Abstract
An amplifier that uses an analog resistive trim element (trimistor) that can be reduced in value by Al/Si filaments formed by an alloying process is described. Filament generation and their lengths are controlled by current pulses through the element. A general in-package trim technique was developed using the trimistor and a high-voltage high-current diode, allowing the package pins to be multifunctional. This combination permits the input offset voltage for each channel of a quad op amp to be trimmed in the package to 10 /spl mu/V. The differential input stage utilizes JFET followers, which allows the separation of JFET/bipolar biasing currents. This results in a low offset voltage temperature coefficient (1/spl sigma/) of 2.5 /spl mu/V//spl deg/C. The gain-bandwidth product is enhanced over the unity-gain frequency by using a dual-doublet frequency-compensation technique. One doublet is defined using the JFET follower with feedforward capacitance, and the second doublet is formed by local positive AC feedback applied to the input current mirror. The amplifier is unity-gain stable, with a 100 MHz gain-bandwidth product (at 100 kHz) and 25 V//spl mu/S slew rate. The symmetrical quad layout is 80/spl times/120 mil/SUP 2/ with 6% of the area dedicated to trim. The die is suitable for a 14-pin narrow-body surface-mount package.
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