JP2011228588A - Light receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light receiving circuit for suppressing peaking while deterioration of passband width of a damping circuit is suppressed.SOLUTION: The light receiving circuit includes: a first individual damping circuit which is connected between a light receiving element and reference potential and has a series circuit consisting of an inductor element, a resistance element and a capacitor element; a second individual damping circuit which is connected in parallel to the first individual damping circuit between the light receiving element and the reference potential, has a series circuit consisting of an inductor element, a resistance element and a capacitor element, and has a passband different from the first individual damping circuit; and a node which is arranged between the capacitor element and the light receiving element at least in the first or second individual damping circuit and supplies power which reverse biases the light receiving element.

Description

  The present invention relates to a light receiving circuit including a light receiving element.

  An optical receiver is a device that converts light into an electrical signal using a light receiving element. For example, a PIN photodiode can be used as the light receiving element. The light receiving element and another device such as an amplifier may be connected by a bonding wire. In this case, since the bonding wire has an inductance component, it may affect the reception performance. Therefore, Patent Document 1 discloses a technique for suppressing peaking by providing a damping resistor.

Japanese Patent Laid-Open No. 2004-119885

  When the technique of Patent Document 1 is used, the damping resistance value must be increased when the peaking amount is large. However, when the damping resistance value is increased, the pass bandwidth of the damping circuit is deteriorated due to the effect of the frequency characteristic limitation by the damping resistance.

  An object of the present invention is to provide a light receiving circuit capable of suppressing peaking while suppressing deterioration of the pass bandwidth of the damping circuit.

  A light receiving circuit according to the present invention is connected between a light receiving element and a reference potential, and includes a first individual damping circuit including a series circuit including an inductor element, a resistance element, and a capacitor element, the light receiving element, and the reference potential. A second individual damping circuit that is connected in parallel with the first individual damping circuit and includes a series circuit including an inductor element, a resistance element, and a capacitor element, and has a pass band different from that of the first individual damping circuit; A node for supplying a power source that reversely biases the light receiving element, provided between the capacitor element and the light receiving element in at least one of the first and second individual damping circuits. To do. In the light receiving circuit according to the present invention, since the first individual damping circuit and the second individual damping circuit have different pass bands, the peaking is suppressed while suppressing the deterioration of the pass bandwidth of the damping circuit. Can do.

  A node for supplying power to reverse bias the light receiving element may be provided between the capacitor element and the resistance element of either the first individual damping circuit or the second individual damping circuit. A node for supplying power for reverse-biasing the light receiving element may be provided between the capacitor element and the resistance element in both the first individual damping circuit and the second individual damping circuit. An amplifier for converting an input current from the light receiving element into a voltage proportional to the input current may be further provided.

  According to the light receiving circuit of the present invention, peaking can be suppressed while suppressing the deterioration of the pass bandwidth of the damping circuit.

FIG. 3 is a circuit diagram of a light receiving circuit according to the first embodiment. FIG. 5 is a circuit diagram of a light receiving circuit according to a second embodiment. 10 is a diagram for explaining a comparative example 1. FIG. 10 is a diagram for explaining a comparative example 2. FIG. 1 is a diagram for explaining Example 1. FIG.

  Hereinafter, the best mode for carrying out the present invention will be described.

(First embodiment)
FIG. 1 is a circuit diagram of a light receiving circuit 101 according to the first embodiment. As shown in FIG. 1, the light receiving circuit 101 includes a light receiving element 10, a wire 20, a damping circuit 30, and the like. The output side of the light receiving element 10 is connected to one end of the wire 20. The other end of the wire 20 is connected to the ground via another device such as an amplifier. Note that the other end of the wire 20 may be connected to a reference potential. The power supply side of the light receiving element 10 that is the other end of the output side terminal of the light receiving element 10 is connected to one end of the damping circuit 30. The other end of the damping circuit 30 is connected to the ground. Note that the other end of the damping circuit 30 may be connected to a reference potential.

