MEMS try to invade quartz territory: A frontline report

BY RICHARD COMERFORD
Editor

The battle over who will provide the stable time bases that all electronic systems need to operate properly continues to rage. MEMS technology, which has been growing more widespread and capable, is still looking to unseat quartz crystals, the dominant IC timing device.

According to the latest Gartner (www.gartner.com) report, Market Trends: MEMS-Based Timing Controllers Still Chase Crystal Oscillator Slots in Advanced Communications Equipment by Sergis Mushell and Steve Ohr, principal and research analysts (respectively), “Micro-electromechanical systems-based oscillators are promising to take shares from the $3.5-billion quartz crystal oscillator-based timing control market. MEMS vendors are promoting smaller size and lower power, but stability issues will limit MEMS penetration of high-frequency applications.”

The consumer invasion
One of the points of attack is the consumer market, where new types of personal devices offer a beachhead for a MEMS invasion. Take, for example, the 32-kHz SiT15xx series of oscillators (Fig. 1) from MEMS oscillator pioneer SiTime (www.sitime.com). Introduced last year, these devices were the first MEMS-based oscillators designed specifically for mobile and wearable electronics, such as handsets, tablets, activity trackers, smart watches, GPS modules, and the Internet of Things (IoT).

Fig. 1: Compared to traditional quartz devices, SiTime's SiT15xx series devices are 85% smaller in size than , a critical parameter for mobile and wearable products.

According to the company, these MEMS oscillators are up to 85% smaller, consume, 50% less power, and have 15 times greater reliability than traditional quartz products. Piyush Sevalia, executive vice president of marketing at SiTime, notes that the new oscillators “enable [our customers] to differentiate their products and increase their revenue,” which has led to their being designed into high-volume mobile and wearable designs.

For consumer apps, the oscillators, which are factory programmable from 1 Hz to 32 kHz, offer a frequency tolerance at room temperature of 10 ppm and stability over a -40° to +85°C range of 100 ppm, all in a 1.5 x 0.8-mm CSP or  2.0 x 1.2-mm DFN package. Further, they typically draw just 900 nA from a 1.2 to 3.63-V source such as a coin-cell or supercap, thus helping provide longer battery life for mobiles.

The second front
Long known for its crystal-based products, Micrel last year acquired Discera, another MEMS-oscillator pioneer. At the time, Ray Zinn, Chairman and CEO of Micrel (www.micrel.com), noted that “the acquisition of Discera substantially enhances Micrel's penetration into the timing market and provides a strong MEMS-based platform for further growth.” Micrel already had MEMS experience, having built MEMS devices for 15 years for its foundry customers. Zinn added that “the Discera technical team gives Micrel the intellectual property and technical know-how to pursue not only MEMS-based timing devices, but also other types of MEMS devices.”

This month, Micrel introduced the DSC400 (Fig. 2 ), a four-output clock generator based on the Dicera-developed Crystal-less technology. Using Micrel’s PureSilicon technology for the first time in a MEMS-based timing product, the generator is said to provide excellent jitter and stability, while also incorporating additional device functionality.

Fig. 2: Micrel's DSC400 is targeting applications in networking that are the stronghold of quartz.

Significantly, the device, which has a $3.90 starting price, targets a broad range of high-frequency applications, including communications networks (Ethernet 1G, 10GBASE-T/KR/LR/SR, and FCoE), storage area networks (FC, SATA, SAS, FTTH EPON, 10G-EPON, GPON, and 10G-PON), and; HD/SD/SDI video and surveillance, to name a few. According to Rami Kanama, vice president of Micrel’s timing and communications business group, the DSC400’s reliance on an integrated MEMS resonator instead of an external crystal “enhances performance and reliability by enabling tight frequency stability over a wide temperature range. In addition, it has high resistance to shock and vibration which slows the aging rate and translates into much improved product life in the system.”

The 2.3 to 460-MHz device typically has RMS phase jitter of less than 1 ps and high-stability options of ±25 and ±50 ppm; supply noise rejection is -50 dBc. Each of the device’s four outputs may be independently configured for LVPECL, LVDS, HCSL, or LVCMOS format. With high shock/vibration immunity and temperature stability, the 5 x 3.2-mm-footprint (20 QFN) device is qualified to military standard MIL-STD-88 and automotive standard AEC-Q100.

But quartz is by no means surrendering this market. TXC’s (www.txc.com) 7N series Stratum-3 temperature-compensated crystal oscillator (TXCO) is also aiming for networking dollars by offering exceptional performance. With frequencies of 10 to 52 MHz, the 7N series (Fig. 3 ) is designed for high stability in such applications as base stations, small-cell networks and smart grids that need a reference clock with ±0.28- or ±0.14-ppm frequency stability over temperature, as well as outstanding short-term and long-term frequency stability. In fact, TXC says the 7N series can achieve free-run stability of ±4.6 ppm over 20 years.

 
Fig. 3: The 7N series from TXC was designed to provide networks with high
frequency stability of the long term.

To ensure performance, parts are subjected to 100% temperature testing, short-term stability testing, and electrical testing. Housed in a 7.0 x 5.0-mm-footprint package, the oscillator works from a 2.7 to 5.5-V supply and supports CMOS or clipped-sinewave output.