JP4253308B2 - Optical receiver circuit device - Google Patents

Description

  The present invention relates to an optical receiver circuit device that receives an electrical signal obtained by photoelectrically converting an optical signal such as optical communication, and more particularly to an integrated optical receiver circuit device connected to a photoelectric conversion element.

  As an example of an optical communication apparatus, a conventional technique of a high-speed optical receiver using a PIN photodiode and a transimpedance amplifier circuit will be described. In general, since a PIN photodiode and a transimpedance amplifier have different elements, the PIN photodiode is manufactured as an element chip and the transimpedance amplifier is manufactured as an integrated circuit by different processes. The two are electrically coupled. In general, however, the method does not deteriorate the high frequency characteristics, so that they are mounted on the substrate in close proximity and are electrically coupled by bonding wires.

  In general, an optical receiver needs to operate in a wide dynamic range from a minute optical signal to a large optical signal. The DC (direct current) current component included in the signal output from the photodiode generates a small DC current in the case of a minute optical signal, and generates a large DC current in the case of a large optical signal. Accordingly, the signal amplitude changes and the DC current also changes. When this DC current flows into the transimpedance amplifier, the operation state of the circuit is shifted. Therefore, processing is performed by a circuit that sucks in the DC current at the input part of the transimpedance amplifier.

  On the other hand, since the input signal component is directly input to the transimpedance amplifier, when a large signal is generated from the photodiode, the transimpedance amplifier is saturated and there is a problem that normal operation cannot be performed. In order to avoid this, the gain of the transimpedance amplifier may be lowered. In this case, however, there is a problem that noise increases when a small signal is input. Because of these problems, the transimpedance amplifier has a problem that the dynamic range cannot be increased.

In order to solve this problem, an automatic gain switching type burst optical receiver circuit as described in Patent Document 1 is provided as a conventional example. In this burst light receiving circuit, a transimpedance amplifier that converts a light receiving current of a photodiode into a voltage signal, a negative feedback circuit that determines the gain of the transimpedance amplifier, and a peak detection that detects the peak of the light receiving current When a circuit is provided and the photodiode outputs a large amplitude signal, the gate is opened by peak detection, and the signal component is allowed to pass. This avoids circuit saturation for large amplitude signals, closes the gate for small signals, increases gain, and improves noise characteristics.
JP 2000-252775 A

  With a conventional burst light receiving circuit, the transimpedance amplifier can operate regardless of whether a large signal is input or a small signal is input, and a wide dynamic range can be obtained. However, the conventional optical receiver circuit requires a peak detection circuit, which makes the circuit configuration very complicated, causing problems such as malfunction, enlargement of chip area, and complexity of testing, which in turn increases cost and consumption. There were drawbacks such as increased power. Further, in the case of peak detection, since a high frequency must be detected, an error occurs in the control system.

  An object of the present invention is to provide an optical receiver circuit device that detects a signal input having a large signal amplitude with a simple circuit configuration, performs gain control based on the detection result, and operates in a wide dynamic range.

  One aspect of the present invention extracts a light receiving element that converts an optical signal into a current signal, a conversion amplifier that variably converts the current signal of the light receiving element into a voltage signal, and a DC current generated from the light receiving element. DC current absorption circuit, absorption current amount detection circuit for detecting current absorbed in the DC current absorption circuit, and amplification factor for controlling the amplification amount of the transimpedance amplifier based on the detection result of the absorption current amount detection circuit An optical receiver circuit device comprising a control circuit is provided.

  In the present invention, the circuit configuration becomes simple because the gain of the conversion amplifier is controlled by detecting the DC current of the light receiving element drawn out by the DC current absorption circuit. In addition, the addition of a signal inflow prevention circuit has the effect of reducing the noise when inputting a small signal and expanding the dynamic range.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIG. In FIG. 1, the electric signal amplification IC module 11 is shown in a portion surrounded by a dotted frame. The photoelectric conversion circuit 12 including a photodiode is disposed outside the IC module 11 and bonded to the IC module 12 by bonding.

  The electric signal amplification IC module 11 is provided with an electric signal amplification circuit 13 and a direct current absorption circuit 14. The electric signal amplifier circuit 13 is connected to the output part of the photoelectric conversion circuit 12 to amplify the light reception signal of the photoelectric conversion circuit 12, and the direct current absorption circuit 14 is direct current to absorb all the direct current (DC) current of the light reception signal. It is connected to the output part of the current absorption circuit 14. The direct current absorption circuit 14 is connected to the amplification factor control circuit 16 through the absorption current detection circuit 15. The amplification factor control circuit 16 controls the gain of the electric signal amplification circuit 13 according to the amount of absorption of the DC current detected by the absorption current detection circuit 15.

