Sizing Up Advances In Frequency Synthesizers

Synthesizer specifiers are expecting more performance in smaller packages, with lower power consumption and improved phase noise in support of digitally modulated communications systems.

Microwave frequency synthesizers are shrinking. To summarize the major trend in the technology, modern frequency synthesizers offer better performance than units many times their size from a decade earlier. Most are designed upon modular platforms, allowing customization of step size, control logic, power supplies, and even choice of reference source, for ease of integration into modern systems. In addition to smaller sizes, customers are seeking lower power consumption, lower cost, and lower phase noise. In a frequency synthesizer, less is more.

For example, measuring just 0.8 x 0.8 x 0.15 in., the HLX series of surfacemount synthesizers (see figure) from EM Research can be ordered with as much as 30-percent bandwidths from 50 MHz to 12 GHz. A typical unit, model HLX-5900-XX, operates from 5600 to 5900 MHz with 100-kHz steps tuning steps. It provides +5-dBm output power across that range, with -15 dBc harmonics and -55 dBc spurious content. The phase noise is -80 dBc/Hz offset 10 kHz from the carrier and -100 dBc/Hz offset 100 kHz from the carrier. The synthesizer draws 60 mA at +5 VDC.

Synergy Microwave Corp. also offers miniature surface- mount frequency synthesizers, such as the model MTS2500- 200400-10 in a package measuring just 1.025 x 1.950 x 0.470 in. It can be programmed for switching steps as fine as 1 Hz from 2000 to 4000 MHz and provides +8 dBm output power across that frequency range. Spurious content is typically -60 dBc while harmonics are typically -10 dBc. The synthesizer, which draws 70 mA at +5 VDC, requires less than 10 ms to settle to within 1 kHz of a new frequency. The phase noise is -86 dBc/Hz offset 10 kHz from the carrier and -100 dBc/Hz offset 100 kHz.

For stabilizing a tunable oscillator, the model ADF4108 phase-lock-loop (PLL) synthesizer circuit from Analog Devices ( measures just 4 x 4 mm in a chip-scale package but can stabilize input signals to 8 GHz. The phase noise is a mere -81 dBc/Hz offset 1 kHz from a 7.9-GHz carrier.

The SMS-B frequency synthesizer from Spinnaker Microwave is supplied in a machined housing measuring 2.9 x 3.0 x 0.7 in. It weighs less than 7 oz., but tunes from 2.0 to 20.0 GHz in 10-MHz steps with 50-microsecond tuning speed. Spurious content is -60 dBc.

Wideband Systems has adopted a modular design approach to build both compact modules and rack-mount synthesizers. The company packs coverage of 2 to 18 GHz and output power of +10 dBm into a module measuring just 6 x 6 x 1 in. The frequency resolution can be as fine as 5 kHz, with 5 PPM frequency accuracy. The switching speed is better than 3 s, with -60 dBc spurious levels and -26 dBc harmonic levels.

Some companies, such as Mini-Circuits, invite customers to submit a set of electrical and mechanical requirements and will design and manufacture a low-cost, custom frequency synthesizer to meet or exceed those requirements. These custom frequency synthesizers can be designed to fit a variety of packages, with or without connectors, including drop-in and surface-mount styles.

For companies in need of adding a high-performance synthesizer to a system-on-chip (SoC) integrated-circuit (IC) design, Kaben Wireless Silicon offers frequency synthesizer intellectual property (IP) cells for integration into SoCs. The company's synthesizers make use of Integer-N, fractional-N, and delta-sigma fractional-N synthesis architectures in support of applications through 6 GHz. For example, the model K-SI-60-IBM- 7WL-01 integer-N frequency synthesizer cell is designed for fabrication with the IBM 7WL process. It can be used for frequencies from 0.5 to 6.0 GHz and supplies from +2.7 to +5.5 VDC, wih 24 mA current consumption at +5 VDC. The synthesizer, which is suitable for portable wireless circuits, achieves phase noise of -77 dBc/Hz offset 1 kHz from a 5.8-GHz carrier.

Phase Matrix has developed a line of frequency synthesizes based on its phase-refining technology (see Microwaves & RF, October 2008 Cover Feature). The firm's QuickSyn frequency synthesizers are based on a core design using a fundamental- frequency voltage-controlled oscillator (VCO) with frequency coverage of 2 to 10 GHz. The addition of direct-digital-synthesis (DDS) technology provides frequency resolution as fine as 0.001 Hz. The typical phase noise is -120 dBc/Hz offset 10 kHz from a 10-GHz carrier and -131 dBc/Hz offset 10 kHz from a 2-GHz carrier.

Elcom Technologies recently announced orders totaling $2.8 million for the firm's rack-mount UFS series direct-analog frequency synthesizers. When smaller synthesizers are needed, the company offers the WMFS series octave-band sources. With frequency coverage from 1 to 23 GHz in bands as wide as 6 GHz, the WMFS series synthesizers measure just 5.1 x 5.6 x 0.9 in. The phase noise at 10 GHz is -80 dBc/Hz offset 10 kHz and -95 dBc/Hz offset 100 kHz.

The BTE series of Ku-band frequency synthesizers from MITEQ are low-cost sources for INTELSAT satellite-communications (satcom) applications from 12.72 to 14.84 GHz. Measuring just 8.0 x 5.0 x 0.7 in. and weighing typically 2 lbs., the frequency synthesizers tune in typically 1-kHz steps. The phase noise is typically -87 dBc/Hz offset 1 kHz from the carrier and -91 dBc/Hz offset 100 kHz.

The series VSS frequency synthesizers from Herley-CTI measure just 2.80 x 2.64 x 0.5 in. with SMA connectors, but offer bandwidths to 14 percent of 0.5 to 14.0 GHz with output levels as high as +17 dBm. 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.

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