Clock/data recovery PLL using half-frequency clock

A CMOS clock and data recovery PLL is described for serial nonreturn-to-zero (NRZ) data transmission. The voltage controlled oscillator (VCO) works at half the data rate, which means for a 1-Gb/s data rate, the VCO runs at 500 MHz. A specially designed phase comparator uses a delay-locked loop (DLL) to generate the required sampling clocks to compare clock and data. The VCO can typically be tuned from 350 MHz to 890 MHz, and the phase-locked loop (PLL) locks between 720 Mb/s and 1.3 Gb/s. Data recovery is error free up to 1.2 Gb/s with a 9-b pseudorandom data sequence. The core consumes 85 mW (3.3 V) at 1 Gb/s.