JPH1155194A - Bias control system for optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical receiver capable of being operated normally, regardless of the characteristic of a photodetector by controlling an automatic gain control circuit so that the bias voltage of the photodetector does not exceed the voltage that is acquired by a maximum multiplication factor of the photodetector, when power supply is turned on. SOLUTION: This system is provided with a control circuit 3 that has a comparator 4 which controls an automatic gain control circuit 2, so that bias voltage of a photodetector 1 does not exceed voltage that is acquired by a maximum multiplication factor of the photodetector 1, when power supply for bias of the photodetector 1 and power supply for the circuit 2 are turned on. Bias voltage is controlled, when an output Vpp of a peak detection circuit becomes a peak value detection voltage or less which corresponds to the maximum multiplication factor, by providing the circuit 3 consisting of the comparator 4 and a switching device.Thus,it is possible to operate the circuit 2 normally, i.e., to have an AGC circuit operate normally regardless of the characteristic of a used photodetector 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias control method for an optical receiver, and more particularly to a bias control method for an optical receiver which is characterized by a bias control method for an APD (avalanche photodiode) used in an optical communication system. It is about the method.

[0002]

2. Description of the Related Art Optical fiber communication has been widely used for trunk line communication since a large amount of information can be transmitted by one optical fiber, but recently, multimedia information has been provided to ordinary households. FTTH (Fiber to
the Home) has been proposed and is becoming more realistic.

[0003] The transmitter and receiver used in such an optical communication system are modularized with a light emitting element and a transmitting circuit or a light receiving element and a receiving circuit, and are treated as one component in response to a demand for compactness in recent years. Have been done.

[0004] Such modules are required to operate normally under various conditions. In particular, light-receiving element modules need to operate normally without being affected by the characteristics of the light-receiving element. It is.

Here, referring to FIGS. 5 and 6 (a),
A configuration of a conventional optical receiver and a bias control method of the optical receiver will be described. Referring to FIG. 5, in the conventional optical receiver 31,
The optical signal sent by the optical fiber is detected by the APD 32, and the detected output is equalized and shaped into a required waveform by the equalizing amplifier 34 (Reshaping) and amplified.
Using a part of the output, a timing signal is obtained from the optical signal in a timing extraction circuit 35, and a correct identification time is recognized in the identification circuit 36 using the timing signal, and the amplified output of the optical signal is regarded as a data output. Separately output to clock output.

The APD 32 accelerates the photocarriers in the avalanche region with a high electric field to cause avalanche doubling. Therefore, the APD 32 needs to be reverse-biased at a high voltage value. The control is performed such that the bias voltage _Vra at which a predetermined gain is obtained through the control circuit.

In this case, a peak detection circuit 37 and a bias circuit 33 are provided so that a constant output can be obtained by automatically correcting the amount of attenuation in the optical fiber and the amount of attenuation caused by the difference in connection points. Automatic gain control circuit (AGC: Automatic Gain Control)
l) is provided.

In such an AGC circuit, the peak amplitude of the output amplitude of the equalizing amplifier 34 is detected by a peak detection circuit 37, and the peak value detection voltage _Vpp is input to an amplifier 38 constituting a bias circuit 33, and the output thereof is output. in controlling the reverse bias voltage V _ra applied to APD32 by controlling the operation of the transistor 39 connected between the APD32 and high voltage power supply.

In such an optical receiver 31, when the intensity of the optical signal transmitted through the optical fiber is high, the peak value detection voltage V _pp also increases, so that the voltage applied to the transistor 39 via the amplifier 38 also increases. Since the current becomes large, the current from the high-voltage power supply is drawn to the ground side via the transistor 39, and the reverse bias V _ra decreases, thereby reducing the current flowing to the APD 32 and keeping the output amplitude of the equalizing amplifier 34 constant. Control.

On the other hand, when the intensity of the optical signal transmitted through the optical fiber is low, the peak value detection voltage V _pp also decreases,
Therefore, the voltage applied to the transistor 39 via the amplifier 38 is also reduced, so that the amount of current from the high voltage power supply drawn to the ground side via the transistor 39 is reduced, and the reverse bias _Vra is increased.
Control is performed so that the current flowing through the equalizer 32 increases and the output amplitude of the equalizing amplifier 34 becomes constant.

[0011]

However, in such a bias control method for an optical receiver, the multiplication factor of the APD used varies, and depending on the APD used, control of the bias voltage (V _ra ) is performed. This will be described with reference to FIG.

FIGS. 6A and 6B show various APs.
FIG. 4 is a graph showing the dependence of a multiplication factor (M) on the bias voltage (V _ra ), where the multiplication factor (M) is an amplification factor due to avalanche multiplication, and is a bias voltage of a current (I _ao ) flowing through the APD. (V _ra ).

