Requiring only two ICs to monitor a train of positive pulses, this circuit produces a single positive output pulse for each input pulse whose duration is either too long or too short. You specify the minimum and maximum limits by adjusting the trimming potentiometers, R1 aod R2. You cao set the value of the acceptable pulse width from approximately 50 ns to 10 f-!S, for a 74123 monostable multivibrator. The leading edge of ao input pulse triggers one shots IClA and IClB as you cao see from the timing diagram.
Each NAND-gate output is high unless either or both inputs are low, so outputs X aod Y are high unless the circuit encounters an out-of-range pulse. IC2D then gates a negative pulse from IC2B or ICZC to produce the circuit"s positive output pulse.