 is switched to the side that grounds one terminal of the amplifier 4, and when there is no signal between repeated signals, the amplifier output in that state is sent to the sample hold circuit 5. Hold the sample. When an optical signal is input, the analog switch 7 is switched to ground one terminal of the amplifier 4 and the output side of the sample hold 5 to compensate for the dark current of the photoelectric conversion circuit and the temperature drift and time drift of the amplifier offset output.

0003

However, the conventional photodetector amplifier compensation circuit does not compensate for the magnitude of the leakage current of the capacitor forming the sample and hold, the temperature drift of the leakage current, and the time drift of the leakage current. When the repetitive signal period is long, when the ratio of no-signal time to one period is small even if the repetitive signal period is short, or when used at a high temperature of approximately 40°C or higher, the output of the photoreceptor amplifier is It has the disadvantage that it is affected by various influences related to leakage current and the input bias current of amplifiers and switches connected to the subsequent stage.

For example, as shown in a part of the time chart of the conventional example in FIG. 2 shown in FIG. The sample and hold output of FIG. 4(c) is shown by the timing signal of . As shown by symbol A in FIG. 4(c), the input bias current is affected by the leakage current of the sample-and-hold capacitor and the amplifier and switch connected to the subsequent stage.

The present invention has been made based on the above-mentioned background, and its purpose is to eliminate the need to incorporate parts or the entire device into a thermostatic chamber, which would increase costs and complicate the circuit configuration. Another object of the present invention is to provide a light receiving and amplifying device that can perform temperature compensation without using a temperature sensing element such as a platinum resistance thermometer.

[0006]

[Means for Solving the Problems] The light receiving and amplifying device of the present invention photoelectrically converts an optical signal that is repeatedly incident at a constant period or a non-constant period, including when there is no signal, and
In an amplifying circuit, for example, a circuit that converts the separated light of each wavelength of a spectrometer into an electrical signal and amplifies it, or a circuit that converts backscattered light in an optical fiber into an electrical signal and amplifies it, the repeating signal is The amplifier output obtained when there is no signal is sampled and held and fed back to the amplifier. In order to reduce the effects of sample-and-hold leakage current, temperature drift and time drift of the leakage current, the light receiving and amplifying device of the present invention converts the amplifier output into a digital form,
The A/D conversion value obtained when there is no repetitive signal is latched by a flip-flop, etc., and the latch output is converted to a D/D converter.
It is characterized by having a circuit that performs A conversion and feeds it back to the amplifier.

[0007]

[Operation] The light receiving and amplifying device of the present invention having the above configuration includes a circuit for photoelectrically converting a repeatedly incident optical signal, an amplifier circuit for amplifying the photoelectrically converted signal, and a feedback circuit for feeding back a part of the amplifier output. In a light receiving amplifier, when there is no signal in a repeating signal period, the amplifier output with one terminal of the differential input of the amplifier circuit grounded is sampled and held, A/D converted, latched as a digital signal, and then D/A A circuit for converting the signal and feeding it back to the amplifier circuit of this device at the time of the signal of the next repetition signal period, and a circuit for feeding back to the amplifier circuit of this device when there is no signal of the repetition signal, one terminal of the differential input of the amplifier circuit of this device is connected to the ground side, When an optical signal is input, it is latched as a digital signal after the A/D conversion, and is further equipped with an analog switch that switches to the D/A converted feedback signal side, and controls the dark current of the photoelectric conversion circuit of the light receiving amplifier and the amplifier offset output. to compensate for temperature and time drifts.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a light receiving and amplifying device according to the present invention, and FIG. 2 shows an example of a time chart for each part of the light receiving and amplifying device according to the present invention (FIG. 1).

In the embodiment of FIG. 1, the bias circuit 21
When an optical signal enters the light-receiving element 22 attached to the light-receiving section, current flows through the resistor 23, and the voltage drop is converted to the amplifier 2
4, the signal is extracted and sampled and held in a sample and hold circuit 25. The A/D conversion circuit 26 installed after the sample hold circuit 25 converts the A/D
Perform the conversion and extract the output signal. Here, the light receiving element 22
When no optical signal enters, the analog switch 30 is switched to the side that grounds one terminal of the amplifier 24, and when there is no repeating signal, the amplifier output in that state is sampled and held, A/D converted, and a flip-flop etc. 27 and apply the latch. When an optical signal is input, the analog switch 30 is connected to one terminal of the amplifier 24 and the D/A converter 28.
Switch to the connection side, and D/A convert the compensation signal latched by the flip-flop etc. 27 when there is no signal, and reduce the dark current of the photoelectric conversion circuit including the light receiving element, and the temperature drift and time drift of the amplifier offset output to zero. do.

Note that in FIG. 1, the A/D conversion circuit and the D
The adjustment section and the peripheral section including the clock input section in the /A conversion circuit are omitted.

FIG. 2 shows a time chart of the embodiment shown in FIG. As shown in FIG. 2(a), when the amplifier 24 outputs (logarithmic scale) and then the sample and hold signal is output (FIG. 2(b)), the timing signal at the time of no signal shown in FIG. 2(c) In contrast, the output after D/A conversion shown in FIG. 2(d) is obtained.

0012

As described above, according to the present invention, when there is no signal in a repeating signal period, one terminal of the differential input of the amplifier circuit is grounded by the analog switch, and the output of the amplifier at that time is A/D converted. By simply adding a circuit for latching, D/A converting, and applying feedback to the amplifier, temperature drift and time drift of the light receiving and amplifying device including the light receiving element can be easily compensated for.

Furthermore, since the feedback value is determined every time there is no signal in the repeated signal period, compensation can be performed in real time while reducing the leakage current of the capacitor.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a light receiving and amplifying device according to the present invention.

FIG. 2 is a time chart of the light receiving and amplifying device according to FIG. 1;

FIG. 3 is a configuration diagram of a conventional light receiving and amplifying device.

FIG. 4 is a time chart of the light receiving and amplifying device according to FIG. 3;

[Explanation of symbols]

1 Bias circuit 2 Light receiving element 3 Resistor 4 Amplifier 5 Sample and hold circuit 6 Analog switch switching logic element 7 Analog switch 21 Bias circuit 22 Light receiving element 23 Resistor 24 Amplifier 25 Sample and hold circuit 26 A/D converter 27 Latch such as flip-flop Circuit 28 D/
A converter 29 Analog switch switching logic element 30 Analog switch

Claims (1)

[Claims] 1. A light receiving amplifier comprising: a photoelectric conversion circuit that converts a repeatedly input optical signal into an electrical signal; an amplifier circuit that amplifies the photoelectric conversion signal; and a feedback circuit that feeds back part of the amplifier output. (a) When there is no signal between repeated signals, one terminal of the differential input of the amplifier circuit is grounded, the output of the amplifier circuit in that state is sampled and held, and the sample and hold signal is A/D converted; b) A circuit that latches the A/D conversion signal within the operation period of (a) above and holds it as a digital signal, (c) A circuit that D/A converts the hold output of (b) above, and (d) At the time of the repeated signal, the above (c)
An analog switch for turning on/off the feedback signal is provided so that the D/A conversion output of the photoelectric conversion circuit can be negatively fed back to one terminal of the differential input of the amplifier circuit, and the temperature drift of the dark current of the photoelectric conversion circuit and the amplifier offset output can be reduced. , a light receiving amplification circuit characterized by compensating for time drift.