A 2.5-Mb/s GFSK 5.0-Mb/s 4-FSK automatically calibratedΣ-Δ frequency synthesizer

This paper describes a new sigma-delta (Σ-Δ) frequency synthesizer for Gaussian frequency and minimum shift keying (GFSK/GMSK) modulation. The key innovation is an automatic calibration circuit which tunes the phase-locked loop (PLL) response to compensate for process tolerance and temperature variation. The availability of this new calibration method allows the use of precompensation techniques to achieve high data rate modulation without requiring factory calibration. The calibration method can be applied to GFSK/GMSK modulation and also M-ary FSK modulation. The PLL, including 1.8-GHz voltage controlled oscillator (VCO), Σ-Δ modulator, and automatic calibration circuit, has been implemented in a 0.6-μm BiCMOS integrated circuit. The test chip achieves 2.5 Mb/s using GFSK and 5.0 Mb/s using 4-FSK