JP2004254125A - Light receiving module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light receiving module in which ground potential of a preamplifier is stabilized. <P>SOLUTION: The light receiving module 1 has a stem 2, a die cap capacitor 9 is provided on the stem 2 and a light receiving element 10 which receives an optical signal and converts it into an electric signal is loaded on the top surface of the die cap capacitor 9. In addition, the preamplifier 22 which amplifies the output signal of the light receiving element 10 is provided on the stem 2 and adjacent to the die cap capacitor 9. Furthermore, pole parts 25 for ground are erected on both sides of the die cap capacitor 9 on the stem 2. A signal input pad 29 of the preamplifier 22 is electrically connected with an electrode 12 of the light receiving element 10 via a boding wire 37, each ground pad 32 of the preamplifier 22 is electrically connected and grounded with each pole part 25 for ground via a bonding wire 40. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical receiving module for performing optical communication.
[0002]
[Prior art]
As a conventional optical receiving module, for example, a module described in Patent Document 1 is known. The optical receiving module described in this document has a light receiving element that converts an optical signal into an electric signal, and a preamplifier that amplifies an output signal of the light receiving element, and these components are mounted on a TO package.
[0003]
[Patent Document 1]
JP-A-8-139342
[Problems to be solved by the invention]
When a high-speed signal up to the GHz band is handled as an optical signal, the light receiving element and the preamplifier need to be arranged close to each other. In this case, the ground pad of the preamplifier and the TO package, which is the ground potential, are connected. It becomes difficult to secure a space for disposing a bonding wire therebetween. For this reason, a bonding wire connecting the ground pad of the preamplifier and the TO package must be routed and disposed, and the bonding wire becomes longer. When the wire length is increased as described above, the inductance component existing in the bonding wire increases, so that the impedance of the bonding wire increases. As a result, the ground potential of the preamplifier becomes unstable, and the frequency characteristics may deteriorate.
[0005]
An object of the present invention is to provide an optical receiving module that can stabilize the ground potential of a preamplifier.
[0006]
[Means for Solving the Problems]
An optical receiving module according to the present invention includes a metal stem, a light receiving element provided on the stem, for receiving an optical signal and converting the signal into an electric signal, and a preamplifier provided on the stem for amplifying an output signal of the light receiving element. And a metal grounding post provided on the stem so as to be electrically connected to the stem, wherein the grounding post and the preamplifier are electrically connected. It is.
[0007]
By providing the grounding pillar on the stem in this way, the preamplifier is electrically connected to the stem and grounded simply by directly connecting the preamplifier and the grounding pillar with, for example, a bonding wire. Therefore, the ground bonding wire for connecting the preamplifier to the ground potential (stem) is shortened as a whole. Accordingly, since the inductance existing in the bonding wire for grounding is reduced, the impedance of the bonding wire for grounding becomes low, for example, when transmitting a high-frequency signal in the GHz band. As a result, the ground potential of the preamplifier is almost equal to the potential of the stem and is stabilized. As a result, transmission can be performed with the signal waveform kept good.
[0008]
Preferably, the light receiving element is disposed at the center of the stem, and the grounding pillars are disposed on both sides of the light receiving element. In this case, ground bonding wires are provided on both sides of the signal bonding wire for inputting the output signal of the light receiving element to the preamplifier. For this reason, the impedance of the signal line is reduced, so that the signal waveform can be better maintained.
[0009]
Preferably, the preamplifier has a signal input pad and a ground pad disposed adjacent to the signal input pad, and the signal input pad and the light receiving element are electrically connected via a first bonding wire. The ground pad and the ground post are electrically connected via a second bonding wire. Thus, the electrical connection between the light receiving element and the preamplifier and the electrical connection between the grounding pillar and the preamplifier can be easily and reliably performed.
[0010]
Further, preferably, the stem and the grounding pillar are formed of Kovar. Kovar is a common package material and has good high-frequency characteristics.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an optical receiving module according to the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a plan view showing an embodiment of the optical receiving module according to the present invention, and FIG. 2 is a vertical sectional view of the optical receiving module shown in FIG. FIG. 3 is a circuit diagram of the optical receiving module shown in FIG.
