JP2005124085A - Optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a gain and a frequency band characteristic of a preamplifier constituting an optical receiver.
A control circuit transmits a bias signal to a photodiode and a preamplifier based on a predetermined control signal received from the outside of the optical receiver. A bias signal output from the control circuit 11 is applied to the photodiode 13 as a reverse bias. The preamplifier 14 which is a variable gain / band amplifier changes the gain and the frequency band based on the bias signal output from the control circuit 11. The main amplifier 15 amplifies the voltage signal output from the preamplifier 14. In the optical receiver 1 configured as described above, the gain and frequency band characteristics of the preamplifier 14 can be controlled according to the content of the bias signal.
[Selection] Figure 1

Description

  The present invention relates to an optical receiver.

  Patent Documents 1 and 2 below disclose an optical receiver including a photodiode and an amplifier (preamplifier, main amplifier) as main parts. In such a conventional optical receiver, a fixed signal transmission speed is generally used. Therefore, the conventional optical receiver has been designed so as to perform an optimum operation at a target signal transmission speed.

In recent years, modularization of optical transceivers has progressed, and a pluggable module such as SFP (Small Form Factor Pluggable) has been demanded. Such standardized optical transmission modules are not used only in a single application, but are used in a plurality of applications. Therefore, in consideration of maintainability, future expandability, etc., a plurality of applications, that is, optical receivers that operate at a plurality of transmission speeds are required. As such an optical receiver operating at a plurality of transmission speeds, a broadband amplifier corresponding to a high-speed signal is provided in advance, and an optimum band filter is selected from a plurality of band filters provided at the subsequent stage of the amplifier. Some optical receivers are operated at a plurality of transmission speeds (see Patent Document 3).
JP 09-260961 A Japanese Patent Laid-Open No. 09-232877 Japanese Patent Laid-Open No. 10-150417

  However, in general, in an amplifier, a gain-bandwidth (GB) product is constant. Therefore, when an amplifier corresponding to a wide band is provided in advance like the optical receiver described in Patent Document 3 described above, the gain of this amplifier must be limited. Therefore, the application of the amplifier is limited.

  Therefore, in order to solve the above-described problems, an object of the present invention is to provide an optical receiver that can control the gain and frequency band characteristics of a preamplifier among amplifiers constituting the optical receiver. .

  An optical receiver according to the present invention includes a photodiode that converts an optical signal into a current signal, a preamplifier having a function of converting a current signal output from the photodiode into a voltage signal, and changing a gain or a frequency band. The photodiode and the preamplifier receive a bias signal for the photodiode, and the preamplifier changes the gain and the frequency band based on the received bias signal.

  According to the present invention, the bias signal output to the photodiode is also output to the preamplifier, and the preamplifier changes the gain and the frequency band based on the bias signal. Thus, the gain and band characteristics of the preamplifier can be controlled. Also, since the same bias signal is output to both the photodiode and the preamplifier, the bias signal to the photodiode and the gain / band control signal to the preamplifier can be shared, and fewer signal paths Can be configured.

  The optical receiver of the present invention further includes a light receiving module for optical communication having a lead pin, and the photodiode and the preamplifier are provided in the light receiving module for optical communication and are provided in the light receiving module for optical communication. A bias signal is received through one lead pin. Thus, the photodiode and the preamplifier can receive a bias signal through one lead pin provided in the optical communication light receiving module. Therefore, in the optical communication light receiving module having only a limited number of lead pins, Without increasing the number, a bias signal and a gain / band control signal can be applied to the photodiode and the preamplifier.

  The optical receiver of the present invention further includes a control circuit that outputs a bias signal to the photodiode and the preamplifier, and the control circuit is disposed outside the light receiving module for optical communication and receives a predetermined control signal received from the outside. It is preferable to output a bias signal based on the above. In this way, the predetermined control signal can include, for example, information on the transmission rate, and a bias signal corresponding to the transmission rate can be output. This makes it possible to perform optimal control corresponding to a wide range of transmission speeds.

