An Energy Efficient Oscillator Frequency Calibration Methodology Using Fraction Phase Computation

Wireless Sensor Nodes (WSNs) require a frequency calibration unit for correcting the spectral mask errors in its Radio Frequency (RF) front-end, which is caused by process, voltage and temperature (PVT) variations of the RF oscillator. In WSN applications, the conditions dictate such a frequency calibration unit to be energy efficient (i.e. both low power and having a fast settling time). In this paper, we propose an on-chip, fully embedded frequency calibration methodology, the corresponding algorithm and the hardware architecture, which are suitable for ultra-low power WSNs that use Frequency Shift Keying (FSK) as its modulation scheme. The architecture is based on computation of the fraction-phase of an RF oscillator frequency, when the former is divided by a reference frequency value. The proposed technique, though analogous to a fraction-N frequency synthesizer, requires no phase-locking mechanism and, therefore, requires no Phase Locked Loop (PLL). Simulation results have been presented showing the improved performance metrics over the state-of-the-art frequency calibration techniques used in WSNs.