Eye opening monitor

摘要

An eye opening monitor for a binary waveform such as provided as the video output of a demodulator. At the decision sample time, the video is compared to -Vth and +Vth reference voltages to determine if it falls in the range defined therebetween. If it does, a counter is reset. Because the carry-out pulses of the counter are used to produce -Vth and +Vth, the range defined therebetween is decreased by the additional time required to count to the carry-out after the counter is reset. The loop stabilizes with the range from -Vth and +Vth being quantitatively indicative of the eye opening. A voltage derived from Vth is visually displayed.