A fast-tuned, injection locked, DDS-based local oscillator for the 3.6 to 4.1 GHz frequency range

A fast-tuned (100-n) synthesized local oscillator for the 3.6.4.1-GHz frequency range is described in which a direct digital synthesizer (DDS) is used to high-order subharmonically injection lock a voltage-controlled oscillator (VCO) and thereby upconvert and broaden the DDS frequency range. This is a design approach that combines the beneficial features of a DDS, namely its fine frequency resolution and fast switching speed, with the fast locking time (40 ns), in situ amplification, and high-order multiplication advantages that are intrinsic to subharmonic injection locking. A method is demonstrated that enhances, by a factor of 5, the narrow locking bandwidth normally associated with conventional subharmonic injection locking. A measurement of the locking transient and locking time of the injection process at a microwave frequency is reported. The measured 40-ns locking time is more than an order of magnitude faster than that of conventional phase locking.< >