An agile ISM band frequency synthesizer with built-in GMSK datamodulation

摘要

In this paper, a high-resolution fractional-N RF frequencynsynthesizer is presented which is controlled by a fourth-order digitalnsigma-delta modulator. The high resolution allows the synthesizer to bendigitally modulated directly at RF. A simplified digital filter whichnmakes use of sigma-delta quantized tap coefficients is included whichnprovides built-in GMSK pulse shaping for data transmission. Quantizationnof the tap coefficients to single-bit values not only simplifies thenfilter architecture, but the fourth-order digital sigma-delta modulatornas well. The synthesizer makes extensive use of custom VLSI, with only ansimple off-chip loop filter and VCO required. The synthesizer operatesnfrom a single 3-V supply, and has low power consumption. Phase noisenlevels are less than -90 dBc/Hz at frequency offsets within the loopnbandwidth. Spurious components are less than -90 dBc/Hz over a 19.6-MHzntuning range