High-performance frequency-hopping transmitters using two-point delta-sigma modulation

This paper presents a 2.4-GHz high-performance frequency-hopping (FH) transmitter using two-point delta-sigma modulation (TPDSM). Two bottleneck problems in the implementation have been studied rigorously. One is the nonlinear performance of a phase-locked loop (PLL). The other is the inherent gain and delay mismatches between two modulation points. Both nonlinear and mismatch factors dominate the modulation accuracy in the closed PLL. Our formulation can predict the dependencies of modulation accuracy on both factors quite successfully. Comparison of the averaged frequency deviation and frequency-shift-keying (FSK) error between theory and measurement shows excellent agreement. The implemented TPDSM-based FH Gaussian FSK transmitter can achieve 2.5-Mb/s data rate along with 15-μs PLL stable time with only 2.2% FSK error under good design and operating conditions.