We propose a digitally controlled injection-locked RF oscillator with an auxiliary loop as an alternative to the conventional capacitive fine-tuning of an LC-tank. The oscillator is injection locked to a time-delayed version of its resonating voltage and its frequency is modulated by manipulating the phase and amplitude of injected current. The injection strength can be programmed for the DCO step size to be as fine as 9 kHz at 4 GHz. Alternatively, with large injection strength, the tuning range can reach up to 200 MHz. The proposed oscillator is experimentally verified in TSMC 40 nm digital CMOS.
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