A digitally controlled phase-locked loop with a digital phase-frequency detector for fast acquisition

A digitally controlled phase-locked loop (DCPLL) that achieves fast acquisition by employing a digital phase-frequency detector (DPFD) and a variable loop gain scheme was developed for an advanced clock synthesizer and was fabricated in a 3.3-V 0.6-mum CMOS process. The DPFD was developed to measure the frequency difference. and to generate digital outputs corresponding to the difference. Using these features, the DCPLL achieves ideally one-cycle frequency acquisition when programmed with an appropriate gain. The experimental results show that the fabricated DCPLL exhibits three-cycle and one-cycle frequency acquisitions, when locking to 400 MHz (VCO at 800 MHz) and 200 MHz (VCO at 400 MHz), respectively.