A High-Gain Acquisition System With Very Large Input Range

A signal acquisition system is presented for the recording of small signals in the presence of low-frequency interference. In a conventional design, high-pass filters precede the input stage to remove the impeding signals. However, filters limit the recording bandwidth, can lead to long settling time after disturbance, and potentially valuable information about the interfering signal is removed. Also, the required large components are impractical for a fully integrated solution. In this paper, a flexible, low-cost, filterless system is proposed and demonstrated, which extends the available input range to accommodate interference instead of rejecting it. An integrated system using digitally controlled floating batteries to compensate for interference at the amplifier input is presented. A digital postprocessing algorithm suitable for integration is proposed and evaluated. Measured results of the acquisition front-end realized in 0.35 mum CMOS technology confirm a more than sevenfold extension of the original input range and the usable dynamic range. The system is further verified using electrocardiography as a typical biomedical application.