Fast hopping frequency synthesis techniques using injection locking.

Abstract

The use of fast-hopping frequency synthesis is a critical component of frequency-hopped spread spectrum (FHSS) systems. FHSS offers many advantages including high resistance to narrow-band interference, low probability of intercept and capability to share spectrum with other narrow-band systems. Such qualities make FHSS a particularly attractive scheme for military applications. In commercial applications, the WiMedia specification for ultra-wideband (UWB)/Wireless-USB presents another standard that uses fast frequency-hopping. The most stringent constraint on the frequency synthesizer in these systems is the band-switching time. This thesis presents novel techniques for fast-hopping frequency synthesis based on injection locking. First, extensive study of the transient behavior of oscillators under injection is presented. Analystical expressions are used as the basis for the study and interesting aspects of the locking process of an injection-locked oscillator (ILO) are identified. Two techniques, lock-range dependent fast-locking and predictive fast-locking, are then presented. In the first technique, fast locking times are achieved by using large lock-ranges for the ILO. Phase dependence of lock-time is exploited in the second technique and extremely fast settling is achieved. These theoretical findings are verified through simulation and measurements from a multiple of oscillator prototypes. Measurements from a low-speed Colpitts oscillator running at 57 MHz are used to verify tracking, out-of-lock behavior and frequency settling of ILOs. Measurements from an LC-oscillator implemented in 0.13-um CMOS technology operating at a free-running frequency of 3.4 GHz are used to verify the dependence of locking time on the lock range and the initial phase of injection. Novel architectures for fast frequency-hopping synthesizers and high frequency direct-digital synthesizer are then presented. Finally, a complete prototype for WiMedia-UWB/Wireless-USB-compliant fast-hopping frequency synthesizer architecture with quadrature outputs, based on sub-harmonic injection-locking, is presented. The synthesizer features a cross-coupled quadrature digitally-controlled oscillator, that is injection-locked to a sub-harmonic frequency. An intuitive closed-form expression for the dynamics of the quadrature injection-locked oscillator is derived. The overall design is a CMOS-only implementation and has been fabricated in 0.13-um SiGe BiCMOS process. Measurement results indicate lock-times of less than 2.5 ns, a locked phase noise of -114 dBc/Hz at 1 MHz offset and a quadrature accuracy of better than 0.5 deg. The frequency synthesizer (excluding output buffers) occupies an area of 0.27 mm2 and consumes 14.5 mW of power. The best and worst-case spur suppression achieved are 47 and 31 dB, respectively. This is the lowest power fast-hopping quadrature frequency synthesizer reported to-date.