To more efficiently use spatial and temporal spectrum from 50 MHz to 10 GHz, many are eying cognitive radio (CR). On a system-on-a-chip (SoC), however, a heterodyne approach requires multiple local oscillators (LOs) to handle the potentially independent operations of the CR RF transceiver. Such an implementation can be very tricky, as the design of LO for CR applications demands silicon-area compactness and low power consumption. Recently, a low-quadrature LO was designed and implemented by the University of California’s Ning-Yi Wang, Mau-Chung Frank Chang, and Jianhua Lu (who is also with Peregrine Semiconductor Corp.). Their LO can create 13.3-to-20.0-GHz signals from a differentially tuned, inductive-capacitive voltage-controlled oscillator (LC-VCO). It converts those signals to the 5-to-10-GHz band with continuous frequency coverage.
In this design, a frequency-extension solution takes advantage of the natural characteristics of a four-stage, differential, injection-locked ring oscillator (ILRO) to obtain the desired quadrature outputs with a precise 50% duty cycle. Impressively, both the output 50% duty cycle and quadrature matching can be maintained even with the input signal’s duty cycle deviating from 50%. The team implemented the integrated, quadrature-phased LO in 65-nm general-purpose CMOS integrated-circuit (IC) technology. It occupies less than 0.11 mm2 and consumes a maximum of 22 mA current from a 1-V supply. The LO exhibits worst-case phase noise of −104 dBc/Hz at 1 MHz offset across the entire 5-to-10-GHz band. See “A Compact and Low Power 5-10 GHz Quadrature Local Oscillator for Cognitive Radio Applications,” IEEE Journal Of Solid-State Circuits, May 2012, p. 1131.