Microwave and Wireless Synthesizers: Theory and Design

APPENDIX D

MMIC-BASED SYNTHESIZERS

The design of MMIC-based synthesizers is limited to companies equipped with GaAs foundries, but the synthesizers are interesting in the sense of seeing where the frequency limitations lie. As previously outlined, the millimeter-wave oscillators generally have a low Q and therefore are fairly noisy. This means they either have to be cleaned up by a wide loop bandwidth or special precautions must be taken to make them high performance.

Figure D-1 shows the component diagram of such a VCO. This particular VCO has been selected on the basis of common source, common gate, and common drain as outlined in Figure D-2.

Figure D-3 shows the measured phase noise of such a VCO at 18 GHz using a characteristic MMIC chip. In order to obtain the appropriate frequency division, a parametric type of frequency divider must be used, as shown in Figure D-4. The dividers can be characterized as either regenerative, dynamic, or static devices. The dynamic frequency divider refers to a “flip-flop” type of frequency divider using a delay line between the input and output and is built on a heterojunction bipolar approach. These types of divider have been built up to 26 GHz. The regenerative frequency dividers are built on the popular principle shown in Figure D-5. A modification of this principle using a double-balanced mixer can also be used as a frequency doubler. This KU band frequency synthesizer is contained in two GaAs monolithic chips, as shown in Figure D-6.