A resistance-variation-tolerant constant-power heating circuit for integrated sensor applications

Abstract

We report a novel CMOS circuit that is capable of maintaining constant heating power when heater resistance varies. This type of constant-power heater circuit finds application in various types of thermal-based sensors, such as vacuum sensors, ac power meters, gas-flow sensors, and gas-detection sensors. The heating power is kept constant by controlling a reference current. The circuit uses a bipolar-like translinear loop. To our knowledge, this is the first reported translinear loop implemented in CMOS. The prototype is implemented using a MOSIS 2-/spl mu/m ORBIT n-well CMOS process. Experimental results showed that the heating power can be maintained to 3% with /spl plusmn/50% variation in resistance when the heater resistance is 1 K/spl Omega/. The maximum recorded heating power is about 11 mW for R/sub load/ of 1 K/spl Omega/.