JP3314568B2 - Protection device for APD measurement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection device for an APD (avalanche photodiode, hereinafter referred to as "APD") measuring circuit, and more particularly, to protecting an APD from an abnormal state in a measuring circuit using the APD. The present invention relates to a protection device for an APD measurement circuit to be used.

[0002]

2. Description of the Related Art A measuring circuit using an APD according to the prior art will be described with reference to FIG. The conventional APD measuring circuit includes an APD 1 having one end grounded via a terminating resistor 3, a high voltage generating circuit 2 having an output voltage connected to the other end of the APD 1, and the like. A circuit power supply is connected to the high-voltage generating circuit 2 via a variable resistor 10 and a resistor 11. By adjusting the variable resistor 10, the output voltage of the high-voltage generating circuit 2 becomes variable. ing. The output voltage of the high voltage generation circuit 2 is reverse biased to the APD 1. Then, by measuring the output current from the APD 1 due to the light input via the terminating resistor 3, the light intensity and the like are measured.

[0003]

However, the conventional APD
In the measurement circuit, when there is an optical input with an excessive intensity, or when a reverse bias voltage exceeding the rating of the APD from the high voltage generation circuit is applied, the output current of the APD becomes excessive. There was a problem that was damaged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a protection device for an APD measuring circuit that easily and automatically prevents the APD from being damaged.

[0005]

To achieve this object, the present invention comprises an APD having one end grounded through a terminating resistor, and measuring the output current from the APD through the terminating resistor. In the APD measurement circuit, voltage supply means for supplying a reverse bias voltage to the APD, first detection means for detecting that the output current from the APD has become equal to or more than a predetermined value, and detection output of the first detection means And a voltage adjusting means for lowering the reverse bias voltage.

The voltage supply means includes, for example, a high voltage generation circuit, a variable resistor for supplying an adjustment voltage for varying the output voltage from the high voltage generation circuit, and a first reference scale voltage supplied to the variable resistor. And a first reference scale voltage supply circuit for supplying the first reference scale voltage.
Switch means operated by the detection output of the detection means of
A second reference scale voltage supply circuit for supplying a second reference scale voltage lower than the first reference scale voltage to the variable resistor by an operation of the switch means.

[0007] Alternatively, the voltage adjusting means includes a switch means which is operated by detecting the output of the first detecting means, and a voltage drop circuit to reduce the reverse bias voltage by operation of the switch means, the further voltage regulating means, wherein Of the first detecting means
Switch means operated by a detection output, and the switch
Voltage drop that lowers the reverse bias voltage by the operation of the means
Circuit, and the voltage supply means includes a high voltage generation circuit.
And the output voltage from the high voltage generation circuit is made variable.
Variable resistor for providing an adjustment voltage for the variable resistor
Supply the reference scale voltage to the reference scale voltage supply circuit
And a road.

Further, the apparatus further comprises second detecting means for detecting that the reverse bias voltage from the voltage supplying means has become equal to or less than a predetermined value, and the voltage adjusting means is disabled by the detection output of the second detecting means. It is good also as composition which becomes.

[0009]

According to the protection device of the APD measurement circuit of the present invention, the APD measurement circuit is designed to be operated due to excessive light input or abnormality of the APD itself.
When a current exceeding the rated value is output from the APD, that is, when the output current from the APD becomes a predetermined value or more, the voltage adjustment means operates according to the detection output of the first detection means , and the APD
Quickly and automatically reduce the reverse bias voltage to a safe lower voltage. Therefore, it is possible to automatically prevent the APD from being damaged.

[0010]

Next, a first embodiment of the present invention will be described.
This will be described with reference to FIG. In FIG. 1, the protection circuit of the APD measurement circuit includes an APD 1 having one end grounded via a terminating resistor 3, a high voltage generation circuit 2 having an output voltage connected to the other end of the APD 1, and an output voltage of the APD 1 as a reference. Voltage 4A
A comparator 4 for detecting the above (abnormal output from the APD 1) and a comparator 5 for detecting that the output from the high voltage generating circuit 2 has become equal to or lower than the reference voltage 5A.
And a flip-flop (hereinafter referred to as “FF”) 6 for storing the detection output of the comparator 4 (for storing an abnormal state), and supplying a normal reference scale voltage to one end of the variable resistor 10. Constant voltage element 7, resistor 11, FF
6, a switching element 9 for switching the reference scale voltage as described later, and an adjustment voltage for varying the output voltage from the light emitting diode 8 and the high voltage generating circuit 2 which are driven by the switching element 9. It comprises a variable resistor 10 and the like.

In this embodiment, the FF 6 has a configuration as shown in FIG. 3, for example. In other words, it includes the transistors 31 to 33 and the resistors 34 to 38 including the reset circuit. For example, when the voltage supplied to the set input S becomes larger than 電源 of the power supply voltage + V, the apparatus enters the set state, and the voltage supplied to the reset input R becomes about 0.7 times less than the power supply voltage + V.
It is set so as to be in a reset state when V becomes low.

