JP3785035B2 - APD bias voltage control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an APD bias voltage control circuit for an optical receiver using an APD (avalanche photodiode) applied to an optical transmission apparatus.
[0002]
[Prior art]
A circuit using a multiplication action in the vicinity of the breakdown voltage of the APD is used for the part that converts the optical transmission signal into an electric signal. A conventional method for APD bias voltage control is shown below.
[0003]
(1) Gain fixed method (fixed bias method)
FIG. 5 is a conceptual diagram of the multiplication factor fixing method. Here, when the applied voltage is small, a small current substantially equal to the current flowing through the normal photodiode flows, and the applied voltage becomes large, and a large amount of current flows through the APD near the breakdown voltage. The ratio between the large current and the small current is called a multiplication factor M.
[0004]
In FIG. 5, reference numeral 51 denotes a DC voltage source that applies a DC voltage to the APD with a reverse bias. A load resistor R0 for I / V conversion is connected to the anode side of the APD. The potential at the connection point between the load resistor R0 and the APD is applied to a preamplifier (preamplifier) 52.
[0005]
In this circuit, since the DC voltage applied to the APD is constant regardless of the magnitude of the input light, the preamplifier 2 may be saturated when the input light increases.
[0006]
(2) FULL AGC method
FIG. 6 is a conceptual diagram of the FULL AGC method. The same components as those in FIG. 5 are denoted by the same reference numerals. In this method, the DC voltage source 51 is controlled so that the output amplitude of the equalizing amplifier 53 is constant. As the optical input increases, the APD bias voltage (voltage applied to both ends of the APD) Vapd decreases, and the multiplication factor M is approximately 1 near the maximum reception level, so that the dynamic range of the reception level can be widened. .
[0007]
On the other hand, in the vicinity of the minimum reception level, the multiplication factor M has a negative slope with respect to the optical input, so that the S / N ratio becomes constant even when the optical input increases, and an error floor (bending of the error rate curve) occurs. There is a problem. Further, since the negative feedback circuit is configured, there is a problem that the circuit scale becomes large.
[0008]
In a known example (Japanese Patent Laid-Open No. 6-164495), as shown in FIG. 9, an optical receiver circuit is configured by the FULL AGC method, and APD characteristic data stored in a memory, temperature detection data by a temperature sensing element, By controlling the driving voltage of the APD so that the output signal level becomes constant based on the signal level detection data, fine APD temperature compensation can be performed with high accuracy corresponding to element variations and the like.
[0009]
In the system shown in FIG. 9, reference numeral 1 denotes an optical space transmission device as a whole, which drives a laser diode 2 with a predetermined information signal and emits a transmission light beam L 1 having a predetermined polarization plane from the laser diode 2. Further, in the optical space transmission device 1, the transmission light beam L 1 is converted into parallel rays by the lens 4, and then transmitted through the deflection beam splitter 6 and guided to the lens 8. Here, the lens 8 converts the transmission light beam L1 into a convergent light and emits it, and the large-diameter lens 10 converts this convergent light into a substantially parallel beam and emits it.
[0010]
Thereby, in the optical space transmission apparatus 1, an information signal is transmitted to the transmission target via the transmission light beam L1 having a predetermined polarization plane. Further, in the optical space transmission device 1, the received light beam L 2 arriving from a desired transmission target is received by the large-diameter lens 10 and guided to the deflection beam splitter 6 through the lens 8. Here, the reception light beam L2 is transmitted from the transmission object so that the plane of polarization is orthogonal to the transmission light beam L1. Thus, in the optical space transmission device 1, the reception light beam L2 is deflected by the deflection beam splitter 6. Reflected and guided to the beam splitter 12. The beam splitter 12 transmits a part of the received light beam L2 and emits it to the lens 14, and the lens 14 condenses the transmitted light on the APD 16.
[0011]
In the optical space transmission device 1, the output signal of the APD 16 is output to a predetermined signal processing circuit for processing, thereby receiving the information signal to be transmitted via the reception light beam L2. Further, the beam splitter 12 reflects a part of the received light beam L2 and transmits the reflected light beam L2 to the lens 18. The lens 18 condenses the reflected light L3 by the positioning sensor 20. Here, the positioning sensor 20 is a position detection light-receiving element whose output signal changes in accordance with the condensing position of the reflected light L3. In this embodiment, the output signal of the positioning sensor 20 is output to the position detection circuit 22. Then, the condensing position of the reflected light L3 is detected.
