Remote frequency calibration of passive wireless transponders using injection-locked PLL

This paper proposes a remote frequency calibration method that allows a passive wireless transponder to adjust the frequency of its local oscillator to a desired value using an injection-locked phase-locked loop (IL-PLL). The relaxation oscillator of the proposed IL-PLL employs a current pulse generator to generate the effective hysteresis needed for oscillation without using a Schmitt trigger. Integrating feedback is also proposed and used to increase the lock range and hold the frequency of the oscillator once the oscillator is locked and the injection signal is removed. The system has been designed and fabricated in TSMC-0.18µm 1.8V 6-metal 1-poly CMOS technology. The measured power consumption of the oscillator is 525 nW while that of the IL-PLL is 960 nW. The measured lock range of the system is 30 KHz without integrating feedback and 400 KHz with integrating feedback (one side). The total chip area including bonding pads is 850 µm × 600 µm. The frequency of the locked oscillator drifts over time at a rate of 5 Hz/ms when the external injection signal is removed.