JP3106435B2 - Optoelectronic integrated circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optoelectronic integrated circuit (OEIC array) used for a light receiving portion of optical fiber communication.

[0002]

2. Description of the Related Art Conventionally, as this kind of OEIC array, there is an OEIC array disclosed on pages 1833 to 1834 of the following literature, and its schematic configuration is shown in a circuit diagram of FIG.

[0003] Electronics Letters, vol. 26, No. 22, 25th
October 1990 `` MONOLITHIC INTEGRATION OF AN InP / I
nGaAs FOUR-CHANNEL TRANSIMPEDANCE OPTICAL RECEIVER
ARRAY ”In this OEIC array, four optical input channels constituting an optical receiver are monolithically integrated. The first channel is one of them, PIN photodiode PD _1, the input resistor R _f1, and a junction transistor Q ₁₁ to Q ₁₉ and the level shift diode LSD _1. The transistors Q _{11 to} Q _11
13 constitute an amplifying stage for amplifying an electrical signal photoelectrically converted by the photodiode PD _1. Further, the transistors Q ₁₄ and Q ₁₅ and the diode LSD ₁ constitute a level shift stage for converting the DC voltage level of the amplified signal output from the amplification stage. Also, the transistors Q _{16 to} Q ₁₉
Reduces the output impedance of the light reception output O / P _1, constitute a source follower stage to ensure fanout. The other second, third, and fourth channels also
It has the same circuit configuration as the channel. The illustration of the second and third channels is omitted in FIG. The level shift stage is a stage unique to the transimpedance type circuit, and is not always necessary for the preamplifier. However, the source follower stage is indispensable for driving an external circuit connected to the output terminal.

There is also an OEIC array disclosed in the following document, and its schematic configuration is shown in a circuit diagram of FIG.

[0005] Optical Fiber Communication Conferenc
e, Tuesday, Feburary 19,1991, Lecture No.TuB2 `` High-
speed eight-channel optoelectronic integrated rece
iverarrays comprising GaInAs pin PDs and AlInAs / Ga
InAs HEMTs "In this OEIC array, eight optical input channels are monolithically integrated. One of the first channels is a PIN photodiode PD ₁ ,
Resistor R ₁₁ to R ₁₄ and the high electron mobility transistor (HE
And a MT) Q ₁₁ ~Q _15. The transistors Q ₁₁ and resistors R ₁₂ of constitutes the amplifier stage.
The transistor Q ₁₂ to Q ₁₅ and resistors R _13, R ₁₄ forms a source follower stage of two-stage configuration.

[0006]

The power supply to each preamplifier in the conventional OEIC array shown in FIG. 2 is performed by a power supply V _DD1 via a power supply line common to each channel in the amplification stage and the level shift stage. Is supplied. In the source follower stage, power supply V _DD2 is supplied via another power supply wiring common to each channel. On the other hand, the power supply to each preamplifier in the OEIC array shown in FIG. 3 is performed by supplying the power supply V _DD via a power supply line common to each channel for all stages constituting each preamplifier. I have. In each of the above-described conventional OEIC arrays configured as described above, a large modulation current is generated in the level shift stage and the source follower stage due to an input signal as described later. For this reason, large fluctuations occur in the power supply for supplying power to these stages due to the modulation current. This power supply voltage variation affects the power supply of each channel commonly connected to these stages. That is, the influence of the power supply voltage fluctuation generated in one channel by the optical input signal also affects the power supply of another channel, and the voltage fluctuation occurs at the output terminal of another channel. That is, crosstalk occurs between the channels. As a result, there arises a problem that the minimum receiving sensitivity of each optical receiving circuit formed in each channel is deteriorated due to the crosstalk.

The main cause of the crosstalk is considered as follows.

OEIC using HEMT shown in FIG.
The array will be described below with reference to FIG. 4 which schematically illustrates the OEIC array. That is, for example, an optical signal inputted to the first channel is converted into an electrical signal by photodiode PD _1, when it is amplified by a preamplifier comprised of amplifier stages and the source follower stage, a large modulation current due to the optical signal input It is assumed that ΔI _m1 has occurred. 90% or more of the modulation current ΔI _m1 is generated in the source follower stage. Then, when the modulation current ΔI _m1 flows through the wiring of the resistor R _p , a voltage fluctuation ΔV _D occurs. The wiring resistance R _p is equivalently represented as shown to the power supply terminal V _DD portion for supplying power commonly to the respective preamplifier, to which said modulation current [Delta] I _m1 voltage fluctuation by the flow [Delta] V _D ( = ΔI _m1 × R _p ). This voltage fluctuation ΔV _D becomes the power supply voltage fluctuation of the preamplifier of another channel as it is. Generally, when the power supply voltage fluctuates, the output voltage of the preamplifier fluctuates. Therefore, when an optical signal is input to a certain channel, the power supply voltage of the preamplifier of another channel fluctuates, which fluctuates the output voltage of another channel, and crosstalk occurs.