[0012]
Further, in this embodiment, the optical space transmission device 1 inserts the deflection beam splitter 26 between the beam splitter 12 and the lens 14 and rotates the deflection beam splitter 26 by a predetermined angle about the optical axis of the deflection beam splitter 26. Thus, the deflection beam splitter 26 is used as an optical attenuator, and the incident light quantity of the avalanche photodiode 16 is maintained at a constant value.
[0013]
  The signal detected by the APD 16 is amplified by the preamplifier 36 and further amplified by the AGC circuit 38. The output of the AGC circuit 38 is converted into digital data by the A / D converter 40 and given to the system control unit 30. The system control unit 30 converts the received digital signal into an analog signal by the D / A converter 42,HighA voltage power source 44 is provided. TheHighThe output of the pressure power supply 44 is applied to the APD 16. A feedback circuit is formed by the above loop, and the optical signal detected from the APD 16 can be made constant.
[0014]
However, this method also does not solve the problem of the error floor when the optical input level is small as long as the control with a constant output signal level is performed.
(3) Self-bias method
FIG. 7 is a conceptual diagram of the self-bias method. The same components as those in FIG. 5 are denoted by the same reference numerals.
[0015]
In this method, as shown in FIG. 7, a bias voltage control resistor R1 is installed between the DC voltage source 51 and the APD cathode, and the APD bias voltage Vapd decreases with increasing light input by using this voltage drop. To control.
[0016]
FIG. 8 is a diagram illustrating an example of the Pin-Iapd characteristic. The vertical axis represents Iapd [μA], and the horizontal axis represents optical input power [dBm]. As shown in the figure, Iapd is small in the vicinity of the minimum reception level, so that the change in the multiplication factor with respect to the optical input in this vicinity is small compared to the FULL AGC system. C connected to the APD is a noise removing capacitor.
[0017]
Further, if the resistance value is increased to some extent, the multiplication factor M can be made approximately 1 near the maximum reception level due to a voltage drop. Thus, by setting the DC voltage source 51 so that the optimum multiplication factor is obtained at the minimum reception level and setting the bias voltage control resistor to an appropriate value, the minimum reception levels of (1) and (2) described above, The problem near the maximum reception level can be solved.
[0018]
[Problems to be solved by the invention]
(A) Adjustment of DC voltage source and bias voltage control resistor in self-bias method
The self-bias method described above can solve the above-mentioned problems of the multiplication factor M fixed method and the FULL AGC method, but the DC voltage source is adjusted with respect to individual variations and temperature characteristics of the APD breakdown voltage. There is a problem that it is necessary to compensate, and furthermore, it is necessary to individually set the resistance value of the bias voltage control resistor.
[0019]
(1) DC voltage source adjustment, temperature compensation
The multiplication factor M of the APD is determined by the relationship between the breakdown voltage Vb and the APD bias voltage (voltage applied to both ends of the APD) Vapd as shown in the following equation.
[0020]
M = 1 / {1- (Vapd / Vb)ⁿ} (1)
Here, n is a coefficient determined by the material and structure of the element. Vb has a large individual variation, and changes at a certain slope Γ with respect to temperature. The multiplication factor is obtained by a ratio of Iapd when the APD bias voltage is small and Iapd when the APD bias voltage is sufficiently large.
[0021]
For this reason, in the self-bias method, it is necessary to adjust the output voltage Vdd of the DC voltage source 51 so that the multiplication factor is optimized near the minimum reception level for each APD. Further, it is necessary to compensate for the voltage Vdd of the output of the DC voltage source 51 with respect to the temperature characteristic Γ of each APD so that the multiplication factor M is constant with respect to temperature fluctuation.
[0022]
(2) Bias voltage control resistor setting
Next, in the state where the DC voltage source 51 is adjusted and temperature-compensated as described above, when the optical input is increased from near the minimum reception level, the bias voltage control resistor R1 increases with the APD current Iapd. Vapd becomes smaller due to the voltage drop. Iapd and Vapd at a certain optical input Pin can be obtained from the following equations.
[0023]
Iapd = SM / Pin (2)
Here, S is the APD light receiving sensitivity [A / W].
