JPS62135004A - Gain control system of avalanche photo diode - Google Patents

Abstract

PURPOSE:To attain the total gain control of an avalanche photo diode (APD) with less hardware by applying a reverse bias voltage control to control the current gain only to one of APDs and supplying a reverse bias voltage in common to all the other APDs. CONSTITUTION:Reception circuits 11, 21, 31 convert a current from APDs 10, 20 and 30 into a voltage by a prescribed gain respectively to generate an external supply voltage in response to the 1st optical signals 13, 23 and the 2nd optical signal 33. A reverse bias voltage control circuit 32 inputs a voltage from the reception circuit 31 to control a reverse bias voltage VB so that the amplitude of the voltage is a constant value thereby controlling the gain of the APD30. The reverse bias voltage VB is supplied in common to all anodes of the APDs 10, 20 and 30, the APDs 10, 20 and 30 are formed on one and same semiconductor substrate, and since the cause to the gain fluctuation such as temperature acts equally on all the APDs, the control of the reverse bias voltage VB makes the gain of all the APDs constant.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an avalanche photodiode (rAPDj).
) gain control method, more specifically, APD gain control that can be suitably used for optical data communication for connection between units in a local network or information processing equipment in an information processing mode that employs a distributed processing method. Regarding the method.

(Prior art) As is well known, in APD, a reverse voltage is sufficiently applied to a PN junction or a PIN junction to expand a depletion layer, and the ``electrons and holes χ depletion'' generated in the depletion layer by the original irradiation are removed. By accelerating it with a high electric field applied to the layer and colliding with atoms, V * electron/hole pairs are generated in an avalanche manner, and the amplification of the Genton flow is performed.And the gain is due to the reverse bias. Depends on voltage, operating temperature, etc.

Since APD has a high gain, it is widely used as a suitable means for converting an original signal sent through an original fiber cable into an electrical signal.

- It is necessary to prevent gain changes due to temperature changes, etc. to ensure error-free operation.

FIG. 4 is a diagram showing an example of a conventional APD gain control method.

When the original signal 13 is input, APDlo converts it into a current and supplies it to the receiving circuit 11.

The receiving circuit 11 inputs the output current from APDIO)1
It is converted into pressure, amplified and supplied to the outside.

On the other hand, when the original signal 23 is input, the APD 20 converts it into a current and supplies it to the receiving circuit 21 as described above. The receiving circuit 21 inputs the output current from the APD 20, converts and amplifies it into a voltage, and then supplies the voltage to the outside. The reverse bias voltage control circuit 12 inputs the output voltage of the receiving circuit 11 and controls the reverse bias voltage IIi of APDlo in response to its peak value.

Similarly, the reverse bias voltage control circuit 22 receives the output voltage of the receiving circuit 21 and controls the reverse bias voltage value of the AP D 20 in response to its peak value.

(Problems to be Solved by the Invention) The gain control circuit of the conventional API is configured as described above, and the APDIO and the APD 20 are not formed on the same semiconductor substrate. Therefore APDlo and APL
) 20, reverse bias voltage control circuits 12, 22' corresponding to APDIo, 20, respectively.
We are prepared. Therefore, it is necessary for APD gain control.
-There is a disadvantage that the amount of hardware increases.

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems, and to provide a gain control method for an avalanche photodiode that allows stable API current control with a small amount of hardware.

(Means for Solving the Problem) In order to achieve the above object, the gain control method of the avalanche photodiode according to the present invention is implemented by forming the avalanche photodiode on the same semiconductor substrate, inputting the first optical signal, and the like. a second avalanche photodiode formed on the semiconductor substrate and converting the input signal into a current; The avalanche photodiode is supplied with the same reverse voltage and a reverse bias voltage control circuit that controls the reverse bias voltage from the output of the second avalanche diode.

(Example) The present invention will be described in more detail below with reference to the drawings.

In general, the main causes of APD gain fluctuations are A
Variations in characteristics of semiconductor substrates forming PDs, various 4Q
Examples include variations in manufacturing conditions, variations in operating temperature, and reverse bias voltage.

The APDs of the present invention are formed on the same semiconductor substrate so that the engravings of the three causes mentioned above are made the same for each APD, and the reverse bias voltage is controlled from the output of one APD. Reverse bias pressure for all APDKs
710 and all APLs) are made to have the same gain.

With such a configuration, even if there are variations in the characteristics of the semiconductor substrates or variations in the manufacturing conditions for each APDK, it will affect each APDK uniformly within the same semiconductor substrate, so the variations in the characteristics between the APDKs will be reduced. In addition, within the same semiconductor substrate, since the thermal resistance of the substrate is small and the substrate can be made compact, each APL) is strongly thermally coupled, and almost no temperature difference occurs between the APLs.

The present invention makes use of the characteristics of A and PD which are so-uniformed in this way, and is applied to one of a plurality of APDs formed on the same semiconductor substrate and sharing a reverse bias voltage. By controlling the reverse bias voltage value to control the current gain, the gain of all APDs is made constant against common causes of gain fluctuations to all APLs.

