JPS59107650A - Drift compensating circuit of photoelectric converter - Google Patents

Abstract

PURPOSE:To quicken the response speed of signal conversion and to improve the S/N by varying a bias voltage of a photoelectric converter in response to temperature, and feeding back an output of an operational amplifier of a signal converting circuit to make the amplification degree of a photoelectric converter constant. CONSTITUTION:A bias circuit 12 varies a bias voltage based on a signal detected by a temperature sensor 14 so as to control th amplification factor of the photoelectric converter 11 to a constant value at all times independently of temperature change. A signal converting circuit 15 quickens the response speed by feeding back an output of an operational amplifier 15a via a feedback resistor 15b to an input terminal side to increase the signal amplification degree and the S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drift compensation circuit for a photoelectric conversion device applied to, for example, an optical pulse testing device, etc. The present invention relates to a drift compensation circuit for a photoelectric conversion device that compensates for temperature drift in an amplifier including a photoelectric conversion device.

Photoelectric conversion devices are used for various purposes, one of which is, for example, a light/luminus test device. This test equipment inputs a light pulse generated by a laser diode into the optical fiber under test via a directional coupler, reflects it within the optical fiber, and returns it via the directional coupler. After receiving the backscattered light with a photoelectric converter and amplifying it with an amplifier, appropriate signal processing is performed to convert the backscattered light into C.
By displaying or recording on an RT or recording device, the loss of the optical fiber under test, connector connection loss, break point position, etc. are measured.

By the way, conventionally, backscattered light incident through a directional coupler is converted into an electrical signal using a photoelectric conversion device as shown in FIG. 1 to obtain a desired signal. One specific example of this device is that when an optical signal 3 is incident on a photoelectric converter 2 such as an avalanche JJ field whose amplification is kept constant by a bias power supply 1, a photocurrent flows and the resistor 4 A voltage corresponding to the intensity of the optical signal 3 is generated at both ends. The voltage generated across this resistor is amplified by an amplifier 5 to a signal level necessary for subsequent signal processing (not shown), and then a differentiating circuit consisting of a capacitor 6 and a resistor 7 cuts the DC component and removes the drift component.

However, the photoelectric conversion device as described above has the following problems.

■ One of them is the photoelectric converter 2 that amplifies the photocurrent.
has nominal voltage-dark current characteristics and negative voltage-amplification characteristics as shown in Figs. 2 and 3, but these characteristics differ depending on the ambient temperature T1 z T2 ,...
It means that it changes depending on the change in. In this case, the differentiating circuit consisting of the capacitor 6 and the resistor 7 can remove the direct current component, but in the case of dark current that changes with temperature changes and low frequency components that change slowly, such as the amplification degree, it is removed. I can't. In particular, since backscattered light is a weak optical signal, it has the disadvantage of being influenced by backscattered light and causing measurement errors.

(2) Furthermore, since the response speed of the photoelectric converter 2 is determined by the internal space of the photoelectric converter 2, the human power capacity of the amplifier 5, and the resistance value of the resistor 4, there is a drawback that the response speed is slow.

(2) In addition, the amplifier 5 amplifies a weak optical signal as an electrical signal and simultaneously amplifies its own temperature drift caused by temperature changes, but since this temperature drift is a low frequency component that changes slowly, Similar to the above, there is a drawback that cannot be removed by a differentiating circuit.

■ When measuring the loss of an optical fiber from the attenuation rate of the signal waveform, as in the optical ZOLS tester, the differentiating circuit that cuts the DC component causes waveform distortion and measurement errors. In order to reduce measurement errors, it is necessary to increase the time constant of the differentiator circuit. However, if the time constant of the differentiator circuit is increased, the surge current will increase, so this has the disadvantage that it does not have an adverse effect on the circuit.

The present invention has been made in view of the above-mentioned circumstances, and it compensates for changes in the dark current and amplification degree of the photoelectric converter caused by temperature changes, as well as the temperature drift of the amplifier, etc. with a simple configuration, and increases the response speed to J : An object of the present invention is to provide a drift compensation circuit for an lth0Mi conversion device.

