Optical receiver suitable for optical interconnects

Details Optical receiver suitable for optical interconnects Optical receiver suitable for optical interconnects

1997-05-12

2001-04-17

Pascal, Leslie (Department: 2733)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

Reexamination Certificate

active

06219166

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to optical receivers, especially but not exclusively optical receivers for use in optical interconnects.
2. Background Art
Optical interconnects are used to convert optical signals to electrical signals and vice versa. They are used in optical communications systems, for interconnections between equipment, such as computers, which transfer data at high rates, and within such equipment to transfer data between components such as integrated circuits.
The typical optical interconnect comprises an interconnect transmitter which converts electrical pulses representing digital data into pulses of light for transmission via an optical transmission path, which might be free space. An interconnect receiver at the other end of the transmission path converts the pulses of light back into electronic pulses for processing by electronic circuitry.
Optical interconnects for inter- or intra-computer communications may comprise a multiplicity of links requiring perhaps thousands of receivers in an array on a miniature device such as an integrated circuit. Consequently, such receivers must be small and have a low electrical power consumption, yet still be highly sensitive and fast.
A typical receiver comprises a photodetector to receive the light pulses and convert them into electrical pulses which will then be amplified and processed in known manner. The light-absorbing area of the photodetector is critical to the performance of the receiver. The input capacitance of the receiver is dominated by the capacitance of the photodetector, so it is usual for known optical receivers to have a detector with a small area, and hence small input capacitance, which will reduce the time constant and lead to improved bandwidth and sensitivity. Unfortunately, reducing the area of the photodetector makes it more difficult to align the input light beam onto the absorbing region of the photodetector. This can result in problems, especially where a large number of receivers must be provided in a small area, such as when interconnecting integrated circuits and other components.
SUMMARY OF THE INVENTION
An object of the present invention is to mitigate the afore-mentioned difficulties and provide an optical receiver which will tolerate a relatively high input capacitance for a given speed and sensitivity.
According to the present invention, there is provided an optical receiver comprising a photodetector unit for converting an optical signal incident thereupon into a corresponding electrical photodetector current and a current-mode circuit having a low impedance, low capacitance input coupled to the photodetector for receiving the electrical photodetector current, and a high impedance output for outputting an electrical output current corresponding to said electrical photodetector current.
The current-mode circuit may comprise a current conveyor, conveniently followed by a current-to-voltage converter and a thresholder for providing a digital output signal in dependence upon the photodetector current. Alternatively, the current-mode circuit may comprise a sense amplifier providing directly a digital output signal varying in dependence upon the photodetector current. The current conveyor or the sense amplifier, as the case may be, may use CMOS devices.
In preferred embodiments, the photodetector unit comprises a pair of photodetectors, for example PIN photodiodes, connected so as to provide a differential optical input stage.
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which like components have the same reference numbers.


REFERENCES:
patent: 3582689 (1971-06-01), Smith et al.
patent: 5548434 (1996-08-01), Shimonaka et al.
A High-Speed Clamped Bit-Line Current-Mode Sense Amplifier, Travis N. Blalock and Richard C. Jaeger, IEEE Journal of Solid State Circuits, vol. 26, No. 4, (Apr. 1991) pp. 542-548.
622MHz Current-Mode Sense Amplifier, J. Alowersson and P. Andersson, Electronic Letters (Feb. 1, 1996) vol. 32, No. 3, pp. 154-156.
Clocked-Sense-Amplifier-Based Smart-Pixel Optical Receivers, IEEE Photonics Technology Letters, vol. 8, No. 8, (Aug. 1996) pp. 1067-1069.
Optical Receivers for Optoelectronic VLSI, IEEE Journal of Selected Topics in Quantum Electronics vol. 2, No. 1 (Apr. 1996), pp. 106-116.
Analysis and Design of Analog Integrated Circuits, Paul R. Gray and Robert G. Meyer, Second edition, John Wiley & Sons, pp. 244-246, p. 300.
Using Current Conveyors, Brett Wilson, Electronic & Wireless World (Apr. 1986) pp. 28-32.
Wideband Class AB (Push-Pull) Current Amplifier in CMOS Technology, Electronics Letters (Apr. 12, 1990) vol. 26, No. 8, pp. 543-544.
Fast CMOS Current Amplifier and Buffer Stage, Electronics Letters (Jun. 18, 1987) vol. 23, No. 13.

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