A 32-nm CMOS Frequency Locked Loop for 20-GHz Synthesis with ± 7.6 ppm Resolution

In this work, a digitally assisted frequency locked loop is implemented using 32-nm CMOS technology and acts as a 20-GHz frequency synthesizer. The frequency difference between the reference clock and the VCO output is obtained using a pair of 18- bit counters. Also, an offset value is added to the counter output to tune the VCO frequency in closed loop. The frequency synthesizer resolution is ± 7.6 p.p.m. over a measured locking range equal to 300 MHz.