Frequency synthesizers are among the most complex of function modules in an RF design. While they once conjured up images of mammoth proportions—machined boxes with mazes of semirigid coax to keep things connected—the RF/microwave frequency synthesizer has come a long way in terms of mechanical and electrical parameters.

Certainly, the 19-in. rack-mount versions are still out there, largely because that form factor is convenient for legacy systems and rack-mount automatic-test-equipment (ATE) systems. But with today's technology, it is feasible to implement a high-performance frequency synthesizer with low phase noise and impressive switching speed that fits in a surface-mount package easily mistaken for a standard crystal oscillator.

A few years ago, Micro Lambda Wireless (www.microlambdawireless.com) made a bold entrance into the synthesizer market with a line of compact modules based on their YIG-tuned oscillator technology. Upon visiting a major test-equipment manufacturer, and seeing their latest measurement-grade instrument with the cover off, it was clear that the RF deck that usually dominated the inside of the enclosure had shrunk to a fraction of its normal size. And there in the middle of the RF deck was the little synthesized source module from Micro Lambda Wireless.

Many customers, both commercial and military, are asking for smaller synthesizers in order to achieve the same result as the test instrument above. EM Research (www.emresearch.com), Universal Microwave Corp. (www.vco1.com), and Synergy Microwave Corp. (www.synergymwave.com) are among the companies trying to push the limits of synthesizer miniaturization. For example, EM Research's HLX Series of synthesizers covers bands from 50 MHz to 3.6 GHz in hermetic packages measuring just 0.805 X 0.805 X 0.148 in.

The model PNP-752-P22 from Universal Microwave Corp. is a phase-locked-loop (PLL) synthesizer that tunes from 950 to 2150 MHz and measures a mere 0.6 X 0.6 X 0.220 in. Synergy's FSFS315555500 tunes from 3150 to 5550 MHz but is only 1.25 X 1.00 in.

Of course, making a synthesizer small requires trade-offs, such as using an external reference source. And smaller designs owe a great deal to the semiconductor suppliers, such as Analog Devices (www.analog.com) and National Semiconductor (www.national.com), who provide building-block integrated circuits (ICs), such as PLL chips. Still, the commercial and military products that these synthesizers go into are packing more non-RF processing than ever before, and little synthesizers are making it possible.