Micropower analog structures for a CMOS heart rate indicator

A micropower heart-rate indicator integrated with CMOS technology and using several micropower blocks is currently under development. So far the complete DC-compensated preamplifier and the switched capacitor (SC) filter have been designed and tested. The designs of these structures and measurement results are presented. The SC filter consists of several sections, including an input decimator, lowpass filter, decimation/SH section, and highpass filter. Filter performance was measured by varying the temperature, supply voltage, and bias current. The temperature effects were minor, but any reduction in the GBW of the operational amplifiers with reduced bias current caused marked variations in the results. In addition, any reduction in the supply voltage below ±1 V caused an abrupt attenuation of the amplitude response of the filter as the on-resistance of the CMOS switches increased due to inadequate clock amplitude