A Digital Isolator is a device that isolates digital signals between elements of a system without requiring the use of optocouplers. They do this by combining CMOS and monolithic air core transformers on a single device, making them very small and low cost. Digital Isolators typically support multiple signal path channels.

 

Digital Isolators consume very little power (in the milliwatts range per channel) can interface relatively high-speed signals (up to 150Mbps), and have high electrical isolation of up to 5kV. Isolation is important because the electrostatic discharge, or other noise spikes inadvertently coupled logic circuits can damage integrated circuits. The high voltage spike is filtered from the signal line by placing an isolator in series with the signal circuit, preventing this damage from occurring.

 

Internally, Digital Isolators filter an input signal (glitch filter), detect edges of the signal and drive the primary coil of a transformer implemented on the silicon. The signal is coupled across to the secondary coil (transformer provides isolation) where it is detected and decoded back to signal levels and output from the device. Other technologies used by Digital Isolators include capacitive coupling rather than inductive coupling transformers.

 

Common applications that require the use of Digital Isolators include digital high-speed multichannel circuits, serial interface isolation and instrumentation for monitoring digital signals like logic analyzers. Digital Isolators are AC coupled, with the DC component of a signal not able to be communicated. Digital Isolators require clock encoded data – this clocking may be built into the device as part of the driver and receiver of the inductive or capacitive isolator and not visible to the user.