KR20100120808A - A method to supply pulse bias to an avalanche photo diode by optically utilizing serially connected photo diode to it and to eliminate after pulse using flyback diode in an optical detection circuit operated in geiger mode constructed with an avalanche photo diode. - Google Patents

Abstract

PURPOSE: A trigger pulse offering method using a trigger pulse and an after pulse removing method using a flyback diode are provided to reduce the noise generated by the combination of the pulse signal. CONSTITUTION: An avalanche photodiode(10) is serially connected with a photodiode in a Geiger mode. An anode of a flyback diode(102) is connected to the anode of the avalanche photo diode. A cathode of the flyback diode is connected to the separate power source. An afterpulse signal is outputted to the power connected to the cathode of the fliyback diode.

Description

In optical reception circuit using avalanche photodiode operating in Geiger mode, optically providing trigger pulse using photodiode connected in series to avalanche photodiode and after-pulse removal method using flyback diode {A method to supply pulse bias to an avalanche photo diode by optically utilizing serially connected photo diode to it and to eliminate after pulse using flyback diode in an optical detection circuit operated in geiger mode constructed with an avalanche photo diode. }

The present invention relates to a circuit for detecting a weak optical signal, and more particularly to an optical receiving circuit for operating the avalanche photodiode in Geiger mode.

Optical signal detection is required in a wide variety of fields such as optical communication, energy, material inspection, and space science. The light to be measured ranges from a large signal for illumination to a weak signal for communication and aerospace. The optical elements used in the measurement range vary from CdS cells to phototransistors and photodiodes. Moreover, the light intensity of the object to be detected is becoming smaller and smaller, and the detection of extremely weak light is required. Photo multipliers and photo diodes are used to measure such weak signals. Photodiodes are manufactured using semiconductors, and as the semiconductors develop, operating frequencies are increased and performances are improved. Photodiode can be divided into pin photodiode and avalanche photodiode according to the operation method, and avalanche photodiode has 10 times better reception sensitivity than pin photodiode. In particular, in the encryption communication of information using light, signal measurement of a single photon size is required. An avalanche photodiode is used to detect such weak light. A single photon detection circuit using an avalanche photodiode has higher detection efficiency, higher gain, smaller size, lower power consumption, and relatively low cost compared to photomultipliers.

   1 is a receiving circuit diagram using the avalanche photodiode 10. It is composed of an avalanche photodiode 10, a termination resistor 12, an amplifier 11, a current limiting resistor 15, and a bias power supply 14. In a general optical receiver circuit, the bias voltage 14 of the avalanche photodiode is applied to a voltage slightly lower than the breakdown voltage Vbr of the avalanche photodiode. However, applying a reverse bias voltage above the brake voltage to the avalanche photodiode results in very high detection efficiency. In a single photon detection circuit, to exploit this effect, the avalanche photodiode is operated by applying a bias to a voltage above the breach voltage. The cause of the avalanche in the avalanche diode is first, the incident photons are converted into charges, and the incident photons are converted to charges, leading to avalanches, being caught by internal defects in the semiconductor, and slowly released. The charge generated by the after pulse and finally by the third row. Passive quenching and active quenching methods are used for the avalanche photodiode at a bias voltage above the breakdown voltage, and the active suppression method is called a Geiger mode. The passive suppression circuit is shown in FIG. The operation of this circuit is as described below. In the circuit of FIG. 1, the avalanche photodiode is applied with a reverse bias slightly higher than the brake voltage sidewalk. If an avalanche occurs in this avalanche photodiode for one or more of the three causes described above, the avalanche current starts from the bias supply and goes to ground through the current limiting resistor avalanche photodiode, termination resistor. Will flow. The current flowing through the termination resistor is converted into voltage and input to the amplifier, and the output signal is amplified by the amplifier.

If the current limiting resistance is set to a large value, the reverse bias voltage applied to the avalanche photodiode decreases as much as the voltage generated by the avalanche current flowing through the current limiting resistor, and the avalanche phenomenon is stopped when the lowered voltage falls below the breakdown voltage.

If there is no more cause of the avalanche, there is no current flowing through the circuit, so the avalanche photodiode returns to the original reverse bias voltage. While the bias voltage is restored, the detection efficiency of the avalanche photodiode is much lower than that of the original bias. Furthermore, if a new avalanche occurs during the bias recovery time, the current accumulates and the circuit becomes inoperative, causing dead time. do. The bias recovery time is expressed as the product of the current limiting resistor, the capacitor of the avalanche photodiode, and the parasitic capacitor of the circuit, which is very long, a few microseconds (~ us). It causes lowering.

