Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1997-07-15
2001-03-27
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06208446
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel optical detector system, and also to optical communication apparatus including the novel detector system. The invention is particularly useful in receivers, transmitters and transceivers of binary-coded optical data in the infrared region, and is therefore described below with respect to such an application, but it will be appreciated that the invention could advantageously be used in many other applications.
U.S. Pat. No. 5,355,242 discloses an optical receiver which includes a photo detector array generating an electrical current according to the light received thereby. The output of the photo detector is fed to a transimpedance amplifier which includes a feedback resistor, and then through a limiter circuit which includes a bandpass filter and a limiting amplifier. The system described in that patent further includes an untuned transformer which returns to ground the direct current arising from ambient light while the binary encoded data signals are passed via the secondary winding of the untuned transformer to the transimpedance amplifier.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an optical detector system having an increased sensitivity such that it is capable of increasing the signal-to-noise ratio (SNR). Another object of the present invention is to provide an optical detector system having an adaptive sensitivity, which automatically changes in response to the ambient light conditions. Further objects of the invention are to provide a transceiver and also a transmitter particularly useful with the novel optical detector system.
According to one aspect of the present invention, there is provided an optical detector system, comprising: a photo detector generating an electrical current according to light received thereby; voltage terminals at opposite sides of the photo detector for connection to a voltage source; a pair of resistors each connected between a voltage terminal and the respective side of the photo detector; a pair of matched amplifiers each having an input connected between the respective resistor and the respective side of the photo detector, each of the amplifiers having an input resistance substantially less than that of the resistor to which it is connected; and an output circuit combining the outputs of the matched amplifiers.
As will be described more particularly below, such a system utilizes the current produced by the photo detector twice, and thereby increases the sensitivity and SNR.
According to further features in the described preferred embodiment, the matched amplifiers are transimpedance amplifiers; also, the output circuit includes a bandpass filter, preferably having a bandpass of 1-15 MHz, and a gating circuit operated by a threshold level signal.
According to another aspect of the present invention, there is provided an optical detector system, comprising: a photo detector generating an electrical current according to light received thereby; and an output circuit receiving the output of the photo detector; the output circuit including a gating circuit having a threshold level generator for generating an adaptive threshold level signal varying with ambient light intensity for gating the output circuit.
Since the sensitivity of the system is adaptive to variations in the ambient light intensity, false digital pulses, generated in the quantizer portion of a digital receiver usually caused by increased noise level relative to an otherwise fixed threshold level, are thus avoided.
According to a still further aspect of the present invention, there is provided a light transmitter for transmitting code pulses, comprising: a light source; an input port for receiving the code pulses to be transmitted; and a pre-equalization circuit connected to the input port for receiving the code pulses to be transmitted, and for utilizing them to drive the light source while compensating for amplitude and phase distortions caused by different attentuations of the code pulses of different durations in the transmission system (transmitter, medium and receiver). The invention is particularly useful in systems wherein the code pulses are Manchester encoded pulses, and include a train of pulses of 50 nsec and 100 nsec duration. The transmission system attenuates pulses of 50 nsec more than 100 nsec pulses. Therefore pre-equalization ensures that both the 50 nsec and 100 nsec pulses will be roughly the same amplitude at the output of the bandpass filter of the receiver. Maximum sensitivity of the receiver is achieved in this way. The pre-equalization circuit reduces the current through the LEDs when a 100 nsec pulse is being transmitted. After 50 nsec of a 100 nsec pulse, the current level is reduced to approximately ⅔ of its peak for the remaining 50 nsec.
Further features and advantages of the invention will be apparent from the description below.
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Chan Jason
Helfgott & Karas P.C.
iRLAN Ltd.
Sedighian Mohammad
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