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The EMXO manufacturing process starts with substrate assembly. Substrates are fabricated with thick film screen-printing techniques with each deposition layer subjected to three different process stages — print, dry and fire. Crystal clips are attached to the gold conductor trace on a substrate with high thermal conductivity. All active and passive components are mounted on the substrate using a conductive adhesive and then moved to a convection oven for curing. After the cure process, the hybrid is cleaned to remove organic and non-organic contaminants. Wires are bonded on the hybrid circuit as interconnects. The hybrid circuits are then attached to the cold-weld package with adhesive. Finally, blank crystals are mounted onto the clips and tuned to the nominal frequency needed, by an evaporation process, to a typical accuracy of 1 ppm. The units are then cold-weld sealed. The oven is heated by direct thermal conduction applied to a heat-conductive substrate.

The oscillator is essentially a CMOS gate type with an additional varactor diode and LC trap for overtone select. The resonator is a third overtone, AT or doubly rotated cut as required by the application, both of which offer superior aging performance when compared to a traditional fundamental resonator.

It is anticipated that the EX-380 series will find applications where performance in severe mechanical environments is equally important to electrical performance. An additional focus for the EX-380 series, therefore, was to provide robust construction to withstand high shock and vibration and to yield good G-sensitivity performance. For example, when the physical orientation of an oscillator is changed, there is a small frequency change (typically not more than several parts in 10-9 for a 90° rotation due to change in stress on the crystal blank resulting from the gravitational effect upon the crystal supports. This characteristic is known as “tip-over” and is expressed in 10-9/g where one g represents one-half of a 180° orientation change. To minimize this change and to enhance performance under shock and vibration, the crystal blank is mounted in a symmetrical mounting structure, instead of the more traditional two or three points. This helps to achieve a high shock and vibration endurance level, low g-sensitivity performance and symmetrical heat transfer. Also, when a crystal oscillator is operating and subjected to vibration, spurious frequencies are generated, offset from the frequency of oscillation by the frequency of vibration. These are commonly referred to as “vibration-induced sidebands” and these sidebands behave similarly to phase noise. The amplitude of these spurious outputs is related to the amplitude of vibration, the mechanical design of the crystal supports, and the mechanical design of the oscillator assembly, including the crystal mounting. Here, the symmetrical crystal mounting structure helps reduce unwanted noise.

Both AT and doubly rotated crystals can be used in the EX-380 and EX-620 series. Even though many types of doubly rotated crystals produce lower amplitude spurs under vibration than the AT, this characteristic is primarily determined by the mechanical design of the crystal and oscillator rather than the specific crystal cut. In many applications, Vectron uses doubly rotated resonators in the oscillator to provide lower close-in phase noise, better aging rates and reduced acceleration sensitivity. In less-critical applications, less-expensive AT cut crystals are used.

Figures 2-6 represent the typical actual test data on qualification samples for various characteristics. The frequency vs. temperature performance of the EX-380 is demonstrated in Figure 2 showing that the performance doesn't degrade from an OCXO while the size has been significantly reduced. The EMXO's fast warm up time and low power consumption required for portable applications is demonstrated in Figures 3 and 5. Figures 4 and 6 show the EMXO's OCXO like aging and phase noise performance, which is usually demanded from test and communication equipment OEMs.

The unit provides exceptionally low aging rates and high temperature stabilities in an extremely small package over a wide range of environmental conditions. It provides aging rates of <1×10-9/day average, <1×10-7 for the first year and <1×10-6 for 10 years with temperature stabilities to ±1×10-7 over -40 °C to +85 °C. Wider temperature ranges are available from -55 °C to +85 °C. In essence, the EMXO bridges the gap between current large, high-precision OCXOs and smaller TCXOs and becomes the most economical choice where there is a need for spectral purity, short-and long-term stability, with small size and dramatically reduced power consumption.

The world's smallest ovenized oscillator, the half DIP EX-620 EMXO will be available for sampling in the fourth quarter. Its performance will be similar to EX-380 but at half the size.

Dave Bail is the director of product development at Vectron International's Mount Holly Springs facility in Pennsylvania. Bail joined Vectron in 2004 following the acquisition of Corning Frequency Controls, where he served as North America PME, and was named director of products in 2005. He began his career in the frequency control industry in 1995 as a design engineer and then as director of engineering for Oak Frequency Control Group, which Corning acquired in 2000. He holds a B.S. in engineering physics from the University of Maine, an M.S. in electrical engineering from Syracuse University and an MBA from Temple University.