The method of improving the disadvantages of the passive suppression circuit described above is an active suppression circuit operating in Geiger mode. FIG. 2A is a Geiger mode circuit, in which a pulse generator 20 and a pulse signal coupling capacitor 21 are added to a passive suppression circuit. FIG. 2B illustrates the reverse bias voltage of the avalanche photodiode with time in FIG. 2A.

In this circuit, the voltage of the bias power supply 13 is set slightly lower than the brake voltage Vbr of the avalanche photodiode. The pulse voltage 24 overlaps the bias voltage during the gate time and the superimposed reverse bias voltage becomes higher than the break voltage Vr of the evaluative photodiode. With the exception of the short pulse rise and fall times, which are negligible in active suppression circuits, the avalanche photodiode is controlled in two states: response time and dead time. This allows for faster suppression and bias recovery. In this circuit, the trigger pulse signal is coupled to the termination transition term Rt by the pulse coupling capacitor Cp and the intrinsic capacitor of the avalanche photodiode, and the charge generated by the previously generated avalanche is released in dead time. After pulses appear on the output. These two signals appear as noise in the output signal and there are several ways to reduce them.

3 is a circuit for removing the noise and the after-pulse noise generated by the trigger pulse signal coupled to the output in the active suppression circuit. This circuit is configured by adding a signal divider 30, a signal delay circuit 31, and a differential amplifier 32 to the output of the circuit of FIG. The delay time of the signal delay circuit is equal to the gate period. An avalanche generated during the gate on time exhibits a positive pulse on the output and a negative pulse on the subsequent gate off time. If the signal is decomposed in half and one signal is delayed for one period, then the difference between the two signals is obtained through the differential amplifier, and the avalanche signal is doubled, while the lock signals of the same size are removed from each other.

In the above active suppression circuit, the delay time of the signal delay circuit must be exactly the same as the pulse period, the distribution ratio of the signal divider must be perfectly matched, and the subtraction function of the differential amplifier must be perfect. Since the signal delay circuit is difficult to vary the delay time, it is difficult to change the pulse period. Even if the conditions of all circuits are met, the coupling to the output of the pulse signal is difficult to eliminate completely.

First of all, the above-described technical problem is to achieve the purpose of reducing noise generated by coupling a pulse signal to an output, and then preventing an after pulse from appearing on the output.

The present invention for achieving the above technical problem is to connect a separate optical device for applying a pulse bias to the avalanche photodiode in series with the avalanche photodiode so that the pulse signal is not coupled to the output, By inputting the photodiode to act as a switch, an equivalent pulse bias is applied to the avalanche photodiode so that the pulse signal is not coupled to the output. A flyback diode is added to provide a path through which the after-pulsed current flows out of the terminal resistor, rather than through the terminating resistor, to prevent the after-pulse signal from appearing at the output.

According to the present invention, it is possible to prevent the trigger signal from being coupled to the output by replacing the trigger pulse signal with an optical pulse, and to increase the detection efficiency by preventing the after pulse from being emitted to the outside. In addition, the conventional method uses a trigger signal of a high pulse voltage (6 ~ 10V), but in the present invention uses an optical pulse, the pulse signal for generating the optical pulse can be lowered because the magnitude of the pulse signal can be less than 1V. Signals emitted to the outside can also be significantly reduced. Optical pulses can generate higher frequencies than high voltage electrical pulses, which can dramatically increase the operating frequency of the circuit.

Hereinafter, with reference to the accompanying drawings in the optical receiving circuit using an avalanche photodiode operating in a Geiger mode according to a preferred embodiment of the present invention by using a photodiode connected in series to the avalanche photodiode optically providing a trigger pulse The after-pulse removal method using the method and the flyback diode will be described in detail. The circuit according to the invention is characterized by the addition of a flyback diode optically providing a pulse for the Geiger mode and providing an emission path for the after pulse.

     4A is a circuit diagram for a specific embodiment of the present invention, an avalanche photodiode 10 for detecting an incident optical signal and a photodiode for receiving a trigger light pulse and applying a pulse signal to the avalanche photodiode 100, a termination resistor 12 for converting a signal current into a voltage, an amplifier 11 for amplifying a detected signal, a flyback diode 102 for emitting an after pulse to the outside,

Figure 4 (c) shows the operation of the circuit when there is a trigger light pulse. As shown in the figure, the photodiode is replaced by an equivalent resistor when there is a trigger light pulse, which depends on the intensity of the trigger light pulse, but if the light intensity is large enough, the resistance is small enough and the avalanche photodiode has a bias power supply. It is applied as a reverse bias to create a condition where an avalanche occurs. In this condition, the flyback diode is reverse biased, leaving it equally open. When light enters and an avalanche occurs, this current flows through the photodiodes to the termination resistor.