[0013]
In each of the drawings, an optical receiving module 1 of the present embodiment has a substantially circular stem 2 made of Kovar, and a plurality of (here, five) lead pins 3 to 7 are provided on the stem 2. ing. The lead pin 3 is a pin for setting the stem 2 to the ground potential, and is fixed to the back surface of the stem 2 at the center of the stem 2. The lead pins 4 and 5 are pins for supplying a power supply voltage, and the lead pins 6 and 7 are pins for outputting an electric signal. These lead pins 4 to 7 penetrate the stem 2 and are fixed to the stem 2 via the insulating glass 8. Although not shown, a lid having a spherical lens at the center is attached to the stem 2.
[0014]
A die cap capacitor (parallel plate capacitor) 9 is provided on the stem 2, and a light receiving element 10 is mounted on an upper surface of the die cap capacitor 9. The light receiving element 10 is a semiconductor element that receives an optical signal emitted from an optical fiber (not shown) disposed above the optical receiving module 1 and converts the optical signal into an electric signal. The die cap capacitor 9 is arranged so that the light receiving element 10 is located at the center of the stem 2. Thus, the light emitted from the optical fiber is efficiently incident on the light receiving element 10 via the spherical lens (described above).
[0015]
The light receiving element 10 has a photodiode 11 as shown in FIGS. 3 and 4. The anode of the photodiode 11 is connected to the electrode 12, and the cathode of the photodiode 11 is connected to the electrode 13. The cathode of the photodiode 11 is connected to an electrode 15 via a resistor 14, and a diode 16 is connected in parallel to both ends of the resistor 14.
[0016]
The electrode 15 is electrically connected to the lead pin 4 via bonding wires 17 and 18 and an upper electrode of a die cap capacitor 19 provided on the stem 2. As a result, the power supply voltage from the lead pin 4 is applied to the light receiving element 10.
[0017]
The lower electrode of the die cap capacitor 19 is electrically connected to the stem 2 and is grounded. As a result, the die cap capacitor 19 functions as a coupling capacitor for the power applied to the light receiving element 10.
[0018]
The upper surface electrode of the die cap capacitor 9 on which the light receiving element 10 is mounted is electrically connected to the electrode 13 of the light receiving element 10 via a bonding wire 20. The lower surface electrode of the die cap capacitor 9 is electrically connected to the stem 2 and is grounded. As a result, the die cap capacitor 9 and the resistor 14 form a CR filter (LPF) circuit, and the light receiving element 10 can realize a stable operation.
[0019]
The upper surface electrode of the die cap capacitor 9 is formed with a groove 21 for stopping the flow of the die bonding material, which is opened on the upper surface. Accordingly, when the die bonding material is applied to the chip mounting area on the upper surface of the die cap capacitor 9 in order to fix the light receiving element 10 on the upper surface of the die cap capacitor 9, the die bonding material flows over the die cap capacitor 9 and spreads. Is prevented. Therefore, wire bonding between the upper surface electrode of the die cap capacitor 9 and the light receiving element 10 can be reliably performed.
[0020]
On the stem 2, on the opposite side of the die cap capacitor 19 with respect to the die cap capacitor 9, a preamplifier 22 is provided so as to be adjacent to the die cap capacitor 9. The preamplifier 22 is an integrated circuit (IC) that amplifies an output signal of the light receiving element 10, and has OP amplifiers 23 and 24 connected in multiple stages as shown in FIG. On the stem 2, on both sides of the die cap capacitor 9, grounding pillars 25 made of Kovar having a rectangular parallelepiped shape are respectively provided upright. Outside the grounding pillars 25, die cap capacitors 26 are provided. , 27 are arranged.
[0021]
As shown in FIGS. 3 and 5, the preamplifier 22 has a power supply pad 28, a signal input pad 29, signal output pads 30, 31, ground pads 32, 33, and an auxiliary pad 34. I have. The power supply pad 28 is electrically connected to the lead pin 5 via the bonding wires 35 and 36 and the upper surface electrode of the die cap capacitor 26. As a result, the power supply voltage from the lead pin 5 is applied to the preamplifier 22.
