JPS61214809A - Hybrid ic optical receiver - Google Patents

Abstract

PURPOSE:To reduce the floating capacity equivalently and to reduce the influence upon a band by dividing and earthing the floating capacity which is parasitic between both ends of a feedback resistance belonging to an amplifier. CONSTITUTION:A case 10 of a hybrid IC optical receiver is closed with a metallic cover 30 whose outline is indicated by a dotted line, and the cover 30 is earthed. Thus, a capacitor is formed between a feedback resistance 26, namely, RL of an amplifier 18 and the cover 30, and this capacitor is distributed through the feedback resistance RL and has one pole earthed. Consequently, when this state is indicated equivalently, a parasitic capacity CL is not inputted in parallel to the feedback resistance RL, and the capacity is divided to an input side CL1 and an output side CL2. As the result, the floating capacity CL is made very small, and the influence upon the band is reduced considerably.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical receiver used for receiving an optical signal and converting it into an electrical signal in optical communications, etc., and particularly relates to a hybrid IC type optical receiver. .

Conventional technology Optical receivers used in optical communications etc. employ various circuit configurations, but high-speed, high-sensitivity optical receivers use a transimpedance receiver circuit as shown in Figure 4. There are many.

In FIG. 4, a light receiving element 1 that receives light such as a laser beam
is connected to the human power of the inverting amplifier 2, and the amplifier 2
A feedback resistor 3 is connected between the 0 input and the output. As the light receiving element 1, a photodiode, a PIN photodiode, an avalanche photodiode, etc. can be used. Then, assuming that the input terminal of the amplifier 2 is 8 and the resistance value of the feedback resistor 3' is R4, the output voltage Vo is expressed as follows.

Vo=-is-Rt...(1) In order to achieve high speed in such a receiving circuit, it is necessary not only that the light-receiving element itself has a high speed that can handle the speed, but also that the receiving circuit has high speed. Bandwidth must be widened. Currently, extremely high-speed light-receiving elements that can handle high-speed operations have been developed. Furthermore, elements constituting the receiving circuits themselves have been developed to be able to cope with high speeds. Therefore, as a problem of the element itself, its high speed can be addressed.

For example, in order to receive a 100 Mb/s NRZ signal, the optical receiving circuit must have a band of approximately 70 MHz (3 dB drop range).
Is required. However, this value increases or decreases depending on the light source, optical fiber, etc. used in combination.

However, when an optical receiving circuit is actually configured, various parasitic capacitances occur, which limit the band.

The factors that limit the band include: 1) the junction capacitance of the photodiode, 2) the input capacitance of the amplifier, the amplification factor, and the band, and 2) the capacitance connected in parallel to the feedback resistor. If these are taken into consideration comprehensively and expressed as an equivalent circuit, the result will be as shown in FIG. On the right side of FIG. 5, Ci, is the sum of the junction capacitance of the photodetector and the input capacitance of the amplifier, CL is the stray capacitance parasitic in parallel with the feedback resistor 3, and -A (s) is This is the frequency characteristic of the amplification factor of the amplifier.

Further, its frequency characteristics are as shown in equation (1).

From this equation (2), the following can be seen. If RL is made smaller, the time constant with CI, . . . , CL becomes smaller, and the band becomes wider. However, if RL is made smaller, the output voltage becomes smaller and the reception sensitivity decreases, as can be seen from equation (1). Therefore, it is desirable to widen the band while keeping the RL large.

Next, regarding C1n, by increasing the absolute value of A (s), it is possible to widen the band even if C1h becomes large. However, in reality, it cannot be expanded without limit.

On the other hand, regarding CL, the band is limited by the time constants of Ct and RL. In other words, in order to keep RL large, Ct needs to be made as small as possible.

For example, if Ci n is 5 pF and A(S), then the gain is 10
0 times, band 5 MHz, Rt = 50Ω, CL = 0
If so, a band of about 20 MHz can be obtained. Here, C
Even if t n is 10 pF, the gain is 2 as A (s).
By increasing the frequency by a factor of 00, a band of approximately 20 MHz can be secured.

However, if CL is 0.5 pF, then 6
The band is about MHz, and this is C1ns.

It cannot be improved by A (s) etc., and in order not to degrade the 20M) Iz band, the capacity must be 0.159 F or less, which is a very strict condition.

As mentioned above, in order to sufficiently widen the frequency band of conventional hybrid IC type optical receivers, the parasitic stray capacitance of the feedback resistor must be kept below 0.15 pF. Very strict conditions were required.

For this reason, conventional efforts have been made to prevent stray capacitance from entering on the input side and output side of the amplifier, that is, on both ends of the feedback resistor.

However, it is difficult to satisfy such conditions, and very strict precision is required, which makes it unsuitable for mass production.

Therefore, the present invention aims to provide a hybrid IC type optical receiver that has sufficient required bandwidth, has a simple configuration, and can be manufactured without requiring strict manufacturing conditions. .

Means for solving the problem, according to the present invention, is a hybrid having a light receiving element and an amplifier having an input connected to the light receiving element, configured in a transimpedance type circuit system, and provided on an insulating substrate. The IC type optical receiver is configured so that the parasitic stray capacitance between both ends of the feedback resistor attached to the amplifier is divided and grounded.

In the hybrid IC type optical receiver having the above configuration, the parasitic stray capacitance between both ends of the feedback resistor between the input and output of the amplifier is divided and grounded. In other words, one of the divided stray capacitances is added to the input capacitance of the amplifier, and the other is added to the output capacitance. Therefore, the capacitance component in parallel with the feedback resistance of the amplifier is equivalently reduced. That is, a hybrid IC type optical receiver having a small CL as described above can be realized and can have a sufficient bandwidth.