Also, in the OEIC array using the junction type transistors shown in FIG. 2, a modulation current is generated due to an optical signal input. 90% or more of the modulation current is generated in the level shift stage and the source follower stage. The power supply voltage V _DD1 is supplied to the amplification stage and the level shift stage of each preamplifier via a common power supply line. For this reason, when a modulation current is generated in a level shift stage of a certain preamplifier, a voltage fluctuation ΔV _D is generated in the common power supply wiring as described above. This voltage fluctuation ΔV _D changes the power supply voltage of the preamplifier of another channel via this power supply wiring, and fluctuates the output voltage. That is, the output voltage of another channel fluctuates due to an optical signal input to a certain channel, and crosstalk occurs.

The reason why the output voltage fluctuates when the power supply voltage of the preamplifier fluctuates is as follows. That is, as shown in FIG. 4, the preamplifier includes an amplification stage, a level shift stage, and a source follower stage. Of these, the output voltages of the level shift stage and the source follower stage hardly change even when the power supply voltage changes. However, the output voltage of the amplification stage fluctuates in the range of 50% to 100% of the power supply voltage fluctuation and is sensitive to the voltage fluctuation. For this reason, when a voltage fluctuation due to a power supply voltage fluctuation occurs in the output of the amplification stage of a certain preamplifier, the influence of the voltage fluctuation directly affects the source follower stage and the level shift stage. That is, when the power supply voltage of the preamplifier fluctuates, the output voltage fluctuates.

As described above, the minimum receiving sensitivity of each optical receiving circuit formed in each channel is degraded by the crosstalk caused by such factors.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. In a preamplifier integrated on a semiconductor substrate, a base terminal is a light receiving element and an emitter terminal is a reference potential line. An amplification stage including a first bipolar transistor having a collector terminal connected to a first power supply line via a load, a base terminal connected to the collector terminal of the first bipolar transistor, and a collector terminal connected to the first power supply. A level shift stage for shifting the level of the electric signal amplified by the amplifier stage, the second bipolar transistor being connected to a second power supply line different from the line, and a base terminal having an emitter terminal of the second bipolar transistor The collector terminal is connected to the second power supply wiring,
A third terminal in which the emitter terminals are connected to the reception output terminals, respectively;
And an emitter follower stage including the bipolar transistor.

[0013]

The power supply to the amplification stage of each preamplifier that is sensitive to voltage fluctuations is performed independently of the power supply to other stages than the amplification stage of each preamplifier such as an emitter follower that mainly generates a modulation current. Therefore, even if a modulation current is generated in an emitter follower stage or the like by an optical signal input to a certain channel, and as a result, a voltage fluctuation occurs in a power supply supplied to the emitter follower stage or the like, amplification of another channel that is sensitive to the voltage fluctuation occurs. The power supply voltage of the stage does not change. Therefore, the output voltage of the other channel does not fluctuate even if an optical signal is input to a certain channel, and no crosstalk occurs.

[0014]

FIG. 1 is a circuit diagram showing a schematic configuration of an OEIC array according to an embodiment of the present invention.

In the OEIC array according to the present embodiment, the number of channels is not particularly limited, but generally 4 to 12 channels depending on the application. In the figure, the first channel and the last n-th channel (n = 4 to 12) are shown, and the second to (n-1) -th channels are omitted. These channels are monolithically integrated on the same semiconductor substrate. 0.8μ for this semiconductor substrate material
GaAs is employed in optical communication in the m wavelength band. In optical communication in the 1.3 μm and 1.55 μm wavelength bands, InP is adopted. The configuration of each of these channels is the same as that of the first channel, and performs the same circuit operation.

The first channel includes photodiodes PD ₁ ,
Resistor R ₁₁ to R ₁₄ and the bipolar transistor Q ₁₁ to Q
_It is composed of ₁₃ . MSM type or PIN type photodiode is used for the photodiode PD _1.
In addition, the bipolar transistor Q ₁₁ ~Q _13, InP
/ GaInAs heterojunction, or AlGaAs / Ga
A heterojunction bipolar transistor (HBT) using an As heterojunction is used. Among these combinations, the most excellent in operation performance is that a PIN photodiode and an InP / G
This is a combination in which an HBT using an aInAs heterojunction is formed.

