Abstract: A passive resistive element is provided in series with a digital variable impedance to produce a highly linear output impedance for a transmission path over a wide range of operating conditions.

Abstract: An apparatus and method is provided that improves the dynamic range of an optical transimpedance receiver. The receiver includes a photodetector, a transimpedance front end amplifier and a non-liner feedback. The non-linear feedback means consists of a Schottky diode and shunting the transimpedance resistor with a parasitic capacitor. A lead compensation network is further included in the feedback circuitry to provide stability to the non-linear circuit by advancing the phase shifting of the transimpedance front end by 45 degrees. By stabilizing the frequency off the circuit, the dynamic range is increased from 26.6 dB to 40 dB.

Abstract: A high-speed driver for LED data communications systems. A differentiator provides a turn-on and a turn-off pulse of current to the LED. The amount of charge delivered during turn-off is adjusted to sweep substantially all of the carriers from the LED without reverse-biasing the LED.

Abstract: An LED pulse shaping circuit is disclosed which is capable of providing improved rise time (using current peaking) and fall time (using charge extraction). The pulse shaping circuit consists of a conventional differential current switch coupled to a pair of switching elements and resistance elements. A first switching element is activated at the beginning of a pulse to provide for an initially increased drive current to the LED, the value of a first resistance element used to determined the level of the increased drive current. The current peaking thus results in decreasing the rise time of the LED. The remaining switching element and resistance are utilized, in conjunction with the differential current switch, to provide a reverse current flow through the LED at the end of the pulse. The charge extraction thus results in decreasing the fall time of the LED.

Abstract: A binary data receiver data modulated light signals and applies them to a photodetector for producing electrical data signals which are amplified and applied to a data decision circuit. The data decision circuit compares the instantaneous value of the amplified data signals with a fixed threshold to determine if a logic high or low level is received. A portion of the signal path between the photodetector and the data decision circuit is ac coupled, whereby the moment-to-moment variations of duty cycle of the signal due to the information content of the data causes variations in the peak excursions of the signal which may adversely affect the data decisions or processing of the data. Open-circuit correction of the average value is accomplished by a correction signal generator which receives an ac coupled data sample, and rectifies both positive-going and negative-going excursions relative to ground to produce positive and negative average value signals.

Abstract: A transimpedance amplifier for data signals from a high impedance source includes a forward voltage amplifier and a feedback resistance. The feedback includes an FET. The resistance of the FET is controlled by a control signal derived from the data signal at the output of the transimpedance amplifier by a differentiator which generates pulses for each data transition and an average detector which generates a control signal responsive to the number of transitions per unit time, which is the data rate. The resistance of the FET is high when the data rate is low, reducing the noise magnitude and decreasing the noise bandwidth. When the data rate increases, the resistance of the FET decreases, providing greater bandwidth for handling the signal. The change in gain caused by the bandwidth control tends to change the magnitude of the output data signal. This may be corrected by an AGC loop which controls the open loop gain of the voltage amplifier.

Abstract: A simple, reliable, and inexpensive method for cleaving small diameter optical fibers comprises the steps of heating the fiber at a point along its length by contacting the fiber with an electrically heated wire and contacting the fiber, including the heated portion, with a volatile liquid whereby the fiber is cooled. The fiber may be cooled by spraying it with a liquid fluorocarbon.