PPK2 showing Different current reading on different sampling rate settings

[dnyaneshvar]

I have connected BLE device to the Nordic's power profiler kit 2 to do power analysis.

My BLE device advertises every 5 seconds.

I can see current consumption spike every 5 sec in Power profiler waveform.

First I saw waveform with 100 sample per seconds setting.

After that I analyzed after changing the sampling rate to 1000 samples per seconds.

I saw that current value measured by analyzer changes proportionally as I increase the sampling rate setting.

Please help me to understand what is the actual current being consumed by my device?

For reference this the table of actual measured values.

Samples/Seconds setting	Measured Current
100	1.4mA
1000	6.1mA
10000	8.5mA
100 000	15.5mA

Thank you

Dnyaneshvar

[helsing]

Hi Dnyaneshvar, sorry for the delay.

The average current consumption is the most important measurement to pay attention to. If you sample with at a high sample rate and read out maximum current, you get to see where the largest current spikes are. If you sample at a lower sample rate, then the largest spikes will have been averaged out over the sample interval. This will result in the maximum current displayed as lower than for high sample rate. The average current is still very similar.

The schematics for PPK2 can be found on our website if you would like to take a closer look.

Hope this answers your question.

[dnyaneshvar]

Hi helsing,

1) The average current consumption is the most important measurement to pay attention to.  - Okay.

2) If you sample at a lower sample rate, then the largest spikes will have been averaged out over the sample interval.

This will result in the maximum current displayed as lower than for high sample rate.- I am talking about the instantaneous values of current. Instantaneous current consumed by advertising interval of load device. It can be clearly seen that it's values measured by PPk2 are all different at four different sampling rate.

Yes, Averaging is done with respect to the sampling frequency, I agree.

Increasing sampling rate would result in increase in the accuracy of measured parameters.

But how come the value of instantaneous current consumed become different for different sampling rate.

How the current of 1.4mA becomes 15.5mA when sampling frequency changes from 100 to 100 000 samples per seconds?

[Stian Røed Hafskjold]

dnyaneshvar said:

So for waveforms other than mentioned above how can I identify the current spikes shown by PPK2 KIT are due to the artifact from the PPK2 itself and is not part of the actual current?

You can identify the artifact by looking at the current before and after. When it switches measurement ranges, i.e. going from a low current consumption to a high current consumption, it may overshoot.

[ATla5]

Hello,

I want to investigate the artifacts of the current measurement caused by the PPK2 and I want to know

1. The type of (professional lab) measurement equipment including settings used to perform the measurement.

2. Was the current measurement performed with the PPK2, nRF52840 and the professional lab equipment in series or individually meaning first PPK2 and nRF52840, then the professional equipment and the nRF52840.

In general I would appreciate more details about the measurement setup.

Best regards

ATla5

[Stian Røed Hafskjold]

Hi,

The lab equipment used was a Keysight N6705B. Measurements were conducted individually, on the same DUT. Both PPK and N6705B were configured in source meter mode with 3V output.

[Searcher]

When will the current range switches? I met an issue that average is 0.48uA, but the max is 18.48uA(every 200ms the current spikes will appear).

[Stian Røed Hafskjold]

Hi, this is normal and is called refresh mode. When the current consumption is low, the regulator turns off to save power, and internal current is only drawn from the DEC4 capacitor (regulator output). The spikes you see is the regulator waking up to recharge the DEC4 capacitor. If you probe the DEC4 voltage you will see that there is a corresponding saw tooth shape to the input current.

[Searcher]

Thanks very much for the explaination.  Stian Røed Hafskjold