2012 Volume 48 Issue 10 Pages 607-613
This paper describes a novel low-powered preamplifier for capacitive sensor using electret film such as a condenser microphone. Due to the expansion of sensor applications as ambient sensors such as the smart fire alarm, general purpose security sensor and vital sign detection sensor, it must work for at least one year with a small dry buttery. The conventional amplifier requires about 500µA current for the 3.0V voltage to make the sensor work stably. Even the recently developed capacitor-voltage transforming IC required the current in the range of 35µA to 530µA. In this paper, we present a preamplifier circuit combining the differential amplifier and the current miller transconductance amplifier which is robust to low frequency drift noise and the output is single (not differential) and low current driving circuit. The current required for stable operation of the sensor was 20µA, which is about one-twenty third of the conventional amplifier.
