Microchip Ruggedizes Evacuated Miniature Crystal Oscillators

Microchip Technology recently announced the EX-423 evacuated miniature crystal oscillator (EMXO), a timing device that delivers high-frequency stability with minimal power and space requirements. The company created the EX-423 as an addition to its EX-421 timing device portfolio for battery-powered and harsh environments.

The EX-423 is designed for battery applications, ocean bottom nodes, military portable radios, satellite communications, and more. Image used courtesy of Microchip

With mechanical ruggedization and a lower steady-state power profile, the EX-423 is suitable for use in GNSS tracking systems, military portable radios, and airborne equipment.

An Evacuated Miniature Crystal Oscillator

Microchip designed the EX-423 (datasheet linked) to use less space and power without compromising on features. The device comes in a 15.2 mm x 15.2 mm package and draws 0.20 W at 3.3 V in steady state, while delivering a frequency range of 10 MHz to 20 MHz and accepting either 3.3 V or 5.0 V input power. 

The company also added many features to the EX-423 to ruggedize it for harsh environments. For example, Microchip included a four-point crystal mount that distributes force across the crystal blank. The spread stresses functionally reduce g-sensitivity to less than 1 ppb/g per axis and qualifying shock survivability to 1,000 g per MIL-STD-202 Method 213 Condition E. 

Typical phase noise of the EX-423. Image used courtesy of Microchip

Meanwhile, frequency stability over temperature is rated at ±5 ppb from 0°C to +50°C, ±10 ppb from −20°C to +70°C, and ±20 ppb from -40°C to +85°C, covering the full military operating range. The EX-423 also features a vibration endurance of 15 g peak and 15 g RMS from 10 Hz to 2000 Hz.

Many of the remaining features Microchip implemented in the EX-423 improve its compatibility for designers. To aid interfacing with digital logic and RF signal chains, the company allows designers to configure the EX-423’s RF output as CMOS or sinewave.  

Vacuum Thermal Insulation and Crystal Mounting in Oscillators

An EMXO oscillator is a device that achieves frequency stability by using a vacuum as a passive thermal barrier. With no gas molecules to conduct heat between the crystal and its enclosure, the crystal temperature changes more slowly as ambient conditions shift. 

This architecture also has power benefits. Namely, an EMXO uses less steady-state power than an oven-controlled crystal oscillator (OCXO), which runs an active heater to hold the crystal at a fixed temperature setpoint. Since this mechanism typically requires 1–2 W or more in steady state, it is not ideal for battery-powered designs, making EMXOs the de facto favorite.

G-sensitivity measurement using the tipover test. Image used courtesy of Microwave Journal

EMXOs can also exhibit improved frequency stability when designers employ clever mounting structures. When a crystal oscillator experiences vibration or mechanical shock, the resulting acceleration forces act on the crystal blank, shifting its resonant frequency. In field-deployed systems such as military radios or seismic nodes, this frequency shift may degrade the timing reference for as long as the vibration persists, compromising navigation accuracy, communication synchronization, or data integrity. 

Therefore, a crystal’s mounting structure can significantly impact the oscillator’s sensitivity to external forces, also known as g-sensitivity. Distributing mounting, for example, lowers the oscillator’s g-sensitivity because it uses more attachment points to reduce net strain on the crystal for a given shock amplitude.

Availability

The EX-423 is now available in SMD and through-hole configurations. The device is RoHS 6-compliant, with an optional Sn63/Pb37 solder coating.