Programmable Switched-Capacitor Filter Design Tool for Biomedical Signal Acquisition

This paper presents an open source design support tool for a respiratory and cardiac signal acquisition system that utilizes programmable switched-capacitor analog filters in the analog front end. The proposed filter topologies are based on cascaded second-order-section filters and are designed to be programmable in terms of the cut-off frequency via the switching frequency. The design support tool is written in Python and is capable of calculating the capacitance ratios for a given second-order filter topology, generating a parameter file, and performing periodic AC simulations of the designed circuit in SpectreRF. The tool uses a simple estimation algorithm to find the best possible integer fit with an error cost function. Two sets of 6th-order switched-capacitor filter sets are designed using biquadratic sections in 180nm CMOS process. The proposed design methodology offers a better area fraction reduction compared to simple integer ratio designs. Post-layout simulation results demonstrate the effectiveness and efficiency of the proposed design support tool for switched-capacitor analog filters in respiratory and cardiac signal acquisition systems.