[0022]
The lower electrode of the die cap capacitor 26 is electrically connected to the stem 2 and is grounded. As a result, the die cap capacitor 26 functions as a coupling capacitor for the power supply applied to the preamplifier 22.
[0023]
The signal input pad 29 is arranged to face the light receiving element 10 and is electrically connected to the electrode 12 of the light receiving element 10 via a bonding wire 37. Thus, the output signal of the light receiving element 10 is input to the signal input pad 29.
[0024]
The signal output pads 30 and 31 are electrically connected to the lead pins 6 and 7 via bonding wires 38 and 39, respectively. The signal output pad 31 outputs a complementary signal whose phase is different from the signal output from the signal output pad 30 by 180 degrees. Thereby, the output signal of the preamplifier 22 is sent to the outside via the lead pins 6 and 7.
[0025]
The ground pads 32 are arranged on both sides of the signal input pad 29, respectively, and form a pseudo coplanar structure. Each ground pad 32 is electrically connected to each ground post 25 via a bonding wire 40 and is grounded. This makes it possible to reduce the impedance of the signal line. The ground pad 33 is directly electrically connected to the stem 2 via a bonding wire 41 and is grounded.
[0026]
The auxiliary pad 34 is electrically connected to an upper electrode of the die cap capacitor 27 via a bonding wire 42. The lower electrode of the die cap capacitor 27 is electrically connected to the stem 2 and is grounded. The die cap capacitor 27 is externally provided to compensate for a capacity shortage of the CR filter circuit (LPF) built in the preamplifier 22.
[0027]
FIG. 6 is a plan view showing one conventional optical receiving module as a comparative example. In the figure, members that are the same as or equivalent to those of the optical receiving module 1 are given the same reference numerals, and descriptions thereof are omitted.
[0028]
In the figure, an optical receiving module 50 has a die cap capacitor 51 provided on a stem 2, and an upper surface electrode of the die cap capacitor 51 is divided into four electrode portions 52 </ b> A to 52 </ b> D. The lower electrode of the die cap capacitor 51 is electrically connected to the stem 2 and is grounded. The light receiving element 10 is mounted on the electrode portion 52B located at the center of the stem 2, and the light receiving element 10 is electrically connected to the electrode portion 52B via the bonding wire 53.
[0029]
The electrode portion 52D at one end of the die cap capacitor 51 is electrically connected to a power supply pad of the preamplifier 22 via a bonding wire 54, and is also electrically connected to the lead pin 5 via a bonding wire 55. . The electrode portion 52D and the lower surface electrode of the die cap capacitor 51 function as a coupling capacitor for a power supply applied to the preamplifier 22.
[0030]
The other two electrode portions 52A and 52C of the die cap capacitor 51 are electrically connected to the ground pads of the preamplifier 22 via bonding wires 56, respectively, and are connected to the stem 2 via bonding wires 57, respectively. It is electrically connected. That is, each of the electrode portions 52A and 52C functions as a relay point of the wiring connecting the ground pad of the preamplifier 22 and the stem 2.
[0031]
However, in such a structure, since the bonding wire for setting the ground pad of the preamplifier 22 to the ground potential becomes longer as a whole, the following problems occur. That is, for example, in a normal bonding wire having a diameter of 30 to 50 μm, it is considered that an inductance of 1 nH per 1 mm in length is parasitically present. This inductance corresponds to an impedance of several Ω for a signal of 1 GHz, so that an impedance of several tens of Ω is generated when a high-speed signal of 10 GHz is handled.
[0032]
In the optical receiving module 50, the ground pad of the preamplifier 22 reaches the die cap capacitor 51 via the bonding wire 56 having an impedance of several Ω, and the connection between the electrode portions 52A and 52C of the die cap capacitor 51 and the lower surface electrode. After taking into account the capacitance between them, it further reaches the stem 2 from the die cap capacitor 51 via the bonding wire 57 having an impedance of several Ω. That is, the configuration is such that the ground pad of the preamplifier 22 reaches the stem 2 through the equivalent circuit of L, C, and L.