EXAMPLES Hereinafter, hybrid I according to the present invention will be described with reference to the accompanying drawings.
An example of a C-type optical receiver will be described.

FIG. 1 is a schematic diagram of a first embodiment of a hybrid IC type optical receiver according to the present invention.

The illustrated hybrid IC type optical receiver has a case 10, and one end of the case 10 is provided with a connector 12 for receiving an optical connector, and a photodiode 14 is arranged in alignment with the connector 12. has been done. Further, a ceramic substrate 16 such as alumina is housed and fixed in the case 10, and wiring patterns, printed elements, etc. are formed on the ceramic substrate 16. Therefore, parts not directly related to the present invention are omitted.

An IC packaged amplifier 18 is mounted on such a ceramic substrate 16.

The input of the amplifier 18 is connected to the photodiode 14 via a conductor pattern 20 formed on the ceramic substrate 16.
is connected to one terminal of the Note that the connection of the other terminal of the photodiode 14 is not shown for the sake of simplification of the drawing.

Another conductor pattern 22 branches off from the conductor pattern 20, and a printed resistor 2 serving as a feedback resistor is attached to the end of the conductor pattern 22.
One end of 6 is connected. A further conductor pattern 28 extends from the other end of the printed resistor 26 to the output of the amplifier 18. Note that the wiring for guiding the output of the amplifier 18 to the outside of the case 10 is also omitted for the sake of simplification of the drawing.

The case 10 of such a hybrid IC type optical receiver is sealed with a metal lid 30 outlined in dotted lines in FIG. 1, while the metal lid 30 is grounded.

The equivalent circuit of the hybrid IC type optical receiver thus constructed is shown in FIG. That is, a capacitor is formed between the feedback resistor 26, that is, RL, and the metal lid 30, and the capacitor is connected to the feedback resistor R.
L is distributed throughout the entire area, and one pole is grounded. Therefore, if the state is shown equivalently, as shown in Figure 2,
The parasitic capacitance CL does not enter parallel to the feedback resistor RL, and the input side C
The capacitance is divided between LI and output side CL2. the result,
The above-mentioned stray capacitance CL becomes extremely small, and its influence on the band is significantly reduced.

In the above embodiment, the stray capacitance CL in parallel with the feedback resistor RL
The divided earthing is realized by making the lid of the case 10 made of metal, but it can also be realized by other methods.

For example, as shown in FIG.
Another conductor pattern 3 is placed on the ceramic substrate 16 between the
2 and ground it. Then, an insulating film 34 is formed on the conductor pattern 32 as shown by the dotted line,
A printed resistor 26 is formed thereon. Further, without providing an insulating film, both ends of the chip resistor are connected to the conductor patterns 24 and 28 by floating from the conductor pattern 32. Note that in FIG. 3, other parts are the same as those in FIG. 1, so illustration of the case 10 and other parts is omitted.

With this configuration, the feedback resistor 26 and the conductor pattern 3
2, and one pole of the capacitor can be grounded, creating a circuit similar to the equivalent circuit shown in FIG.

Effects of the Invention As is clear from the above explanation, in a hybrid IC type optical receiver using a photodiode, the stray capacitance generated around the feedback resistor between the output sides of the amplifier is divided into the input side and the output side and grounded. Therefore, the stray capacitance component parallel to the feedback resistor can be significantly reduced. Therefore, the band of the optical receiver is not limited by the stray capacitance in parallel with the feedback resistor, and can have a wide frequency band. Therefore, an optical receiver with extremely high response speed can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a first embodiment of a hybrid IC type optical receiver according to the present invention, FIG. 2 is an equivalent circuit diagram of the hybrid IC type optical receiver of FIG. 1, and FIG. 3 is a diagram of the present invention. A schematic configuration diagram of the main part of a second embodiment of the hybrid IC type optical receiver according to the invention, FIG. 4 is a circuit diagram of a receiving circuit of a conventional hybrid IC type optical receiver, and FIG. 5 is a diagram of a conventional actual hybrid FIG. 2 is an equivalent circuit diagram of an IC type optical receiver. [Main reference numbers] 1. Photodetector, 2. Amplifier, 3. Feedback resistor, 10. Case, 12. Connector, 14. Photodiode, 16.
Ceramic substrate, 18...Amplifier, 20.24.28.
32...Conductor pattern, 26...Printed resistor, 30...Metal lid, 32...Insulating film

Claims (6)

[Claims] (1) In a hybrid IC type optical receiver having a light receiving element and an amplifier having an input connected to the light receiving element, configured in a transimpedance type circuit system, and provided on an insulating substrate, a feedback resistor attached to the amplifier is used. 1. A hybrid IC type optical receiver characterized in that the parasitic stray capacitance between both ends of the receiver is divided and grounded. (2) The feedback resistor is a printed resistor formed on the insulating substrate, and includes a conductive region spaced apart from the printed resistor and having a size that at least substantially covers the printed resistor, and the conductive region is The hybrid IC type optical receiver according to claim 1, wherein the optical receiver is grounded. (3) The hybrid IC type optical receiver according to claim (2), wherein the conductive region is a metal lid of a package housing the hybrid IC type optical receiver. . (4) a conductive pattern is provided on the insulating substrate below the feedback resistor, and the conductive pattern is grounded;
The hybrid IC type optical receiver according to claim 1, wherein the feedback resistor and the conductive pattern are electrically insulated. (5) The hybrid IC type optical receiver according to claim (4), wherein the feedback resistor is a printed resistor formed on the conductive pattern via an insulating film. (6) The hybrid IC type optical receiver according to claim (4), wherein the feedback resistor is a resistor chip that does not come into contact with the conductive pattern.