Despite an industry-wide trend toward miniaturization, medical device designers have often been forced to use larger-sized oscillators in order to achieve the necessary phase noise performance for a given medical application. In response to this limitation, Bliley Technologies has developed the Apollo oven-controlled crystal oscillator (OCXO), which the company claims offers superior phase noise performance in a compact footprint requiring less than half the space of existing designs.
|Suited for use in MRI equipment, Bliley's Apollo OCXO measures just|
1 × 1 in.
Suited for use in MRI equipment, conventional OCXOs demonstrate good phase noise, which helps drive optical picture clarity. But as phase noise degrades, image quality is sacrificed, making it more difficult to analyze critical test results, according to Dennis Barrick, Bliley's vice president of marketing and business development. In light of this issue, medical device designers have grappled with how to achieve a smaller form factor without sacrificing phase noise performance.
In development for the past two and a half years, the Apollo OCXO addresses this problem by offering good phase noise performance in a low-profile, 1 × 1-in. package size. This space reduction, Barrick notes, can be attributed to an improved circuit design that reduces component count. "We've been working several years trying to continuously achieve the best phase noise performance in the smallest package," Barrick says. "Other companies provide low phase noise OCXOs, but none have achieved this level of performance in a 1-in. square package."
The close-to-carrier phase noise performance of the Apollo OCXO can be attributed to the use of stress-compensated (SC) cut resonators, according to the company. These SC crystals provide compensation for thermal transient and planar stress effects, in contrast to temperature-compensated or voltage-controlled oscillators, which require a compensation network to bring the frequency back to its center point. But because SC crystals don't function well in ambient temperatures, they are placed in an oven so that temperature changes are never seen on the crystals themselves. "They have extremely good phase noise," Barrick remarks. "Everything is housed inside an oven inside the package."
The company also dedicated its design efforts to ensuring that the crystals are hermetically sealed. Other manufacturers, Barrick states, often put a crystal blank inside a package with other components. "As soon as you do that, you can age the part, contaminating the crystal from other components," he says. "Our hermetically sealed crystal never sees other circuitry."
Available with frequencies ranging from 30 to 130 MHz, the oscillators are customizable and can be provided in RoHS-compliant versions as well.