Designers of oscillators and synthesizers need creative ways to achieve low phase noise in smaller packages in order to serve shrinking systems. To accomplish this, some manufacturers are using advanced materials and circuit techniques, as well as the latest software design tools, which can allow for extremely accurate simulations and speed time to market. Once a prototype is in hand, designers need to leverage the most robust methods and equipment to test it.
The pressure is definitely on to minimize phase noise in oscillators and synthesizers, even as applications move into higher frequency bands. "The general trend has been to develop higher frequency solutions with better noise performance (>10 GHz) and octave tuning solutions in the S and C bands," notes Daniel Loomis, Sr. Applications Manager, Z-Communications. According to Stuart Rumley, Owner, Valon Technology LLC, the ability to keep phase noise in check is being helped by the availability of low-power, highly integrated semiconductor devices, especially phase-locked loops (PLLs) with integrated voltagecontrolled oscillators (VCOs). Rumley notes, "I will say that one key is to use the very lowest noise LDO regulators and buffer all RF outputs."
Some companies are leveraging new technologies and methods. For instance, Z-Communications reports that it is applying thick-film component technology in a multilayer substrate to address phase-noise concerns. At Synergy Microwave, Bill Becker, Sales & Applications Regional Manager, explains, We apply our patented, lowphase- noise techniques to both the larger (0.5 x 0.5 in.) VCO packages and the smaller (0.3 x 0.3 in.) packages to achieve the lowest phase noise over a greater-than-octave operating frequency band. The technology emulates the high Q required for low phase noise with hybrid-mode planar resonators and three-dimensional structures."
New oscillators and synthesizer designs with admirable phase noise specifications continue to roll out. Leveraging four differential voltagecontrolled oscillators (VCOs), the SKY73134 synthesizer from Skyworks Solutions is housed in a 5 x 5 mm, 32-pin RF land grid array (RFLGA) package. Particularly well suited for use in cellular base stations, the SKY73134 features normalized in-band phase noise of 211 dBc/Hz in a 30-kHz PLL bandwidth. Wenzel Associates also has a line of crystal oscillators for base stations, as well as other communications, military, and test equipment applications. The Small Fry oven-controlled crystal oscillator (OCXO), for instance, is optimized for use in Global Positioning System (GPS) receivers and demonstrates phase noise of 165 dBc/ Hz at 10 kHz offset. It measures 1.5 x 1.5 x 3 in.
Endwave Corporation recently announced its EWV0800YF dual-output VCOs that cover 3.65 to 4.4 GHz and 7.3 to 8.8 GHz. Phase noise for these components is specified at 116 dBc/Hz offset 100 kHz from the carrier in either band, with subharmonics of typically 41 dBc and second harmonics of typically 10 dBc. The company's VCO portfolio includes dual-output models that operate through 15.5 GHz.
EM Research continues its commitment to miniature frequency synthesizers, recently announcing a series of frequency synthesizers and phase-locked oscillators targeted at very-small-aperture-terminal (VSAT) satellite communications systems. Earlier this year at IMS 2010, the company also announced dual-output VCOs for applications to 15.5 GHz. The phase noise for these units is 112 dBc/Hz offset 100 kHz from the carrier, while subharmonic levels are typically 40 dBc and second-harmonic levels are typically 30 dBc.
Vectron International recently announced a new ultra-low-noise oven-controlled crystal oscillator (OCXO), the OX-045, claiming that the new source demonstrates industry-leading close-in phase noise for a 10-MHz OCXO, at 140 dBc/ Hz at 10 Hz offset and a 163 dBc/ Hz noise floor.
Z-Communications released a new low-noise VCO, the SMV1205C-LF, which spans 1185 to 1225 MHz and features phase noise of -103 dBc/Hz at 10 kHz offset. This little VCO is housed in a sub-L package, which measures 0.3 x 0.3 x 0.08 in. The company also recently released a 13.5-GHz fixed-frequency synthesizer, the SFS13500Z-LF, with typical phase noise of 80 dBc/Hz at 10 kHz offset with typical reference spur suppression of 65 dBc.
Synergy Microwave Corp. has announced the FCTS-series of phase-locked clock translator frequency sources (Fig. 1). The company reports that they exhibit better phase noise than crystal-based reference oscillators that are multiplied to higher frequencies. These new sources have phase noise performance of 150 dBc/Hz at a 10 kHz offset from a fundamental frequency of 1000 MHz. Mini-Circuits offers extensive lines of surface-mount VCOs, including the 0.5 x 0.5 in. model ROS-2082-119+ with low 118 dBc/Hz phase noise offset 100 kHz from the carrier. It tunes from 1700 to 2082 MHz.
Moving away from the miniature and looking at the modular, there are a number of new synthesizer products available to help improve RF and microwave testing, including the 5003 and 5005 dual-synthesizer modules from Valon Technology. These are self-contained, board-level signal sources based on Flash memory. Designers can program the units in a lab, for instance, to implement a complete RF receiver or transmitter on the bench. Because they are dualsynthesizer modules, these products can also be used as a frequency translator (by adding two mixers and a filter).
