A State-Space Model for the Analysis of VCO-Based Filters using PFM

Voltage controlled oscillators (VCOs) were demonstrated to be an efficient hardware alternative to analog integrators in supply constrained nanometer CMOS technologies. Notably, various filter designs have found applications in voice feature extraction and communication systems. However, a deep understanding of the trade-offs in their design and their system-level limitations has not yet been described. This paper proposes an analysis of linear filters approximated using VCO-based integrators and provides insights in the design aspects of these systems.