A 2.4 GHz two-point Δ-Σ modulator with gain calibration and AFC for WPAN/BAN applications

A 2.4GHz two-point phase modulator system based on a fractional-N phase-locked loop (PLL) for wireless personal and body-area network (WPAN/BAN) transceivers applications is proposed. It employs the digital baseband Gaussian Minimum Shift Keying (GMSK) modulation. A switched-capacitors bank LC tank voltage-controlled oscillator (VCO) is used to operate in a wide-band frequency range. Using an adaptive frequency calibration (AFC) technique to choose the proper capacitor bank, the lock time is reduced. The performance of the two-point modulation suffers a lot from the gain mismatch and timing mismatch of the two modulation paths. The timing mismatch is compensated by adding a tunable digital delay block, and a 6-bit gain calibration word is used to calibrate the gain mismatch. The two-point phase modulator can achieve the EVM value of 1.7% in simulation, with the 1Mbps data rate.