Vapd = Vdd− (R1 + R0) · Iapd (3)
Here, when the bias voltage control resistor R1 of the self-bias method of FIG. 7 is large, Vapd near the maximum reception level becomes too small, and the frequency band degradation of the APD occurs. On the contrary, when the resistance value of R1 is small, M at the maximum reception level is not sufficiently small, so that Iapd exceeds the allowable maximum value of the input current of the preamplifier 52, the preamplifier 52 is saturated, and the waveform is deteriorated. Occurs.
[0024]
  FIG. 10 is a diagram illustrating an example of the Pin-Vapd characteristic, where (a) shows the overall characteristic and (b) shows an enlarged view. (B) is from (a)BreakThe enlargement of the area A enclosed by the line is shown. The vertical axis represents Vapd, and the horizontal axis represents the optical input power Pin. When R1 is large, the voltage Vapd applied to the APD decreases as the optical input power Pin increases. In (b), a region B indicates an APD band deterioration limit region.
[0025]
  FIG. 11 is a diagram illustrating an example of the Pin-M characteristic. The vertical axis represents the multiplication factor M, and the horizontal axis represents the optical input power Pin. (A) the whole, (b) of (a)BreakThe enlarged view of the area | region C enclosed with the line is shown. R1 resistance is smallNoIn this case, since M in the vicinity of the maximum reception level does not become sufficiently small, Iapd exceeds the allowable maximum value of the input current of the preamplifier 52, and waveform degradation occurs in the output of the preamplifier 52. Note that the maximum value of the load resistor R0 in FIG. 7 is determined by the APD capacity and the required frequency band.
[0026]
As described above, with the self-bias method, it is difficult to simplify the adjustment of the optical receiver module (optical receiver unit) and to make components common and generalized due to individual variations in the APD breakdown voltage and temperature characteristics. It has become.
[0027]
The present invention has been made in view of such a problem, and can be used for a general-purpose combination of an optical receiver module and an APD bias voltage control unit. The optical receiver module can be downsized by externally attaching an APD bias voltage control unit. It is another object of the present invention to provide an APD bias voltage control circuit that can make the structure of a PIN element optical receiver module common.
[0028]
[Means for Solving the Problems]
(1) FIG. 1 is a principle block diagram of the present invention. The same components as those in FIG. 7 are denoted by the same reference numerals. In the figure, 60 is an optical receiver (optical receiver module) that receives an optical signal (Opt In), converts it into an electrical signal, and outputs output data, and 70 has an optimum bias voltage for the APD of the optical receiver 60. This is an APD bias voltage controller to be applied. The optical receiver 60 and the APD bias voltage controller 70 are configured separately.
[0029]
  In the APD bias voltage controller 70, 71 is a DC voltage source capable of controlling its output voltage, R10 is connected to the DC voltage source 71,controlA bias voltage control variable resistor (hereinafter simply referred to as a variable resistor) 72 whose resistance value is variable by a signal, 72 is a CPU that performs various controls. The CPU 72 gives control signals to the DC voltage source 71 and the variable resistor R10.
[0030]
In the optical receiver 60, reference numeral 61 denotes a memory in which a breakdown voltage and its temperature gradient are stored. The breakdown voltage Vb and the temperature gradient Γ read from the memory 61 are supplied to the CPU 72. The optical receiver 60 includes a temperature sensor 62 and outputs the ambient temperature of the APD.
[0031]
With this configuration, the CPU 72 compensates the voltage so that the reception characteristic is optimal and the multiplication factor M is constant with respect to the temperature variation based on the ambient temperature and the breakdown voltage of the APD at that time. Since the variable resistor R10 is set to a resistance value that controls the DC voltage source 71 to a value and M and Vapd are optimal near the maximum reception level, the optical receiver module and the APD bias voltage control unit 70 To provide an APD bias voltage control circuit that can be combined in various ways, and that can downsize the optical receiver 60 by externally attaching an APD bias voltage controller 70, and that can share the structure of the PIN element optical receiver 60. Can do.
[0032]
  Further, since the APD bias voltage controller 70 is automatically controlled based on the individual information of the optical receiver 60 combined therewith, any combination of the optical receiver 60 and the APD bias voltage controller 70 becomes possible. In addition, optimum reception characteristics can be obtained without individually adjusting the optical receiver 60 with respect to individual variations and temperature characteristics of the APD break voltage.Further, the ambient temperature data T necessary for bias voltage control and the breakdown voltage Vb at that time can be given to the CPU 72, and the APD bias voltage can be set optimally.
