Digital isolators
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 10/1/2003 2:00:00 AM
Essentially a transformer on a chip, the iCoupler line of digital isolators from Analog Devices (www.analog.com/icoupler) replace optoisolators when you need to isolate digital signals and prevent ground loops.
The iCoupler consists of two separate die—a transmitter and a receiver—packaged into one device. The device's transformer consists of two pairs of coils separated by a 20-µm solid isolation barrier. Planar structures that form primary coils sit vertically above the structures of the secondary coils. Bond wires connect the primary transformer coils to its input die.
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Digital isolators use transformers on silicon to replace optoisolators. |
The figure shows a block diagram of the device. A Schmitt-trigger inverter ensures that the encoder receives a clean, bounceless edge. The encoder looks for transitions and at each transition creates a pulse that can traverse a tranformer's isolation barrier. Depending on the incoming edge's direction (rising or falling), the encoder sends its output to one of the two primary transformer windings. Upon receiving the signal from the transformer's secondary, the transmitter's decoder can determine the outgoing signal's edge direction, and recreate the original signal edge.
Because the iCoupler uses a transformer to isolate its output, it uses only about 10% of the power that an optoisolator requires to drive its LED. Analog Devices says that the device's bit rate and timing accuracy exceed those of common optoisolators by a factor of 10.
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