Figure 4 (d) shows the operation of the circuit when there is no trigger light pulse. As shown in this figure, without pulsed light, the photodiode does not flow open and the flyback diode flows in the forward direction. The trapped current formed by the avalanche that occurred in the previous gate-on state can be discharged during this time, which flows through the flyback diode towards the excess applied power.

By using the light receiving circuit according to the present invention, a circuit having low noise and low power characteristics and operating at high frequency can be configured, and this circuit can be configured to detect a system that can detect extremely weak light. It can be widely used in the field, weak optical communication field and spacecraft measurement field.

1 illustrates an Avalanche Photodiode (APD) 10, a bias power supply 13 that is a power supply for biasing an APD, a termination resistor 12 that converts current output from the APD into a voltage, and a termination resistor. It is a light receiving circuit using APD consisting of an amplifier 11 for amplifying the generated signal.

FIG. 2 (a) is a Geiger mode light receiving circuit in which the APD is operated in the Gaire mode by adding the pulse generator 14 in the circuit of FIG. 1, in which the pulse signal condenser 15 and the pulse signal are lost to the bias power supply. Is an APD Geiger mode light-receiving circuit composed of a current limiting resistor 16 which serves to limit the current of the APD.

 FIG. 2B is a voltage waveform applied to the APD along the time axis in the APD Gaires mode light receiving circuit of FIG. 2-1.

3 is a light receiving circuit for removing the after-pulse of the APD by using the signal divider 17 and the differential amplifier 18 in the Geiger mode light receiving circuit of FIG.

4 (a) is a configuration diagram of the present invention, which provides a trigger light source to a light-receiving diode 21 for supplying a Geiger mode bias voltage of an APD, a flyback diode 23 for removing an after pulse, and a photodiode 21. It consists of the laser diode 25.

FIG. 4B is a voltage waveform applied to the APD with time in the circuit of FIG. 4-1.

4C is an equivalent circuit of a circuit receiver when a trigger light pulse is present.

FIG. 4D is an equivalent circuit of the circuit receiver when there is no trigger light pulse.

<Explanation of symbols for the main parts of the drawings>

 10 AVALANCH PHOTO DIODE: APD

 11 Amplifier (AMPLIFIER: Amp)

 12 TERMINATION RESISTOR: Rt

 13 Reverse voltage applied to APD (REVERSE VOLTAGE: Vr)

 14 bias power (BIAS VOLTAGE SOURCE: Vbias)

 15 CURRENT LIMIT RESISTOR: Rl

 20 Pulse Generator

 21 Pulse Signal Coupling Capacitor (PULSE COUPLING CAPACITOR: Cp)

 Breakdown voltage of 22 APD (BREAK DOWN VOLTAGE: Vbr)

 23 Pulse signal voltage (PULSE VOLTAGE: Vp)

 30 signal splitter

 31 DEFFERENTIAL AMPLIFIER

 100 Photodiodes (PHOTO DIODE: PD)

 101 OPTICAL FIBER

 102 Flyback Diodes (FLYBACK DIODE: FD)

 103 Forward Voltage of Flyback Diode (DIODE FORWARD VOLTAGE: Vfd)

 104 APD bias voltage above breakdown voltage when trigger light is present

        EXCESS VOLTAGE SOURCE VE TO APPLY

 105 Bypass Capacitor (BYPASS CAPACITOR: Cb)

 106 Pulse Light Source

 107 Equivalent Resistor of Resistor in Photodiode with Trigger Light

 108 SIGNAL CURRENT Is

 109 AFTER PULSE CURRENT: Ia

Claims (3)

In a circuit that operates the avalanche photodiode in Geiger mode, a separate photodiode is connected in series with the avalanche photodiode to apply a trigger signal with an optical pulse.      In the circuit using the method of claim 1, after the anode of the flyback diode is connected to the anode of the avalanche photodiode and the cathode of the flyback diode is connected to a separate power source. How to emit a signal to a power source connected to the cathode of a flyback diode    The method of claim 1, wherein a trigger pulse is applied by connecting another switching element instead of the photodiode between the anode and the ground of the avalanche photodiode.

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