  FIG. 2 shows waveforms when a small signal and a large signal of an optical signal are input. When a small signal is input, a signal with a small amplitude and a certain bias current value Ib1 are shown. When a large signal is input, the signal amplitude increases, and the bias current value Ib2 increases accordingly. From this relationship, in order to detect a large signal, it is only necessary to detect the value of the bias current value Ib2, and it is not necessary to detect the peak of the signal. Therefore, the circuit configuration of FIG. 1 detects the signal amplitude by the DC absorption current, and controls the amplification factor of the electric signal amplifier circuit 13 based on the result.

  With the above circuit configuration, the electric signal amplifier circuit 13 does not enter a saturated state when a large light signal is input, and stable operation is possible. Further, when the small signal is input, the current absorption circuit 14 hardly absorbs current, so that the amplification factor of the electric signal amplification circuit 13 is in a maximum state. Therefore, a high gain state with low noise can be maintained. As a result, the optical receiver circuit device of the present invention can operate in response to an optical signal with a wide dynamic range.

  FIG. 3 shows an optical receiver circuit according to a second embodiment of the present invention. A portion surrounded by a dotted frame indicates the electric signal amplification IC module 11. Similar to the first embodiment, the photoelectric conversion circuit 12 is provided outside the IC module 11. In the second embodiment, a signal blocking circuit 17 is further provided in front of the current absorption circuit 14 in the first embodiment.

  Also in the second embodiment, the photoelectric conversion circuit 12 photoelectrically converts an optical signal and outputs an electrical signal. The outputted electric signal is inputted to the electric signal amplifying circuit 13 of the IC module 11. The input electrical signal is voltage amplified and output to the outside of the IC module 11.

  A current absorption circuit 14 is connected to a signal input portion of the electric signal amplification circuit 13 via a signal blocking circuit 17. The current absorption circuit 14 is generally controlled by a current detection circuit provided at the output portion of the photoelectric conversion circuit 12 or the electric signal amplification circuit 13 and absorbs all DC current generated from the photoelectric conversion circuit 12. The DC current value absorbed by the current absorption circuit 14 is detected by the absorption current detection circuit 15, and when the absorption DC current value reaches a certain value, the amplification factor of the electric signal amplification circuit 13, that is, the amplification factor control circuit 16 that controls the gain is provided. Control. As a result, the gain of the electric signal amplifier circuit 13 is controlled by the amount of current absorbed by the current absorption circuit 14.

  The signal blocking circuit 17 is a circuit for blocking an electric signal from flowing into the current absorption circuit 14, and the blocking amount is adjusted according to the detection result of the absorption current amount detection circuit 15.

  With this circuit configuration, in addition to the effects described in the embodiment of FIG. 1, there is an effect that the signal does not flow into the current absorption circuit 14, and further, the amount of inhibition can be adjusted, so that the current absorption circuit 14 maintains a normal bias level. , You can get the maximum effect. That is, the signal blocking amount is set large when a small signal is input, and the signal blocking amount is set small when a large signal is input. Thereby, noise characteristics can be improved for small signals, and the amount of current absorption can be improved for large signals. The electrical signal amplifier circuit 13 corresponds to an optical signal having a wider dynamic range than that of the embodiment of FIG. Can work.

  FIG. 4 shows an optical receiver circuit device that is a specific implementation of the circuit of FIG. According to this circuit device, the electric signal amplifying circuit 13 in FIG. 3 includes the electric signal amplifier 21 and the resistor 26 connected in parallel to the electric signal amplifier 21, and the photoelectric signal from the photodiode 22 of the light conversion circuit 12 is received. Variable conversion to voltage signal and amplification. The signal blocking circuit 17 includes a resistor 24 connected between the photodiode 22 and the current absorber 23, and a MOS transistor 25 having a source and a drain connected to both ends of the resistor 24, respectively. The gate of the MOS transistor 25 is connected to the output terminal of the absorbed current amount detection circuit 15. The amplification factor control circuit 16 includes a MOS transistor 27 having a source and a drain connected to both ends of the resistor 26, respectively.