  The damping circuit 30 includes a series circuit (hereinafter referred to as a first individual damping circuit) in which an inductor element 31a, a damping resistor 32a, and a capacitor element 33a are sequentially connected from the light receiving element 10 side, and an inductor element 31b from the light receiving element 10 side. This is a parallel circuit in which a series circuit (hereinafter referred to as a second individual damping circuit) in which the damping resistor 32b and the capacitor element 33b are sequentially connected is connected in parallel. The inductor elements 31a and 31b are bonding wires having an inductance component, for example. The set values of the elements constituting the first individual damping circuit and the second individual damping circuit are set so that the first individual damping circuit and the second individual damping circuit have mutually different pass bands. In the present invention, the pass band refers to a frequency band in a range until the peak value of the OE transfer characteristic of each individual damping circuit is halved.

  Of the desired frequency band, when one individual damping circuit is used, the band whose transfer characteristics deteriorate is supplemented by another individual damping circuit, so that the deterioration of the pass bandwidth of the damping circuit 30 can be suppressed. . As long as the deterioration of transfer characteristics can be suppressed, the passbands of the individual damping circuits may be overlapped or separated from each other as long as the transfer characteristics can be suppressed.

  Positive DC power supply 40 that functions as a power supply for applying a reverse bias to the light receiving element 10 at a node provided between the damping resistor 32a and the capacitor element 33a and between the damping resistor 32b and the capacitor element 33b. Is connected.

  The light receiving element 10 operates upon receiving a drive voltage supplied from the DC power supply 40. As an example, a PIN photodiode can be used for the light receiving element 10. The wire 20 is a wire for connecting the light receiving element 10 and another device such as an amplifier, for example, a bonding wire. As an amplifier in this case, a TIA (transimpedance amplifier) can be used. TIA is an amplifier that converts an input current from the light receiving element 10 into a voltage proportional to the input current.

  The wire 20 has an inductance component. Thereby, a high-frequency signal (for example, a frequency signal in the GHz band) included in the output current of the light receiving element 10 is hindered from being input to other devices such as an amplifier due to the inductance of the wire 20. Specifically, the input impedance from the light receiving element 10 to another device greatly increases at a specific frequency due to the inductance of the wire 20 or the like. As a result, peaking occurs.

  In this embodiment, since the damping resistor 32a and the damping resistor 32b are provided in the damping circuit 30, the input impedance from the light receiving element 10 to another device is suppressed. Thereby, the occurrence of peaking is suppressed. Furthermore, since the first individual damping circuit and the second individual damping circuit have different pass bands, the deterioration of the pass bandwidth of the damping circuit 30 is suppressed. From the above, it is possible to suppress peaking while suppressing deterioration of the pass bandwidth of the damping circuit 30.

In the present embodiment, the DC power supply 40 is connected to both the first individual damping circuit and the second individual damping circuit, but is not limited thereto. The DC power supply 40 may be connected to any one of the individual damping circuits.
However, the combined resistance decreases by connecting the DC power supply 40 between the damping resistors of the plurality of individual damping circuits and the capacitor elements. Thereby, the voltage drop by a damping resistance can be suppressed.

(Second Embodiment)
FIG. 2 is a circuit diagram of the light receiving circuit 102 according to the second embodiment. The light receiving circuit 102 is different from the light receiving circuit 101 in FIG. 1 in that a damping circuit 30 a is provided instead of the damping circuit 30. The damping circuit 30a includes three rows of individual damping circuits. Specifically, the damping circuit 30a further includes a third individual damping circuit in which an inductor element 31c, a damping resistor 32c, and a capacitor element 33c are sequentially connected in series from the light receiving element 10 side.

  In the present embodiment, the set values of the elements constituting the first to third individual damping circuits are set so that the first to third individual damping circuits have different pass bands. Of the desired frequency band, a band whose transfer characteristic is deteriorated by one individual damping circuit is supplemented by another individual damping circuit, so that the deterioration of the pass bandwidth of the damping circuit 30b can be suppressed.

  The DC power source 40 that functions as a power source for the light receiving element 10 is provided between the damping resistor 32a and the capacitor element 33a, between the damping resistor 32b and the capacitor element 33b, and between the damping resistor 32c and the capacitor element 33c. Connected to the other node.

  In the present embodiment, since three individual damping circuits having different pass bands are provided, the pass bandwidth of the damping circuit 30a is expanded. Thus, peaking can be suppressed while suppressing deterioration of the pass bandwidth of the damping circuit 30a. Note that four or more individual damping circuits may be provided.

