Harris Corporation

Steven Robert Jost

Gregg D Croft

Sang-Gug Lee

A current generator and method of making a current generator in which two resistors are provided, each in series with one of two transistors in the generator, and in which one of the resistors is trimmed if the reference current is too large and the other is trimmed if the reference current is too small, thereby obviating the problems of the prior art in which one resistor must be trimmed by a potentially large and unacceptable amount. The two resistors are formed with a distribution of resistances which is centered on their corresponding target resistance values so that the number of resistors to be trimmed and the amount of trimming per resistor are reduced. The appropriate target resistances of the resistors can be determined if a maximum trim factor is set. The method is insensitive to variations in the process by which the resistances of the resistors are initially set and reduces the variability of the untrimmed reference current with respect to resistor critical dimensions.

Method of making a reference current generator

A buffer amplifier configuration simultaneously reduces d.c. voltage offsets through the signal flow path between its input and output and maintains a high input impedance and a low output impedance. In a preferred embodiment, high input impedance is achieved by coupling the input transistor's collector to a high impedance current source, which is coupled to one of the buffer's power supply rails. The emitter of the input transistor is coupled to the input terminal and its base of the base of a like polarity bipolar output transistor, the emitter of which is coupled to an output terminal and the collector of which is coupled to one supply rail. Since both the input and output transistors are of the same polarity type (so that they can be reasonably well matched during manufacture) and have their base-emitter junctions connected back-to-back between the input and output terminals, they impart effectively no Vbe-based d.c. offset voltage through the buffer. To ensure a high input impedance regardless of output load and output stage gain an isolating emitter-follower transistor stage is preferably coupled between the collector of the input transistor stage and the base of the output transistor stage.

Growing community of inventors

Palm Bay, FL, United States of America

Steven Robert Jost