JP2000058881A - Light receiving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration in band characteristics of a light receiving circuit by connecting the anode or cathode of a light receiving element directly with the signal input pad of a preamplifier chip through extremely short wire bonding and limiting the parasitic inductance component to one point while shortening the connection length thereby reducing the parasitic inductance component. SOLUTION: A chip of a preamplifier 3 is mounted closely to a light receiving element in 1 flush with the plane of carrier 2 mounting the light receiving element. Since the light receiving element is connected directly with the signal input pad of the preamplifier chip through extremely short wire bonding 15, parasitic inductance is limited to one point and self inductance itself is decreased resulting in enhancement of frequency characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband optical semiconductor device, and more particularly to a light receiving circuit having a built-in preamplifier.

[0002]

2. Description of the Related Art In recent years, high bit rates have been demanded in optical communication systems irrespective of trunk systems and subscriber systems, and high-speed compatible optical transmitting and receiving devices have been developed that can meet this requirement. To make the light receiving element modular,
The performance such as frequency characteristics and S / N greatly depends on the mounting method of the light receiving element and the preamplifier chip and the connection method between these elements. Therefore, it is necessary to pay sufficient attention to the mounting method.

In an optical communication system in which light wavelengths of 1.3 μm and 1.55 μm are mainly used, the light receiving characteristic of a light receiving element and the amplification characteristic of a preamplifier for converting a photoelectric conversion current by the light receiving element into a voltage are optimized. For this purpose, in the current device technology, individual devices are manufactured from different materials such as InGaAs for the light receiving element and Si for the preamplifier, and are used by modularizing them by a so-called hybrid integration technology.

FIG. 3 shows a conventional light receiving circuit having a hybrid integrated structure. Optical fiber 100 for guiding signal light to light receiving element
, Light receiving element 1 and carrier 2 on which only this light receiving element is mounted
And the preamplifier 3 constitute the main components, and the light receiving surface of the light receiving element must be mounted on a surface perpendicular to the optical axis of the optical fiber. Make the surface with the light-receiving element adhered vertically,
The chip of the preamplifier 3 is provided on a substrate surface to which the carrier 2 is adhered, with its back surface adhered. A lens for condensing the output light of the optical fiber used as necessary on the light receiving surface is omitted in the drawing. The electrical connection between the light receiving element 1, the carrier 2 and the preamplifier 3 is such that the signal output from the light receiving element 1 is once applied to the carrier electrode pattern 8 of the carrier 2 on which only the light receiving element is mounted.
The connection is made via a carrier connection bonding wire 13 and from the carrier to the preamplifier by a different bonding wire, a carrier-preamplifier connection bonding wire 14.

[0005] For this reason, the carrier electrode pattern 8 on the carrier 2 on which two connecting wires and the light receiving element are mounted is further provided.
In addition, the addition of the carrier electrode pattern 9 increases the parasitic inductance between the element and the preamplifier, causing deterioration of the band characteristics of the light receiving circuit or peaking at high frequencies.

[0006] For example, between the light receiving element and the preamplifier,
When a connection wire having a thickness of about 30 μmφ, which is generally used, is used, in the case of the conventional structure, the connection distance is 5 mm or more, and the inductance of the wire itself is 5 nH or more.
Therefore, the band is limited to about 2 to 3 GHz.
Further, since the connection distance between the light receiving element and the preamplifier is long, signal reflection occurs due to impedance mismatch between the light receiving element and the preamplifier, and the frequency band is limited.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the deterioration of the band characteristic of the light receiving circuit based on such a conventional mounting method is described.
This is intended to be avoided by improving the implementation.

[0008]

According to the present invention, a preamplifier chip is mounted in the same plane as a surface on which a light receiving element is mounted on a carrier on which the light receiving element is mounted, in the vicinity of the light receiving element.
This is a light receiving circuit characterized in that the anode or cathode of the light receiving element is directly connected to the signal input pad of the preamplifier chip by a single wire bonding that is extremely short.

[0009]

Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention. An optical fiber for guiding light to a light receiving surface of a light receiving element 1 and a lens for condensing light on the light receiving surface are the same as those in FIG. Therefore, it is omitted.

Light receiving element 1 for converting an optical signal into an electric signal
However, a preamplifier 3 for amplifying an electric signal is similarly adhered to the same plane as the light receiving element 1 by metal bonding to a rectangular parallelepiped ceramic carrier 2. This surface of the carrier 2 to which the light receiving element 1 and the preamplifier 3 are adhered receives light emitted from an optical fiber on which the light receiving element 1 is placed horizontally.
The optical fiber is installed upright on a vertical light emitting end face and vertically on a horizontal plane. Further, on the surface of the carrier 2, carrier electrode patterns 8 to 12 and a metal film pattern necessary for bonding the elements are formed by plating or the like before bonding the elements.