  In the circuit of FIG. 4, the direct current of the photoelectric conversion current output from the photodiode 22 is absorbed by the current absorber 23 via the resistor 24. At this time, when a smaller direct current is absorbed by the current absorber 23, the current amount detection circuit 15 supplies a gate signal corresponding to the direct current to the gate of the MOS transistor 25 to turn off the MOS transistor 25. Thereby, the outflow of the small signal is limited by the resistance, and the current blocking amount of the signal blocking circuit is increased. On the other hand, when a large direct current is taken into the current absorber 23, the current amount detection circuit 15 supplies a gate signal corresponding to the large direct current to the gate of the MOS transistor 25 to turn on the MOS transistor 25. Thereby, a large signal flows out through the MOS transistor 25. That is, the current blocking amount of the signal blocking circuit is reduced.

  The detection signal of the absorption current amount detection circuit 15 is also supplied to the gate of the MOS diode 27 of the amplification factor control circuit, but when a large current is supplied from the photodiode 22, the detection signal of the absorption current amount detection circuit 15 is the MOS signal. The diode 27 is turned on, the amplification factor of the amplifier circuit 13 is lowered, and the amplifier circuit 13 is prevented from being saturated.

  FIG. 5 shows a receiving circuit according to the third embodiment of the present invention. In the present embodiment, in the electric signal amplification IC module 11, the signal blocking circuit 17 is configured by resistors 32 and 33 connected in series and a MOS transistor 34 having a source and a drain connected to both terminals of the resistor 33. Both terminals of the resistor 33 are connected to the input part of the DC current amount detection circuit 15. The output portion of the DC current amount detection circuit 15 is connected to the gate of the MOS transistor 27 via the control circuit 35. The control output of the control circuit 35 is connected to the gate of the MOS transistor 34.

  The MOS transistor 36 constitutes a current absorption circuit and absorbs all the DC current from the photodiode 22 in accordance with a control signal from the DC current absorption amount control circuit 37. The DC current absorption amount control circuit 37 normally inputs an ON signal to the MOS transistor 36 when the current signal of −3 dBm that saturates the amplifier is input to the amplifier 21, and turns on the MOS transistor 36.

  The signal blocking circuit 17 controls the signal blocking amount by the MOS transistor 34. The transimpedance amplifier 21 and the resistor 26 constitute an electric signal amplifier circuit, and the MOS transistor 27 constitutes an amplification factor control circuit. Vpd is the power supply voltage of the photodiode 22 and is connected to the cathode terminal of the photodiode.

  An optical signal is input to the photodiode 22, and an electric signal is output to the anode terminal by photoelectric conversion. The output electric signal is input to the electric signal amplifier circuit 13. The signal current from the photodiode 22 does not flow into the current absorption circuit 36 due to the resistance 32 of the blocking circuit, but flows into the electric signal amplification circuit 13.

  The absorption current amount detection circuit 15 calculates a voltage value in which the voltage is dropped by the resistor 32. When this value falls below a certain value, the absorption current amount detection circuit 15 determines that a large current has been input, controls the control circuit 35, and turns on the MOS transistor 27. As a result, the current signal that has flowed to the resistor 26 flows to the MOS transistor 27 and the gain decreases. Therefore, even if a large current is input, the electric signal amplifier circuit 13 can operate normally without being saturated. Further, when a small current is input, the control circuit 35 is turned off, and all the signals inputted in the off state of the MOS transistor 27 pass through the resistor 26 to contribute to amplification and reduce noise. As a result, a circuit with a wide dynamic range can be provided by using this circuit.

  FIG. 6 is a modification of the third embodiment of FIG. 5, and a hysteresis circuit 38 and a high frequency compensation resistor 39 are provided in the circuit of FIG. 5. The hysteresis circuit 38 is connected between the control circuit 35 and the gate of the amplification factor control circuit MOS transistor 27 and is provided to compensate for the fluctuation of the ON / OFF operation of the MOS transistor 27. The high frequency compensation resistor 39 is provided to prevent the influence of high frequency signal deterioration when the MOS transistor 27 is OFF.

  A fourth embodiment will be described with reference to FIG. According to the third embodiment, a dummy circuit is provided, and the amount of direct current drawn is controlled according to the direct current difference between the main circuit and the dummy circuit.

