MEMS-based resistor divider sets ohmic resistance and TCR
By Margery Conner, Technical Editor -- EDN, August 13, 2007
Temperature-sensitive circuits, such as those in analog instrumentation, optical networks, or power supplies, usually require temperature compensation. For those applications, Microbridge has added electronic temperature compensation to its line of MEMS (microelectromechanical-system)-based adjustable resistors, which the company calls “rejustors,” to make a passive electronic-temperature-compensation-resistor divider (see “Rejustors change resistance by thermal annealing of polySi”).
The highly accurate, 30-kΩ MBT-303-A divider comprises two resistors in series. You can set each resistor’s value to 21 to 30 kΩ with an accuracy of 0.01%. You can adjust both ohmic resistance and the positive and negative TCR (temperature coefficient of resistance) for each resistor after you mount the chip in a PCB (printed-circuit board), allowing compensation for any stresses or changes during manufacturing. Setting the rejustor takes approximately a second. The MBT-303-A requires no power source during operation, has no wiper resistance, and needs no external temperature sensor because it has its own temperature sensor and adjustment controller. It can handle as much as 1 mW of power and frequencies into the gigahertz range. Available in a 16-lead QFN package or an eight-pin SOIC package, the new MBT-303-A passive rejustor is currently available for sampling and costs $1.67 (1000).
