An analysis of phase noise requirements for ultra-low-power FSK radios

Abstract

This paper presents an analysis of the influence of phase noise (PN) on FSK radios and derives the total PN requirement for a low power FSK link based on Bit Error Rate (BER) performance. A simple noise model is built, including phase noise and white noise from the AWGN channel, to analyze its influence on the BER of an ULP FSK RX. It shows that to achieve a 10−4 BER, the minimum PN requirement can be more relaxed than current synthesizer designs. The trade-off between PN, data rate, and frequency deviation of FSK modulation is also studied, showing how bandwidth can be traded for relaxed PN while maintaining the same spectral efficiency (bits/Hz). This result implies we could migrate from LC-VCOs to ring oscillators with a simple PLL for wireless communication using FSK and significantly reduce the power of radios. A chip was fabricated to test the accuracy of the model at different PN levels, showing agreement among theoretical analysis, simulations, and measurements.