SET_TIME_WINDOWS_WITHIN_A_CLOCK

Published:2009/6/22 22:49:00 Author:Jessie | From:SeekIC

At times, it is necessary to produce pulses of adjustable width and whose start times might vaty with reference to a master clock. The input signal is inverted and buffered by U1A, while U1B and U1C reinvert the signal to produce square, buffered renditions of the input signal. Potentiometers R3 and R4 set references for the comparators.The input polarity of U2A keeps its output transistor tumed on until the voltage at the nonin-verting input exceeds the reference set by R4 (the rising edge adjustment). When this reference voltage is exceeded, the output transistor is turned off and the output signal is pulled up via R6.Meanwhile, the input polarity of U2B keeps its output transistor turned off until the voltage at the in-verting input exceeds the reference set by R3 (the falling edge adjustment). When this reference voltage is surpassed, the output transistor of U2B is turned on, pulling the output signal low through the wired-OR conftguration of U2. The output of U2 is then double-inverted and buffered by U1D and U1E. What results is a pulse whose start time (rising edge) can be adjusted by R4, and whose stop time (falling edge) can be adjusted by R3.The output of the comparators is pulled up to the input waveform through resistor R6 to U1C.This prevents the comparators from switching during the low cycle of the input waveform, regard-less of the positions of R3 and R4. This has the effect of locking out changes during the low period of the input signal, and would probably require additional logic if it were done strictly in the digital domain.The circuit, with the component values shown, works well between about 50 and 150 kHz.



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