An embodiment of the present invention will be described below with reference to FIG. In the figure, reference numeral 11 denotes a photoelectric converter such as an avalanche photodiode, which is biased by a bias circuit 12, and when a weak optical signal 13 such as backscattered light is incident, it converts the optical signal 13 into an optical signal. It not only converts photocurrent into photocurrent, but also amplifies photocurrent. A temperature sensor 14 for detecting the ambient temperature is placed near the photoelectric converter 1 or at a location that satisfies the same ambient conditions as the photoelectric converter 11, and the signal detected by the sensor J4 is supplied to the IAS circuit 12. It has become so. The temperature sensor 14 and the bias circuit 12 constitute the bias control circuit of the photoelectric converter 11. Specifically, the bias circuit 12 varies the bias voltage based on the signal detected by the temperature sensor 14 to control the photoelectric converter 11. By supplying it to the converter 1, the amplification degree of the photoelectric converter 11 is always controlled to be constant regardless of temperature changes. 15 is a signal conversion circuit that converts the photocurrent converted by the photoelectric converter 1 into a required voltage signal. This signal conversion circuit 15 includes an operational amplifier 15t
First, the response speed can be increased by feeding back the output of the operational amplifier 15m to the input end side via the feedback resistor 15b. Second, by increasing the signal amplification degree, S/
It is possible to improve N. Furthermore, a signal correction circuit 16 is connected to the output side of the signal conversion circuit 15 to remove dark current of the photoelectric converter 11 and temperature drift of the operational amplifier 15a including the photoelectric converter 11. The signal correction circuit 16 includes an amplifier 16a that amplifies the difference between two signals, a timing signal generation circuit 16b that generates a timing signal when there is no signal, and a sun f/l/hold circuit 16C. The timing signal generating circuit 16b is configured to generate a timing signal, for example, a predetermined time before the optical pulse is generated from the laser diode. Further, the sample and hold circuit 16c includes a pair of switch sections that receive a timing signal and output the output of the amplifier 16a. Note that the signal correction circuit 16
On the output side of the switch circuit 1, the input end of a connection circuit (not shown) is grounded when a timing signal is generated, and the subsequent circuit is connected to the signal correction circuit 16 when a timing signal is not generated.
7 is provided.

Next, we will discuss the operation of the device configured as described above in the fifth section.
This will be explained with reference to the figures. Now, light A as shown in Fig. 5 (A) is emitted from the laser diode to the optical fiber under test. It is assumed that the optical fiber under test has already been powered on and that the device shown in No. 41M+ is
It is assumed that the photoelectric converter 11 is in a state where it can receive backscattered light from various sources and convert it into an electrical photocurrent. Therefore, in this state, the dark current and amplification degree of the photoelectric converter 11 change due to changes in ambient temperature. Here, this device detects the ambient temperature using the temperature sensor 14, and the bias circuit 12 varies the Guiasmi pressure based on the detection signal from the temperature sensor 14, so the photoelectric converter The amplification degree of 1 can be kept constant regardless of temperature changes.

However, at this stage, the dark current of the photoelectric converter 11 and the temperature drift of the operational amplifier 15a change due to temperature changes, and the 〆L difference component signal v1 shown in FIG. 5(B) is output from the output terminal of the signal conversion circuit 15. It is being output. Therefore,
The error component signal mentioned above is compensated by the signal correction circuit 16. That is, from the laser diode to the fifth II (A)
A timing signal shown in FIG. 5(C) is generated from the timing signal generating circuit 16b a predetermined time before the light/yellow pulse shown in FIG. 5C is generated. Then, this timing signal causes the switch circuit 17 to be connected to the ground side.

Here, when the AJ switch section is closed □, the amplifier 16a
The error component signal A shown in ) in FIG. 5 appearing at the output terminal of is sampled and held by the sample and hold circuit 16c.

