Abstract: An interface circuit for connecting a signal source [10], such as a variable reluctance sensor, to a digital circuit [20] such as a microprocessor. A comparator [40] generates a logic signal [at 49] indicating whether the signal from the source is greater than or less than the signal's average value. The inputs to the comparator are connected across a pair of back-to-back diodes [44,46] which are serially connected with a current limiting resistor [42] between the source and the output of an operational amplifier [35] which generates an average value voltage. The operational amplifier's output is directly connected to its negative input so that it exhibits unit gain, and the operational amplifier's input is connected to the sensor voltage by a low-pass filter [32,34] so that amplifier responds only to the DC content of the sensor's output signal.

Abstract: The programmable time advance circuit functions to offset the inherent delay occasioned by the phase lock loop and the drive circuits of a printed circuit board test system to provide a clock signal at the output of the printed circuit board test system that exactly matches the clock signal of the printed circuit board under test at the printed circuit board under test. This is accomplished by inserting a clock advance signal into the phase locked loop to advance the timing of the clock signal generator circuit in the printed circuit board test system to compensate for the delay occasioned by the conductors and driver circuits in the printed circuit board test system.