[0033]
In this case, the ground pads provided on both sides of the signal input pad of the preamplifier 22 so as to form a coplanar structure do not function effectively in the GHz band, especially in an ultra-high frequency band exceeding the 10 GHz band. turn into. Specifically, the ground potential of the ground pad of the preamplifier 22 becomes unstable due to the impedance of several Ω to several tens Ω present in the bonding wires 56 and 57, so that the operation of the preamplifier 22 also becomes unstable and a good signal waveform is obtained. It becomes difficult to obtain.
[0034]
On the other hand, in the optical receiving module 1 of the present embodiment, the grounding columns 25 are provided on both sides of the die cap capacitor 9 on which the light receiving element 10 is mounted, and the grounding columns 25 and the grounding pads 32 of the preamplifier 22 are connected. Since the connection is made directly by the bonding wire 40, the length of the bonding wire required for grounding the ground pad 32 can be reduced. Therefore, the inductance component of the bonding wire 40 is reduced, and the impedance of the bonding wire 40 is reduced. Further, there is no equivalent circuit of L, C, and L between the ground pad 32 of the preamplifier 22 and the stem 2. As a result, the ground potential of the ground pad 32 can be effectively matched with the potential of the stem 2. Therefore, even in a high-frequency signal band exceeding the 1 GHz band, the operation of the preamplifier 22 is stabilized and the signal waveform is maintained in a good state.
[0035]
Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the grounding pillars 25 are arranged on both sides of the die cap capacitor 9, and each grounding pillar 25 is directly connected to the ground pad 32 of the preamplifier 22 by the bonding wire 40. The number of the grounding pillar portions 25 may be one, or may be three or more. Further, as the metal material of the stem 2 and the grounding pillar 25, in addition to the above-mentioned Kovar, a material in which iron is plated with nickel or a material in which copper is plated with nickel may be used. Further, as a member for electrical connection of each component, a ribbon may be used in addition to the bonding wire.
[0036]
【The invention's effect】
According to the present invention, a metal grounding pillar is provided on the stem so as to be electrically connected to the stem, and the grounding pillar and the preamplifier are electrically connected. The ground potential can be stabilized. This makes it possible to stabilize the operation of the preamplifier and prevent signal oscillation and the like.
[Brief description of the drawings]
FIG. 1 is a plan view showing an embodiment of an optical receiving module according to the present invention.
FIG. 2 is a sectional view taken along line II-II of FIG.
FIG. 3 is a circuit configuration diagram of the optical receiving module shown in FIG. 1;
FIG. 4 is an enlarged plan view of the light receiving element shown in FIG.
FIG. 5 is an enlarged plan view of the preamplifier shown in FIG.
FIG. 6 is a plan view showing one conventional optical receiving module as a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light receiving module, 2 ... Stem, 10 ... Light receiving element, 22 ... Preamplifier, 25 ... Grounding pillar part, 29 ... Signal input pad, 32 ... Grounding pad, 37 ... Bonding wire (first bonding wire), 40 ... Bonding wire (second bonding wire).

Claims (4)

A metal stem,
A light receiving element provided on the stem, for receiving an optical signal and converting it into an electric signal;
A preamplifier provided on the stem and amplifying an output signal of the light receiving element;
A metal grounding pillar provided on the stem so as to be electrically connected to the stem,
An optical receiving module, wherein the ground post and the preamplifier are electrically connected. The light receiving element is disposed at a central portion of the stem,
The optical receiving module according to claim 1, wherein the grounding pillars are respectively arranged on both sides of the light receiving element. The preamplifier has a signal input pad and a ground pad arranged adjacent to the signal input pad,
The signal input pad and the light receiving element are electrically connected via a first bonding wire, and the ground pad and the grounding pillar are electrically connected via a second bonding wire. The optical receiving module according to claim 1 or 2, wherein: The optical receiving module according to any one of claims 1 to 3, wherein the stem and the pillar for grounding are formed of Kovar.

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