Measure power electronics with 80dB range at 1GHz – fully isolated
Tek has opted for a “soft” launch of this product, which will be known as IsoVu. It was previewed prior to, and at, the US APEC exhibition and again at PCIM: when I saw it in Germany, the Tek team confirmed it would be an “orderable” product within weeks, although no pricing information was available. First deliveries are expected in the third quarter of 2016.
The problem that the IsoVu probing system was conceived to solve is the need to make high-speed measurements on high-voltage components, with a high level of resolution. Tek’s Tom Neville, Product Planner and Product Marketing Manager for Power Probes, says the classic problem is trying to capture what is happening on the gate of the high-side switch in an inverter or power converter. With today’s fast switches (and even faster GaN or SiC parts coming on-stream) this means seeing activity of (at most) a few Volts, on a base level of several hundred Volts, at multi-MHz edge speeds. With conventional probing techniques, Neville says, you are very nearly ‘blind’ to the detail you need to see, “a lot [of engineers today] don’t even try”.
As can be seen from my photograph, IsoVu will take the form of a two-module probe, interconnected by a purely optical cable (four channels in the photo). Neville is careful not to disclose any details,but the ‘base’ module contains laser source(s) that are launched to the probe-head module. Sufficient laser energy is sent over the link to convert to electrical power that drives the probe-head. A CW laser also provides the signal path, launched down the cable, modulated by the captured signal, and returned to the base unit. The signal information is recovered from the modulated optical and passed to the ‘scope; all of this is analogue – no A/D conversion takes place until the DSO. Neville confirms the specification points noted in our initial report;
… greater than 120 dB common mode rejection from DC to 100 MHz… 80 dB (10,000:1) common mode rejection at 1 GHz, which is more than a thousand times (60 dB) better than previously available measurement systems… engineers will be able to accurately measure small differential signals (5 mV – 50V) in the presence of large common mode voltages less than 2 kV from DC to 1 GHz… common mode voltage capability does not de-rate over bandwidth.
In this domain, EMI will be ever-present and shielding will be key; Tek has designed a number of probing options that allow shielded probing right down to the target trace on the PCB. There is a solder-down option based on the MMCX RF connector; you can use 2-pin test points with conventional 0.1-in. spacing or a new ‘mini’ version of the same concept – and Tek has a shielded sleeve probe to slip over a 2-pin termination to preserve noise exclusion.
A member of the Tek team re-iterates, “80 dB at 1 GHz bandwidth – there isn’t anything else out there that comes close.”
Tektronix; www.tektronix.com
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