  In the optical receiver of the present invention, it is preferable that the control circuit includes an output current monitoring unit, and the output current monitoring unit monitors a current output from the control circuit to the photodiode. This makes it possible to control the gain of the entire optical receiver in accordance with the monitoring result of the current flowing through the photodiode.

  The optical receiver of the present invention further includes a buffer circuit having a high input impedance for receiving the bias signal output from the control circuit, the buffer circuit being disposed in the light receiving module for optical communication, and the preamplifier being The gain and the frequency band are preferably changed based on the signal output from the buffer circuit. By further providing a buffer circuit having a high input impedance in this way, it is possible to prevent the current flowing through the preamplifier from being mixed into the current flowing through the photodiode to be monitored. That is, the output current monitoring accuracy can be increased.

  According to the optical receiver of the present invention, it is possible to control the gain and frequency band characteristics of the preamplifier among the amplifiers constituting the optical receiver.

  Hereinafter, embodiments of an optical receiver according to the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

[First embodiment]
First, a first embodiment of the present invention will be described. FIG. 1 is a diagram illustrating a schematic configuration of an optical receiver in the first embodiment. As shown in FIG. 1, the optical receiver 1 includes a control circuit 11, an optical transmission line 12, a photodiode 13, a preamplifier (preamplifier) 14, and a main amplifier (main amplifier) 15.

  The control circuit 11 transmits a bias signal to the photodiode 13 and the preamplifier 14 based on a predetermined control signal received from the outside of the optical receiver 1. Here, as the predetermined control signal, for example, when the optical receiver has an interface with the center CPU such as SFP (Small Form Factor Pluggable), the control signal output from the center CPU is applicable. To do. In addition, the predetermined control signal includes, for example, information regarding the transmission rate. As a result, the control circuit 11 can output a bias signal corresponding to the transmission speed. Therefore, optimal control corresponding to a wide range of transmission speeds can be performed.

  For example, an optical fiber corresponds to the optical transmission line 12. The photodiode 13 receives the output light from the optical transmission line 12 and converts the optical signal into a current (electric) signal. A bias signal output from the control circuit 11 is applied to the photodiode 13 as a reverse bias. Here, the photodiode 13 can respond to the optical signal (convert the optical signal into a current signal) even when the reverse bias is not applied. However, it is possible to reduce the junction capacitance of the photodiode 13 by applying a reverse bias to the photodiode 13. Thereby, the response speed of the photodiode 13 can be improved.

  The preamplifier 14 converts the current signal output from the photodiode 13 into a voltage signal. The preamplifier 14 in the present embodiment is a variable gain / band amplifier, and changes the gain and frequency band based on the bias signal output from the control circuit 11. The main amplifier 15 amplifies the voltage signal output from the preamplifier 14.

  Here, a specific circuit configuration of the preamplifier 14 which is a variable gain / band amplifier will be described with reference to FIG. As shown in FIG. 2, the preamplifier 14 is configured as a closed loop circuit, and a feedback resistor Rf (transimpedance) is provided on the feedback loop. The FET Qf is connected in parallel to the feedback resistor Rf, and the feedback resistor Rf is connected between the drain terminal and the source terminal of the FET Qf. The bias signal output from the control circuit 11 is input to the gate terminal of the FET Qf. The amplifying section of the preamplifier 14 is configured by connecting three FETs Q1, Q2, and Q3 in series. The output side of the light receiving photodiode 13 is connected to the gate terminal side of the FET Q1. An FET Q2 is connected between the drain terminal of the FET Q1 and the source terminal of the FET Q3. The gate terminal of the FET Q2 is grounded. A circuit composed of FETs Q5 to Q8 is connected to the source terminal side of the FET Q3.

  The optical transmission path 12, the photodiode 13, and the preamplifier 14 described above are arranged in a receiving optical sub-assembly (ROSA) 10 that is a light receiving module for optical communication.