The light-emitting diode 8 detects that the output current from the APD 1 is equal to or higher than a predetermined value, that is, the output voltage of the APD 1 is equal to or higher than the reference voltage 4 A (in an abnormal state).
And is lit while the switch element 9 is on. In this example, an NPN transistor was used for the switch element 9.

In the protection circuit of the APD measurement circuit according to the first embodiment, the reference scale voltage at the time of normal measurement is supplied to one end of the variable resistor 10 by the power supply voltage + V, the resistor 11 and the constant voltage element 7. You. The adjustment voltage from the variable resistor 10 is changed by appropriately dividing the reference scale voltage by the variable resistor 10. Then, the reverse bias voltage from the high voltage generation circuit 2 to the APD 1 changes by appropriately changing the adjustment voltage from the variable resistor 10 to the high voltage generation circuit 2.

In this embodiment, for example, the reference scale voltage for normal measurement is set to 12 V, and the reference scale voltage for abnormal measurement is set to 1.2 V. Needless to say, it can be arbitrarily changed from the required reverse bias voltage or the like. However, it is necessary to set the reference scale voltage at the time of abnormality to a voltage that can surely reduce the output of the high voltage generation circuit 2.

The output voltage of the APD 1 is equal to the reference voltage 4
If the abnormal state is detected by the comparator 4, the output is output from the comparator 4 to the set input S of the FF 6, and the output sets the FF 6, and the fact that the abnormality has occurred is stored. Is done. In addition, the switch element 9 is turned on by the Q output from the FF 6 due to the setting of the FF 6, and as a result, the forward scale voltage of the light emitting diode 8 supplies the reference scale voltage at the time of the abnormality. The reference scale voltage by the light emitting diode 8 is lower than that by the constant voltage element 7, and when supplied to the high voltage generation circuit 2, the multiplication factor of the APD 1 of the high voltage generation circuit 2 becomes close to 1. The voltage is set so that only such a voltage can be output.

As described above, in the first embodiment, the APD is protected by lowering the output of the high voltage generation circuit 2. Then, when removing the cause of the abnormality and restarting the measurement, the FF 6 needs to be reset. Therefore, there is no abnormality detection output from the comparator 4 and
It is necessary to make the output of the high voltage generation circuit 2 smaller than the reference voltage 5A. After resetting FF6,
The voltage applied to the APD 1 is increased by moving the variable resistor 10. In this process, by observing the voltage change of the terminating resistor 3 with respect to the rise of the applied voltage, it becomes possible to know whether or not the APD 1 has a characteristic abnormality when the APD abnormality occurs.

That is, after the occurrence of an abnormality, the cause of the abnormality is eliminated by removing excessive input light or the like, and then the input voltage of the high voltage generation circuit 2 is varied according to the magnitude of the reference voltage 5A of the comparator 5. By lowering the voltage by the resistor 10, the reverse bias voltage to the APD is returned to a safe low voltage state, and then a return operation is performed to return to a state where normal measurement can be performed.

In this embodiment, although the light emitting diode 8 that emits light when energized by turning on the switch element 9 is provided, an abnormality can be notified to an operator or the like.
If such notification is not necessary, the light emitting diode 8 may be omitted and the resistor 11 may be directly connected to the switch element 9. Further, instead of the light emitting diode 8, for example, a constant voltage element such as a Zener diode, or
A configuration using a resistor or the like having a resistance value corresponding to the voltage drop of the light emitting diode 8 can also be adopted.

Next, a specific operation of the first embodiment will be described. For example, the output voltage of the high voltage generating circuit 2 when the normal reference voltage is 12 V is 200 V, the terminating resistor 3 is 1 kΩ, the reference voltage 4 A is 2 V,
The reference voltage 5A is set to 2V. When the voltage applied to the APD 1 is 160 V, the APD 1
It is assumed that a situation occurs in which the output current of 1 exceeds 2 mA.
Then, the FF 6 obtains the abnormality detection output of the comparator 4 and stores the abnormal state instantaneously, whereby the switch element 9 is turned on, and the reference scale voltage drops to 1/10 of the normal voltage. As a result, the voltage applied to the APD 1 is reduced to 16 V, and the light emitting diode 8 is turned on.

On the other hand, when canceling this abnormal state,
First, the cause of the abnormality is removed, and then the variable resistor 10 is operated to lower the voltage applied to the APD 1 to less than 2V. When the applied voltage becomes less than 2V, FF6 is reset,
The switch element 9 turns off and the light emitting diode 8 turns off. In addition, the reference scale voltage to the high voltage generation circuit 2 returns to 12V which is a normal voltage. In this state, since the variable resistor 10 is moving as described above,
The voltage applied to the APD 1 is not 160 V but less than 20 V. Of course, the applied voltage can be appropriately increased or decreased by operating the variable resistor 10.

