We present a nonlinear event-driven model of a Digital PLL used in the context of a polar modulation. This modeling has shown that the estimation method of the TDC gain has a big impact on the EVM for wideband modulation and a solution has been proposed which consists to add the modulation on the gain after calibration of the gain offset. This transforms the classical two-points modulator into a three-points modulator. This implementation has been validated for WCDMA standard.
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R. B. Staszewski, K. Muhammad, D. Leipold, C.-M. Hung, Y.-C. Ho, J. L. Wallberg, C. Fernando, K. Maggio, R. Staszewski, T. Jung, J. Koh, I. Yuanying Deng, V. Sarda, O. Moreira-Tamayo, V. Mayega, R.Katz, O. Friedman, O. EytanEliezer, E. de-Obaldia and P. T. Balsara, “All-digital TX Frequency Synthesizer and Discrete-time Receiver for Bluetooth Radio in 130-nm CMOS,” IEEE J. Solid-State Circuits, Vol. 39, No. 12, 2004, pp. 2278-2291. doi:10.1109/JSSC.2004.836345
J. Zhuang, K. Waheed and R. B. Staszewski, “A Technique to Reduce Phase/Frequency Modulation Bandwidth in a Polar RF Transmitter,” IEEE Transactions on Circuits System I, Reg. Papers, Vol. 57, No. 9, 2010, pp. 2196-2207.