JP2008236506A - Amplification apparatus and optical receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a high-speed response and to perform gain adjustment that is stable over a wide frequency band. <P>SOLUTION: An optical receiver 10 includes: a photodiode 11 which outputs a light reception signal Iin of a current value corresponding to light reception power and is capable of controlling the current value; a feedback amplifier 15 which amplifies and outputs the light reception signal Iin output by the photodiode 11 with a fixed gain; and an inverse bias voltage control circuit 16 which controls a current value outputted from the photodiode 11 based on a voltage of an output signal Vout output by the feedback amplifier 15, wherein a digital signal is demodulated on the basis of a signal output by the feedback amplifier 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an amplification device and an optical reception device suitable for use in optical communication.

In recent years, with the widespread use of network services such as FTTH (Fiber To The Home) using optical communication, the need for analog ICs that operate at high speed in the G (giga) bps class and support burst signals is increasing.
In optical communication, the power of light output from the transmission side is affected by the communication path, so the optical power received at the reception side is not constant. For this reason, the optical receiving device requires a circuit that varies the gain according to the received optical power and maintains the output constant.
In particular, in order to expand the dynamic range of received light power while enabling high-speed operation, a variable gain circuit capable of high-speed response to fluctuations in received light power is important.

  Therefore, conventional optical receivers generally convert and amplify the current output of a light receiving element such as a photodiode (PD: Photo Diode) that outputs a current corresponding to the received light power of the received light and the current output of the light receiving element. A preamplifier circuit for output, and a feedback amplifier is employed for the preamplifier circuit. As shown in FIG. 6, the feedback amplifier has a group delay characteristic obtained by differentiating the phase characteristic with respect to frequency and becomes flat over a wider frequency band than a general amplifier. Therefore, this feedback amplifier is employed in the preamplifier circuit. By doing so, a stable amplification operation is possible over a wide frequency band.

In this type of preamplifier circuit, as shown in FIG. 7, the preamplifier circuit is provided in order to maintain the duty ratio of the signal waveform output from the preamplifier circuit even when the received light power is large. In some cases, the feedback resistor of the feedback amplifier 1 is a variable feedback resistor R1.
In recent years, as shown in FIG. 8, a MOS transistor M1 is connected in parallel to a feedback resistor R2 having a fixed resistance value to form a substantially variable feedback resistor R2. Further, the gate of the MOS transistor M1 Even if the light receiving power received by the light receiving element is increased by using the feedback type amplifier 2 configured to feed back the output voltage of the preamplifier circuit to the base (in the case of a bipolar transistor), the preamplification is performed. A technique has been proposed in which the gain of the feedback amplifier 2 is adjusted so as to keep the duty ratio of the output signal waveform of the circuit substantially constant (see, for example, Patent Document 1 and Patent Document 2).
JP 2006-148651 A JP 2005-223638 A

However, in the conventional feedback amplifiers 1 and 2, since the feedback resistors R1 and R2 are made variable, there is a problem that the stability of the amplification operation of the feedback amplifiers 1 and 2 is impaired.
More specifically, as shown in FIG. 9, due to the difference between the resistance values of the feedback resistors R1 and R2 and the ideal resistance value that stabilizes the phase, the parasitic capacitance around the feedback resistors R1 and R2, and the like. In the feedback amplifiers 1 and 2, compared with a general feedback amplifier, the group delay becomes large in the high frequency region, and the amplification operation becomes unstable.
The present invention has been made in view of the above-described circumstances, and provides an amplifying apparatus and an optical receiving apparatus capable of high-speed response and capable of performing stable gain adjustment over a wide frequency band. Objective.

  In order to achieve the above object, the present invention outputs a light reception signal having a current value corresponding to a light reception power, a light receiving element capable of controlling the current value, and a light receiving signal output from the light receiving element with a constant gain. An amplifier device comprising: an amplifier that amplifies and outputs the signal; and a control circuit that controls a current value output from the light receiving element based on a voltage of a signal output from the amplifier.

According to this configuration, the current value output from the light receiving element is controlled by the control circuit based on the voltage of the signal obtained by amplifying the current value output from the light receiving element with a constant gain. As a result, the current value output from the light receiving element is feedback-controlled, and the current value can be kept constant and the voltage of the signal output from the amplifier can be maintained at a predetermined value regardless of the magnitude of the received light power. It becomes.
In other words, since there is no need to adjust the gain with a feedback amplifier using a variable resistor as a feedback resistor as in the prior art, the operation of the amplifier does not become unstable in a high-frequency region, and it can be performed at high speed and in a wide frequency band. Gain adjustment over a wide range.

