The latest generation of compact frequency synthesizers is matching the small size of discrete-component oscillators while providing fast tuning speeds and low phase noise.
Size, speed, and power savings are key drivers for frequency synthesizers. A sign of the current trend in frequency synthesizers is the growing number of integrated miniature phase-lock-loop (PLL)/voltage-controlled- oscillator (VCO) combinations. What were once multiple components on a printed-circuit board (PCB) are now in a single surface-mount device.
Requirements for frequency synthesizers in commercial and industrial applications are somewhat different than those for military applications (see this month's supplement on specifying frequency synthesizers for EW applications). In addition to the stricter cost constraints, frequency synthesizers for commercial applications are generally aimed at specific operating bands, rather than the broad frequency ranges of electronic countermeasures (ECM) and electronic-warfare (EW) systems. And while they must also deliver excellent stability and spectral characteristics, they usually must operate on lower voltages and consume less power.
The FST series of fast-switching synthesizers from EM Research is a good example of how outstanding performance can be packed into a small coaxial package. With narrowband models spanning 80 to 4500 MHz, the sources measure just 3.5 x 2.5 x 0.6 in. (Fig. 1). As an example of the product line, model FST-4500-XX operates from 4400 to 4500 MHz with an external 10-MHz reference, switching in 50 kHz steps in 1 s or less. The synthesizer exhibits phase noise of -85 dBc/Hz offset 10 kHz from the carrier and -110 dBc/Hz offset 100 kHz from the carrier.
Hittite Microwave Corp. offers a series of fractional- N synthesizers with integrated VCOs. Model HMC764LP6CE tunes from 7.3 to 8.2 GHz with +15 dBm typical output power in a 6 x 6 mm QFN surface-mount package (Fig. 2). It has a settling time of 87 s for a 100-MHz step. The phase noise is -116 dBc/Hz offset 100 kHz from the carrier for the VCO in open-loop operation and typically -98 dBc offset 10 kHz for fractional-N synthesizer operation.
Synergy Microwave Corp. has been able to shrink the size of its VCO-based frequency synthesizers by developing its own lines of miniature VCOs. The firm's MFSH series of miniature frequency synthesizers take advantage of the small size and performance of the DCO and DXO oscillators to provide synthesized performance in a surface-mount package measuring just 0.6 x 0.6 in. Model MFSH495550-100 is an example of the compact frequency synthesizer line, tuning from 4950 to 5500 MHz in 1-MHz steps with settling time of less than 1 ms. It typically draws 30 mA current from a +5-VDC supply and offers phase noise of -80 dBc/Hz offset 10 kHz from the carrier and -106 dBc/ Hz offset 100 kHz from the carrier. The synthesizer line is available in models from 1 to 8 GHz.
Broadband single-loop SMS series synthesizers from Spinnaker Microwave, Inc. combine design simplicity with small size, covering a total frequency range from 100 MHz to 26 GHz in a package just measuring 1.9 x 1.9 x 0.45 in. Ideal for EW and ECM applications, they can be specified with bandwidths to one octave (such as 2 to 4 GHz). The sources provide 500-s switching speed for steps from 200 kHz to 10 MHz. The phase noise is typically -80 dBc/Hz offset 10 kHz from a 10-GHz carrier.
Swedish synthesizer specialist Sivers IMA AB supplies high-performance miniature frequency synthesizers in bands from 6 to 20 GHz. As an example, a unit designed for test, satcom, and digital radios from 8 to 9 GHz measures only 75 x 50 x 15 mm. It switches in less than 1 ms for a 100-MHz change in frequency. The synthesizer delivers typical phase noise of -80 dBc/Hz offset 10 kHz from the carrier and -100 dBc/Hz offset 100 kHz from the carrier.
Micro Lambda Wireless has designed miniature frequency synthesizers measuring just 2.5 x 2.5 x 1.9 in. based on its permanent-magnet YIG-tuned oscillators (PMYTOs). The MLSL series of frequency synthesizers has four models covering 2 to 8 GHz with 3-GHz bandwidths. Model MLSL-0306, for example, tunes in 500-kHz steps from 3 to 6 GHz with 100 ms switching speed. The phase noise is -65 dBc/Hz offset 1 kHz from the carrier and -122 dBc/Hz offset 100 kHz from the carrier.
Microsemi-RFIS also offers single-loop and multiloop frequency synthesizers based on PMYTOs (when low noise is required) and VCOs (when switching speed is important). Operating to 18 GHz, the PMYTO frequency synthesizers achieve 150 ms maximum switching speed at X-band with phase noise of -100 dBc/ Hz offset 10 kHz from the carrier and -128 dBc/Hz offset 100 kHz.
Teledyne Microwave has developed a compact VCO-based frequency synthesizer for C-band applications from 4.4 to 5.6 GHz. It provides 10-ms worst-case switching speed for 1-kHz steps. The synthesizer has phase noise of -85 dBc/ Hz offset 1 kHz from the carrier and -112 dBc/Hz offset 100 kHz from the carrier. The frequency synthesizer measures 6.19 x 3.91 x 0.85 in.
Compact frequency synthesizers from Spectrum Microwave include the model 456080 for applications from 4.0 to 4.5 GHz. It tunes in 10 MHz steps with 5-s switching speed in a package measuring just 3.25 x 3.00 x 0.28 in. The phase noise is -86 dBc/Hz offset 1 kHz from the carrier and -122 dBc/Hz offset 100 kHz from the carrier.
Mini-Circuits offers engineering services to help customers develop their own custom fixed-frequency and tunable-frequency synthesizer solutions in narrowband, medium-band, or wideband units. As an example of the firm's expertise in developing miniature frequency synthesizers, a 1200-to-2200-MHz DSN series unit tunes in 10-MHz steps with 0.5-s settling time. It measures a mere 1.25 x 1.00 x 0.20 in. with -97 dBc/Hz phase noise offset 1 kHz from the carrier and -106 dBc/Hz phase noise offset 100 kHz from the carrier.
The CFS series of synthesizers from MITEQ provide dual outputs at 1150 MHz and a tunable range of 12.46 to 13.28 GHz for frequency upconverters and downconverters. Supplied in a 5.50 x 12.35 x 1.44 in. housing, the dual synthesizer exhibits -85 dBc/Hz phase noise offset 1 kHz from a Ku-band carrier and -97 dBc/Hz offset 100 kHz from the same carrier. The phase noise is -95 dBc/Hz offset 1 kHz from the L-band carrier (1150 MHz) and -105 dBc/Hz offset 100 kHz.