Companies within Dover Corp.'s Electronic Technologies have for years designed and manufactured RF/microwave products. But, as last month's first installment in this three-part article series pointed out, the RF/microwave companies are only now learning what is possible through teamwork. For three companies in particular, Dielectric Laboratories (www.dilabs.com), K&L Microwave (www.klmicrowave.com), and Vectron International (www.vectron.com), the whole effort can lead to much greater returns than the sum of the parts. Part 2 of this series details the design of a highperformance narrowband voltage-controlled- oscillator (VCO) by two of the three team members.
The role of the "component" supplier has changed drastically over the years. Firms once asked to supply frequency mixers are now directed to add local oscillators (LOs) and filters in order to create a smaller, more integrated front end. The trend for higher levels of integration has spread throughout the industry, to the point where component suppliers are finding themselves becoming small-scale "subsystem" houses. As last month's article examined, this trend toward higher levels of integration helped bring together the three Dover Electronic Technologies companies, Dielectric Laboratories Inc. (DLI), K&L Microwave, and Vectron International.
For Vectron International, this fortuitous partnering brought them closer to the high-performance ceramic materials and resonators developed by DLI (visit the Microwaves & RF website at www.mwrf.com for copies of two White Papers on DLI's "Disruptive Technology"). For DLI, this blending of talents gave them a chance to see how those resonators might fare when installed in the well-designed oscillator circuitry. As noted earlier, these resonators represented the opportunity for Vectron to break the "2-GHz ceiling" that the company had faced for several years by working with its own surfaceacoustic- wave (SAW) technologies.
Jeff Mink, Vectron's Engineering Director for VCSO/SO Development, coordinated the integration and development of a narrowband VCO using Dielectric Laboratories' ceramic resonators. Because neither company possessed active-device technology at frequencies above 2 GHz, a third, non-Dover partner was brought into the project, Mimix Broadband (www.mimixbroadband.com). The three companies' teamwork resulted in a presentation earlier this year at the MTT-S Symposium and Exhibition in Honolulu, HI, on an oscillator design that would figuratively lift the roof from Vectron's 2- GHz ceiling and show impressive capabilities at 10 GHz. This narrowband oscillator consisted of a single-frequencyceramic- resonator (SFCR) and two Bar Cap® single-layer capacitors from DLI, and a custom monolithic microwave integrated circuit (MMIC) from Mimix Broadband. The oscillator integration, assembly, and characterization was provided by Vectron International.
Mink and Vectron were initially attracted to DLI's ceramic technology due to the outstanding characteristics demonstrated for temperature stability and quality factor (Q). Measured results for the 10 GHz VCO revealed temperature stabilities less than 0.035 percent (350 ppm) which approach the stability levels obtained by SAW-based oscillators (200 ppm). The temperature stability would actually match that of SAW-based oscillators if the turnover position of the resonator temperature characteristic were adjusted lower.
According to Mike Busse, vice president for DLI, the firm has developed more than 100 proprietary and/or patented ceramic formulations with dielectric constants as low as 4 to more than 40,000. The wide choice makes it possible to tailor the materials and the resonators to the desired tuning range of an oscillator design. Materials such as the company's CF materials can be produced with frequency tolerances as tight as 0.1 percent (1000 ppm), or laser trimmed by the company's in-house machining capabilities to an exact frequency.
On its own, DLI has developed cavity resonators with quality factors (Qs) as high as 2000 and covering frequency ranges from less than 3 GHz to beyond 67 GHz. The SFCR designs offer Q performance comparable to bulk-acousticwave (BAW) resonators, with higher frequency capability and many other benefits in terms of circuit integration. In addition to being one of the key elements for the company's lines of miniature ceramic filters, the resonators are suitable for use in stable oscillators for commercial and military systems.