  When three or more rows of individual damping circuits are provided, a plurality of individual damping circuits having the same passband may be used. When the transfer characteristics in a certain frequency band are more deteriorated, the amount of signal deterioration in that frequency band can be further suppressed by using a plurality of individual damping circuits that pass the signal in the deteriorated frequency band. Degradation of the pass bandwidth can be suppressed.

  In addition, although the DC power supply 40 in each said embodiment uses the positive power supply, a DC power supply may be a negative power supply. In this case, the terminal to which the reverse bias of the light receiving element 10 is applied is the anode, the output side of the light receiving element 10 is the cathode, and the damping circuit and the DC power source 40 are connected to the anode side.

  Hereinafter, a simulation result regarding the characteristics of the light receiving circuit according to each of the above embodiments will be described in comparison with a comparative example.

(Comparative Example 1)
FIG. 3A is a circuit diagram of a light receiving circuit according to Comparative Example 1. As shown in FIG. 3A, unlike the light receiving circuit 101 of FIG. 1, the light receiving circuit according to Comparative Example 1 does not include the second individual damping circuit and does not include the damping resistor 32a. The DC power supply 40 is connected between the inductor element 31a and the capacitor element 33a. The inductance element 34 provided between the inductance element 31a and the capacitor element 33a and between the DC power supply 40 is provided to increase the impedance on the inductance element 31a and capacitor element 33a side as compared with the DC power supply 40. It is assumed that the inductance of the wire 20 is 0.2 nH, the inductance of the inductor element 31 a is 0.1 nH, and the capacitance of the capacitor element 33 a is 100 pF.

  In the light receiving element 10, the parasitic capacitance Cpd is 60 fF, the internal resistance Rpd is 10Ω, the inductance Lpd of the internal wiring is 0.1 nH, and the parasitic capacitance Cpad of the bonding pad to which the light receiving element 10 is connected is 10 fF. Suppose that Further, it is assumed that the wire 20 is grounded via the TIA, and the internal resistance of the TIA is 50Ω.

  FIG. 3B is a diagram illustrating a relationship between the signal frequency included in the output current of the light receiving element 10 and the OE transfer characteristic in the light receiving circuit according to the first comparative example. The OE transfer characteristic is an attenuation ratio of a frequency component photoelectrically converted in the light receiving element 10.

  As shown in FIG. 3B, in Comparative Example 1, peaking exceeding 2 dB occurs in the vicinity of 20 GHz. This is because the input impedance from the light receiving element 10 to the TIA greatly increases in the vicinity of 20 GHz due to the inductance of the wire 20 and the like. Thus, if no damping resistor is provided, peaking occurs at a predetermined frequency.

(Comparative Example 2)
FIG. 4A is a circuit diagram of a light receiving circuit according to Comparative Example 2. As shown in FIG. 4A, the light receiving circuit according to Comparative Example 2 does not include the second individual damping circuit, unlike the light receiving circuit 101 in FIG. The DC power supply 40 is connected between the damping resistor 32a and the capacitor element 33a. It is assumed that the inductance of the wire 20 is 0.2 nH, the inductance of the inductor element 31 a is 0.1 nH, the resistance value of the damping resistor 32 a is 0 to 100Ω, and the capacitance of the capacitor element 33 a is 100 pF.

  In the light receiving element 10, the parasitic capacitance Cpd is 60 fF, the internal resistance Rpd is 10Ω, the inductance of the internal wiring is 0.1 nH, and the parasitic capacitance Cpad of the bonding pad to which the light receiving element 10 is connected is 10 fF. Suppose there is. Further, it is assumed that the wire 20 is grounded via the TIA, and the internal resistance of the TIA is 50Ω.

  FIG. 4B is a diagram showing the relationship between the signal frequency included in the output current of the light receiving element 10 and the OE transfer characteristic in the light receiving circuit according to the comparative example 2. FIG. 4B shows the results when the resistance value of the damping resistor 32a is 0Ω, 5Ω, 10Ω, 25Ω, 50Ω, and 100Ω. As shown in FIG. 4B, peaking occurs when the damping resistance is small. On the other hand, when the damping resistance increases, peaking does not occur, but the OE transfer characteristics deteriorate in the high frequency band. Thus, in Comparative Example 2, it is impossible to suppress both the occurrence of peaking and the deterioration of the OE transfer characteristics.

