direct analog synthesis frequency
Hi, all. Direct analog frequency synthesis refer to the method of frequency generation using mixing, frequency multiplication and abundent of filtering to generate the desired output. The base frequency is usally a stable oscillator with good phase noise. DAS yield good switching speed and phase noise, with good spurious performance. The is an old book "Frequency Synthesizer Design" ( I can remember exactly) published by John Wiley. It has detailed discussion on DAS. Alternatively, you can visit trak microwave website for some info.
PLLs are referred to as a indirect method of frequency generation.