Comparator circuit

Abstract

A comparator circuit is provided for producing a voltage across the base and collector electrodes of an output transistor to drive the output transistor to either a conducting condition, or a nonconducting condition, selectively in accordance with an input signal. A switching circuit, responsive to the input signal, is coupled between a current source and the base electrode of the output transistor for electrically coupling the current source to the base electrode of the output transistor when the output transistor is driving from the conducting condition to the nonconducting condition and for electrically decoupling the current source from the base electrode of the output transistor when such output transistor is driving from the nonconducting condition to the conducting condition. With such arrangement, when the switching circuit couples the current source to the base electrode of the output transistor, the current source provides a discharge circuit for base charge in the output transistor. Further, when the switching circuit decouples the current source from the base electrode of the output transistor, such current source is coupled to a resistor coupled between a voltage source and the base electrode of an active pull-up transistor. With such arrangement, the resistance of such resistor may be reduced thereby reducing the time constant associated with such resistor and the inherent capacitance of such active pull-up transistor.