Recent years have seen major changes in the frequency synthesis art. Ultra-low-noise discrete VCOs, the heart of low noise synthesizers for decades, now find themselves challenged by integrated VCOs. The best discrete VCOs still enjoy 20-30 dB phase-noise superiority, but IC companies are conducting an asymmetric battle to dominate the market with full integration based not on the best VCO noise, but on architectural innovations that often render free-running VCO noise less important.
This is achieved by putting good VCOs on die, suppressing that noise down to a very low level via feedback, and then dividing down to the application band for a further phase noise reduction. The challenge now facing discrete VCO suppliers is to extend the outstanding phase noise they get in application bands to higher frequency where they also can get the full architectural benefit of the latest synthesizer innovations.
This first article of a five-article series will review modern advanced design methods. This is the online version, which is moderately more complete than the printed version. See the publications page at www.longwingtech.com for considerably more detailed versions of these articles. The next four articles in this series will cover detailed noise analysis (two articles), key parts and tools for low noise implementation, and examples requiring low noise that illustrate current state of the art performance.