Microwave and Wireless Synthesizers: Theory and Design

6

A HIGH-PERFORMANCE HYBRID SYNTHESIZER

The previous chapters have dealt with the design principles of frequency synthesizers and the effect that parameters have on the loop performance. It is impossible to show all details relevant to the design of frequency synthesizers, especially regarding the selection of components, PC board layouts, and which principle to use over another, as sometimes they are equally good and the choice is very difficult. Engineers typically want to reinvent everything themselves. This is not a very economical way to do research, and inasmuch as one relies on literature, it is also good to take a look at proven designs. A nonworking novel approach is more difficult to digest than looking at a reliable and working approach and trying to improve this and also to understand why it has been done the way it has been done.

In this chapter we will look at a high-performance hybrid synthesizer as a combination of most of the technologies we have analyzed thus far.

Frequency agile synthesizers can now be built easily, essentially by using off-the-shelf available integrated circuits. If very fine resolution is required, one either ends up with a multiloop synthesizer or a combination of a phase-locked loop (PLL) synthesizer and a fine-resolution loop. The two commonly used choices for fine resolution are fractional division N synthesizers and direct digital synthesizers (DOSs). Fractional division N synthesizers, as previously described, are usually found in test ...