Multiple trim structure

Abstract

A trim structure having a nominal resistance value can be adjusted to have a higher or lower value by a combination of fuse blowing and zener zapping. In the preferred embodiment a pair of integrated circuit pads are employed in a trim structure along with a pair of back-to-back zener diodes, a fuse link, and four resistors. In its initial state, with both diodes and the fuse link intact, a particular or nominal resistance value is available. Blowing the fuse link alone produces a second or highest resistance value. Shorting, or zapping, one zener diode produces a third higher than nominal but lower than highest resistance value. Shorting, or zapping, the other zener diode produces a fourth, lower than nominal, resistance value. Shorting, or zapping, both zener diodes produces a fifth lowest resistance value. Thus, five different resistance values are available using only two integrated circuit pads. If desired, the five resistance steps can be made linear by properly selecting the resistor values. In addition, one of the circuit pads can be a common power supply terminal so that only one pad need be added to the integrated circuit chip. Two or more such structures can be fabricated with a common pad by the addition of one additional pad for each such structure.

Dependencies are inferred from the claim text.