JP2009033378A - Optical receiver - Google Patents

Abstract

An optical receiver capable of miniaturization while preventing band degradation of a parallel feedback differential amplifier circuit unit is provided.
An optical receiver includes a photodiode that is a light receiving element unit that receives an optical signal, and a differential of a parallel feedback type differential amplifier circuit unit that outputs the output of the photodiode as one input (IN1). The amplifier unit 3 a and the distributed constant circuit unit 4 provided at the other input (IN 2) of the differential amplifier unit 3 a and having an impedance approximate to that of the photodiode 2 are provided. The distributed constant circuit unit 4 includes an initial stage part 4a and a multi-stage part 4b cascade-connected to the initial stage part 4a by one or more. The first stage portion 4a includes a capacitor C1, and one of the capacitors C1 is connected to the input IN2, and the other is grounded. The multistage portion 4b includes a resistor R4 and a capacitor C1, and one end of the capacitor C1 is connected to the first stage portion 4a via the resistor R3, and the other is grounded.
[Selection] Figure 1

Description

  The present invention relates to an optical receiver having a parallel feedback differential amplifier circuit that amplifies a signal from a light receiving element.

  There is a parallel optical receiver described in Patent Document 1 as a conventional optical receiver. The parallel optical receiver described in Patent Document 1 includes a receiving photodiode that receives an optical signal at one input of a parallel feedback type differential amplifier circuit unit, and a dummy photodiode that does not receive light at the other input. The two photodiodes are formed monolithically and have the same bias condition.

As described above, the receiving photodiode and the dummy photodiode are input to the parallel feedback type differential amplifier circuit unit, so that the differential input capacitance of the parallel feedback type differential amplifier circuit unit can be matched. Therefore, it is possible to prevent deterioration of the band characteristics at high frequencies.
JP 2000-68551 A

  However, when a dummy photodiode is formed in order to prevent the bandwidth degradation of the parallel feedback differential amplifier circuit portion as in the parallel optical receiver described in Patent Document 1, the area occupied by this photodiode on the integrated circuit Is large, the entire integrated circuit becomes large, which is an obstacle to downsizing.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical receiver that can be downsized while preventing band degradation of a parallel feedback differential amplifier circuit.

  The optical receiver according to the present invention includes a light receiving element unit that receives an optical signal, a parallel feedback differential amplifier circuit unit that receives the output of the light receiving element unit as one input, and the parallel feedback differential amplifier circuit unit. And a distributed constant circuit section provided at an input and having an impedance approximate to the light receiving element section.

  In the present invention, the light receiving element portion provided at one input of the parallel feedback differential amplifier circuit portion can be matched with the differential input capacitance, and the occupied area in the integrated circuit can be reduced. It is possible to reduce the size of the feedback differential amplifier circuit unit while preventing the deterioration of the bandwidth.

  The first invention of the present application includes a light receiving element unit that receives an optical signal, a parallel feedback differential amplifier unit that receives the output of the light receiving element unit as one input, and other inputs of the parallel feedback differential amplifier unit. And a distributed constant circuit portion having an impedance approximate to that of the light receiving element portion.

  Since the optical receiver of the present invention is provided with a distributed constant circuit section having an impedance approximate to the light receiving element section at the other input of the parallel feedback differential amplifier section, the parallel feedback differential amplifier section The light receiving element portion provided at one input can be matched with the differential input capacitance. Accordingly, it is possible to prevent the parallel feedback type differential amplifier circuit section from being greatly deteriorated in bandwidth due to mismatch of input capacitance. Further, the distributed constant circuit portion can be formed of only passive elements, and it is not necessary to receive light like a dummy photodiode, so that the area occupied in the integrated circuit can be reduced.

  The second invention of the present application is characterized in that the distributed constant circuit portion is formed by cascading one or more multi-stage portions having a capacitor grounded through a resistor to a first stage portion having the capacitor grounded.

