FPGA Implementation of Sigma-Delta Modulators in Fractional-N Frequency Synthesis

This paper presents three high performance sigma-delta modulators (SDMs) including a single stage third order modulator and two MASH modulators. The SDMs are successfully implemented by FPGA. Both simulated and measured results are presented and compared discussed. By employing the proposed techniques, the fractional-N frequency synthesiser presented a tonal-free spectrum without the affections of integer or fractional spurs. The in-band phase noise of the synthesiser is lower than -90 dBc/Hz. The final output spectrum of the frequency synthesiser demonstrates the advantage and extensibility of this technique.