Bandpass sigma-delta (Σ-Δ) architecture based efficient FM demodulator for software radio

A bandpass sigma-delta (Σ-Δ) modulator architecture based FM demodulator, suitable for software radio technology is investigated. The I-F stage of the circuit separates the inphase and quadrature (I and Q) signals using a single circuit path, thus eliminating any I-Q differences due to component mismatch. The separated I-Q signals are used in a subsequent FM demodulator that is compatible with digital wireless or FM receiver systems. The performance of the single path circuit, e.g. quantization noise and I-Q signal mismatch effects and FM demodulation errors are analyzed in detail. Based on this analysis, criteria for the selection of designing parameters, such as sampling frequency and over-sampling ratio are presented. Issues related to hardware realization of the system using a Field Programmable Gate Array (FPGA) are noted.