At&t Bell Laboratories

Suk K Kim

Edward J Zimany, Jr

Hanafy E Meleis

Thayamkulangara R Viswanathan

Current source circuitry consisting of a first n-channel field effect transistor (FET) and voltage generator circuitry coupled to the gate of the first FET. The voltage generator circuitry acts to control the current through the first FET such that it is essentially constant even with power supply, temperature, and many processing variations. The voltage generator circuitry consists of a second FET, a two input differential operational amplifier, a resistor, and an n-p-n transistor if the resistor has a positive temperature coefficient. A negative feedback path using the amplifier and the second FET ensures against current changes in the first and second FETs even if there are changes in one of the power supply levels and/or many semiconductor processing variations.

Temperature and power supply stable current source

A voltage generator circuit consists essentially of two separate groups of serially connected semiconductor junctions with one group having one more junction than the other, two groups of constant current sources, and a differential operational amplifier. The circuit generates a reference voltage which in one embodiment is close to the bandgap voltage of silicon and is essentially constant over an operating temperature range of 25-85 degrees C. and does not require the trimming (adjusting) of resistor values. This circuit is particularly useful in CMOS CODECs. The circuit is designed such that the input offset voltage of an operational amplifier is not multiplied by the gain of the amplifier.

Trimless bandgap reference voltage generator

A high impedance is implemented in the input bias path of an integrated instrumentation amplifier. The implementation includes a normally on transistor switch. A signal from the output of the amplifier is used to turn the switch off to provide the requisite high impedance. Otherwise, the switch is on to provide low impedance for proper biasing. The circuit is adapted for encoded input signals such as occur in capacitive coupled credit card encoding circuits.

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Bridgewater, NJ, United States of America

Suk K Kim