  Here, a basic configuration of the ROSA 10 will be described with reference to FIG. The ROSA 10 shown in FIG. 3 is configured as a coaxial (TO type) package. The photodiode 13 is disposed at the center of the ROSA 10. The preamplifier 14 is arranged next to the photodiode 13 (upper side on the paper surface of FIG. 2). As described above, the preamplifier 14 is arranged in the immediate vicinity of the photodiode 13 because the current signal output from the photodiode 13 is very small and is easily influenced by an external electromagnetic field, and thus it is necessary to improve noise resistance characteristics. Because there is. The optical transmission path 12 is provided at the center of the lid (not shown) of the ROSA 10 so that light emitted from the tip of the optical transmission path 12 is irradiated to the photodiode 13 through a lens (not shown). Be placed. Further, the ROSA 10 is provided with a lead pin LP for exchanging signals with the outside of the ROSA 10. These lead pins LP are used, for example, for supplying bias to the photodiode 13, supplying power to the photodiode 13, supplying power to the preamplifier 14, and outputting from the preamplifier 14.

  In addition, the length of the package described above is generally about 4 to 6 mm, but due to the recent downsizing of the module, a package having a length of about 3 mm has been required. Therefore, the number of lead pins LP provided in the ROSA 10 is inevitably limited, and it is necessary to configure the ROSA 10 with fewer lead pins LP.

  In the optical receiver 1 having such a configuration, when the bias signal (voltage) output from the control circuit 11 is increased, the reverse bias to the photodiode 13 is increased. As a result, the junction capacitance of the photodiode 13 is reduced, the voltage at the pn junction interface is increased, and the response speed of the photodiode 13 is improved. In other words, the current signal output from the photodiode 13 can be applied in a direction that widens the band.

  Further, when the bias signal output from the control circuit 11 is increased, the gate bias of the preamplifier 14 to the FET Qf is increased. Thereby, since the drain current flowing between the drain terminal and the source terminal of the FET Qf increases, the equivalent resistance (feedback resistance) decreases. When the feedback resistance of the preamplifier 14 is reduced, the closed loop gain of the preamplifier 14 is reduced and the frequency band is widened. For these reasons, when the bias signal output from the control circuit 11 is increased, the optical / electrical signal conversion gain of the entire ROSA 10 including the preamplifier 14 is reduced, but the frequency band can be extended to a wide band. On the other hand, when the bias signal output from the control circuit 11 is reduced, the optical / electrical signal conversion gain of the entire ROSA 10 including the preamplifier 14 is increased, but the frequency band is narrowed. Therefore, the gain and band characteristics of the preamplifier can be controlled according to the content of the bias signal output from the control circuit 11.

  As described above, according to the optical receiver 1 in the first embodiment, the bias signal output to the photodiode 13 is also output to the preamplifier 14, and the gain and the frequency band are increased by the preamplifier 14 based on the bias signal. Be changed. Therefore, the gain and band characteristics of the preamplifier 14 can be controlled according to the content of the bias signal. In addition, since a common bias signal is output to both the photodiode 13 and the preamplifier 14 provided in the ROSA 10, the bias signal to the photodiode 13 and the gain / band control signal to the preamplifier 14 are shared. The ROSA 10 can be formed through fewer lead pins (signal paths).

[Second Embodiment]
Next, a second embodiment of the present invention will be described. First, the schematic configuration of the optical receiver in the second embodiment will be described with reference to FIG. As shown in FIG. 2, in the optical receiver 2 in the second embodiment, the main amplifier 15a is a variable band amplifier, and the control circuit 11a transmits a band control signal for controlling the frequency band to the main amplifier 15a. This is different from the optical receiver 1 in the first embodiment. Accordingly, since the other configuration and function are the same as the configuration and function of the optical receiver 1 in the first embodiment, the same reference numerals are given to the respective components, and the description thereof will be omitted. Differences from the first embodiment will be described in detail.

  For example, a limit amplifier can be used as the main amplifier 15a. The limit amplifier is an amplifier circuit that sets an amplification gain large and has a limiter for the signal amplitude so that the amplitude of the output signal is constant regardless of the magnitude of the input signal. As a circuit for setting the amplification gain large, for example, there is a method of increasing the load of the differential amplifier circuit and connecting the differential amplifier circuits in a plurality of stages in series. On the other hand, as a circuit that gives a signal amplitude limiter, for example, there is a method of making the output width constant by a low current source connected to a common emitter terminal (source terminal) of a differential amplifier circuit.