The photodiode PD ₁ and the resistor R ₁₁ constitute a light detection stage, and the transistor Q ₁₁ and the resistor R ₁₁
Reference numeral ₁₂ denotes an amplification stage that amplifies the input signal detected by the light detection stage. The transistor Q ₁₂ and resistors R ₁₃
Constitutes a level shift stage. The transistor Q ₁₃ and the resistor R ₁₄ constitute emitter followers stage. That is, the detected light signal to the photodiode PD ₁ is converted into a photocurrent, the photoelectric current is converted to a voltage signal by the resistor R _11. This voltage signal is applied to the base of the transistor Q ₁₁ to the resistor R ₁₂ and the load, is amplified to a predetermined times. The DC level of the amplified input signal is shifted by the next level shift stage. Its shift amount is substantially determined by the resistance value of the resistor R _13. Finally,
Output impedance of the preamplifier is reduced by emitter follower stage, fan-out of the received output signal O / P ₁ is ensured.

In this embodiment, the power supply V _C1 is supplied in common to each channel to the level shift stage and the emitter follower stage other than the amplification stage of each preamplifier, and the power supply V _C2 is supplied to each amplification stage of each preamplifier. Are commonly supplied to each channel. In other words, the power supply wiring for supplying the power supply V _C2 to the amplification stage is electrically separated from the power supply wiring for supplying the power supply V _C1 to other stages other than the amplification stage. Therefore, power supply to the amplification stage of each preamplifier that is sensitive to voltage fluctuations is performed independently of power supply to the level shift stage and the emitter follower stage where the modulation current mainly occurs. Therefore, the output voltage of another channel does not fluctuate due to the optical signal input to a certain channel.

That is, the modulation current ΔI is applied to the level shift stage or the emitter follower stage of a certain preamplifier.
_m , the voltage fluctuation ΔV caused by the modulation current
The effect of _D does not extend to each amplification stage of all other preamplifiers. Therefore, power supply to each amplification stage is performed stably,
Further, noise signal components are not unnecessarily amplified in each amplification stage, and accurate optical communication can be performed.

According to the configuration according to this embodiment,
Conventionally, crosstalk, which was about -30 dB, can be suppressed to -40 dB or less, and in parallel optical fiber communication, it is possible to reduce deterioration in minimum receiving sensitivity due to crosstalk.

[0021]

As described above, according to the present invention, power supply to the amplification stage of each preamplifier which is sensitive to voltage fluctuation
The power supply is performed independently of the power supply to other stages other than the amplification stage of each preamplifier where the modulation current mainly occurs. Therefore,
The output voltage of another channel does not fluctuate due to an optical signal input to a certain channel, and no crosstalk occurs. Therefore, an OEIC array capable of effectively preventing the minimum receiving sensitivity from deteriorating due to crosstalk is provided.

[Brief description of the drawings]

FIG. 1 is an optoelectronic integrated circuit (OE) according to an embodiment of the present invention;
FIG. 2 is a circuit diagram illustrating a schematic configuration of an (IC array).

FIG. 2 is a circuit diagram showing a schematic configuration of a first conventional OEIC array.

FIG. 3 is a circuit diagram showing a schematic configuration of a second conventional OEIC array.

FIG. 4 is a circuit diagram for explaining the principle of occurrence of crosstalk in a second conventional OEIC array.

[Explanation of symbols]

PD ₁ ... first channel photodiode R ₁₁ to R ₁₄ ... first channel resistor Q ₁₁ to Q ₁₃ ... transistor O / P ₁ ... optical receiver output signal V _C1 ... level of each channel of the first channel of the first channel Power supply supplied to the shift stage and the emitter follower stage V _C2 ... power supply supplied to the amplification stage of each channel

────────────────────────────────────────────────── ⁷ Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H03F 3/68 (56) Reference "MONOLITIC INTEGRATION OF AN InP / InGaAs FOUR-CHANNEL TRANSIMPEDANCE OP TICAL RECEIVER ARy Anywhere", terts, 1990, Vol. 26, No. 22, p. 1833-1834 (58) Field surveyed (Int.Cl. ⁷ , DB name) H03F 3/08 H03F 3/68 H01L 27/04 H01L 27/14 H01L 31/10

Claims (1)

(57) [Claims] 1. A semiconductor substrate comprising: a light receiving element for converting a received optical signal into an electric signal; a preamplifier for amplifying an output signal of the light receiving element; and a reception output terminal receiving the amplified output. A plurality of optoelectronic integrated circuit elements integrated on the light emitting element, wherein the preamplifier has a base terminal connected to the light receiving element, an emitter terminal connected to a reference potential line, and a collector terminal connected to a first power supply wiring via a load. An amplification stage including the first bipolar transistor, and a second terminal having a base terminal connected to a collector terminal of the first bipolar transistor and a collector terminal connected to a second power line different from the first power line. A level shift stage that includes a bipolar transistor and shifts the level of the electric signal amplified by the amplification stage; An emitter follower stage including a third bipolar transistor having an emitter terminal connected to the second power supply line, a collector terminal connected to the second power supply line, and an emitter terminal connected to the reception output terminal, respectively. Integrated circuit.