An Ultra-Low-Jitter, mmW-Band Frequency Synthesizer Based on Digital Subsampling PLL Using Optimally Spaced Voltage Comparators

This article presents a cascaded architecture of a frequency synthesizer to generate ultra-low-jitter output signals in a millimeter-wave (mmW) frequency band from 28 to 31 GHz. The mmW-band injection-locked frequency multiplier (ILFM) placed at the second stage has a wide bandwidth so that the performance of the jitter of this frequency synthesizer is determined by the GHz-band, digital subsampling phase-locked loop (SSPLL) at the first stage. To suppress the quantization noise of the digital SSPLL while using a small amount of power, the optimally spaced voltage comparators (OSVCs) are presented as a voltage quantizer. This article was designed and fabricated using 65-nm CMOS technology. In measurements, this prototype frequency synthesizer generated output signals in the range of 28–31 GHz, with an rms jitter of less than 80 fs and an integrated phase noise (IPN) of less than −40 dBc. The active silicon area was 0.32 mm2, and the total power consumption was 41.8 mW.