GMR isolator for digital lines keeps"nasties"away
-- EDN, June 10, 1999
The neat, clean digital world has a weakness: The real world of ground differentials, ground loops, and common-mode differences can compromise signal integrity, damage I/O interfaces, and even present a user shock hazard. Galvanic isolation is your defense, and you can now add another tool to your isolation kit in addition to opto-, capacitive-, and transformer-based isolation. The single-channel, giant-magnetoresistive (GMR) IL-0710 digital isolator from Nonvolatile Electronics offers 10-nsec propagation delay and 2-nsec pulse-width distortion, plus 4000V-dc isolation.
The GMR isolator, a monolithic silicon device, includes GMR materials, coils, and active circuitry and operates at -40 to +125°C. Current from the signal to be isolated drives the coil windings, and the GMR structure senses the magnetic field that the windings generate across a thick dielectric film. The resistor structure is sensitive to such fields in the plane of the substrate. (This technique contrasts with Hall-effect devices, which sense fields that are perpendicular to the substrate.) Internal active circuitry boosts the sensed-field signal to generate a standard-level, isolated output.
The company plans to announce multichannel devices as well as the initial single-channel IL-0710. You can also fabricate other active circuitry, such as amplifiers, converters, and switches, into the IC. The IL-0710 comes in an eight-pin SOIC or DIP and costs $2.10 (1000).
Nonvolatile Electronics Inc, Eden Prairie, MN. 1-612-996-1610, fax 1-612-829-9189, www.nve.com.
-by Bill Schweber
