JP2751229B2 - APD bias voltage control circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system, and more particularly to an avalanche photodiode (hereinafter, referred to as APD) bias voltage control circuit.

[Conventional technology]

In high-speed digital communication systems using optical fibers,
APDs are often used as light receiving elements.

This APD has the function of multiplying the photocurrent. Since the multiplication factor depends on the bias voltage of the APD, the APD multiplication factor (APD bias voltage) can be manipulated even if the received signal level fluctuates. Conventionally, a method of applying feedback so that the amplitude of an electric signal to be supplied is constant has been used. Then, as shown in FIG. 2, which shows a configuration of a commonly used APD control system, an equivalent amplifier circuit 11 and a peak detection circuit 12 are provided.
And an APD bias voltage control circuit 13.

In FIG. 2, reference numeral 14 denotes an APD, and 15 denotes an optical fiber transmission line. S is a signal voltage output, and the signal voltage output S is configured to be introduced to the peak detection circuit 12 and sent to the identification circuit 16.

FIG. 3 is a block diagram showing an example of a conventional APD bias voltage control circuit, which comprises an oscillation circuit 21, an oscillation voltage control terminal 22, a step-up transformer 23, and a rectifying / smoothing circuit 24.

In FIG. 3, reference numeral 25 denotes an APD, reference numeral 26 denotes an optical fiber transmission line, reference numeral 27 denotes an equalizing amplifier circuit, and this equalizing amplifier circuit 27 corresponds to the equalizing amplifier circuit 11 in FIG.

In the APD bias voltage control circuit configured as described above, the AC voltage obtained by the oscillation circuit 21 is
After the voltage is boosted by the rectifying / smoothing circuit 24 and the ripple is removed by the rectifying / smoothing circuit 24, the bias voltage of the APD 25 is obtained. By applying to the voltage control terminal 22,
The APD2 controls the amplitude of the AC voltage input to the step-up transformer 23 in proportion to this.
The bias voltage of 5 is controlled.

[Problems to be solved by the invention]

In the above-described conventional APD bias voltage control circuit, when controlling the APD bias voltage, the output voltage of the rectifying / smoothing circuit is directly used, so that the response of the APD bias voltage is limited by the time constant of the smoothing circuit. Is receiving.
And since the time constant is usually several seconds, when the light receiving level of the APD suddenly changes due to a mechanical disturbance on the optical fiber transmission line, the bias voltage of the APD cannot follow and the signal voltage amplitude changes, There is a problem that the data is not correctly reproduced by the identification circuit and an error occurs.

[Means for solving the problem]

The APD bias voltage control circuit according to the present invention includes a high-voltage generation circuit that connects a cathode of an avalanche photodiode whose anode is grounded via a first resistor via a second resistor and applies a bias voltage to the avalanche photodiode. A peak detection circuit connected to the anode of the avalanche photodiode and detecting the peak value of the output signal of the avalanche photodiode, and an inverting amplifier circuit connected to the peak detection circuit and inverting and amplifying the output voltage of the peak detection circuit And a transistor having a collector connected to the cathode of the avalanche photodiode, an emitter grounded, and a base connected to the output side of the inverting amplifier circuit.

(Operation)

In the present invention, the bias voltage of the APD is controlled by controlling the base voltage of the transistor.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of an APD bias voltage control circuit according to the present invention.

In the figure, 1 is a control terminal, 2 is an inverting amplifier circuit, 3 is a high voltage generating circuit, 4 is a resistor (resistance value R), 5 is a transistor, 6 is an APD, 7 is an optical fiber transmission line, and 8 is an equalizing amplifier. In the circuit, the equalizing amplifier circuit 8 corresponds to the equalizing amplifier circuit 11 in FIG.

The anode of the APD 6 is grounded via the first resistor, and the cathode of the APD 6 is connected to the cathode of the APD 6 via the second resistor 4.
A high voltage generating circuit 3 for applying a bias voltage to D6 is connected. Further, a peak detection circuit 12 for detecting a peak value of an output signal via an equalizing amplifier circuit 8 is connected to the anode of the APD 6.
Is connected to the peak detection circuit 12, and the inverting amplification circuit 2 is connected to the peak detection circuit 12. The collector of the transistor 5 is connected to the cathode of the APD 6, the emitter is grounded, and the base is connected to the output side of the inverting amplifier circuit 2. The bias voltage of the APD 6 is controlled by the base voltage of the transistor 5.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to FIG.

Peak detection circuit shown in FIG. 2 applied to control terminal 1
The output voltage of 12 is inverted and amplified by the inverting amplifier circuit 2 and applied to the base of the transistor 5.

At this time, the output voltage of the high voltage generation circuit 3 is set to I _C × R by the collector current determined by the V _B -I _C characteristic of the transistor 5.
[V] By dropping the voltage to the bias voltage of APD6,
Controls the photocurrent multiplication factor of APD6.

〔The invention's effect〕

As described above, the present invention connects the collector of the transistor to the output terminal of the high-voltage generation circuit via a resistor,
The emitter of this transistor is grounded, the collector of the transistor is connected to the APD, and the bias voltage of the APD is improved by controlling the bias voltage of the APD by controlling the base voltage of the transistor. There is an effect that the signal voltage amplitude can be kept constant even for a sudden change in the light receiving level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an APD bias voltage control circuit according to the present invention, FIG. 2 is a block diagram showing a commonly used APD control method, and FIG. 3 is an example of a conventional APD bias voltage control circuit. FIG. 1 ... Control terminal, 2 ... Inverting amplifier circuit, 3 ... High voltage generation circuit, 4 ... Resistance, 5 ... Transistor, 6 ... APD
(Avalanche photodiode).

Claims (1)

(57) [Claims] A high-voltage generation circuit having an anode connected to a cathode of an avalanche photodiode grounded via a first resistor via a second resistor and applying a bias voltage to the avalanche photodiode; A peak detection circuit connected to an anode of an avalanche photodiode and detecting a peak value of an output signal of the avalanche photodiode; and an inverting amplifier circuit connected to the peak detection circuit and inverting and amplifying an output voltage of the peak detection circuit. A transistor having a collector connected to the cathode of the avalanche photodiode, an emitter grounded, and a base connected to the output side of the inverting amplifier circuit, wherein a bias voltage of the avalanche photodiode is set at a base voltage of the transistor. To be controlled Characteristic APD bias voltage control circuit.