JPH05343926A - Optical reception circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit configuration and to control a reverse bias voltage impressed on an avalanche photo diode(APD) in response to an optical input signal. CONSTITUTION:An optical input signal is converted into an optical current in response to its intensity at an APD1. The current is subject to current-voltage conversion, amplified at a preamplifier 3 and an output signal is obtained. In this case, a voltage drop across a resistor 4 by the optical current is proportional to the optical current. Thus, so long as a voltage of a bias power supply 2 is constant, a reverse bias voltage to the APD1 is changed. That is, when the optical input signal strength is small, the reverse bias voltage to the APD1 is large and when the optical input signal strength is large, the reverse bias voltage to the APD1 is small as automatic variable setting, resulting that the current amplification factor of the APD1 is varied with the optical input signal strength. In other words, the current amplification factor of the APD1 is changed to be an optimum amplification factor in response to the optical input signal strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical receiving circuit including an avalanche photodiode capable of high photoelectric conversion efficiency and high-speed response. Particularly, the circuit configuration is simplified and the current multiplication factor in the avalanche photodiode is improved. The present invention relates to an optical receiving circuit that can be optimally controlled according to the magnitude of an optical input signal.

[0002]

2. Description of the Related Art A conventional optical receiving circuit including an avalanche photodiode (hereinafter, simply referred to as APD) as an optical signal receiving element is shown in FIG.
1, a high constant reverse bias voltage is simply applied from the bias power source 2, or the high reverse bias voltage applied to the APD is variably changed by feedback control as described in JP-A-3-136419. It is controlled. The preamplifier 3 in FIG.
This is for converting a photocurrent generated by photoelectric conversion in PD1 into a voltage and then amplifying it.

[0003]

However, the APD
When a high reverse bias voltage is simply applied as a constant voltage, the S / N ratio of the output signal cannot be optimally controlled according to the intensity of the optical input signal. Further, according to the above publication, the APD is changed according to the intensity of the optical input signal.
Although the reverse bias voltage to V is variably controlled by the feedback control, it is inevitable that the circuit configuration becomes complicated. An object of the present invention is to provide an optical receiving circuit in which the circuit configuration is simplified and the reverse bias voltage applied to the avalanche photodiode can be optimally controlled according to the magnitude of the optical input signal.

[0004]

The above object can be achieved by inserting and connecting at least a resistor in series to an avalanche photodiode.

[0005]

The APD outputs a photocurrent according to the magnitude of the optical input signal. As the photocurrent increases, the voltage drop at the resistor connected in series to the APD increases. On the contrary, the voltage applied to the APD is automatically controlled so as to become smaller, and as a result, the current multiplication factor in the APD can be optimally controlled according to the magnitude of the optical input signal. Generally, the smaller the intensity of the optical input signal, the smaller the current multiplication factor (optimum multiplication factor) that maximizes the S / N of the output signal from the preamplifier. Therefore, regardless of the intensity of the optical input signal, With APD, the optimum multiplication factor can be maintained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIG. FIG. 1 shows the configuration of the main part of an optical receiving circuit according to the present invention. As shown, an APD as an optical signal receiving element
1 is used in a state of being reverse-biased by the bias power supply 2, and at that time, the larger the reverse-bias voltage is, the more the light-receiving sensitivity and noise in the APD 1 are multiplied. Therefore, the magnitude of the reverse bias voltage is generally set to a value considerably smaller than the breakdown voltage of APD1.

In the light receiving circuit according to the present invention, the AP
Resistor 4 is connected in series with D1 and AP
D1 is set in a reverse bias state by the bias power supply 2. In this state, an optical input signal from the outside is converted into a photocurrent according to its intensity by photoelectric conversion in the APD 1, and further is current-voltage converted and amplified in the preamplifier 3 to be output as an output signal. Although the voltage drop at the resistor 4 due to the photocurrent is proportional to the magnitude of the photocurrent at that time, as long as the power supply voltage of the bias power supply 2 is constant,
The magnitude of the reverse bias voltage applied to the APD 1 can be changed.

That is, when the intensity of the optical input signal is small, the reverse bias voltage to the APD1 is increased, and when the intensity is large, the reverse bias voltage to the APD1 is automatically decreased. As a result of being variably set to, the current multiplication factor in the APD1 is also changed according to the intensity of the optical input signal. In other words, the current multiplication factor in the APD 1 is changed as much as possible to be the optimum multiplication factor according to the intensity of the optical input signal.

[0009]

As described above, according to the first aspect, the circuit configuration is simplified and the reverse bias voltage applied to the avalanche photodiode is optimally controlled according to the magnitude of the optical input signal. It is a reward.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of an optical receiving circuit according to the present invention.

FIG. 2 is a diagram showing a configuration of an optical receiving circuit according to a conventional technique.

[Explanation of symbols]

1 ... APD, 2 ... Bias power supply, 3 ... Preamplifier, 4 ...
resistance

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Claims (1)

[Claims] 1. An optical receiving circuit including an avalanche photodiode reverse biased with a high voltage as an optical signal receiving element, wherein the avalanche photodiode is connected to at least a resistor in series with the avalanche photodiode. Then, an optical receiver circuit configured to be reverse biased with a high constant voltage.