Also working at the module level, Phase Matrix recently introduced its latest QuickSyn frequency synthesizer that operates from 200 MHz to 20 GHz with phase noise of 110 dBc/Hz offset 10 kHz from the carrier. Designed to be dramatically smaller than a traditional rack-mount unit, the Phase Matrix device weighs in at 2.1 lbs. and measures 5 x 7 x 1 in. Alexander Chenakin, Ph.D., Vice President, Signal Sources, Phase Matrix, Inc. says that this version delivers the best phase noise/ switching speed performance for its device class. He explains that they use their patented phase-refining technology, which removes the divider from the PLL feedback path. This inverts the PLL division ratio, applying multiplication within the PLL, which improves phase-noise and spurious characteristics. Since removing the divider affects the frequency resolution, Phase Matrix uses direct digital synthesis (DDS) to achieve sub-1-Hz steps.
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Chenakin also notes, "Today's trend (and the major technology challenge) is to achieve fast tuning while preserving low-phase-noise characteristics. The time spent by the synthesizer transitioning between frequencies becomes increasingly valuable since it cannot be used for data processing."
But what are the design challenges for rolling out new oscillator and synthesizer designs? Rumley notes that his concerns center on shielding and isolation, "You always need some degree of shielding, but packaging and cost become a major issue. Also, once a board-level product is shielded, it is difficult or impossible to rework it in any way."
Becker sees size as a major constraint, "The most pressing design challenge is the dynamic requirements for component size reduction. This will eventually take the technology from discrete to integrated monolithic structures."
Some tools that are helping designers and similar manufacturers include custom software programs and the latest signal analyzers and vector network analyzers. Loomis reports that Z-Communications uses Microwave Office from AWR Corp. and the Advanced Design System (ADS) software from Agilent Technologies to build initial designs, and then follows up with testing on the Agilent 5025B analyzer.
Recent product news in the test equipment arena suggests that oscillator and synthesizer designers can have a robust tool box. For instance, Anritsu recently introduced the MG3690C series of signal generators. Bob Buxton, Anritsu's Manager of Product Marketing reports that this series provides industry leadership in both phase noise and the ability to generate signals ranging from 0.1 Hz to 70 GHz from a single synthesizer. Models in this series are available with frequency ranges extending to 10 GHz, 20 GHz, 31.8 GHz, 40 GHz, 50 GHz and 70 GHz. So, how are the test equipment houses helping out their customers with the phase noise/high-frequency/ size challenge?
"We are always trying to work in collaboration with our customers to provide the best solution for their test needs," notes Guillaume de Giovanni, President of Noise Extended Technologies S.A.S. (Noise XT). "For example, we launched a differential input and output to interface with the latest devices. We also have a high impedance input option for very low power devices. With over 200 options in our intellectual property knowledge base, we usually always have a solution to satisfy our customers' challenges."
Specifically engineered to allow oscillator designers to characterize their devices with better accuracy at extremely low levels, NoiseXT's Dual Core Noise Test System (DCNTS) claims to offer the lowest phase noise floor in the industry. The DCNTS (Fig. 2) is a two-channel phase and amplitude noise analyzer designed with a dual demodulator architecture. This allows the system to use cross-correlation to cancel internal noise.
Darren McCarthy, RF Technical Marketing Manager, Tektronix, builds on de Giovanni's concern, "One of the challenges with modern synthesizer design is the ability to characterize phase noise and stability during frequency-hopping applications. While most phase noise test solutions require a frequency stable signal, our unique implementation of combined spectrum analyzer and software applications enables designers to fully characterize the time settling and concurrent phase noise performance of hopping synthesizers."
Tektronix has recently introduced some new measurement software options for making automatic frequency and phase settling versus time on the RSA6000 series of performance spectrum analyzers (Option 12) and SignalVu for DPO/DSA/MSO series performance oscilloscopes (Option SVT). These options could be particularly well suited to carry out the automatic and repetitive measurements commonly used on synthesizers and oscillators. When used in conjunction with the existing phase noise measurement capability and the enhanced DPX Live RF processing, the Tektronix RSA6000 can be used to test synthesizers and oscillators at fundamental frequencies to 20 GHz. The instrument's DPX Live RF spectrum and DPX Density measurements also enable the characterization of problems like microphonics and phase-hits.
"Engineers are working to improve phase noise even as they make synthesizers and oscillators both smaller and lower in power consumption (and less expensive too)," observes Ben Zarlingo, Product Manager for communications test, Agilent Technologies. Zarlingo points out that Agilent has numerous approaches to help designers to face these challenges. One is the company's E5052 signal source analyzer, which uses an innovative phase-noise measurement technique and is particularly well suited for modern compact oscillators and synthesizers. Another choice is moderate (or better) performance spectrum analyzers with available phase noise options. "These phase noise applications automate the phase noise measurement and display operations (including the removal of AM noise from measurements measurements) and provide a phase noise measurement solution in a hardware package that is already on the bench of most engineers," adds Zarlingo. Agilent's recent news for phase-noise testing includes the introduction of the PXA signal analyzer (Fig. 3) with a phase-noise measurement application, which it says eliminates the need for a dedicated phase noise test solution. As designs of oscillators and synthesizers continue to improve, designer's testing options are keeping pace with the need to achieve the lowest possible phase noise.