JPS5995711A - Driving circuit of avalanche photodiode - Google Patents

Abstract

PURPOSE:To prevent the effect due to difference of inidividuality and temperature fluctuation by constituting a transistor circuit in which a bias voltage impressed to an Avalanche diode is expressed by a specific equation and providing a negative characteristic to temperature to a resistor. CONSTITUTION:A control signal Vc is applied to a positive input of an operational amplifier A and a feedback signal is inputted to a negative input respectively. A resistance circuit comprising R1, R2 and R3 is connected to an outut of the amplifier A and a potential at a connecting point between the resistors R1 and R2 is fed back to the negative input of the amplifier A. When 1<<R1/ (R2+R3) is established, an output VB is given by an equation (where; Vc is a control signal). In using a negative resistance element as the resistor R2, the temperature characteristic of (1+alphat) is given to the output VB, allowing to avoid the effect due to temperature fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an avalanche photodiode drive circuit that can compensate for the effects of temperature characteristics and maintain a constant multiplication factor.

Avalanche photodiodes (hereinafter abbreviated as APD) have a multiplication function during photoelectric conversion, and are therefore widely used in optical receivers, mainly for long-distance transmission. However, in order to cause the APD to perform a multiplication effect, a very high bias voltage (for example, about 200 .ANG.) is required, and control is difficult due to individual differences and temperature fluctuations. FIG. 1 is a diagram showing the characteristics of APD. In the figure, the horizontal axis shows the bias voltage, and the vertical axis shows the multiplication factor.

vBRViAPD breakdown voltage. As is clear from the figure, the multiplication factor changes significantly as the bias voltage changes, and also changes significantly with temperature changes. Therefore, the APD drive circuit is designed to change the bias voltage depending on the temperature so that the multiplication factor is not affected by temperature changes.

FIG. 2 is an electrical configuration diagram showing a conventional example of an APD drive circuit. In the figure, R,,R,,R4,R5 are resistances,
R2 is a negative resistance element, such as a thermistor. Did
APDSVce ld power supply voltage. The drive circuit shown in the figure uses the divided voltage of a voltage dividing circuit composed of a resistor R4, thermistor R2, and resistor R3 as the bias voltage of the APD. It is designed to compensate and obtain a constant multiplication factor.

Such conventional circuits cannot absorb variations in the multiplication factor due to individual differences in APDs, and the multiplication factor M is fixed at a constant value and the value of M cannot be changed as necessary.

In optical receivers, the APDO multiplication factor is often included inside the MiAGC loop. FIG. 3 is a block diagram showing the configuration of the optical receiver. The output of the drive circuit 1 including the APD is
Signal output VS via preamplifier 2 and variable gain amplifier 3
is output as

A portion of the output signal Va enters the level detector 4.

The output of the level detector 4 is matched with a reference voltage EB by an AGC control amplifier 5, and a control signal Ec corresponding to the output level is output from the amplifier.The control signal is used to control the variable gain amplifier 3. In addition to working as a signal,
It controls the value of the power supply voltage VCCO that enters the DC/DC converter 6 and is applied to the drive circuit 1. If a conventional circuit as shown in FIG. 2 is used as the APD drive circuit 1 of the AGC circuit shown in the figure, the APD multiplication factor M changes greatly depending on the vCCO value and thus the bias voltage VB, so temperature compensation must be performed. I couldn't do it.

The present invention has been made in view of the above points, and is based on the bias voltage VB and flake-down voltage vB of the APD.
We have realized an APD drive circuit that is unaffected by individual differences and temperature fluctuations by utilizing the characteristic of APDs that if the ratio vB/vB□ with R is kept constant, the multiplication factor M is also kept constant. It is something.

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

The relationship between the bias voltage VB of the APD and the control signal vc is expressed as follows: Vs = K Vc The temperature characteristics of the APD are made to match the temperature characteristics of the breakdown voltage Vl]R of the APD.

"BR has a temperature characteristic that is well approximated by VBR=vBRo(1+αt) (2). Here, ■BRot-1
A constant determined by individual differences, t is the temperature, and α is the temperature coefficient, which has a value of approximately 2xlO-3 (/°C': l. Therefore, the proportionality constant K also has the following formula: K = Ko (1 + αt) (3)
Provides temperature characteristics similar to VBR as expressed by . Here, Ko is a constant that is independent of temperature and absorbs individual differences. That is, let Ko- be a constant that satisfies vBRo(K,; constant) (4).

Incidentally, although the multiplication factor M of the APD is a complex function of the bias pressure Vn, it is known that if VB/BR is kept constant, M can also be kept constant. The following equation holds true from (1) to (3).

(5) and (4), vB/vBR is expressed by the following equation.

From equation (6), it can be seen that ■B/vBR is constant.

