Introduction
Direct frequency synthesizers use digital techniques to generate lower frequencies with fine step sizes
- Usable bandwidth of output is limited to 1/4 fclock usually in the range of 1/8-3/8, 5/8-7/8, or possibly 9/8-11/8 fclock
Indirect synthesizers use phase-locked techniques to multiply an input reference with moderate output frequency range and step sizes
- Primary use is to multiply an input clock to a higher frequency
Hybrid synthesizers use PLL, DDS, and RF upconversion to achieve both fine step sizes and high frequency output
- Achieves wide tuning bandwidth at the expense of size and power