A VLSI demodulator for digital RF network applications: theory and results

An all-digital demodulator/detector which is suitable for both analog FM and digital phase/frequency modulations is presented. The system uses complex sampling, which employs a single A/D (analog/digital) converter to sample the signal at an intermediate frequency (IF) and produce baseband in-phase (I) and quadrature phase (Q) signals, and a simplified technique for reducing the effect of the I/Q timing misalignment usually associated with this approach. The system also includes two detectors which operate simultaneously to provide noncoherent and differentially coherent detection, as well as automatic gain control (AGC) and automatic frequency control (AFC). The flexibility afforded by the two concurrent detectors in this all-digital system is shown to make it suitable for a wide range of applications. The theory behind the demodulator/detector system is described, and an implementation using a 1.25-μm bulk CMOS VLSI process is presented. Methods are shown for extending and improving the I/Q sampling misalignment correction technique, as well as for reducing the A/D sampling rate for a given IF frequency. Simulation and experimental results illustrate system performance for both analog and digital modulations