[0033]
(2) The invention described in claim 2The temperature sensor is installed at a location thermally separated from the APD, and the CPU of the APD bias voltage controller converts the temperature detection data into the APD element temperature, and reads this value from the optical receiver. Based on the breakdown voltage value of the APD and its temperature characteristic data, the APD bias voltage value and the resistance value of the variable resistor for controlling the bias voltage are calculated, and these values are obtained. To control the DC voltage source and the bias voltage control variable resistorIt is characterized by that.
[0034]
  If configured in this way,Even if the temperature sensor is installed away from the APD, it is converted into the APD element temperature, and the CPU determines the APD bias voltage from the breakdown voltage Vb at that time.Can be set optimally.
[0037]
In the present invention, in the configuration of the optical receiving unit and the APD bias voltage control unit, the CPU and the variable resistor for bias voltage control are installed in the optical receiving unit, and the CPU uses the breakdown voltage value of the APD previously stored in the memory. The resistance value of the variable resistor for bias voltage control is automatically set so that the receiving characteristic of the optical receiver is optimized based on the temperature characteristic data and the APD element temperature detection data by the temperature sensor. The APD bias voltage value at which the receiving characteristic of the receiving unit is optimal is output. On the other hand, the APD bias voltage control unit automatically sets the APD bias voltage to this value by automatically controlling the DC voltage source. can do.
[0038]
In the present invention, if the breakdown voltage of the APD and its temperature characteristics, the detection output of the temperature sensor, the DC voltage source control signal, and the bias voltage control variable resistance setting signal are discrete digital signals, The CPU 72 can optimally set the APD bias voltage based on these digital signals.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 2 is a block diagram showing a first embodiment of the present invention. The same components as those in FIGS. 1, 6, and 7 are denoted by the same reference numerals. In the optical receiver (optical receiver module) 60, 61 is a memory in which a breakdown voltage corresponding to temperature characteristic data is stored, and 62 is a temperature sensor provided around the APD. C is a noise removing capacitor provided on the cathode side of the APD. A variable resistor R10 of the APD bias voltage controller 70 is connected to the cathode side of the APD, and a resistor R0 is connected to the anode side.
[0040]
52 is a preamplifier connected to the anode side of the APD, 53 is an equalizing amplifier that receives the output of the preamplifier 52, and 54 extracts data and a clock from the output of the equalizing amplifier 53 and outputs them to the outside. It is an identification regenerator. Reference numeral 61 denotes a memory in which the relationship between the temperature characteristic data and the breakdown voltage is stored. In the memory 61, the temperature characteristic data Γ and the breakdown voltage Vb can be set. The output of the memory 61 is input to the CPU 72 of the APD bias voltage controller 70. Reference numeral 62 denotes a temperature sensor arranged around the APD, and its output is input to the CPU 72. The operation of the circuit thus configured will be described as follows.
[0041]
Individual information (temperature characteristic Γ, breakdown voltage Vb) of the mounted APD is written into the memory 61 built in the optical receiver 60. When purchasing an APD, the individual information is attached to each APD, so that information may be written. These temperature characteristics Γ and breakdown voltage Vb are given to CPU 72. On the other hand, the temperature sensor 62 detects the temperature Tapd of the APD and gives it to the CPU 72.
[0042]
In the APD bias voltage controller 70, the CPU 72 calculates the optimum voltage value of Vdd and the resistance value of the variable resistor R10 in response to the Γ, Vb output from the memory 61 of the optical receiver 60 and the ambient temperature Tapd of the APD. Then, a DC voltage control signal Vdd Cont and a bias voltage control resistor setting signal R10 Cont are output to control the resistance values of the DC voltage source 71 and the variable resistor R10.
[0043]
As a result, based on the ambient temperature and the APD breakdown voltage at that time, the CPU 72 sets the DC voltage to a voltage value compensated so that the reception characteristics are optimized and the multiplication factor M is constant even with respect to temperature fluctuations. Since the variable resistor R10 is set to a resistance value that controls the source 71 and M and Vapd are optimized near the maximum reception level, there is a general-purpose combination of the optical receiver 60 and the APD bias voltage controller 70. It is possible to provide an APD bias voltage control circuit that is capable of downsizing the optical receiving module by externally attaching the APD bias voltage control unit 70 and further enabling the common structure of the PIN element optical receiving module.