FIG. 1 is a block diagram showing an embodiment of an avalanche photodiode gain control method according to the present invention. In this embodiment, three APDs 10 are formed on the same semiconductor substrate.
．． 20 Oh! and 3o, three receiving circuits 11, 21 and 31, and a reverse bias voltage control circuit 32.

The first two signals 13.23 and the second original signal 33 are input to APDIO%AFL) 20 and API) 30, respectively, from the source of the original data.

APD 10 , APD 20 and APD 30 are
The first original signal 13, 23 and the second original signal 33, respectively.
are converted into currents with a predetermined gain and sent to the receiving circuit 11.
, 21 and 31.

The receiving circuits 11, 21 and 31 each have an APDl
o, the currents from the APD 20 and APD 30 are generated by external supply and pickup voltages in response to the first optical signals 13, 23 and the second source signal 33, respectively, by converting them into voltages with a predetermined gain. .

The reverse bias voltage control circuit 32 receives the voltage input from the receiving circuit 31 and controls the reverse bias voltage VS so that the imaging range of this voltage becomes a constant value, thereby controlling the gain of the APD 30.

The reverse bias voltage VB is commonly supplied to all anodes of APDIo, 20 and 30 and eight PDI0
．． 20 and 30 are formed on the same semiconductor substrate, and the causes of gain fluctuations such as temperature affect the entire APL equally. Therefore, the control of the reverse bias voltage Va as described above is
The gain of D is kept constant.

FIG. 2 is a detailed circuit diagram of the receiving circuit 31 in FIG. 1. It consists of an inverting amplifier 1 and a resistor 2.

The current from APD30 is through inverting amplifier 1 and resistor 2! It is converted to a llt pressure, amplified, and outputted to the reverse bias voltage control circuit 32 and the outside.

FIG. 3 shows the reverse bias tolerance control circuit 32 in FIG.
FIG. Diode 3, capacitor 4.7
, a resistor 5.6, and a Do/Do:3 inverter 8.

The output voltage of the receiving circuit 31 is determined by the diode 3 and capacitor 4.
The peak value is detected by When a voltage higher than the voltage charged in the capacitor 4 is input, the diode 3 becomes conductive and the input voltage increases in the capacitor 4. In other cases, the diode 3 is not conductive and the voltage across the capacitor 4 is maintained. The resistor 5 is used to determine the discharge time of the charge in the capacitor 4.

The peak voltage appearing across the resistor 5 is temporally averaged by an integrating circuit composed of a resistor 6 and a capacitor 7, and is input to a Do/Do converter 8.

If the gain of the APD 30 becomes large for some reason, the amplitude of the output voltage of the inverting amplifier 1 is detected and integrated, and the input voltage of the DO/DO converter 8 becomes higher. . Then, the DC/DC converter 8 responds to this input voltage and sets the reverse bias voltage VBY.
This result allows the gain of APD30 to be returned to its original value.

The reason why the gain of APD30 becomes large is also APD.
Since it acts on IO and APD20 in the same way, APD30
If the gain of APDIO and APD 20 increases, the gains of APDIO and APD20 also increase. Therefore, by lowering the reverse bias voltage vB, the gains of APDlo and APD20 also return to their predetermined values, and as a result, they are maintained at a constant value.

In the embodiments described above, for the sake of simplicity, the number of source data sequences is three, but in reality there may be as many source data sequences as possible. For example, to perform 8-bit parallel original data communication, eight sets of APDs and receiver/multiplier circuits are prepared, and the reverse bias voltage VB controlled by the reverse bias voltage control circuit 32 is supplied to all of these eight APDs. Connect like this.

(Effects of the Invention) As described above in detail, according to the present invention, one reverse bias voltage control is performed to control the current gain of only one of the PDs formed on the same semiconductor substrate.
Since it is configured to supply this reverse bias voltage in common to all other APDs, it is possible to compensate for the cause of gain fluctuations in common to all APDs, and with a small amount of hardware, the APD
It has the advantage of being able to perform collective gain control.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the avalanche photodiode gain control method according to the present invention, FIG. 2 is a detailed diagram of the receiving circuit, and FIG. 3 is a detailed diagram of the reverse bias voltage control circuit. The figure is a circuit block diagram showing an example of a conventional avalanche photodiode gain control method. 1... Inverting amplifier 2, 5.6... Resistor 3...
・Diode 4.7...Capacitor 8...DO
/DC converter 10.20.30...Avalanche photodiode 1
1, 21.31...Reception circuit 12, 22.32...Reverse bias voltage control circuit 13
．． 23...First optical signal 33...Second original signal VB...Reverse bias voltage vf Person who appeared: NEC Corporation agent Patent attorney Inoro Jusai Figure 1

Claims (1)

[Claims] one or more first avalanche photodiodes formed on the same semiconductor substrate, which input a first optical signal and convert it into a current; and one or more first avalanche photodiodes formed on the semiconductor substrate, which input a second optical signal and convert it into a current. a second avalanche photodiode for converting into a second avalanche photodiode, and a reverse bias voltage that applies the same reverse voltage to the first and second avalanche photodiodes and controls this reverse voltage from the output of the second avalanche diode. A gain control method for an avalanche photodiode characterized by comprising a control circuit.