However, the error component signal A is not outputted to the subsequent circuit because it is connected to the ground side of the switch circuit 17.

Next, the generation of the sampling signal is stopped and the optical signal 13 is
When entering the measurement state, the switch circuit is supplied. At this time, assuming that the final optical signal 13 is not manually input, the error component signal output from the signal conversion circuit 15 is subtracted by the sample hold value and becomes zero. Therefore, the error component signal is deleted from the signal correction circuit 16 (as shown in FIG. 5).
A zero level signal as shown in is output.

Thereafter, when the optical signal 13 enters the photoelectric converter 11 due to the generation of the laser beam shown in FIG.
sent to. This signal conversion circuit 15 includes an operational amplifier 15
Since the output of th is fed back through the resistor 15b, the amplification degree of the operational amplifier 15a is A. In this case, the current signal is converted into a voltage signal at a response speed A twice that of the conventional one, and the signal shown in C of FIG. 5 CB) is output. Alternatively, by adding this circuit 15, the S/N ratio can be significantly improved, and there is no need for amplification at a higher amplification degree in a subsequent amplifier.

Then, since the signal converted as described above is error-corrected by the sample-and-hold value by the signal correction circuit 16, the true optical signal 13 as shown in FIG. It is possible to output a signal according to the strength of the signal.

Note that the present invention is not limited to the above embodiments.

In addition to the combination of the subtraction circuit 16a-1 and the operational amplifier 16a-2, the amplifier 16a may be a differential amplifier, a converter, or a converter. Further, the sample and hold circuit 16c is not necessarily required. Also,
Although the above-mentioned embodiment has been described with reference to an example of application to an optical/Grus test device, the present invention can be applied to any device that converts and amplifies an optical signal, which is present or absent, into an electrical signal.

As detailed above, according to the present invention, the bias voltage of the photoelectric converter is varied by detecting changes in humidity, so that the amplification degree of the photoelectric converter, which changes due to temperature changes, can be kept constant at all times. Wear. In addition, the signal conversion circuit that converts the photocurrent output from the photoelectric converter into voltage is configured to feed back the output of the operational amplifier through a resistor, so it is possible to convert the signal at a fast response speed, and as a result, the S
By improving the N ratio and using a sample hold in the circuit design to provide feedback when measuring optical signals, it is possible to completely remove erroneous component signals, and even when optical signals are repeatedly input, samples are always taken as no signal. Therefore, it is possible to provide a drift compensation circuit for a photoelectric conversion device that can reliably compensate even when the error component signal changes over time.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional circuit, FIGS. 2 and 3 are diagrams showing changes in dark current and amplification degree with respect to humidity changes in a photoelectric converter, and FIG. 4 is an implementation of a circuit according to the present invention. A configuration diagram showing an example, and FIG. 5 are timing diagrams illustrating circuit operation. 1 No... Photoelectric converter, 12... Bias circuit, 14
...Temperature sensor, 15...Signal conversion circuit, 15a.
...Operation amplifier, 15b...Feedback resistor, 1
6... Signal correction circuit, 16c... Sandal hold circuit. Applicant's representative Patent attorney Takehiko Suzue 13 - Ibaraki Densaku Communication Research Institute, Nippon Telegraph and Telephone Public Corporation, 162 Shirane, Oaza Shirakata, Tokai-mura, Naka-gun, Ibaraki Prefecture Applicant: Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] a photoelectric converter that converts an optical signal into a current signal; a bias control circuit that detects the ambient temperature of the photoelectric converter and keeps the amplification degree of the photoelectric converter constant based on this detection signal; a signal conversion circuit that feeds back the output of an amplifier that amplifies the output signal of the converter to the input terminal of the amplifier via a resistor; an output of the current-to-voltage conversion circuit with a timing signal received when the optical signal is unattended; A drift compensation circuit for a photoelectric conversion device, comprising: a signal correction circuit that samples and holds the optical signal, and subtracts the sample and hold value from the output of the current-voltage conversion circuit when measuring the optical signal.