FIG. 6A is a diagram showing the dependence of the multiplication factor (M) of a normal APD on the bias voltage (V _ra ). The multiplication factor (M) is the bias voltage (V). increases with increasing _ra), when the breakdown voltage V _B, is approximately expressed by M = 1 / {1- (V ra / V B) n}, n is a coefficient determined by the material, In the case of Si, n = 1.5 to 4.0, and in the case of Ge,
n = 2.5-8.

As described above, in the case of a normal APD, the maximum multiplication factor M _max is obtained at the maximum bias voltage V _rm immediately before the breakdown voltage V _B , so that the bias voltage ( the V _ra) should be used in V _rm vicinity, by setting the initial value of the bias voltage (V _ra) in the vicinity of V _rm or V _rm, above AGC circuit to operate normally.

Referring to FIG. 6B, however, depending on the device, characteristics different from the normal characteristics may be exhibited. As shown in FIG. 6B, when the bias voltage (V _ra ) is increased, V Maximum gain is M at _rm
max , then increasing the voltage will reduce the multiplication factor and eventually yield.

In the case of an element having such characteristics, if the intensity of the optical signal decreases and the bias voltage (V _ra ) of the APD exceeds the voltage V _{rm at} which the maximum multiplication factor M _max is obtained,
If the gain of the APD is reduced and the amplitude is reduced, and then the light is increased, the output amplitude of the equalizing amplifier will only be slightly increased, and therefore the bias voltage (V _ra ), The multiplication factor further decreases, and the control of the bias voltage (V _ra ) does not work.

Accordingly, an object of the present invention is to provide an optical receiver that operates normally without being affected by the characteristics of the light receiving element.

[0018]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. Refer to FIG. 1. (1) In the present invention, in the bias control method of the optical receiver, when the power supply for the bias of the light receiving element 1 and the power supply for the automatic gain control circuit 2 are turned on, the bias voltage _Vra of the light receiving element 1 And a control circuit 3 including a comparator 4 for controlling the automatic gain control circuit 2 so as not to exceed the voltage V _{rm at} which the maximum multiplication factor M _max is obtained.

The bias voltage V of the light receiving element 1 is_ra
Is the maximum multiplication factor M of the light receiving element 1_maxVoltage V obtained_rmTo
Control circuit 3, for example, comparator 4
By providing the control circuit 3 composed of
Output V of detection circuit_ppIs the maximum multiplication factor M_maxCorresponding to
Value detection voltage V_pmIf it becomes less than or equal to, the bias voltage V _ra
To V_rm, The characteristics of the light receiving element 1 used
, The automatic gain control circuit 2, that is, the AGC
The circuit can operate normally.

(2) The present invention is characterized in that, in the above (1), the control of the automatic gain control circuit 2 is performed by comparing a peak value detection voltage of an output of the equalizing amplifier with a reference voltage value. I do.

[0021] Thus, control of the AGC circuit, the output of the peak detector circuit, i.e., the reference voltage a voltage value V _pm to set the bias voltage V _rm that the peak value detection voltage V _pp is the maximum multiplication factor M _max is obtained This can be done by comparing the values.

(3) The present invention is characterized in that, in the above (1), the control of the automatic gain control circuit 2 is performed by comparing the output current value of the light receiving element 1 with a reference current value.

As described above, the control of the AGC circuit is performed by setting the output current value I _ao of the light receiving element 1 to a value corresponding to the peak value detection voltage V _pm which sets the bias voltage V _rm at which the maximum multiplication factor M _max is obtained. It may be performed by comparing I _am as a reference current value.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an optical receiver according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a configuration diagram of the optical receiver according to the first embodiment of the present invention. Like the conventional optical receiver, the optical receiver 11 includes an optical signal transmitted by an optical fiber. 12, a bias circuit 13 for controlling the bias voltage V _ra of the APD 12, an equalizing amplifier 14 for equalizing and shaping the detection output of the APD 12 to a required waveform, and a part of the output of the equalizing amplifier 14. , A timing extraction circuit 15 that obtains a timing signal by using a timing signal, an identification circuit 16 that separates and outputs a data output and a clock output from the output of the equalization amplifier 14 by using the timing signal, and a bias circuit 13
And a peak detection circuit 17 constituting an AGC circuit.

The AGC circuit in the optical receiver according to the first embodiment controls the input to the amplifier 20 of the bias circuit 13 by a control circuit including a switch 18 and a comparator 19, and the comparator 19 detects a peak. The output V _{pp of the} circuit 17 is compared with a reference voltage value V _pm, and the comparison output indicates that if V _pp > V _pm , the amplifier 20 outputs V _pp.
pp is input, and if V _pp <V _pm , V
_The switch 18 is controlled so that _pm is input.

