Timing recovery in CMOS using nonlinear spectral-line method

In a Carrierless AM/PM (CAP) passband modulation scheme where the waveform does not contain a baud rate spectral line due to zero mean-value of the data symbols, the nonlinear spectral-line method is applied to extract the symbol rate. It is achieved first by a squaring function which draws out the higher moments of the signal that are periodic at the symbol rate; then the signal is further processed through a bandpass filter and phase-locked loop (PLL) combination to recover signal timing. All necessary timing recovery functions are implemented in the analog (continuous-time) domain, and the recovered timing information is used by a receive equalizer. The timing recovery block implemented in 0.9 μm CMOS includes a multiplier for the squaring function, a self-tuning bandpass filter, and a PLL using an external VCXO. The 51.84 MHz recovered clock allows a BER of 10^-10 [1]