Window comparator

A window comparator comprised of

• a first means for algebraically subtracting an input signal from a selected set-point voltage to produce a difference output indicating when said input signal exceeds a set-point level established by said set-point voltage, said first means being comprised of an operational amplifier having an inverting input terminal connected to a summing junction and two feedback circuits connecting the output of said operational amplifier to said summing junction, one feedback circuit comprising a first diode in series with a resistor, the first diode having its anode connected to the output of the first operational amplifier, and the other feedback circuit comprising a second diode in series with a resistor, the second diode having its cathode connected to the output of said first operational amplifier;
• a first summing resistor coupling said input signal to said summing junction and a second summing resistor coupling said set-point voltage to said summing junction, said set-point voltag being selected for the set-point level at which the linear output of the first operational amplifier crosses from one polarity to another according to when the algebraic difference between the input signal and the set-point voltage changes polarity, and
• a second means for algebraically subtracting the difference output of said first means from a selected window-width voltage to produce an output signal of a first level until said difference signal indicates said input signal has exceeded said set-point level and, thereafter of a second level until said difference signal exceeds said window-width voltage, at which time said second means produces said output signal of said first level while said difference signal continues to exceed said window-width voltage, said second means being comprised of a high gain differential amplifier having one input terminal connected to the junction between the diode and feedback resistor in one of said feedback circuits and a second input terminal connected to the junction between the diode and feedback resistor in the other one of said feedback circuits, and means for connecting said window-width voltage to one of said two input terminals of said differential amplifier.