  Here, a circuit configuration example of the main amplifier 15a (limit amplifier) that controls the band by the band control signal will be described with reference to FIG. As shown in FIG. 5, the main amplifier 15a includes differential amplifier circuits D1 and D2, switches S1 to S4, and capacitors C1 to C4. The differential amplifier circuit D1 and the differential amplifier circuit D2 are connected in series. In such a main amplifier 15a, the signal amplitude in the subsequent differential amplifier circuit D2 has a relatively large value. A plurality of switches S1 to S4 are inserted in a signal path between the differential amplifier circuit D1 and the differential amplifier circuit D2. Capacitors C1 to C4 having different capacities are connected between the switches and GND, and an RC filter is provided. A circuit is configured. In the main amplifier 15a configured as described above, one of the capacitors C1 to C4 is selected based on the band control signal output from the control circuit 11a. Thereby, the frequency band of the main amplifier 15a is controlled. For example, FET switches can be used as the switches S1 to S4.

  As described above, according to the optical receiver 2 in the second embodiment, in addition to the effects of the optical receiver 1 in the first embodiment described above, the frequency band of the main amplifier 15a is changed according to the content of the band control signal. Can be made.

[Third embodiment]
Next, a third embodiment of the present invention will be described. First, the schematic configuration of the optical receiver in the third embodiment will be described with reference to FIG. As shown in FIG. 6, the optical receiver 3 in the third embodiment is different from the optical receiver 1 in the first embodiment in that it includes a buffer circuit 16 and the control circuit 11b has a function of monitoring the output current. Also, the point that the main amplifier 15a is a variable band amplifier and the control circuit 11b transmits a band control signal to the main amplifier 15a is different from the optical receiver 1 in the first embodiment, but this difference is described above. Since it is the same as that of the difference in 2nd Embodiment, the description is abbreviate | omitted. Furthermore, since the configuration and function other than these are the same as the configuration and function of the optical receiver 1 in the first embodiment, the same reference numerals are given to the respective components, and the description thereof is omitted. Hereinafter, differences from the first embodiment will be described in detail.

  The functional configuration of the control circuit 11b will be described with reference to FIG. The control circuit 11b includes a control unit b1, a D / A conversion unit b2, an output current monitoring unit (output current monitoring unit) b3, and an A / D conversion unit b4. The control unit b1 generates the bias signal and the band control signal described in the first and second embodiments based on a predetermined control signal received from the outside of the optical receiver. The D / A converter b2 performs D / A conversion on the bias signal and the band control signal generated by the controller b1, and outputs the result. The output current monitor b3 monitors the current output from the control circuit 11b to the photodiode 13, and acquires the average value of this current. For example, a current mirror circuit can be used as the output current monitor unit b3.

  Here, a circuit configuration example for realizing the output current monitor unit b3 (current mirror circuit) will be described with reference to FIG. The output current monitor unit b3 includes transistors T1 and T2 and a resistor R. The base terminal of the transistor T1 and the base terminal T2 of the transistor T2 are connected to each other. The emitter terminals of the transistors T1 and T2 are connected to the D / A converter b2 side. The collector terminal of the transistor T1 is connected to the photodiode 13 side, and the collector terminal of the transistor T2 is connected to the resistor R and the A / D converter b4 side. In such an optical receiver having the output current monitor unit b3, the current flowing from the control circuit 11b to the photodiode 13 is supplied to the photodiode 13 via the transistor T1. Further, a current equivalent to the current supplied through the transistor T1 flows through the transistor T2. The output current monitor unit b3 calculates a voltage value by multiplying the current value of the current flowing through the transistor T2 and the resistance value of the resistor R. The A / D conversion unit b4 performs A / D conversion on the voltage value calculated by the output current monitoring unit b3. The control unit b1 performs gain control of the entire optical receiver 3 by an external control signal, but may perform gain control of the entire optical receiver 3 based on the signal A / D converted by the A / D conversion unit b4. Good. The current flowing through the transistor T2 is equal to that of the transistor T1 when the emitter sizes of the transistors T1 and T2 are equal, and the current corresponding to the size ratio when the emitter sizes of the transistors T1 and T2 are different. Flows. The transistors T1 and T2 may be FETs. In this case, the current flowing through the transistor T2 is determined by the gate width of the FETs.