In this case, the reference voltage value V _pm is set to the peak value detection voltage V _pp corresponding to the bias voltage value V _{rm at} which the maximum multiplication factor M _max is obtained, and this bias voltage value V _{rm is set.} , therefore, the reference voltage value V _pm is to determined by measuring in advance the characteristics of individual APD12 used.

FIG. 3 shows the output of the switch and the peak value detection voltage V_ppCorrelation with
And the bias voltage V _raAnd the peak value detection voltage V_ppPhase with
FIG. 4 is a diagram showing a relationship when a high-voltage power supply and a circuit driving power supply are turned on.
Optical signal transmitted through an optical fiber
And the peak value detection voltage V_ppIs the reference voltage value V_pmGreater than
Hour (V_pp> V_pm) Is given by the instruction of the comparator 19
V from switch 18_ppIs output and V_ppReplaces the amplifier 20
Is applied to the transistor 21 through_ppDepends on the size of
Current from the high voltage power supply through the transistor 21
To the ground side, and the bias voltage V_raWho lower
Acts in the opposite direction.

Also, the intensity of the optical signal transmitted through the optical fiber
Slightly smaller, peak value detection voltage V _ppIs the reference voltage value V_pm
When slightly larger (V_pp≧ V_pm) Indicates the comparator 19
The reference voltage value V_pmMore
Or large voltage V_ppIs output and V_ppThrough the amplifier 20
Is applied to the transistor 21 and the current from the high voltage power supply is
Suppress the flow to the ground side via the transistor 21
And the bias voltage V_raTo V_rmSet near.

On the other hand, the intensity of the optical signal transmitted through the optical fiber is further reduced, and the peak value detection voltage V _pp is equal to the reference voltage value V _{pp.
When it is} smaller than pm (V _pp <V _pm ), the switch 18 is switched by the instruction of the comparator 19 to output the reference voltage value V _pm , and V _pm is applied to the transistor 21 via the amplifier 20, Is prevented from flowing to the ground side via the transistor 21, and the bias voltage _Vra is set to a constant _Vrm .

Therefore, when the high-voltage power supply and the circuit driving power supply are turned on, even when the intensity of the optical signal is low, the bias voltage V _ra is not fixed to the bias voltage V _{rm at} which the maximum multiplication factor M _max is obtained. Therefore, even if the intensity of the optical signal increases or decreases, the AGC
The circuit operates normally and a stable data output can be obtained.

Next, an optical receiver according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram of an optical receiver according to a second embodiment of the present invention. As in the first embodiment, the optical receiver 1 has the same configuration as that of the first embodiment.
Reference numeral 1 denotes an APD 12 for converting an optical signal sent by an optical fiber into a current, a bias circuit 13 for controlling a bias voltage V _ra of the APD 12, and an equalization for equalizing and shaping a detection output of the APD 12 to a required waveform and amplifying the same. Amplifier 1
4. A timing extracting circuit 15 for obtaining a timing signal by using a part of the output of the equalizing amplifier 14, and a discriminating circuit for separating and outputting a data output and a clock output from the output of the equalizing amplifier 14 by using the timing signal. 16 and a peak detection circuit 17 which constitutes an AGC circuit together with the bias circuit 13 and the like.

The AGC circuit in the optical receiver according to the second embodiment controls the input to the amplifier 20 by the control circuit including the switch 18 and the comparator 22.
The comparator 22 compares the output current value I _ao of the APD 12 with the reference current value I _am instead of comparing the output V _pp of the peak detection circuit 17 with the reference voltage value V _pm .
Based on this comparison output, the switch 18 is controlled so that V _pp is input to the amplifier 20 when I _ao > I _am and V _pm is input to the amplifier 20 when I _ao <I _am. I do.

[0033] Note that the reference current value in this case is to set the output current value I _am corresponding to the peak value detection voltage V _pm is set to a bias voltage V _rm at the maximum multiplication factor M _max, This bias voltage value V _rm , and thus the reference current value I _am, is determined by measuring the characteristics of the individual APDs 12 to be used in advance.

In this case, when the high-voltage power supply and the circuit drive power supply are turned on, when the intensity of the optical signal transmitted through the optical fiber is large and the output current value I _ao is larger than the reference current value I _am (I _ao > I _am ). is from switch 18 by an instruction from the comparator 19 is output V _pp, V _pp is applied to the transistor 21 via the amplifier 20, the current from the high voltage power supply while depending on the size of the V _pp is the transistor 21 Through the ground, and acts in a direction to lower the bias voltage _Vra .

