60kV fibre-isolated scope probes work up to 1GHz

Micsig SigOfit fibre optic scope probe Micsig Technology is aiming at mains and high-voltage GaN power supply development with a series of optical fibre isolated oscilloscope probes, with bandwidths up to 1GHz and risetimes down to ≤350ps.

This kind of probe has no electrically-conductive path between probe tip and scope.

Instead, the scope end of the probe and the probe’s head are linked by optical fibres, along which an analogue optical representation of the signal is passed down to the scope-end, while power is passed up to the head, by a laser in this case.

Micsig SigOfit fibre optic scope probe

A bipod supplied with the probe reduces head capacitance to ground

As a result of electrically-insulated signal and power transmission, maximum common-mode withstanding is 60kV.

An amplifier at the head presents 1MΩ in parallel with 10pF to the probe tip via an SMA connector, and probe tips between 10x and 2,000x are available to connect to the signal of interest. Capacitance at the signal interface is ~3pF, and even ~1pF in the x2,000 case (performance tables below).

“Device like GaN and SiC can switch high voltages in a few nanoseconds, containing very high-energy high-frequency harmonics,” according to the company, which is branding the probes SigOfit. “SigOfit probe delivers high common mode rejection ratio: up to 112dB at 100MHz and over 100dB at 500MHz.”

These CMMR figures are at the SMA connector, and reduce somewhat (table below) when the tips are installed.

Micsig SigOfit fibre optic scope probeThe various probe tips (right) give a possible sensed signal range from ±1.25V full-scale to ±2.5kV, and dc gain accuracy ±1% – with a 1.41mVrms noise floor.

The probe tips terminate in a coaxial connector and, for maximum signal fidelity, this should be paired with a matching coaxial socket on the board-under-test.

With no dc reference transferred from tip to head, offset drift is possible. Drift is said to be <500μV after warm-up, and a push button at the scope and of the probe initiates an auto-calibration to remove any zero offset in less than a second.

50Ω is expected at the scopes BNC input, and the scope end box of the probe (which has an internal fan for cooling) is powered from a separate power supply.

A buzzer sounds if the probe over-heats or the input voltage is out of range.

Specifications

MOIP01P MOIP02P MOIP03P MOIP05P MOIP08P MOIP10P
Bandwidth 100MHz 200MHz 350MHz 500MHz 800MHz 1GHz
Rise time ≤3.5ns ≤1.75ns ≤1ns ≤700ps ≤438ps ≤350ps
SMA input impedance 1MΩ || 10pF
Output ±2.5V ±1.25V
Differential
range
1x:±2.5V
10x:±25V
20x:±50V
500x:±1,250V
1,000x:±2,500V
1x:±1.25V
20x:±25V
50x: ±62.5V
1,000x:±1,250V
2,000x:±2,500V
Noise <1.41mVrms
Propagation Delay 15.4ns (2m cable)
Power Supply USB Type-C  5Vdc
DC Gain Accuracy 1%
Common mode Range 60kVpk
Cable length 2m (custom available)
tip type atten input impedance
SMA 1x 1MΩ || 10pF
OP10 10x 10MΩ || 3.0pF
OP20 20x 9.47MΩ || 2.8pF
OP50 50x 9.47MΩ || 2.8pF
OP500 500x 12.27MΩ || 2.6pF
OP1000 1,000x 12.28MΩ || 2.6pF
OP2000 2,000x 30MΩ || 1pF
Common mode rejection ratio
Probe Tip  DC 1MHz 100MHz 200MHz 350MHz 500MHz 800MHz 1GHz
SMA 160dB 152dB 112dB 106dB 102dB 100dB 94dB 92dB
OP10 160dB 120dB 96dB 92dB 90dB 86dB 84dB 82dB
OP20 160dB 120dB 92dB 90dB 86dB 84dB 82dB 80dB
OP50 160dB 115dB 86dB 82dB 80dB 78dB 75dB 74dB
OP500 160dB 96dB 56dB 48dB 40dB 32dB 28dB 26dB
OP1000 160dB 90dB 50dB 42dB 34dB 26dB 22dB 20dB
OP2000 160dB 90dB 50dB 42dB 34dB 26dB 22dB 20dB

The fibre-isolated scope probe web page can be found here

Source

Guidantech
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