TY - JOUR
T1 - A Digital PLL-Based Phase Modulator With Non-Uniform Clock Compensation and Non-linearity Predistortion
AU - Gao, Zhong
AU - Fritz, Martin
AU - Spalink, Gerd
AU - Staszewski, Robert Bogdan
AU - Babaie, Masoud
PY - 2023
Y1 - 2023
N2 - In this article, we present a low-power digital phase-locked loop (PLL)-based phase modulator targeting low error vector magnitude (EVM). We introduce a new non-uniform clock compensation (NUCC) scheme to tackle an EVM degradation resulting from the beneficial use of a time-varying sampling clock that is re-timed to the phase-modulated carrier. We also employ a phase-domain digital predistortion (DPD) to combat the intrinsic non-linearity of an LC-type digitally controlled oscillator (DCO), thus avoiding the complications of frequency-dependent calibrations. The prototype, implemented in 40-nm CMOS, modulates the carrier in the range of 2.7-3.9 GHz from a 40-MHz reference. The measured EVM is -47 dB for a 60-Mb/s 64-PSK modulation under the case that the phase-modulated output is frequency-divided by K=8 , i.e., when the DCO exhibits the most significant non-linearity due to the large fractional FM bandwidth. When K=8 or 4, the measured EVM remains below -43 dB across the carrier-frequency tuning range and without re-calibrating the DCO non-linearity.
AB - In this article, we present a low-power digital phase-locked loop (PLL)-based phase modulator targeting low error vector magnitude (EVM). We introduce a new non-uniform clock compensation (NUCC) scheme to tackle an EVM degradation resulting from the beneficial use of a time-varying sampling clock that is re-timed to the phase-modulated carrier. We also employ a phase-domain digital predistortion (DPD) to combat the intrinsic non-linearity of an LC-type digitally controlled oscillator (DCO), thus avoiding the complications of frequency-dependent calibrations. The prototype, implemented in 40-nm CMOS, modulates the carrier in the range of 2.7-3.9 GHz from a 40-MHz reference. The measured EVM is -47 dB for a 60-Mb/s 64-PSK modulation under the case that the phase-modulated output is frequency-divided by K=8 , i.e., when the DCO exhibits the most significant non-linearity due to the large fractional FM bandwidth. When K=8 or 4, the measured EVM remains below -43 dB across the carrier-frequency tuning range and without re-calibrating the DCO non-linearity.
KW - Digital polar transmitter (TX)
UR - http://www.scopus.com/inward/record.url?scp=85162914845&partnerID=8YFLogxK
U2 - 10.1109/JSSC.2023.3270265
DO - 10.1109/JSSC.2023.3270265
M3 - Article
AN - SCOPUS:85162914845
SN - 0018-9200
VL - 58
SP - 2526
EP - 2542
JO - IEEE Journal of Solid-State Circuits
JF - IEEE Journal of Solid-State Circuits
IS - 9
ER -