An anode or a cathode of the light receiving element 1;
The preamplifier input pad 4 is electrically directly connected by a light receiving element-preamplifier connection bonding wire 15. The difference between the anode / cathode connection is that the anode of the light receiving element connected to the carrier electrode pattern 8 is connected to the anode of the light receiving element when the reverse bias of the light receiving element is a negative power supply, and the light receiving element is connected when the reverse bias of the light receiving element is the positive power supply. It will be connected to the cathode. The light receiving current converted by the light receiving element 1 is amplified by the preamplifier 3, and the output signal of the preamplifier is supplied from the preamplifier output pad 5 to the carrier electrode patterns 10 and 11.
Output to The power of the preamplifier 3 is supplied from the carrier electrode patterns 9 and 12 provided on the carrier to the preamplifier V.
It is supplied to the cc pad 6 and the preamplifier Vee pad 7.

FIG. 2 shows an equivalent circuit from the carrier electrode pattern 8 to the preamplifier output pad 5 in this mounting method. The equivalent circuit elements surrounding the light receiving element 1 can be considered mainly with the equivalent inductance of the carrier electrode pattern 8 and the equivalent inductance of the bonding wire 15 for connecting the light receiving element and the preamplifier. FIG. 4 shows a case where the same equivalent circuit is applied to the case of FIG. 3 which is a conventional mounting method.

As can be seen by comparing the two, the light receiving element 1
FIG. 1 showing a mounting method according to the present invention between FIG.
3, the parasitic inductance generated by the carrier-preamplifier connection bonding wire 14 and the parasitic inductance generated by the carrier electrode pattern 9 appearing in the case of the conventional mounting method shown in FIG. While the frequency characteristics are degraded, in the mounting method of the present invention, these stray inductances are removed, and good frequency characteristics can be obtained. For example, the length of the wire bonding for connection between the light receiving element 1 and the preamplifier input pad 4 is such that the light receiving element and the preamplifier can be placed very close to the same surface on the same carrier. The technology required 5mm,
The width can be reduced to 0.1 mm or less, and an increase in bandwidth due to a decrease in inductance can be expected to be 50 times.

By adopting the mounting method of the present invention, a light-receiving element can be made to have an element based on a high-performance InGaAs crystal growth technique, and a preamplifier chip can have a Si integrated circuit chip or a GaAs integrated circuit chip. Since it can be used without killing, the degree of freedom in module design is greatly improved.

[0016]

In the light receiving circuit based on the conventional mounting method,
The signal output from the light receiving element is once connected to the carrier electrode by a bonding wire, or connected to the carrier electrode pattern, and further connected to the preamplifier input pad by a different bonding wire from the carrier. You. For this reason, wire bonding is 2
The light receiving element and the preamplifier are connected by the pattern of the book or the wire bonding and the carrier electrode, and two parasitic inductance components occur between the light receiving element and the preamplifier. Due to this parasitic inductance component, the S / N of the light receiving circuit deteriorates, and in the frequency characteristic of the photoelectric conversion signal, the high frequency band deteriorates,
Alternatively, peaking occurred at a high frequency.

On the other hand, in the light receiving circuit based on the structure of the present invention, the chip of the preamplifier is mounted close to the light receiving element on the same plane as the light receiving element mounted on the carrier on which the light receiving element is mounted. In order to directly connect the anode or cathode of the light receiving element and the signal input pad of the preamplifier chip by extremely short wire bonding, a parasitic inductance component is provided at one place, and since the connection length is reduced, the parasitic inductance component is reduced. The reduction makes it possible to solve the above problem.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the structure of a light receiving circuit according to an embodiment of the present invention.

FIG. 2 is an equivalent circuit of a light receiving circuit according to the embodiment of the present invention.

FIG. 3 is a perspective view showing the structure of a conventional light receiving circuit.

FIG. 4 is an equivalent circuit of a conventional light receiving circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light receiving element 2 carrier 3 preamplifier 4 preamplifier input pad 5 preamplifier output pad 6 preamplifier Vcc pad 7 preamplifier Vee pad 8 to 12 carrier electrode pattern 13 light receiving element-carrier connection bonding wire 14 carrier-preamplifier bonding wire 15 light receiving element-preamplifier connection Bonding wire

Claims (6)

[Claims] 1. A light receiving circuit, wherein a light receiving element and a preamplifier for amplifying a photoelectric conversion signal of the light receiving element are mounted on the same carrier. 2. A light receiving circuit, wherein a light receiving element and a preamplifier for amplifying a photoelectric conversion signal of the light receiving element are mounted on the same carrier and on the same plane. 3. A light receiving circuit wherein a light receiving element mounted on the same carrier on the same plane and a signal input pad of a preamplifier for amplifying a photoelectric conversion signal of the light receiving element are connected by a single wire bonding. . 4. The light receiving circuit according to claim 1, wherein said carrier is ceramic. 5. The light receiving circuit according to claim 1, wherein the light receiving element is an InGaAs photodiode, and the preamplifier is a Si integrated circuit element. 6. The light receiving circuit according to claim 1, wherein the light receiving element is an InGaAs photodiode, and the preamplifier is a GaAs integrated circuit element.