Analysis and Design of IF and RF Circuits for SDR Receivers: Anti-aliasing Pre-filters, Accurate and Low-noise Quadrature LO Generation and Injection-locked Dividers

The proliferation of bands and modulation formats calls for a universal software-defined radio (SDR) receiver. This digitizes the received waveforms as soon as possible to relegate most of the functionality to DSP. In order to use low-cost ADCs, we envisage the SDR receiver as a signal conditioner which emphasizes the desired channel and de-emphasizes the rest. This approach requires clock-programmable built-in anti-aliasing pre-filters that attenuate interferers to the extent that ADC can resolve the wanted signal and residual blockers without being overloaded. Most of this work is to design and implement such IF filters. In the rest, a complete portrait of LC quadrature oscillator (QOSC) based on injection locking is offered. It is shown that inserting 90 degrees phase-shifters between the two oscillator cores of the QOSC results in a single-mode oscillation with superior phase-noise and minimum sensitivity to mismatches. Finally, the idea of progressive multiple-node injection is described as a method to widen the lock-range of injection-locked dividers.

Ahmad Mirzaei, Sr Staff Scientist at Broadcom Corporation, Irvine, CA.