A bipolar differential amplifying circuit contains a pair of input transistors (3 and 4) for receiving a differential input signal, a pair of differentially-configured first and second transistor circuits (5 and 6) coupled to the input transistors, and a subtracting circuit (11 and 12) for comparing the sum of the currents through first collectors (5C.sub.1 and 6C.sub.1) of the transistor circuits with the current through a second collector (6C.sub.2) of the second transistor circuit to generate an output signal representative of the input signal. A PN diode (13) is coupled to a second collector (5C.sub.2) of the first transistor circuit. The voltages at the collectors are very close, thereby yielding a high common-mode rejection ratio for the input signal.
An input stage of an operational amplifier uses current sources to allow first and second differential input transistor pairs to operate near the power supply rails. The output stage of the operational amplifier also operates within a saturation potential of the power supply rails. The first differential input transistor pair operates when the input signal is less than a predetermined threshold, while the second differential input transistor pair operates when the input signal is greater than the predetermined threshold. A detection circuit at the input terminals prevents phase inversion of the output signal should the inputs be driven beyond the power supply rails. A current cancellation circuit removes current variation induced by voltage changes at the output of the input stage and provides high gain and low input offset voltage.
A stackable voltage comparator circuit that may be used in an analog voltage address decoder circuit for performing voltage window comparisons. The voltage comparator circuit includes a plurality of voltage comparator circuit cells, each of which includes a differential input stage made up of a pair of transistors which receives a current source. A first comparator circuit cell includes a differential input pair of transistors with one of the transistors having a first collector and a second collector, with the second collector being coupled to an output line. The first comparator circuit cell compares an input window with a first threshold voltage and produces an output at the output line. A second comparator circuit cell compares the input voltage with a second threshold voltage and includes a second differential input pair of transistors. The second comparator circuit cell has an input coupled to the output line of the first comparator circuit for receiving current when the input voltage is less than the first threshold voltage and provides an output indicative of whether the input voltage is within a voltage window bounded by the first and second threshold voltages.