[0044]
Further, since the APD bias voltage controller 70 is automatically controlled based on the individual information of the optical receiver 60 combined therewith, any combination of the optical receiver 60 and the APD bias voltage controller 70 becomes possible. In addition, optimum reception characteristics can be obtained without individually adjusting the optical receiver 60 with respect to individual variations and temperature characteristics of the APD break voltage.
[0045]
FIG. 3 is a block diagram showing a second embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, the temperature sensor 62 is moved to the APD bias voltage controller 70 side instead of the optical receiver 60. Other configurations are the same as those in FIG. The operation of the circuit thus configured will be described as follows.
[0046]
When the temperature sensor 62 moves to the APD bias voltage controller 70, the CPU 72 calculates a temperature difference between the output Ta of the temperature sensor 62 and the actual APD element temperature Tapd in advance, and converts Tapd from Ta based on this temperature difference. Vdd temperature compensation is performed. Once Tapd is calculated, the rest is the same as the embodiment shown in FIG.
[0047]
That is, the APD bias voltage controller 70 receives Γ and Vb from the optical receiver 60 output from the memory 61, and the CPU 72 determines the optimum voltage Vdd from Tapd, Γ and Vb, and the variable resistor R10. And the DC voltage control signal Vdd Cont and the bias voltage control resistance setting signal R10 Cont are output to control the resistance values of the DC voltage source 71 and the variable resistor R10.
[0048]
As a result, based on the ambient temperature and the APD breakdown voltage at that time, the CPU 72 sets the DC voltage to a voltage value compensated so that the reception characteristics are optimized and the multiplication factor M is constant even with respect to temperature fluctuations. Since the variable resistor R10 is set to a resistance value that controls the source 71 and M and Vapd are optimized near the maximum reception level, there is a general-purpose combination of the optical receiver 60 and the APD bias voltage controller 70. It is possible to provide an APD bias voltage control circuit that is capable of downsizing the optical receiving module by externally attaching the APD bias voltage control unit 70 and further enabling the common structure of the PIN element optical receiving module.
[0049]
FIG. 4 is a block diagram showing a third embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, as compared with the embodiment shown in FIG. 2, the variable resistor R10 and the CPU 72 are provided on the optical receiver 60 side. The output of the temperature sensor 62 provided around the APD enters the CPU 72, and the temperature characteristic Γ and the breakdown voltage Vb stored in the memory 61 are read and enter the memory 61. Other configurations are the same as those in FIG. In this embodiment, the APD bias voltage controller 70 includes only the DC voltage source 71 and receives the voltage control signal Vdd Cont from the optical receiver 60. The operation of the circuit thus configured will be described as follows.
[0050]
Individual information (temperature characteristic Γ, breakdown voltage Vb) of the mounted APD is written into the memory 61 built in the optical receiver 60. These temperature characteristics Γ and breakdown voltage Vb are given to CPU 72. On the other hand, the temperature sensor 62 detects the temperature Tapd of the APD and gives it to the CPU 72.
[0051]
In response to the temperature characteristic Γ output from the memory 61, the breakdown voltage Vb and the ambient temperature Tapd of the APD, the CPU 72 calculates the optimum voltage value of Vdd and the resistance value of the variable resistor R10, and the DC voltage control signal Vdd Cont. The bias voltage control resistor setting signal R10 Cont is output to control the resistance values of the DC voltage source 71 and the variable resistor R10.
[0052]
As a result, based on the ambient temperature and the APD breakdown voltage at that time, the CPU 72 sets the DC voltage to a voltage value compensated so that the reception characteristics are optimized and the multiplication factor M is constant even with respect to temperature fluctuations. Since the variable resistor R10 is set to a resistance value that controls the source 71 and M and Vapd are optimized near the maximum reception level, there is a general-purpose combination of the optical receiver 60 and the APD bias voltage controller 70. It is possible to provide an APD bias voltage control circuit that is capable of downsizing the optical receiving module by externally attaching the APD bias voltage control unit 70 and further enabling the common structure of the PIN element optical receiving module.
[0053]
In the above embodiment, the breakdown voltage Vb, the APD temperature Tapd, the output Ta of the temperature sensor 62, the DC voltage source control signal Vdd Cont, and the variable resistance control signal R10 Cont may be digital values, It may be an analog value such as a voltage value.
