Amplitude-shift-keyed modulation is a commonly known technique used to modulate rf and optical carriers for the transmission of data. A typical transmission involves sending bursts of carrier signals, the presence of a burst identifying a binary one or zero and the absence of a burst or carrier being representative of the opposite binary digit. Examples of patents describing various ASK modulations are U.S. Pat. Nos. 4,947,407, 4,860,320, and 4,829,560.
Techniques for improving detection of data signals detected with optical receivers are known in the art. In one such technique as shown and described in U.S. Pat. No. 4,431,916 delayed versions of input signals are compared with undelayed versions to reproduce data signals. Threshold values are created from these signals. U.S. Pat. No. 4,507,795 describes an apparatus for locating leading and trailing edges of pulses derived from an RF input.
One problem associated with ASK receivers involves the large amplitude swings of incident RF or optical carrier signals. Such large swings tend to introduce undesirable variations in the output data pulse width. Such variations often are due to the receiver's bandpass filtering which causes sloping, rising and falling edges at the output of the logarithmic amplifier that is commonly used in receivers.