According to the present invention, in the above invention, the control circuit detects a voltage value of a signal output from the amplifier, and a reverse applied to the light receiving element according to the voltage value detected by the voltage detection circuit. And a reverse bias voltage variable circuit that varies the bias voltage.
According to this configuration, the reverse bias voltage applied to the light receiving element is varied according to the output voltage of the amplifier. Thereby, the conversion efficiency of the light receiving element is varied, and the current output from the light receiving element can be easily controlled.

In the invention described above, the amplifier is a feedback amplifier including a feedback resistor having a fixed resistance value.
According to this configuration, a stable amplification operation is realized over a wide frequency band.

In order to achieve the above object, the present invention outputs a light reception signal having a current value corresponding to the light reception power, a light receiving element capable of controlling the current value, and a light receiving signal output from the light receiving element. An amplifier that amplifies and outputs with a gain; and a control circuit that controls a current value output from the light receiving element based on a voltage of a signal output from the amplifier, and outputs a digital signal based on the signal output from the amplifier. An optical receiver characterized by demodulating is provided.
According to this configuration, it is possible to realize an optical receiving apparatus that can change a gain at high speed with respect to fluctuations in received optical power and can stably demodulate and output a received signal over a wide frequency band.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration of an optical receiving device 10 according to the present embodiment.
The optical receiver 10 receives an optical signal transmitted from the optical transmitter on the transmission side, demodulates it into a digital signal, and outputs it.
That is, the optical receiver 10 receives and receives the received light, performs optical-electrical conversion, outputs the light reception signal Iin corresponding to the light reception power, and amplifies the light reception signal Iin output from the photodiode 11 by amplification. The preamplifier circuit 12 that outputs the signal Va, the reference voltage generator circuit 13 that generates the reference voltage Vref, the voltage of the amplified signal Va amplified by the preamplifier circuit 12 is compared with the reference voltage Vref, and the amplified signal Va A comparator that demodulates the digital signal Ds by outputting a high level signal when the voltage is equal to or higher than the reference voltage Vref, and outputting a low level signal when the voltage of the amplified signal Va is less than the reference voltage Vref. Comparator 14.

  More specifically, the preamplifier circuit 12 has a feedback amplifier 15 and a reverse bias voltage control circuit 16, and the photodiode 11 has its anode terminal 110 connected to the output side of the reverse bias voltage control circuit 16. The cathode terminal 111 is connected to the input side of the preamplifier circuit 12, and when an optical signal is received, the optical signal is photoelectrically converted into an electrical signal, and a received light signal Iin having a current level corresponding to the received light power. Is output. The optical signal incident on the photodiode 11 is a signal modulated on the transmission side so that the high level state and the low level state can be averaged at the same ratio.

  As shown in FIG. 2, the feedback amplifier 15 is a negative feedback type amplifier having an amplifier A15 and a feedback resistor R15 for returning a part of the output of the amplifier A15 to an input (inverted input). It operates as a current-voltage conversion circuit that outputs an output signal Vout having a voltage corresponding to the current level. Here, a resistance element having a fixed resistance value is used as the feedback resistor R15 of the feedback amplifier 15. Therefore, the transimpedance gain of the feedback amplifier 15 is constant, and the voltage of the output signal Vout is proportional to the current level of the light reception signal Iin.

  The preamplifier circuit 12 is provided with an amplifier (not shown) that further amplifies the output signal Vout of the feedback amplifier 15 at the subsequent stage of the feedback amplifier 15, and the preamplifier circuit 12 reaches a predetermined voltage level. The amplified signal Va amplified (amplified with a predetermined gain) is input to the comparator 14.

Based on the output signal Vout of the feedback amplifier 15, the reverse bias voltage control circuit 16 maintains the current level of the light reception signal Iin output from the photodiode 11, that is, the potential of the anode terminal 110 of the photodiode 11, that is, This is a circuit for feedback-controlling the reverse bias voltage applied to the photodiode 11, and includes a peak hold circuit 160 and a level converter 161.
The amplifying apparatus includes the reverse bias voltage control circuit 16, the feedback amplifier 15, and the photodiode 11, and adjusts the gain at a high speed according to the fluctuation of the received light power and keeps the voltage of the output signal Vout substantially constant. 100 is configured.