[0054]
Further, the memory 61 described above may be an EEPROM or a FLASH memory.
The variable resistor R10 described above may be an electronic volume or a field effect transistor (FET).
[0055]
The temperature sensor 62 may be a diode or a thermistor. According to the present invention, by controlling the APD bias voltage control unit, a general-purpose combination of the optical reception module and the APD bias voltage control unit becomes possible, and optical reception by externally attaching the APD bias voltage control unit is possible. The unit (optical receiver module) can be downsized, and the structure with the PIN element optical receiver module can be shared. In the conventional self-bias method, not only the DC voltage source is adjusted and temperature compensated for individual variations in the APD breakdown voltage and temperature characteristics, but also the resistance value is individually set for the bias voltage control resistor. Although it was necessary, according to the present invention, these automatic adjustments are possible, and the adjustment of the optical receiving module can be greatly simplified.
[0056]
(Supplementary Note 1) In an APD bias voltage control circuit for controlling a bias voltage of an avalanche photodiode (APD) by a self-bias method,
An optical receiver that receives an optical signal input, converts it into an electrical signal, and outputs output data;
An APD bias voltage control unit that provides an optimum bias voltage to the APD of the optical receiving unit is configured separately.
The APD bias voltage controller is
A DC voltage source capable of controlling the output voltage;
A variable resistor for bias voltage control connected to the DC voltage source, the resistance value of which is variable by an external signal;
It consists of a CPU that performs various controls,
The CPU reads the APD breakdown voltage value and its temperature characteristic data stored in the memory of the optical receiver, and controls the DC power supply and bias voltage so that the reception characteristic of the optical receiver is optimized. An APD bias voltage control circuit that controls a variable resistor.
[0057]
(Supplementary Note 2) The optical receiver is
An APD connected to the bias voltage control variable resistor;
A memory for storing a breakdown voltage value of the APD and its temperature characteristic data;
A temperature sensor that detects the ambient temperature of the APD;
An amplifier for amplifying an electric signal generated in the APD;
An identification regenerator for outputting data and a clock from the output of the amplifier;
The APD bias voltage control circuit according to appendix 1, characterized by comprising:
[0058]
(Supplementary Note 3) The temperature sensor is installed at a location thermally separated from the APD, and the CPU of the APD bias voltage control unit converts the temperature detection data into an APD element temperature, and reads this value and the light receiving unit. Based on the breakdown voltage value of the APD and its temperature characteristic data, calculate the voltage value of the APD bias voltage and the resistance value of the variable resistor for bias voltage control that optimize the reception characteristics of the optical receiver, and these values are calculated. The APD bias voltage control circuit according to appendix 2, wherein a DC voltage source and a bias voltage control variable resistor are controlled.
[0059]
(Supplementary Note 4) In the configuration of the optical receiving unit and the APD bias voltage control unit, the CPU and the variable resistor for bias voltage control are installed in the optical receiving unit, and the CPU uses the APD breakdown voltage value stored in the memory in advance. The resistance value of the variable resistor for bias voltage control is automatically set so as to optimize the reception characteristic of the optical receiver based on the temperature characteristic data and the APD element temperature detection data from the temperature sensor. APD according to appendix 1, wherein the APD bias voltage value at which the receiving characteristic of the receiving unit is optimal is output, while the APD bias voltage control unit automatically controls the DC voltage source to this value. Bias voltage control circuit.
[0060]
(Additional remark 5) The breakdown voltage of APD, its temperature characteristic, the detection output of a temperature sensor, a DC voltage source control signal, and the variable resistance setting signal for bias voltage control are discrete digital signals The APD bias voltage control circuit according to any one of 1 to 4.
[0061]
【The invention's effect】
As described above, according to the present invention, the following effects can be obtained.
(1) According to the first aspect of the present invention, an APD bias voltage control circuit that enables downsizing of an optical receiving unit by externally attaching an APD bias voltage control unit and further enables common use of the structure of the PIN element optical receiving unit. Can be provided.
