Thermally-Adjustable Passive Resistors for Fine-Tuning High-Temperature Electric Circuits

摘要

Rejustors are MEMS-based passive chip-resistors, adjustable by electrical signals. If individual unit-by-unit temperature-conditioning is needed, the TCR can also be adjusted, independently from its resistance. Adjustments can be done in-circuit, using the circuit's output for adjustment feedback, to "null out" cumulative variances and mismatches in the larger circuit. Typical instantaneous adjustment precision is 0.1% or better. Rejustors have favorable characteristics for high temperature operation, and exhibit long-term drift less than ～1% after 1000 hours at 225°C. Resistance vs. temperature curves have a predictable parabolic shape. Two types of "HT-Rejustors" are described for high-temperature applications, having 20% resistance adjustment range: Type-1 features an overall resistance tolerance (including longterm drift) of +/-2.5% over an extended temperature range (-55°C to +250°C). Type-2 features a tighter resistance tolerance of 0.7% over a narrower "focus-range" of temperatures (e.g. 175°C to 225°C). Rejustors can be adjusted in-circuit at room-temperature or at an elevated temperature more suited to the application. After adjustment, these devices are stable purely-passive resistors and do not require power to hold their resistance or TCR setpoints. This enables a family of solutions for high-temperature electric circuit applications, enabling several adjustment strategies for high-temperature circuit operation.