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This letter introduces a systematic procedure for the design of direct frequency demodulators based on injection locking. An oscillator is synchronized to the modulated carrier and the modulation signal is extracted from the time-variation of the current or voltage of the bias-network. The synchronized oscillator is optimized with harmonic-balance techniques specifically developed for this demodulation function. The circuit performance under modulated conditions is evaluated with envelope transient and using a modified Poincare map. The new techniques are illustrated by means of their application to a direct frequency demodulator at 1.2 GHz. The letter shows that provided accurate nonlinear analysis and design techniques are used, injection-locked oscillators constitute a good option for the implementation of direct frequency demodulators.
Date of Publication: Jan. 2008