Next, a second embodiment of the present invention will be described. FIG. 2 is a configuration diagram of a protection circuit of the APD 1 according to the second embodiment. In FIG. 2, components having the same function or performance as those in FIG. 1 are denoted by the same reference numerals. Corresponding description will be made with reference to FIG.

The second embodiment is different from the first embodiment in that
The only difference is that the light emitting diode 8 and the switch element 9 are connected not to the resistor 11 but to the output side of the high voltage generation circuit 2, and the other points are the same as those of the first embodiment.

In the second embodiment, when the output voltage of the APD 1 becomes higher than the reference voltage 4A and an abnormal state is detected by the comparator 4, the FF 6 is set by the output from the comparator 4 to the set input S. And the abnormality is stored. When the switch element 9 is turned on by the Q output from the FF 6, the reverse bias voltage from the high voltage generation circuit 2 to the APD 1 is reduced to a safe low voltage due to the forward voltage drop of the light emitting diode 8.

That is, in the second embodiment, the output of the high voltage generating circuit 2 is directly lowered via the light emitting diode 8 instead of changing the reference scale voltage as in the first embodiment. Things. According to this configuration, since the reverse bias voltage from the high voltage generating circuit 2 is directly operated, the APD 1 can be protected in a very short time. In addition, the return operation after the occurrence of the abnormality
After removing the cause of the abnormality, an operation such as lowering the input voltage of the high voltage generation circuit 2 by the variable resistor 10 in accordance with the magnitude of the reference voltage 5A of the comparator 5 is performed.

Further, similarly to the first embodiment, when it is not necessary to perform the abnormal display by the light emitting diode 8, a configuration using a constant voltage element, a resistor, or the like may be used instead of the light emitting diode 8.

[0026]

According to the present invention, when an abnormal output from the APD is detected, the reverse bias voltage to the APD can be automatically reduced to a safe value, and the APD can be easily and automatically damaged. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a protection device for an APD measurement circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a protection device of an APD measurement circuit according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a configuration of an FF used in an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of an APD measurement circuit according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 APD (avalanche photodiode) 2 High voltage generation circuit 3 Terminating resistor 4 Comparator 5 Comparator 6 FF (Flip-flop) 7 Constant voltage element 8 Light emitting diode 9 Switch element 10 Variable resistor 11 Resistor 31-33 Transistor 34 ~ 38 resistor

Claims (3)

(57) [Claims] An avalanche photodiode (1) having one end grounded via a terminating resistor (3), and an output current from the avalanche photodiode (1) is supplied via the terminating resistor (3). An APD measuring circuit for measuring the voltage by means of a voltage supply means (2, 7, 10, 11) for supplying a reverse bias voltage to the avalanche photodiode (1); First detecting means for detecting that the value has exceeded the threshold
(4) and, said first operating by the detection output of the detecting means (4) has a voltage adjustment means (6, 8, 9) to reduce the reverse bias, the voltage supply means (2,7, 10, 11), but the high-voltage generation circuit (2)
And the output voltage from the high voltage generation circuit (2) is made variable.
A variable resistor (10) for supplying an adjustment voltage for
A first supply of a first reference scale voltage to the variable resistor (10);
And a reference scale voltage supply circuit (7, 11).
The voltage adjusting means (6, 8, 9) is provided by the first detecting means (4).
Switch means (6, 9) operated by the detection output;
The variable resistor (10) is moved forward by the operation of the switch means (6, 9).
A second base having a voltage lower than the first reference scale voltage;
A second reference scale voltage supply for supplying a quasi-scale voltage
APD measurement circuit characterized by comprising a circuit (8).
Road protection device. 2. One end is grounded via a terminating resistor (3).
An avalanche photodiode (1),
The output current from the Lanche photodiode (1) is
In the APD measurement circuit that measures through the end resistor (3)
And a reverse bias voltage is applied to the avalanche photodiode (1).
Voltage supply means (2, 7, 10, 11) for supplying a voltage, and an output current from the avalanche photodiode (1).
Detecting means for detecting that the value has become equal to or greater than a predetermined value
(4) operating by the detection output of the first detection means (4) and
Voltage adjustment means (6, 8, 9) for lowering reverse bias voltage
And the voltage adjusting means (6, 8, 9) is connected to the first detecting means (4).
Switch means (6, 9) operated by the detection output;
Under the reverse bias voltage by operating the switch means (6,9)
The voltage supply means (2, 7, 10, 11), the high voltage generation circuit (2)
And the output voltage from the high voltage generation circuit (2) is made variable.
A variable resistor (10) for supplying an adjustment voltage for
The reference scale that supplies the reference scale voltage to the rheostat (10)
And a voltage supply circuit (7, 11).
APD measurement circuit protection device. 3. The apparatus according to claim 1, wherein said voltage supply means includes a voltage supply means.
Detects that the reverse bias voltage has fallen below a predetermined value.
Further comprising second detecting means (5), wherein the second detecting means
The voltage adjustment means (6,8,9) does not operate due to the detection output of (5)
3. The APD according to claim 1, wherein
Measurement circuit protection device.