A Harmonic-Mixing PLL Architecture for Millimeter-Wave Application

A low-noise synthesizer design in the millimeter-wave (mm-wave) range is complicated by the invariably large closed-loop gain and the high operation frequency of the voltage-controlled oscillator (VCO). To overcome these challenges, this work proposes a harmonic-mixing synthesizer system with a 188-dB figure-of-merit mm-wave VCO. The synthesizer extends the bandwidth to 5 MHz, thereby suppressing VCO noise. Importantly, DSM is not amplified by the $f_{\mathrm{ VCO}}/f_{\mathrm{ ref}}$ gain of the system. A prototype employing a 74-MHz reference achieves a −250-dB phase-locked loop (PLL) figure of merit with a measured 88-fs rms jitter.