[0062]
  Further, since the APD bias voltage control unit is automatically controlled based on the individual information of the optical receiving unit combined therewith, any combination of the optical receiving unit and the APD bias voltage control unit is possible. Optimum reception characteristics can be obtained without individually adjusting the optical receiver with respect to individual variations and temperature characteristics of the break voltage.Also, the ambient temperature data T necessary for bias voltage control and the breakdown voltage Vb at that time can be given to the CPU, and the APD bias voltage can be set optimally.
[0063]
(2) According to the invention described in claim 2,Even if the temperature sensor is installed away from the APD, it is converted into the APD element temperature, and the CPU determines the APD bias voltage from the breakdown voltage Vb at that time.Can be set optimally.
[0065]
In the present invention, the bias voltage control is performed so that the reception characteristic of the optical receiver is optimized based on the breakdown voltage value of the APD stored in the memory in advance, the temperature characteristic data thereof, and the detection data of the APD element temperature by the temperature sensor. The resistance value of the variable resistor is automatically set, and the voltage value of the APD bias voltage at which the reception characteristic of the optical receiving unit is optimized is output. On the other hand, the APD bias voltage control unit sets the DC voltage source to this value. If automatically controlled, the bias voltage of the APD can be set optimally.
[0066]
In the present invention, if the breakdown voltage of the APD and its temperature characteristics, the detection output of the temperature sensor, the DC voltage source control signal, and the bias voltage control variable resistance setting signal are discrete digital signals, The CPU can optimally set the APD bias voltage based on these digital signals.
[0067]
As described above, according to the present invention, a general-purpose combination of the optical receiver module and the APD bias voltage control unit is possible, and the optical receiver module can be downsized by externally attaching the APD bias voltage control unit. It is possible to provide an APD bias voltage control circuit capable of sharing the structure of the receiving module.
[Brief description of the drawings]
FIG. 1 is a principle block diagram of the present invention.
FIG. 2 is a block diagram showing a first exemplary embodiment of the present invention.
FIG. 3 is a block diagram showing a second exemplary embodiment of the present invention.
FIG. 4 is a block diagram showing a third exemplary embodiment of the present invention.
FIG. 5 is a conceptual diagram of a multiplication factor M fixing method.
FIG. 6 is a conceptual diagram of the FULL AGC method.
FIG. 7 is a conceptual diagram of a self-bias method.
FIG. 8 is a diagram illustrating an example of a Pin-Iapd characteristic.
FIG. 9 is a diagram illustrating a known example of an optical space transmission device.
FIG. 10 is a diagram illustrating an example of a Pin-Vapd characteristic.
FIG. 11 is a diagram illustrating an example of a Pin-M characteristic.
[Explanation of symbols]
60 Optical receiver
61 memory
70 APD bias voltage controller
71 DC voltage source
72 CPU
R10 Bias voltage control resistor (variable resistor)

Claims (2)

In an APD bias voltage control circuit that controls a bias voltage of an avalanche photodiode (APD) by a self-bias method,
An optical receiver that receives an optical signal input, converts it into an electrical signal, and outputs output data;
An APD bias voltage control unit that provides an optimum bias voltage to the APD of the optical receiving unit is configured separately.
The APD bias voltage controller is
A DC voltage source capable of controlling the output voltage;
Connected to said DC voltage source, and the bias voltage control - variable resistor whose resistance value is varied by a control signal,
It consists of a CPU that performs various controls,
The optical receiver is
An APD connected to the bias voltage control variable resistor;
A memory for storing a breakdown voltage value of the APD and temperature characteristic data thereof;
An identification reproduction circuit for amplifying the output signal of the APD and outputting the data divided into data and a clock;
A temperature sensor for detecting the ambient temperature of the APD,
Wherein the CPU, the breakdown voltage value of an APD that is stored in the memory of the light receiving unit and reads the temperature characteristic data, so that the reception characteristics of the optical receiver becomes optimum, the said DC voltage supply An APD bias voltage control circuit that controls a variable resistor for bias voltage control. The temperature sensor is installed at a location thermally separated from the APD, and the CPU of the APD bias voltage control unit converts the temperature detection data into the APD element temperature, and reads this value and the light receiving unit. Based on the breakdown voltage value of the APD and its temperature characteristic data, the APD bias voltage value and the resistance value of the bias voltage control variable resistor that optimize the reception characteristics of the optical receiver are calculated, and these values are calculated. 2. The APD bias voltage control circuit according to claim 1, wherein the DC voltage source and the bias voltage control variable resistor are controlled .

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