Demanding requirements for newer communications systems are pushing frequency synthesizer developers to pack more performance into more compact designs.
Jack Browne
Technical Director
Frequency synthesizers are instrumental to modern communications systems, which rely on stable RF signals for frequency downconversion and upconversion in receivers and transmitters, respectively. In response to customer demands for smaller and lower-power signal sources, manufacturers of frequency synthesizers are creating more compact designs that don't sacrifice in performance. What follows is a brief overview of some of the latest miniature frequency synthesizer developments.
It is safe to say that today's frequency synthesizers are rapidly becoming smaller than yesterday's free-running oscillators. The CLX Series of frequency synthesizers from EM Research (www.emresearch.com), for example, are fixed-frequency units available from 200 MHz to 4 GHz and supplied in a surface-mount-technology (SMT) package measuring just 0.75 x 0.75 x 0.25 in. (19 x 19 x 6.5 mm). For a 2450-MHz unit, the output power is +7 dBm with -30 dBc harmonics and -75 dBc spurious content. The phase noise is -102 dBc/Hz offset 10 kHz from the carrier and just -128 dBc/Hz offset 100 kHz from the carrier. The tiny synthesizer is designed to provide this level of performance at operating temperatures from -30 to +70C.
In a slightly larger package, the company's THOR Series of frequency synthesizers are designed for fixed-frequency and tunable satellite- communications applications from 968 MHz through 18 GHz. Supplied in a modular 2.50 x 1.30 x 0.35 in. package with a removable SMA connector for test purposes, the compact synthesizers can be specified with step sizes from 25 kHz through 100 MHz. The typical phase noise is better than -85 dBc/Hz offset 10 kHz from a 13-GHz carrier. Spurious content is -70 dBc at 14 GHz.
Another line of frequency synthesizers with "oscillator-like" dimensions is the FSH family from Synergy Microwave Corp. (www.synergymwave.com). The firm's model FSH250300-1M (Fig. 1), for example, spans 2500 to 3000 MHz in 1-MHz steps but measures a mere 1.040 x 1.145 x 0.230 in. Working with a 10-MHz reference, it achieves -25 dBc typical harmonic levels and -90 dBc spurious levels with +8 dBm or more output power. Based on the company's patent-pending REL-PRO(R) technology, the miniature synthesizer settles to a new frequency in typically 15 ms and delivers typical phase noise of -95 dBc/Hz offset 1 kHz from the carrier, -98 dBc/Hz offset 10 kHz from the carrier, and -122 dBc/Hz offset 100 kHz from the carrier across operating temperatures of -40 to +85C.
The company has also developed FSFS series miniature frequency synthesizers for frequency-agile applications. For example, model FSFS315555-500 tunes across a range of 3150 to 5500 MHz in 5-MHz steps in less than 50-microsecond settling time. Spurious levels are typically -75 dBc while the phase noise is -80 dBc/Hz for offsets to 100 kHz and -100 dBc/Hz offset 1 MHz from the carrier. The fast-switching synthesizer is housed in an RoHS-compliant surface-mount package measuring 1.25 x 1.0 x 0.3 in. Also, Synergy's MTS2500DS frequency synthesizers (Fig. 2) measure just 1.95 x 1.25 in. with coverage of 5 to 6000 MHz in 1-Hz steps. The MTS Series synthesizers provide less than 18 ms fullband frequency switching and less than 1 ms fractional-band switching. The phase noise is less than -95 dBc/ Hz offset 1 kHz from the carrier and less than -113 dBc/Hz offset 100 kHz from the carrier.
In addition to the model AD9913 direct-digital-synthesizer (DDS) chip from Analog Devices (www.analog.com) gracing this month's cover, the firm offers extensive lines of frequency-synthesizer integrated circuits (ICs) based on different technologies. For example, model ADF4360-0 is an integer-N frequency synthesizer with integral voltage-controlled oscillator (VCO) in a 24-lead CSP housing. It features a simple three-wire interface to control on-chip registers and a frequency range of 2400 to 2725 MHz with programmable output power of -13 to -3 dBm. It accepts maximum RF input signals to 250 MHz and generates higher-frequency outputs by merit of its programmable 8/9, 16/17, 32/33 dual-modulus prescalers. It runs on supplies of +3.0 to +3.6 VDC.
STMicroelectronics (www.stmicroelectronics.com) recently introduced a single-chip frequency synthesizer with integrated VCO and output capability to 5 GHz. The firm's model STW81103 (Fig. 2) is fabricated with a half-micron silicon-germanium BiCMOS semiconductor process and covers frequency bands from 625.0 to 762.5 MHz, 1087.5 to 1525.0 MHz, 2175 to 3050 MHz, and 4350 to 5000 MHz in 200-kHz steps. Featuring fast clock time of 150 microseconds, the miniature synthesizer measures just 5 x 5 x 1 mm and operates from a +3.3-VDC supply. The company also makes available a design software tool, the STWPLLSim software, for fast and accurate PLL design and optimization of the STW81103.
