An lower ISM band frequency synthesizer and GMSK data modulator

In this paper a high resolution fractional-N RF frequency synthesizer is presented which is controlled by a fourth-order digital sigma-delta modulator allowing the synthesizer to be digitally modulated directly at RF. For data transmission a simplified digital filter which makes use of sigma-delta quantized tap coefficients is included which provides built in GMSK pulse shaping. The synthesizer makes use of two custom chips, with only a simple off chip loop filter and VCO required. The synthesizer operates from a single three volt supply and the two chips consume a total of 32 mW.