Revolution and Evolution in Frequency Synthesis: How PLL/VCO Technology Has Increased Performance, Decreased Size, and Simplified Design Cycle

Microwave frequency generation has posed significant challenges to engineers over the years, requiring in-depth knowledge of analog, digital, and radio frequency (RF) and microwave electronics—specifically that of phase-locked loop (PLL) and voltage-controlled oscillator (VCO) integrated circuit (IC) components—together with a need for tunable filtering, wideband amplification, and gain equalization.

This article highlights the advances in microwave circuit design in recent years, which now mean that low phase noise VCOs on silicon technology can cover an octave range of frequency. Integrated output dividers on the same IC permit several octaves of lower frequency coverage, and multipliers allow frequencies as great as 32 GHz to be generated using a single IC. Advances in fractional-N PLL synthesizers now mean that overall rms jitter at microwave frequencies can be as low as 60 fs, with infinitesimal frequency resolution and minimal spurious tones. Low insertion loss wideband filters can be used with these integrated PLL/VCO ICs to improve the spectral performance of the entire system, greatly simplifying the challenge of microwave and millimeter wave local oscillator generation.