In slightly larger packages, Micro Lambda Wireless (www.microlambdawireless.com) leverages its proven YIG oscillator technology into stable frequency synthesizers such as the company's MLSL-IC series of frequency synthesizers. Models cover 2-GHz tuning ranges over a total span of 2 to 12 GHz with 100 ms switching speed. Based on permanent-magnet YIG-tuned oscillators (PMYTOs) and with internal crystal oscillators, they measure 3.270 x 2.500 x 1.042 in. and weigh just 7 oz. For example, model MLSL-0406IC operates from 4 to 6 GHz with 500-kHz tuning steps and +12 dBm output power. It exhibits -70 dBc spurious content and -12 dBc harmonics, with -98 dBc/ Hz phase noise offset 10 kHz from the carrier and -122 dBc/Hz phase noise offset 100 kHz from the carrier.
The firm also offers the MLSE Series of broadband frequency synthesizers with coverage a wide as 2 to 20 GHz and 1 to 22 GHz. The modular synthesizer line includes the 2-to-20-GHz model MLSE-0220 with +20 dBm output power and the 1-to-22-GHz model MLSE-0122 with +17 dBm output power. The broadband synthesizers feature frequency switching speed of 32 ms of better, 1-Hz resolution, -60 dBc spurious, and -12 dBc harmonics with phase noise of -101 dBc/Hz offset 1 kHz from a 10-GHz carrier and -117 dBc/Hz offset 100 kHz from the carrier. Each measures 7 x 5 x 2 in. with only 43 W power consumption.
Modular fast-switching frequency synthesizers from Wide Band Systems (www.widebandsystems.com) includes units that cover 2 to 18 GHz in a modular housing measuring just 6.50 x 6.25 x 1.05 inches and consuming only 19 W of DC power. The small size of these synthesizers allows several to be packed within the size of a conventional rackmount signal generator in an automatic-test-equipment (ATE) enclosure for multiple-emitter scenarios.
The Wide Band Systems modular frequency synthesizers offer single, dual, or switched outputs with +10 dBm output power, 1.5 dB output-power flatness over temperature and frequency, and 1.25-dB amplitude balance and 5-degree phase balance between dual or switched outputs. They provide as much as 22-b frequency control for frequency resolution as fine as 5 kHz. For ATE systems requiring fast amplitude and frequency switching for increased test throughput, the modular frequency synthesizers boast maximum switching speed of 5 microseconds, with typical switching speed of 3 microseconds.
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Elcom Technologies (www.elcom-tech.com), perhaps best known for its rugged rack-mount UFS line of direct broadband, fast-switching frequency synthesizers for military applications from 0.3 to 18.0 GHz, recently secured a sizable contract to deliver its compact VME format synthesizers, such as the model VMESG-18, which operates from 0.3 to 18.0 GHz. The card-format synthesizer was developed nominally for synthetic instrument (SI) applications in flight-line testing, EW, and SIGINT systems. It features 10-kHz resolution and 200-microsecond switching speed with -60 dBc spurious content and low -55 dBc harmonics. The output power is flat within 2 dB of +11 dBm and the phase noise is -88 dBc/Hz offset 10 kHz from a 10-GHz carrier and -100 dBc/Hz offset 100 kHz from the same carrier.
Spinnaker Microwave (www.spinnakermicrowave.com) has developed its SMS-B wideband synthesizer for rugged military and industrial applications that require a compact but stable signal source. Supplied in a machined housing measuring 2.9 x 3.0 x 0.7 in., it weighs less than 7 oz. and consumes only 6 W power. The synthesizer tunes in 10-MHz steps with tuning speed of 50 microsecond or better and low spurious content of -60 dBc. The phase noise is -80 dBc/Hz offset 1 kHz from the carrier at operating temperatures from -40 to +85C.
Herley-CTI (www.herley.com) has developed its Series VSS compact frequency synthesizers for digital radio and satellite-communications applications to 14 GHz. Available in wide (to 14 percent) bandwidths from 0.5 to 14.0 GHz, the frequency synthesizers deliver output levels from +12 to +17 dBm depending upon frequency. They feature low spurious content of -65 dBc with harmonics of -15 dBc or better. The phase noise from a 5-GHz carrier is -99 dBc/Hz offset 10 kHz from the carrier and -122 dBc/Hz offset 100 kHz from the carrier. The compact frequency synthesizers are supplied in a machined housing measuring just 2.80 x 2.64 x 0.5 in. with SMA connectors.
TRAK Microwave Corp. (www.trak.com) offers both indirect and direct synthesizer architectures in machined modular housings. Model SYN085 is an example of the first type, measuring just 4.5 x 2.5 x 0.8 in. and weighing 10 oz. and operating from 0.55 to 1.85 GHz with switching speed as good as 35 microseconds. Typical phase noise is -90 dBc/Hz offset 1 kHz from the carrier and -126 dBc/Hz offset 100 kHz.
Model SYN146 is an example of TRAK's direct synthesizer technology, a compact (6.69 x 5.24 x 4.18 in.) fastswitching (less than 500 ns) design that generates output signals from 9.25 to 19.0 GHz. Phase noise is typically -90 dBc/Hz offset 1 kHz from the carrier and -112 dBc/Hz offset 10 kHz.
The list of suppliers for frequency synthesizers is long and this article has only provided a sampling. A follow-up article later this year will detail larger types of frequency synthesizers, including rack-mount units and models developed specifically for measurement applications. In the meantime, readers with an immediate need for a synthesized source are asked to search the online version of the Microwaves & RF Product Data Directory, at www.mwrfpdd.com.