FIG. 3 is a circuit diagram showing a specific configuration of the reverse bias voltage control circuit 16.
The peak hold circuit 160 includes an amplifier A160, a diode D160, a hold capacitor C160, and an N-type MOS transistor M160.
More specifically, the amplifier A160 operates as a comparator, and the output signal Vout of the feedback amplifier 15 is input to its non-inverting input, and a part of the output signal Vp of the amplifier A160 is input to its inverting input. An output signal Vp having a voltage corresponding to the difference between Vout and the output signal Vp is output.

The diode D160 functions as a half-wave rectifier circuit, its anode terminal is connected to the output of the amplifier A160, its cathode terminal is connected to one end of the capacitor C160, and the potential of the output signal Vp of the amplifier A160 is held by the hold capacitor C160. To give. The other end of the hold capacitor C160 is held at the ground potential.
Thereby, the Hall capacitor C160 is charged until the potential difference between both ends of the Hall capacitor C160 becomes equal to the potential of the output signal Vout of the amplifier A160, that is, until the potential at the node N1 at the output end of the amplifier A160 becomes equal to the potential of the output signal Vout. Is done.
The node N1 is connected to the input terminal of the level converter 161, and the potential of the node N1 is input to the level converter 161.

  The MOS transistor M160 is a circuit that resets the potential at the node N1 at the output end of the amplifier A160 to the ground potential, the drain is connected to the node N1, the source is grounded, and the gate is connected to the reset terminal T160. Yes. The reset terminal T160 receives an H level reset signal from a control circuit (not shown) at regular intervals, and the node N1 is grounded by the MOS transistor M160 each time the reset signal is input, and the potential is set to the ground potential. Reset to. As the potential of the node N1 is reset, the potential difference of the hold capacitor C160 is also reset to the ground potential.

  The level converter 161 is a circuit that outputs a reverse bias voltage signal Vb having a voltage corresponding to the voltage of the output signal Vp of the peak hold circuit 160 and applies the reverse bias voltage signal Vb to the anode terminal 110 of the photodiode 11. More specifically, the level converter 161 includes an amplifier A161 that operates as a voltage level converter. The amplifier A161 generates the reverse bias voltage signal Vb having a lower potential as the potential of the output signal Vp of the peak hold circuit 160 is higher.

FIG. 4 is a diagram showing the relationship between the conversion efficiency η of the photodiode 11 and the reverse bias voltage Vc.
The conversion efficiency η of the photodiode 11, that is, the output current (A) with respect to the received light power (W) depends on the reverse bias voltage Vc that is the anode potential with respect to the cathode potential, and is proportional to the reverse bias voltage Vc. Thus, the conversion efficiency η increases, and when the reverse bias voltage Vc exceeds a certain voltage Vh, the conversion efficiency η is saturated.

In the range where the conversion efficiency η of the photodiode 11 is proportional to the reverse bias voltage Vc, when the received light power is P, the current level of the received light signal Iin output from the photodiode 11 is Ain, and the proportionality coefficient is α, The relationship 1) holds.
Current level Ain = proportional coefficient α × reverse bias voltage Vc × light receiving power P (1)
Here, since the voltage level of the output signal Vout of the feedback amplifier 15 is Av × Ain when the transimpedance gain of the feedback amplifier 15 is Av, the above equation (1) is expressed as the following equation (2). be able to.
Voltage of output signal Vout = gain Av × proportional coefficient α × reverse bias voltage Vc × light receiving power P (2)

  Therefore, when the voltage of the output signal Vout of the feedback amplifier 15 increases, the voltage of the output signal Vout of the feedback amplifier 15 decreases by decreasing the reverse bias voltage Vc, and when the voltage of the output signal Vout decreases. Since the voltage of the output signal Vout of the feedback amplifier 15 increases by increasing the reverse bias voltage Vc, the output signal Vout is held constant by controlling the reverse bias voltage Vc regardless of the magnitude of the received light power P. It becomes possible.

  Therefore, when the voltage of the output signal Vp of the peak hold circuit 160 fluctuates, that is, when the voltage level of the output signal Vout of the feedback amplifier 15 fluctuates, the level converter 161 is based on the above equation (2). Then, a reverse bias voltage signal Vb having a voltage for maintaining the output signal Vout of the feedback amplifier 15 (the output signal Vp of the peak hold circuit 160) at a predetermined voltage value is generated and applied to the anode terminal 110 of the photodiode 11.

