A monolithic four-channel digital galvanic isolation buffer in the 0.5 mm silicon on sapphire (SOS) CMOS technology is reported. Advantage is taken of the insulating properties of the sapphire substrate to integrate on the same die both the isolation structure and the interface electronics. Each isolation channel has been tested to operate at data rates over 100 Mbit=s. The system can tolerate ground bounces of 1 V=ms and is tested for 800 V isolation. The system includes an integrated isolation charge pump to power the input circuit and is hence capable of operating from a single 3.3 V power supply.

In this paper, the design and test results of a 4-channel digital isolation amplifier are presented, along with results of a prototype power converter circuit using the amplifier for voltage feedback regulation. The amplifier uses a capacitive coupling technique to transfer digital signals from input to output while preserving galvanic isolation between the two. The isolation amplifier was fabricated in a 0.5 µm Silicon-on-Sapphire (SOS) technology and uses the isolation properties of the SOS substrate to achieve more than 800 V isolation between input and output grounds. Each of the four channels can operate in excess of 100 Mbps using a differential transmission scheme to reject ground bounce transients up to 1 V/µs. The input circuit can be powered from an on-chip charge-pump to permit single supply operation. The device can be used in a wide variety of applications that require passing signals across an isolation barrier: power supplies, remote sensing, and medical and industrial applications.