A ΣΔ based direct all-digital frequency synthesizer with 20 Mbps frequency modulation capability and 3μs startup latency

Abstract

This paper presents an all-digital, direct frequency synthesizer that can support direct modulation data rates up to 20 Mbps for deployment in multi-hop, reconfigurable wireless mesh networks. In addition, this synthesizer can start up in only 3 us which reduces the energy overhead, thus making it attractive for duty cycling. By digitally manipulating time-shifted copies of a temperature-compensated FBAR oscillator signal based on the outputs from a Sigma-Delta modulator (SDM), the synthesizer is able to generate the desired frequency over a wide range. Integrated in a 65 nm CMOS technology, a prototype of this synthesizer generates frequencies from 2.34-2.47 GHz. Being completely digital, this synthesizer occupies a very small area of just 0.035 mm2. The synthesizer consumes 3.9 mA from a 1.1 V supply while achieving a frequency resolution of 180 Hz.