  According to the optical receiver circuit of FIG. 7, the main circuit is connected in parallel to the main electric signal amplifier 21 and the electric signal amplifier 21 that variably converts and amplifies the photoelectric signal from the photodiode 22 of the optical conversion circuit 12 into a voltage signal. And a MOS transistor 27 having a source and a drain connected to both ends of the resistor 26, respectively. On the other hand, the dummy circuit includes a dummy electric signal amplifier 41, a resistor 42 connected in parallel to the dummy electric signal amplifier 41, and a MOS transistor 43 having a source and a drain connected to both ends of the resistor 42, respectively. Composed. Output portions of the main electric signal amplifier 21 and the dummy electric signal amplifier 41 are connected to a DC difference detection circuit 44 and an output differential amplifier 45. The output part of the DC difference detection circuit 44 is connected to the control input part of the current absorber 23.

  According to the optical receiver circuit having the above configuration, the difference between the DC output voltage components of the main electric signal amplifier 21 and the dummy electric signal amplifier 41 is detected by the DC difference detection circuit 44, and the current absorber 23 detects the DC current according to this difference. Control the pull-in amount.

  FIG. 8 shows the result of measuring the code error rate of the signal output from the electrical signal amplifier circuit 13 by inputting the optical signal to the optical signal receiving device of the embodiment of FIG. FIG. 8 also shows the measurement result of the code error rate for the optical signal receiving device when the conventional technique is used at the same time. The solid line shows the measurement result of the embodiment of the present invention, and the dotted line shows the measurement result of the conventional example. The code error rate is evaluated with a constant value set by the standard. In this case, the code error rate at the position of the broken line is a specified value. In the conventional example, when a small signal is input, a low level signal cannot be received due to a large noise. Further, when a large signal is input, a large current cannot be received because a DC current flows into the electric signal amplifier circuit. As a result, the dynamic range remains at 18 dB. On the other hand, in the present invention, since the noise is small when the signal is small, the signal can be received to a low level. When the signal is large, the DC current from the PD is absorbed by the DC current absorption circuit, so that the signal can be received. As a result, the dynamic range can be 28 dB which is 10 dB wider than the conventional one.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  The present invention is applicable as an optical communication system to a long-distance optical communication system or a home optical transmission / reception system such as Gigabit Ethernet.

1 is a block circuit diagram of an optical receiver circuit device according to a first embodiment of the present invention. Waveform diagram of small optical signal waveform and large optical signal waveform The block circuit diagram of the optical receiver circuit device which is the 2nd Embodiment of this invention Circuit diagram of the optical receiver circuit device of FIG. The circuit diagram of the optical receiver circuit device which is the 3rd Embodiment of this invention FIG. 5 is a circuit diagram of an optical receiver circuit device which is a modification of the third embodiment of FIG. The circuit diagram of the optical receiver circuit device which is the 4th Embodiment of this invention The graph which shows the characteristic by this invention and a prior art example

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Electric signal amplification IC module, 12 ... Photoelectric conversion circuit, 13 ... Electric signal amplification circuit, 14 ... Current absorption circuit, 15 ... Absorption current amount detection circuit, 16 ... Amplification rate control circuit, 17 ... Signal blocking circuit, 21 ... Electrical signal amplifier, 22 ... photodiode, 23 ... current absorber, 25 ... MOS transistor, 27, 34, 36 ... MOS transistor, 35 ... control circuit, 37 ... DC current absorption amount control circuit, 38 ... hysteresis circuit, 41 ... Dummy electric signal amplifier, 44 ... DC difference detection circuit

Claims (5)

A light receiving element for converting an optical signal into a current signal, and a conversion amplifier circuit for variably converting amplifying the current signal output from the light receiving element into a voltage signal, the DC current of the current signal outputted from said light receiving element A DC current absorption circuit for absorbing, an absorption current amount detection circuit for detecting the DC current absorbed by the DC current absorption circuit, and an amplification factor of the conversion amplification circuit based on a detection result of the absorption current amount detection circuit. An optical receiver circuit device comprising: an amplification factor control circuit for controlling.   2. The optical receiver circuit device according to claim 1, further comprising a variable signal inflow blocking circuit provided between the DC current absorption circuit and an input terminal of the conversion amplifier circuit.   3. The optical receiver circuit device according to claim 2, wherein the absorption current amount detection circuit includes means for detecting a direct current amount passing through the signal inflow prevention circuit.   4. The optical receiver circuit device according to claim 1, wherein the amplification factor control circuit includes a MOS transistor connected in parallel to a negative feedback element of the conversion amplifier circuit. 5.   5. The optical receiver circuit device according to claim 1, further comprising a hysteresis circuit connected between the absorption current amount detection circuit and the amplification factor control circuit.

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