Example 1
FIG. 5A is a circuit diagram illustrating details of the light receiving circuit according to the first embodiment. The light receiving circuit according to Example 1 is a circuit diagram illustrating details of a light receiving circuit obtained by combining a bypass circuit with the second embodiment illustrated in FIG. 2. The light receiving circuit according to the first embodiment includes a bypass circuit including a capacitor element 33d in addition to the first to third individual damping circuits. The DC power supply 40 is connected to a node provided between the damping resistor 32a and the capacitor element 33a, between the damping resistor 32b and the capacitor element 33b, and between the damping resistor 32c and the capacitor element 33c.

  The inductance of the wire 20 is 0.2 nH, the inductance of the inductor element 31 a is 0.1 nH, the inductance of the inductor element 31 a is 0.2 nH, the inductance of the inductor element 31 b is 0.3 nH, and the inductor element 31 c Is 0.4 nH, the resistance values of the damping resistors 32a to 32c are 40Ω, the capacitance of the capacitor element 33a is 0.1 pF, the capacitance of the capacitor element 33b is 0.8 pF, It is assumed that the capacitance is 100 pF and the capacitance of the capacitor element 33d is 0.22 pF.

  In the light receiving element 10, the parasitic capacitance Cpd is 60 fF, the internal resistance Rpd is 10Ω, the inductance of the internal wiring is 0.1 nH, and the parasitic capacitance Cpad of the bonding pad to which the light receiving element 10 is connected is 10 fF. Suppose there is. Further, it is assumed that the wire 20 is grounded via the TIA, and the internal resistance of the TIA is 50Ω. The cathode current of the light receiving element 10 is represented as Icatode, the current flowing through the first individual damping circuit is represented as Idamping1, the current flowing through the second individual damping circuit is represented as Idamping2, and the current flowing through the third individual damping circuit is represented as Idamping3. The current flowing in the individual damping circuit formed by the capacitor element 33d is expressed as Ibypass.

  FIG. 5B is a diagram illustrating the relationship between Idampings 1 to 3 and Ibypass. In FIG. 5B, the horizontal axis represents the signal frequency (GHz) included in the output current of the light receiving element 10, and the vertical axis represents the current (dBA). As shown in FIG. 5B, the individual damping circuits formed by the first to third individual damping circuits and the capacitor element 33d have different passbands. Thereby, the pass band of the damping circuit is expanded.

  FIG. 5C is a diagram illustrating a relationship between the signal frequency included in the output current of the light receiving element 10 and the OE transfer characteristic in the light receiving circuit according to the second embodiment. FIG.5 (c) shows the result of the comparative example 1 and the comparative example 2 collectively. As shown in FIG. 5C, in the first embodiment, the pass bandwidth is improved. This is because the number of individual damping circuits having different passbands increases, so that the band whose transfer characteristics deteriorate when one individual damping circuit is used is compensated by another individual damping circuit, and the passband width is increased. Because it was enlarged.

  From the above, it was proved that peaking can be suppressed while suppressing deterioration of the pass bandwidth of the damping circuit by connecting in parallel individual damping circuits having different pass bands.

  It should be noted that the present invention is not limited to such specific embodiments and examples, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

DESCRIPTION OF SYMBOLS 10 Light receiving element 20 Wire 30 Damping circuit 31 Inductor element 32 Damping resistance 33 Capacitor element 40 DC power supply 101-103 Light receiving circuit

Claims (4)

A first individual damping circuit that is connected between the light receiving element and the reference potential and includes a series circuit including an inductor element, a resistor element, and a capacitor element;
A series circuit including an inductor element, a resistor element, and a capacitor element is connected in parallel with the first individual damping circuit between the light receiving element and the reference potential, and has a pass band different from that of the first individual damping circuit. A second individual damping circuit comprising:
A node for supplying a power source that reversely biases the light receiving element, provided between the capacitor element and the light receiving element in at least one of the first and second individual damping circuits. The light receiving circuit.   The node for supplying power for reverse-biasing the light receiving element is provided between the capacitor element and the resistance element of either the first individual damping circuit or the second individual damping circuit. 1. A light receiving circuit according to 1.   The node for supplying power to reverse bias the light receiving element is provided between the capacitor element and the resistance element in both the first individual damping circuit and the second individual damping circuit. The light receiving circuit according to 2.   The light receiving circuit according to claim 1, further comprising an amplifier that converts an input current from the light receiving element into a voltage proportional to the input current.

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