Fully integrated signal conditioning of an accelerometer for implantable pacemakers

This paper shows the development of a fully integrated G _m -C 0.5-7 Hz bandpass amplifier (gain G = 400), for a piezoelectric accelerometer to be employed in rate adaptive pacemakers. The circuit, fabricated in a standard 0.8 micron CMOS technology, operates with a power supply as low as 2 V, consumes 230 nA of current, and has only a 2.1 μV_rms input referred noise. Detailed circuit specifications, measurements, and a system performance comparative analysis are presented. The physical activity system includes a fully integrated G _m -C rectifier and 3-second time average. Fully integrated very low frequency circuits were implemented with the aid of series-parallel current division in symmetrical OTAs. OTAs as low as 33 pS (equivalent to a 30 GΩ resistor) were designed, fabricated, and tested.