1GHz optically isolated measurement system features at APEC

The technology will also offer immunity to external interference and radiated emissions, minimising the impact of EMI on measurements.

To date, design engineers working on power device designs involving GaN and SiC technologies and other high-speed applications have had no way to accurately visualise differential signals when common mode interference is present.

As a result, these signals are essentially hidden, making it difficult for engineers to see what is actually occurring inside circuits, slowing debug and characterization efforts.

Engineers also face challenges making measurements in noisy environments or those that have high EMI.

The IsoVu technology being shown at APEC has the potential to resolve these challenges. It utilises an electro-optic sensor to convert the input signal to optical modulation, which electrically isolates the device-under-test from the oscilloscope. IsoVu will incorporate four separate lasers, an optical sensor, five optical fibres, and sophisticated feedback and control techniques.

The sensor head, which connects to the test point, has complete electrical isolation and is powered over one of the optical fibres. Ten patent disclosures have been filed for this technology. 

“This is an outstanding example of the type of innovative thinking that drives us at Tektronix to tackle difficult problems that have never been resolved in the past,” said Earl Thompson, senior vice president, Time Domain Business Unit, Tektronix. “There’s no getting around the fact that an electrical connection between the oscilloscope and the device under test impacts measurement results. By moving to an optical connection, this technology has the potential to eliminate that as a problem and as a result could significantly advance the state-of-the-art in power measurement and EMI test systems.”

As demonstrated, IsoVu technology offers greater than 120dB (1 Million:1) common mode rejection from DC to 100MHz which is 33,000 times better than previously available measurement systems.  At 1GHz, it will provide 80 dB (10,000:1) common mode rejection at 1GHz, which is more than a thousand times better than previously available measurement systems. As a result, users will be able to measure anywhere in their circuit without common mode interference. 

Using this technology, engineers will be able to accurately measure small differential signals (5mV - 50V) in the presence of large common mode voltages less than 2kV from DC to 1GHz. This will be the first signal acquisition product where the common mode voltage capability does not de-rate over bandwidth.

Tektronix plans to offer a 10 meter fibre optic cable option with the same performance specifications as the 3 meter option to allow users to move their test system away from the interference and radiated emissions of the device under test. As such, it will be well-suited for such applications as remote testing and EMI validation.