Overshooting Issues on Biphasic Pulse Stimulation

[angie906]

Hello,

I would like to ask about the overshooting issues occurring both in the SMTP_PC_Software and in the code from GitHub (with the Python wrapper). In both cases, there is an issue of overshooting when stimulating biphasic pulses.

When the pulse changes its value, a peak voltage occurs that is beyond the expected value and is quite significant. For example, I should be getting 4.4V but I am getting 5.2V. (Please refer to the attached photo)
Given that the overshooting is quite substantial, I would like to know if there's a way to fix it in software by changing the code or if I should add a filter in my resistor circuit.

Thank you very much in advance!

[JensGruetzner]

Hello,

can you say something about the measurement setup? What current is set and which resistor do you use to measure the voltage?

The plateaus of the pulses also seem to be higher than 4.4V, is that correct?

[angie906]

Hello, thanks for your response.

It was 2mA and 2.2 Kohms resistor, so it should be around 4.4V peak.
The Plateau is also a little bit higher but not too much (around 4.5~4.6V).
I've checked with different frequency range(50-1000Hz) and pulse width(250-5000micro secs) setups.
But for all cases, there were overshootings at least a bit from 9.4V(4.7V max) to 11.5V(5.55V max) peak to peak voltage.

Since the overshooting is quite big compared to the desired voltage, I wish we could figure out how to minimize it.

[JensGruetzner]

Hello,

the stimulator is designed for currents up to 130 mA. It is characterized by a high slew rate, as it is assumed that the high frequencies also trigger deeper lying nerves.

Therefore, overshooting can hardly be prevented, especially with these low currents. The stimulator's current regulator is set to achieve a good compromise. We consider the amplitude and the short duration of the overshoot to be harmless.

By the way, the IEC 60601-2-10 stimulator standard requires a parameter value accuracy of 20% for the entire pulse.