Fraction phase based low energy frequency calibration: analysis and design

The study presents the algorithm design, non-ideal effect analysis, architectural analysis and design, circuit analysis and design of an iterative frequency calibration system that corrects frequencies consuming very low energy. The method is based on measuring the ‘fraction’ portion when an oscillator frequency (typically of a radio frequency oscillator) is divided by a fixed reference frequency. It then compares the obtained fraction value with the target fraction value (target frequency divided by the same reference) and finally corrects the oscillator frequency so as to converge it to the target. A salient feature of the proposed architecture of the system is the absence of elements in the radio frequency path which is considered to be the main source of power consumption. The system can be used in applications that do not require stringent phase-locking e.g. wireless sensor nodes. Test of the calibration system has been performed in conjunction with a Medical Implant Communication Service (MICS) band (402–405 MHz) oscillator. Successful convergence has been achieved over a wide range of sampler delay variation and oscillator jitter, which are the circuit level non-idealities that arise in the system.