Continuous time bandpass ΔΣ modulators for a software defined radio

A mixed-signal continuous time band-pass delta-sigma modulator (CT BP ΔΣ) is a very attractive circuit category for applications where a time domain signal is to be processed in the digital domain. High-speed applications, such as wireless communications and software defined radio, are in need of a tunable bandpass filter in GHz range. We present a top level analytical model of a tunable 4^th order CT BP ΔΣ modulator which is used for development of our mixed-signal continuous time behavioral circuit model. High speed CT ΔΣ modulators are implemented using both "analog" and "digital" subblocks. We created mixed-signal models of the subblocks in order to efficiently perform simulations in the continuous time domain. The models were built out of primitives available in SPICE and Verilog-A™. Simulation results confirmed validity of the analytical model.