Feed Forward Phase Noise Cancellation in Cellular RF-Receivers

In the current mobile communication standards there is a trend towards higher order modulation schemes in order to meet the rising demand for higher data rates. Higher order modulation schemes require a low error vector magnitude (EVM). The phase noise contained in the LO-signal generated by the all-digital phase-locked loop (ADPLL) of a cellular receiver has a big impact on the EVM. One way to reduce this impact and therefore improve the EVM-performance of the receiver is feed-forward phase noise cancellation (FFNC) applied in the digital baseband. Here the timing error measured by the time-to-digital converter (TDC) of the ADPLL is used to correct the phase error in the baseband. In this work we compare a phase-locked loop (PLL) with and without FFNC where both cases are optimized for a low integrated phase noise (IPN). We examine in simplified theoretical considerations how to choose the PLL- and FFNC-filter bandwidths to minimize the resulting IPN. Additionally we investigate how increased phase noise in the PLL affects the resulting IPN in the case with FFNC. The results from theoretical considerations have been confirmed by simulation using a time-domain MATLAB model of a type-II ADPLL.