Analysis, design, and performance of micropower circuits for a capacitive pressure sensor IC

An integrated circuit has been designed, built, and testing as part of a capacitive pressure transducer. High-accuracy compact micropower circuits utilizing a standard bipolar IC process without any special components or trimming are used. The key circuits for achieving this performance are a Schmitt trigger oscillator and a bandgap voltage reference. The sensor circuits consume 200 μW at 3.5 V, can resolve capacitance changes of 300 p.p.m., measure temperature to ±0.1°C over a limited temperature range, and presently occupy 4 mm/SUP 2/ on a 2 mm×6 mm implantable monolithic silicon pressure sensor. Further scaling of the sensor is discussed showing that a reduction of area by a factor of 4 is achievable.