  In the second invention of the present application, since the distributed constant circuit portion is cascade-connected to the first stage portion where the capacitor is grounded and one or more multistage portions where the capacitor is grounded via a resistor, a monolithic integrated circuit is formed. Sometimes it can be formed easily.

(Embodiment)
An optical receiver according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining a configuration of an optical receiving apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, the optical receiver 1 according to the embodiment of the present invention is an integrated circuit and is a front-stage amplifier circuit of a front monitor.

  The optical receiver 1 includes a photodiode 2 that is a light receiving element portion, a parallel feedback differential amplifier circuit portion 3, and a distributed constant circuit portion 4.

  The photodiode 2 has a photoelectric conversion function of receiving an optical signal and converting it into an electrical signal. The photodiode 2 has a cathode connected to the parallel feedback differential amplifier circuit 3 and an anode grounded.

  The parallel feedback differential amplifier circuit section 3 includes a differential amplifier section 3a and negative feedback resistors R1 and R2. In the parallel feedback type differential amplifier circuit unit 3, a cathode of the photodiode 2 is connected to an input IN1 which is one input of the differential amplifier unit 3a, and a negative feedback resistor R1 is connected.

  Further, the distributed constant circuit unit 4 is connected to the input IN2 which is the other input of the differential amplifier unit 3a, and the negative feedback resistor R2 is connected thereto.

  The negative feedback resistor R1 is connected to an output OUT1 that is one output of the differential amplifier section 3a. The negative feedback resistor R2 is connected to an output OUT2 that is another output of the differential amplifier section 3a. Of course, even if the parallel feedback type differential amplifier circuit unit 3 is a negative feedback type amplifier circuit or a non-inverting amplifier circuit, a similar amplifier circuit unit can be configured.

  The distributed constant circuit section 4 includes an initial stage section 4a and a multistage section 4b that is cascade-connected to the first stage section 4a. In the present embodiment, it is assumed that three stages 4b are connected to the first stage 4a.

  The first stage portion 4a includes a capacitor C1 and a resistor R4. A resistor R4 connected in series to the capacitor C1 is connected to the input IN2, and the capacitor C1 is grounded. The multistage portion 4b includes resistors R3 and R4 and a capacitor C1. The resistor R4 directly connected to the capacitor C1 via the resistor R3 is connected to the initial stage portion 4a, and the capacitor C1 is grounded.

  Although the distributed constant circuit section 4 is configured with a capacitor C1 and resistors R3 and R4 in a distributed constant circuit configuration, the characteristics of the photodiode 2 cannot be made the same as when a dummy photodiode is mounted. Since the impedance of the photodiode 2 can be approximated, it is possible to approximate the input capacitance sufficient to prevent the deterioration of the band characteristics at the high frequency of the differential amplifier section 3a.

  Therefore, the distributed constant circuit section 4 can be more approximate to the characteristics of the photodiode 2 as the multistage section 4b is cascade-connected to the first stage section 4a.

  However, since the proportion of the area occupied by the front monitor increases as the number of multi-stage portions 4b is increased, the first-stage portion 4a is provided with three multi-stage portions 4b in the present embodiment.

  As described above, the optical receiver 1 according to the present embodiment uses the distributed constant circuit unit 4 including the capacitor C1 and the resistor R4 instead of the dummy photodiode, thereby reducing the area of the dummy photodiode. The distributed constant circuit portion 4 can be formed with an area of 1/20 to 1/30. Therefore, downsizing is possible.

