This simple window detector uses only half of a 7400 quad NAND gate plus four resistors, chosen so that the voltage at point A exc.,eds the voltage at point B for any input voltage. With no input applied or when VIN is at ground, the output of gate Gl is one; hence G2`s output is also one. As the input voltage increases, VA rises faster than JOB.
When Va reaches an acceptable one level, the circuit"s output drops to zero. As the input continues to increase, JOB rises to an acceptable level, changing the output of G2 to one.