Next, the operation of the embodiment having such a configuration will be described.
Assuming that the photodiode 11 receives the signal light transmitted on the transmission side, the photodiode 11 converts the received light signal Iin having the current level Ain based on the above equation (1) into the feedback amplifier of the preamplifier circuit 12. 15 is output. As a result, an output signal Vout having a voltage indicated by transimpedance gain Av × current level Ain is output from the feedback amplifier 15, and this output signal Vout is input to the subsequent amplifier and the reverse bias voltage control circuit 16.
In the reverse bias voltage control circuit 16, the peak voltage of the output signal Vout of the feedback amplifier 15 is detected by the peak hold circuit 160 and output to the level converter 161 as the output signal Vp. The level converter 161 responds to the output signal Vp. The reverse bias voltage signal Vb is generated and applied to the anode terminal 110 of the photodiode 11.

  At this time, as shown in FIG. 5, when the received light power P increases at the timing t1, the voltage of the output signal Vp of the peak hold circuit 160 increases accordingly. In this case, the level converter 161 generates a reverse bias voltage signal Vb in which the voltage is reduced based on the above equation (2) so as to lower the output signal Vp to a predetermined voltage value, and is applied to the anode terminal 110 of the photodiode 11. As a result, the current level Ain of the light reception signal Iin output from the photodiode 11 is kept constant by the trade-off with the conversion efficiency η of the photodiode 11 and is output from the feedback amplifier 15. The voltage of the output signal Vout is also kept constant.

As described above, according to the present embodiment, the reverse bias voltage control circuit 16 controls the reverse bias voltage Vc applied to the photodiode 11, and the light reception signal Iin output from the photodiode 11 regardless of the magnitude of the light reception power P. In order to keep the current level Ain constant, the voltage of the output signal Vout output from the feedback amplifier 15 can be kept constant without adjusting the gain by a feedback amplifier using a variable resistor as a feedback resistor.
As a result, the operation of the amplifier does not become unstable in the high frequency region, and gain adjustment can be performed at high speed over a wide frequency band. As a result, it is possible to satisfactorily receive a high-speed digital signal Ds in a wide dynamic range of received light power.

Further, according to the present embodiment, the gain is adjusted by controlling the reverse bias voltage Vc of the photodiode 11, so that the gain adjustment is realized with a simple circuit configuration.
In particular, in a conventional feedback amplifier, it is necessary to design an analog circuit for phase compensation in a high frequency region. However, according to the present embodiment, such a design is not necessary, and design rework is reduced. It also leads to.
It should be noted that the above-described embodiment is merely an aspect of the present invention, and can be arbitrarily modified and applied within the scope of the present invention.

It is a block diagram which shows the structure of the optical receiver which concerns on embodiment of this invention. It is a block diagram which shows the structure of a preamplifier circuit. It is a circuit diagram which shows the specific structure of a preamplifier circuit. It is a figure which shows the relationship between the conversion efficiency of a photodiode, and a reverse bias voltage. It is a timing chart which shows operation | movement of an optical receiver. It is a figure which shows the group delay characteristic of an amplifier and a feedback type amplifier. It is a circuit diagram which shows the structure of the feedback type amplifier with which the conventional optical receiver is equipped. It is a circuit diagram which shows the structure of the feedback type amplifier with which the conventional optical receiver is equipped. It is a figure which shows the group delay characteristic of the feedback type amplifier with which the conventional optical receiver is equipped.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical receiver, 11 ... Photodiode (light receiving element), 12 ... Preamplifier circuit, 15 ... Feedback amplifier (amplifier), 16 ... Reverse bias voltage control circuit (control circuit), 100 ... Amplifier, 160 ... Peak Hold circuit (voltage detection circuit) 161... Level converter (reverse bias voltage variable circuit), Iin... Light reception signal, P.

Claims (4)

A light receiving element that outputs a light receiving signal having a current value corresponding to the light receiving power, and that can control the current value;
An amplifier that amplifies and outputs a light reception signal output by the light receiving element with a constant gain;
And a control circuit that controls a current value output from the light receiving element based on a voltage of a signal output from the amplifier. The amplification device according to claim 1,
The control circuit includes:
A voltage detection circuit for detecting a voltage value of a signal output from the amplifier;
An amplifying apparatus comprising: a reverse bias voltage variable circuit that varies a reverse bias voltage applied to the light receiving element in accordance with a voltage value detected by the voltage detection circuit. In the amplification device according to claim 1 or 2,
The amplifier is a feedback type amplifier including a feedback resistor having a fixed resistance value. A light receiving element that outputs a light receiving signal having a current value corresponding to the light receiving power, and that can control the current value;
An amplifier that amplifies and outputs a light reception signal output by the light receiving element with a constant gain;
A control circuit for controlling a current value output from the light receiving element based on a voltage of a signal output from the amplifier;
A digital signal is demodulated based on a signal output from the amplifier.

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