Frequency synthesizers provide the fixed and tunable signals for local oscillators (LOs) in a wide range of commercial and military communications systems, including in wireless base stations. Technologies for creating frequency synthesizers are diverse, from traditional analog methods using phase-locked loops (PLLs) to direct digital synthesizers (DDSs) that rely on high-speed digital-to-analog converters (DACs) to transform digital input words into analog output signals. But for all the synthesizers integrated into communications radios and wireless base stations, one source may be a surprise to many. Although a supplier of a wide range of active and passive components, including amplifiers, power dividers/combiners, switches, and voltage-controlled oscillators (VCOs), and perhaps best known for frequency mixers (see this month's Cover Feature), Mini-Circuits (Brooklyn, NY) is probably least known for its work on RF/microwave frequency synthesizers.

Working closely with customers, and utilizing their expertise in VCO design, Mini-Circuits has developed more than 150 different frequency synthesizer models at frequencies from 144 MHz to 4.5 GHz, with higher-frequency models currently in development. The firm has produced four distinct families of frequency synthesizers, with fixed-frequency models, narrowband units, wideband models, and frequency synthesizers with fast settling time for frequency-hopping applications. For example, Mini-Circuits has developed numerous fixed-frequency and tunable-frequency synthesizers for customers developing WiMAX systems at 2.3 to 2.7 GHz, 3.3 to 3.6 GHz, and 3.6 to 3.8 GHz (see table). A typical unit, model KSN-3330A-119+ tunes from 3270 to 3330 MHz with single-sideband (SSB) phase noise of -95 dBc/Hz offset 10 kHz from the carrier and -120 dBc/Hz offset 100 kHz from the carrier.

The company has targeted a wide range of commercial applications with the frequency synthesizers, including cellular and WiMAX base stations and even cabletelevision (CATV) systems. For example, frequency synthesizer model DSN-EDR-8812+, with a tuning range of 950 to 1750 MHz with step size of less than 1 kHz, is well suited for CATV applications. It features spurious performance of better than -70 dBc.

Models KSN-EDR-8354/1+ and DSN-EDR-8357/1+ were also developed for CATV applications. The former operates from 1020 to 1055 MHz and measures just 0.6 x 0.8 in. while the latter tunes from 1130 to 2100 MHz and measures just 1.00 x 1.25 in. The frequency synthesizers feature low typical phase noise of -133 dBc/Hz and -120 dBc/Hz, respectively, offset 100 kHz from the carrier for use in the signal upconversion chain of a CATV application.

In addition, the company has developed frequency synthesizers for EDGE/ GSM and TDMA base stations with settling times of 25 s, allowing customers to use a single synthesizer in place of multiple units in frequency-hopping systems. The RSN series frequency synthesizers were developed to reduce cost in an EDGE/GSM base station application, allowing a single source to provide the LO signals for the system in place of several synthesizers previously used. Examples of the series include model RSN-EDR-8430-119, which tunes from 760 to 795 MHz, and model RSNEDR- 8431-119, which tunes from 1543 to 1618 MHz with low phase noise and typically 25 s settling time.

In addition to the compact, surfacemountable frequency synthesizers, the company has also developed a wide range of frequency synthesizers in connectorized cases from 760 to 4500 MHz. Examples include model EDR-9106 for use from 760.6 to 795.4 MHz, model ZSN-3024FA-119+ for 2924 to 3124 MHz, and model ZSN-4500FA-119+ for 4100 to 4500 MHz. The connectorized frequency synthesizers can be programmed for fixed-frequency or swept-frequency operation. They feature an internal reference voltagecontrolled temperature-compensated crystal oscillator (VCTCXO), which can compensate for any frequency drift as a function of time.

Because the firm has maintained a low profile about its frequency synthesizer work, data is not available on the web site. But full details are available by contacting the company with specific requirements. Mini-Circuits, P. O. Box 350166, Brooklyn, NY 11235-0003; (718) 934-4500, FAX: (718) 332-4661, Internet: www.minicircuits.com.

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