Frequency encoded integrators applied to filtering and sigma delta modulation
A theoretical approach to the problem of replicating continuous time systems with frequency modulated oscillators is proposed. It has been shown that continuous time filters and especially, the loop filter of a sigma delta modulator, can be implemented with VCOs and digital circuitry. The analysis of these architectures is usually based on the integral relationship between frequency and phase in an oscillator. However, the spectrum of a modulated oscillator contains components at the harmonics of the oscillation frequency that cannot be easily described using the phase frequency relationship. We propose a model in which a VCO is considered a signal encoder instead of an integrator. This model is applied then to the design of a band pass sigma delta modulator.
2016 IEEE International Symposium on Circuits and Systems (ISCAS)