The fully shielded resonators are suitable for surface-mount and wire-bond manufacturing approaches, manufactured with reliable thin-film gold metalization. The resonators do not require a special enclosure or a hermetic cavity, therefore, they can be easily integrated as the base or lid for the end product. The specified frequency range is not limited to simulations. Rather, the company boasts an impressive line of custom test fixtures and microwave and millimeter-wave test equipment that has allowed them to characterize its high-frequency resonators with extreme accuracy.
In spite of the measurement power, DLI has chosen not to focus on oscillator design for which Vectron International has come to be known. As Vectron's engineers discovered, one of the benefits in working with DLI and its ceramic technologies was the firm's vast experience in also making precision capacitors. As the equivalent circuit for the narrowband VCO's resonator shows (Fig. 1), using the ceramic material presents the opportunity to fabricate an integrated coupling capacitor with a value that can be tailored to a specific oscillator design and frequency requirements.
Mink notes that Vectron was well versed in developing oscillators at lower frequencies, but wanted to extend the frequency range of its designs, and the DLI resonators offered that opportunity: "The majority of our oscillator products are at frequencies less than 1 GHz, we understand the performance trade-offs at these frequencies, but are still in the process of learning what can be done at 10 GHz." Mink sized up companies in the industry producing low-phase-noise oscillators at higher frequencies as a yardstick for his own performance goals, but knew that this first high-frequency oscillator would be a learning experience. "The first circuit was put together in very little time, so we are confident that we will have a 5-to-10-dB improvement in phase noise once it is optimized." He adds that "Frequency multiplication was not used in the oscillator design at 10 GHz, so there isn't the usual degradation in phase noise that results from each doubling of frequency."
Mimix Broadband's contribution involved designing a custom VCO MMIC that would operate at the impedances of the DLI resonator. Developed by Tony Fattorini at Mimix Broadband, the GaAs MMIC chip measures 39.4 x 37.0 x 3.9 mil (1.0 x 0.94 x 0.1 mm). It was fabricated with a 1-micron InGaP HBT process at WIN Semiconductor (www.winfoundry.com) and includes an on-chip varactor diode for tuning, negative resistance oscillator, and buffer amplifier. With the exception of the ceramic resonator and special bypass capacitors supplied by DLI, all circuit elements are integrated on the MMIC chip.
Using DLI's SFCR as the base of the design and Mimix Broadband's MMIC, Vectron's contribution focused on the VCO integration and characterization. The oscillator in the hybrid form factor (nonpackaged) measures only 194 x 170 x 40 mil (4.93 x 4.32 x 1.02 mm). The device draws less than 25 mA from a +3.3- V supply and consumes less than 0.1 mA for control voltages of 0.3 to 3.0 V.
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Packaging the hybrid VCO design is an on-going challenge. The oscillator is planned to be housed in a quad-flat-nolead (QFN) package with 28 terminals, although other packages are also being evaluated. The list of candidates include a liquid-crystal-polymer (LCP) QFN measuring 8 x 8 x 2 mm with 32 terminals, a ceramic package measuring 11.1 x 8.0 x 2.8 mm with 10 terminals, and a TO-8 metal package measuring 12.7 mm diameter by 3.85 mm with 4 leads.
Armed with test equipment such as the Agilent model E5052A signal-source analyzer and Agilent MXA spectrum analyzer from Agilent Technologies (www.agilent.com), the team carefully characterized their collaborative design. They found the oscillator's output power as a function of control voltage to be extremely well behaved at supplies greater than +3.0 V (Fig. 2). Phase-noise measurements at the power supply of +3.3 V and at low, mid, and high voltage control (0.3, 1.65, 3.0 V) revealed levels of -85 dBc/Hz at 10 kHz, dropping consistently to -150 dBc/Hz at 10 MHz offset from the carrier (Fig. 3). Mink is enthusiastic about the results so far: "This will be a great vehicle not only to cover X band (8 to 12 GHz) but also to extend down to 2 GHz."
Next month, this three-part article concludes with a closer look at the way DLI and K&L Microwave work together, specifically, how they created a highly integrated switch-filter assembly.