  The buffer circuit 16 is a buffer circuit with a high input impedance, converts the signal level of the bias signal output from the control circuit 11b, and outputs it to the preamplifier 14. Thus, by providing the buffer circuit 16 with a high input impedance, it is possible to prevent the current output from the control circuit 11b to the preamplifier 14 from being mixed into the current output to the photodiode 13 to be monitored. It becomes possible to do. That is, the accuracy of the monitor signal (output current signal) can be increased. Further, by providing the buffer circuit 16, it is possible to prevent the fluctuation of the potential level generated in one of the bias signal output to the photodiode 13 and the bias signal output to the preamplifier 14 from affecting the other. be able to. In addition, the potential level of the bias signal output to the preamplifier 14 can be converted. As the buffer circuit 16, for example, an emitter follower (source follower) can be used.

  Thus, according to the optical receiver 3 in the third embodiment, in addition to the effects of the optical receiver 1 in the first embodiment and the optical receiver 2 in the second embodiment described above, the current flowing through the photodiode 13 According to the monitoring result, it is possible to monitor the optical power to the optical receiver 3 and to control the gain of the entire optical receiver 3. Further, by providing the buffer circuit 16 having a high input impedance, it is possible to prevent the current flowing in the preamplifier 14 from being mixed into the current flowing in the photodiode 13 to be monitored, and the output current monitoring accuracy. Can be increased.

It is a figure which shows schematic structure of the optical receiver in 1st Embodiment. It is a figure which shows the circuit structure of the preamplifier shown in FIG. It is a figure which shows the circuit structure of ROSA shown in FIG. It is a figure which shows schematic structure of the optical receiver in 2nd Embodiment. FIG. 5 is a diagram showing a circuit configuration of the main amplifier shown in FIG. 4. It is a figure which shows schematic structure of the optical receiver in 3rd Embodiment. It is a figure which shows the function structure of the control circuit shown in FIG. It is a figure which shows the circuit structure of the output current monitor part shown in FIG.

Explanation of symbols

  1, 2, 3 ... optical receivers, 10, 10a ... ROSA, 11, 11a, 11b ... control circuit, 12 ... optical transmission line, 13 ... photodiode, 14 ... Preamplifier 15, 15a ... Main amplifier, 16 ... Buffer circuit, b1 ... Control unit, b2 ... D / A conversion unit, b3 ... Output current monitor unit, b4 ... A / D conversion part.

Claims (5)

A photodiode for converting an optical signal into a current signal;
A preamplifier for converting the current signal output by the photodiode into a voltage signal and changing a gain or a frequency band;
The photodiode and the preamplifier receive a bias signal for the photodiode;
The preamplifier changes a gain and a frequency band based on the bias signal. A light receiving module for optical communication having a lead pin;
The photodiode and the preamplifier are arranged in the light receiving module for optical communication and receive the bias signal through one lead pin provided in the light receiving module for optical communication. The optical receiver according to 1. A control circuit for outputting the bias signal to the photodiode and the preamplifier;
3. The optical receiver according to claim 2, wherein the control circuit is arranged outside the light receiving module for optical communication and outputs the bias signal based on a predetermined control signal received from the outside. The control circuit includes output current monitoring means,
The optical receiver according to claim 3, wherein the output current monitoring unit monitors a current output from the control circuit to the photodiode. A buffer circuit having a high input impedance for receiving the bias signal output by the control circuit;
The buffer circuit is disposed in the light receiving module for optical communication,
The optical receiver according to claim 4, wherein the preamplifier changes a gain and a frequency band based on a signal output from the buffer circuit.

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