Optical isolators are showing their age. Unlike other components on modern circuit boards, which have become ever smaller, these devices still take up a lot of space. They also are slow and operate in a limited temperature range. Newer technology is needed, design engineers say.
Small footprint. ArtCapText
NVE's four-channel isolator chip in the photomicrograph has a footprint of only 2.1 mm
2. Because the device takes up less real estate on the board, there is more room for other functions.
The solution may lie in magnetics. NVE Corporation (Eden Prairie, MN) has developed giant magnetoresistive (GMR)-based isolators that offer better performance than optical isolators for the same cost. The company was significantly helped by research it conducted for BMDO's SBIR program to explore the use of magnetic random access memory (MRAM) for data storage applications.
With speeds up to 100 megabaud (Mbaud), GMR isolators transmit data 4- to 20-times faster and have correspondingly faster rise, fall, and propagation times than their optical brethren. These devices also are 20-percent smaller and draw 1/2 to 1/3 less power. With regard to noise immunity and temperature stability, NVE's devices perform better. They operate up to 25 kV/&s and are stable at 100°C, compared with 10 kV/&s and 75°C for optical isolators.
NVE offers a product family of IsoLoop
™ GMR isolators, which are ideally suited for industrial data bus, analog to digital conversion, and telecommunication applications. This family includes single-channel, dual-channel, and four-channel devices (unid irectional and bidirectional). An isolated RS485 chip is also available. The single and dual-channel isolators are available in 9-pin DIP and 8-pin small outline integrated circuit (SOIC) packages. The four-channel version and the RS485 interface IC are available in wide-body 16-pin SOIC packages.
Distribution channels for NVE's GMR isolators have been established in Europe, Japan, Korea, China, and Taiwan. NVE has also teamed with Digi-Key Corporation, one of the fastest-growing electronic component distributors in the United States. "In the domestic market, Digi-Key is among the top 15 of the more than 800 electronic distributors and has done business with 99 of the top 100 electronic companies," commented Dr. Daniel A. Baker, NVE's president and chief executive officer. "This agreement is a great endorsement of NVE's new components and a key element of our strategy to dramatically broaden our component distribution."
Under a current BMDO SBIR Phase II project, NVE is developing faster, more rugged GMR isolators by combining a novel thin-film linear spin valve structure and low-voltage differential signaling (LVDS) circuitry. The spin valve structure is well-suited for high-speed operation because it is never driven to saturation. Hence, smaller fields/currents can be used to switch the electronics. Using this design, NVE believes it can reduce the isolator's current usage from 50 to 10 milliamps, yielding a corresponding increase in speed from 100 to 500 Mbaud. The company recently demonstrated a prototype with speeds up to 300 Mbaud. The magnetic core of the spin valve structure is also more radiation tolerant than optical isolator cores.
NVE seeks private companies and military organizations interested in exploring potential applications for its GMR isolator technology.
--P. Hartary