In this paper, a high-resolution fractional-N RF frequency synthesizer is presented which is controlled by a fourthorder digital sigma-delta modulator. The high resolution allows the synthesizer to be digitally modulated directly at RF. A simplified digital filter which makes use of sigma-delta quantized tap coefficients is included which provides built-in GMSK pulse shaping for data transmission. Quantization of the tap coefficients to single-bit values not only simplifies the filter architecture, but the fourth-order digital sigma-delta modulator as well. The synthesizer makes extensive use of custom VLSI, with only a simple off-chip loop filter and VCO required. The synthesizer operates from a single 3-V supply, and has low power consumption. Phase noise levels are less than -90 dBc/Hz at frequency offsets within the loop bandwidth. Spurious components are less than -90 dBc/Hz over a 19.6-MHz tuning range.

Additional Metadata
Keywords Frequency synthesizer, GMSK modulation, Radio transmitters, Sigma-delta modulation, Sigma-delta quantized tap coefficients
Persistent URL dx.doi.org/10.1109/4.701242
Journal IEEE Journal of Solid-State Circuits
Citation
Filiol, N.M. (Norman M.), Riley, T.A.D. (Thomas A. D.), Plett, C, & Copeland, M.A. (Miles A.). (1998). An agile ISM band frequency synthesizer with built-in GMSK data modulation. IEEE Journal of Solid-State Circuits, 33(7), 998–1008. doi:10.1109/4.701242