A self-injection locked VCO with adaptive control of injection phase

An adaptive control method of injection phase is proposed to overcome the drawback of conventional self-injection locked VCO. The self-injection locking is an effective method to reduce the phase noise of the VCO, however there are some problems such as a discontinuous frequency and a large phase noise variation. The proposed circuit is composed of a VCO, a phase detector (PD), a delay line and a phase shifter (PS) to optimize the injection phase. In order to obtain an optimum injection phase, the phase shifter is controlled based on the PD output. The IC which includes Ka-band VCO and the PD is designed and fabricated by using a 0.18μm SiGe BiCMOS technology. The proposed self-injection locked VCO using the fabricated IC and the external delay line shows the continuous frequency characteristic. Moreover, much lower phase noise variation of 5 dB is obtained than that of 12 dB of the conventional self-injection locked VCO.