  A state where the distributed constant circuit portion 4 is formed on the wafer will be described with reference to FIG. FIG. 2 is a diagram showing a state in which the distributed constant circuit unit 4 shown in FIG. 1 is formed on the wafer. For example, if the photodiode 2 shown in FIG. 1 is formed in a rectangular shape, the distributed constant circuit portion 4 formed on the wafer has a rectangular region arranged along the wiring L1 as shown in FIG. It is desirable to be. In this rectangular region, the width W is formed to be equal, and the wiring L1 is arranged on one end side. By arranging the wiring L1 on one end side, the wiring resistance between the respective regions (between AB, BC, and CD) becomes the resistance R3, and the capacitance for the wiring L1 between AB, BC, and CD is a capacitor. C1. The capacitor C1 connected to the wiring L1 is connected in series as an internal resistance of the photodiode region where the resistor R4 is divided. Thus, by forming the distributed constant circuit section 4 with the resistors R3 and R4 and the capacitor C1, it is possible to approximate the impedance of the photodiode 2 more.

  If the photodiode is formed in a circular shape, it is desirable that the distributed constant circuit portion formed on the wafer has concentric circular regions. An optical receiver in such a case will be described with reference to FIGS. FIG. 3 is a diagram for explaining the configuration of an optical receiver according to another embodiment of the present invention. FIG. 4 is a diagram showing a state in which the distributed constant circuit portion shown in FIG. 3 is formed on the wafer. In FIG. 3, the same components as those in FIG.

  As shown in FIG. 3, an optical receiver 10 according to another embodiment of the present invention includes, as a distributed constant circuit unit 11, an initial stage unit 11a and a multistage unit 11b cascade-connected to one or more initial stage units 11a. It has.

  As shown in FIG. 4, the distributed constant circuit portion 11 formed on the wafer when the photodiode 2 is formed in a circular shape has concentric circular regions partitioned by wires L2 to L5 at equal intervals in the radial direction. Connection is made by wiring L6.

  By forming the distributed constant circuit portion 11 concentrically, the capacitor C14 has a circular area capacitance with a radius from the middle position between a and bc, the resistor R44 is a resistance of this circular area, and the resistor R33. Is a line-to-line resistance between ab of the wiring L6 and up to an intermediate position between bc. Further, the capacitor C13 has a capacitance of a donut shape region from the middle between bc to the middle position between cd, the resistor R43 becomes a resistance in this region, and the resistor R32 has a middle from bc to the middle position between cd. It becomes the line-to-line resistance. In this way, the resistors R31 to R33, R41 to R44 and the capacitors C11 to C14 can be defined sequentially.

  In this way, by forming the distributed constant circuit section 11 with the capacitors C11 to C14, the resistors R31 to R33, and the resistors R41 to R43, the impedance of the photodiode 2 can be approximated.

  The present invention is suitable for an optical receiver having a parallel feedback type differential amplifier circuit unit that amplifies a signal from a light receiving element, since the size of the parallel feedback type differential amplifier circuit unit can be reduced while preventing the deterioration of the bandwidth of the parallel feedback type differential amplifier circuit unit. is there.

The figure explaining the structure of the optical receiver which concerns on embodiment of this invention The figure which shows the state which formed the distributed constant circuit part shown in FIG. 1 on the wafer The figure explaining the structure of the optical receiver which concerns on other embodiment of this invention. The figure which shows the state which formed the distributed constant circuit part shown in FIG. 3 on the wafer

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,10 Optical receiver 2 Photodiode 3 Parallel feedback type differential amplifier circuit part 3a Differential amplifier part 4,11 Distributed constant circuit part 4a, 11a Initial stage part 4b, 11b Multistage part R1-R4, R31-R33, R41- R44 Resistor C1, C11 to C14 Capacitor IN1, IN2 Input OUT1, OUT2 Output

Claims (2)

A light receiving element for receiving an optical signal;
A parallel feedback type differential amplifier circuit unit having the output of the light receiving element unit as one input;
An optical receiving apparatus comprising: a distributed constant circuit unit provided at another input of the parallel feedback differential amplifier circuit unit and having an impedance approximate to the light receiving element unit. 2. The optical receiver according to claim 1, wherein the distributed constant circuit unit is formed by cascading one or more multi-stage units having a capacitor grounded through a resistor to a first stage unit having a capacitor grounded.

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