When the intensity of the optical signal transmitted through the optical fiber is slightly lower and the output current value I _ao is slightly larger than the reference current value I _am (I _ao ≧ I _am ), the switch 18 is switched by the instruction of the comparator 19. Outputs a voltage V _pp slightly larger than the reference voltage value V _pm , V _pp is applied to the transistor 21 via the amplifier 20, and the current from the high voltage power supply is suppressed from flowing to the ground side via the transistor 21. Then, the bias voltage V _ra is set near V _rm .

On the other hand, when the intensity of the optical signal transmitted through the optical fiber is further reduced and the output current value I _ao is smaller than the reference current value I _am (I _ao <I _am ), the switch 18 is activated by the instruction of the comparator 19. switched reference voltage value V _pm is output, V _pm is applied to the transistor 21 via the amplifier 20, and prevents the flow to the ground current from the high voltage power source via the transistor 21, the bias voltage V _{ra Is} set to a constant _Vrm so that it does not exceed _Vrm .

Therefore, when the high-voltage power supply and the circuit driving power supply are turned on, even when the intensity of the optical signal is small, the bias voltage V _ra is not fixed to the bias voltage V _{rm at} which the maximum multiplication factor M _max is obtained. Therefore, even if the intensity of the optical signal increases or decreases, the AGC
The circuit operates normally and a stable data output can be obtained.

Each embodiment of the present invention described above
The maximum multiplication factor M of each APD_maxObtained
Bias voltage V_rmUsed because of the different multiplication factor dependence
The characteristics of each APD to be measured are measured in advance, and the reference voltage value V
_pmOr the reference current value I_amIs set, but not necessarily
APD maximum multiplication factor M_maxOf the bias voltage V obtained _rm
Reference voltage value V corresponding to_pmOr the reference current value I_amIs
No need, maximum multiplication factor M_maxBias voltage to obtain
V_rmWithin the range that does not exceed
Is the bias voltage V at which_{rm '}(V_{rm '}<V_rm)become
It may be set as follows.

That is, the APD needs to be biased to a high voltage in a range where a predetermined gain can be obtained, but does not necessarily need to be set to the bias voltage _{Vrm at} which the maximum multiplication factor _Mmax is obtained. , APD, the reference voltage value _Vpm or the reference current value _Vam may be set within a range in which a predetermined gain can be obtained and not _{exceeding Vrm} .

The reference voltage _Vpm or the reference current I
Instead of setting _am in accordance with the light receiving element to be used, the characteristics of a plurality of APDs to be used are measured in advance, and the measurement results are statistically processed. The bias voltage V _ra is the bias voltage at which the maximum multiplication factor M _max is obtained. The reference voltage value _Vpm or the reference current value _Vam may be set so as not to exceed V _rm and to obtain a bias voltage V _{rm ′} at which a gain that is practically acceptable is obtained. In this case, once set, there is no need to set again according to each element.

[0041]

According to the present invention, since the control circuit for controlling the AGC circuit is provided so that the bias voltage of the light receiving element does not exceed a predetermined value, the AGC circuit is not affected by the characteristics of the light receiving element. Normal operation is possible, and furthermore, it greatly contributes to the progress of modularization of the optical receiver.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is a configuration diagram of an optical receiver according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a bias voltage according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical receiver according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional optical receiver.

FIG. 6 is an explanatory diagram of characteristics of a conventional APD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light receiving element 2 Automatic gain control circuit 3 Control circuit 4 Comparator 11 Optical receiver 12 APD 13 Bias circuit 14 Equalization amplifier 15 Timing extraction circuit 16 Identification circuit 17 Peak detection circuit 18 Switching device 19 Comparator 20 Amplifier 21 Transistor 22 Comparator 31 Optical receiver 32 APD 33 Bias circuit 34 Equalization amplifier 35 Timing extraction circuit 36 Identification circuit 37 Peak detection circuit 38 Amplifier 39 Transistor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 31/10 H03F 3/08

Claims (3)

[Claims] 1. The automatic gain control circuit according to claim 1, wherein a bias voltage of the light receiving element does not exceed a voltage at which a maximum gain of the light receiving element is obtained when a power supply for biasing the light receiving element and a power supply for the automatic gain control circuit are turned on. A bias control method for an optical receiver, comprising: a control circuit including a comparator for controlling the bias. 2. The bias control method for an optical receiver according to claim 1, wherein the control of the automatic gain control circuit is performed by comparing a peak value detection voltage of an output of the equalization amplifier with a reference voltage value. . 3. The bias control method for an optical receiver according to claim 1, wherein the control of the automatic gain control circuit is performed by comparing an output current value of the light receiving element with a reference current value.