It is possible to eliminate the effects of individual differences and temperature fluctuations. 1. No matter how M changes, temperature correction can be performed at the value of M.

FIG. 4 is an example of an electrical configuration diagram that realizes the above-mentioned technical idea. Resistors and thermistors that are the same as in FIG. 2 are shown with the same symbols. In the figure, A is an operational amplifier, to which a control signal VC is input to its positive input, and a feedback signal is input to its negative input. The output of the amplifier is R,,
A resistor circuit composed of R2 and R3 is connected, and the potential at the connection point of R4 and R2 is fed back to the negative input of the amplifier. Furthermore, the output side of the amplifier A is connected to a series circuit of an APD and a resistor. The signal output Vo of the circuit shown in the figure is taken out from the connection point between the APD and the resistor. Note that the power supply voltage vcc of the circuit is 20
Since the voltage is quite high at 0V, a commercially available operational amplifier cannot be used as it is as the operational amplifier A, so as shown in FIG. 5, a commercially available operational amplifier A,
The output is boosted by a voltage boost circuit using transistors Q and IQ2e.

The output VB of the circuit configured in this way is given by the following equation.

However, the symbols R1 to R1 were used as they were as the values of each resistance. "10R2+R3' in equation (7) corresponds to the constant K in equation <11. Now 1 <<R1/(R2+R,>
Assuming that holds true, equation (7) can be simplified as shown below.

Here, if a negative resistance element such as a thermistor as described above is used as the resistor R2, VB increases as the temperature t rises. That is, it is possible to provide approximately a temperature characteristic of (1+αt).

If VB can have a temperature characteristic of (1+αt), as mentioned above, vB/vBR can be kept constant, and therefore, the APD multiplication factor M can be kept constant regardless of temperature changes. Furthermore, if the resistance R1 is made variable, individual differences in vBRO can also be absorbed, which is convenient. APD that receives such VB as a bias voltage
is the signal Vo from which the effects of individual differences and temperature changes have been removed.
can be output. According to the present invention, no matter how the multiplication factor M changes, temperature correction can be performed using the value at that time. Therefore, even if it is incorporated into an AGC loose as shown in FIG. 3, it will not be affected by temperature changes.

FIG. 6 is an electrical configuration diagram showing another embodiment of the present invention. In the circuit shown in the figure, before inputting the control signal vc '1 to the non-inverting amplifier circuit, the voltage is divided by a voltage divider consisting of R1, R2, and R, and the bias voltage is VB becomes, and characteristics similar to equation (8) can be obtained.

FIG. 7 is a configuration block diagram showing another embodiment of the present invention. 1 is the aforementioned drive circuit, and the output of the drive circuit is transmitted to a transistor drive circuit 20. The voltage is boosted by a DC/DCC/type converter composed of a booster circuit 21 and a rectifier circuit 22, and the output of the converter is used as a bias voltage VB.

In a circuit having such a configuration, a high-voltage power source for the drive circuit 1 is not required. In the figure, drive circuit 1
If we use something like the one shown in Figure 4 as
The output VB shown in the figure is input to the drive circuit 20. In this case, the human PD circuit shown in FIG. 4 is the rectifier circuit 2.
It goes without saying that you should take it after 2.

In the above description, a thermistor was used as an example of the negative resistance element for temperature compensation, but any element whose resistance value decreases as the temperature rises may be used.

As explained in detail above, according to the present invention, the APD
The ratio between the bias voltage VB and the breakdown voltage V
Utilizing the characteristic of the APD that if the B/vBR gold is kept constant, the multiplication factor M is also kept at 1 R, it is possible to realize an APD drive circuit that is not affected by individual differences and temperature fluctuations.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the characteristics of APD, Fig. 2 is an electrical configuration diagram showing a conventional example, Fig. 3 is a block diagram showing the configuration of an optical receiver, and Fig. 4 is an electrical diagram showing an embodiment of the present invention. configuration diagram,
FIG. 5 is a diagram showing the configuration of an operational amplifier, and FIGS. 6 and 7 are electrical configuration diagrams showing other embodiments of the present invention. R,, R3, R4, R5...Resistance,...Negative resistance element, D°°° Avalanche photodiode (AP
D), A, A,... operational amplifier, 1... drive circuit,
2...Preamplifier, 3...Variable gain amplifier, 4.
...Level detector, 5...AGC control amplifier, 6.
...DC/DCC/formula-ta, 20... transistor drive circuit, 21... booster circuit, 22... rectifier circuit.

Claims (1)

[Scope of Claims] In an avalanche photodiode drive circuit, a transistor circuit is configured in which a control signal is VC, resistance values are R4 and R2°R3, and a bias voltage VB to be applied to the avalanche photodiode is expressed by . R2
An avalanche photodiode drive circuit characterized in that the avalanche photodiode has a negative characteristic with respect to temperature.