ETS mode

Having problems ? let us know the details here
Post Reply
PierreH
User
User
Posts: 2
Joined: Tue Nov 29, 2016 6:36 pm

ETS mode

Post by PierreH »

Hi,

I use a Picoscope 3206D MSO and want to measure the phase difference of two analog signals with vary in frequency from 400 kHz to 600 kHz in steps of 200 Hz. The phase difference is in the order of ~ 0 nS up to 2 nS. Therefore I want to use the ETS mode of the Picoscope. I have chosen to write a C++ program which should do the job. Unfortunatedly the ETS produces strange results. Therefore I looked to the description of the ETS mode.

I don't understand the meaning of the parameters etscycles and etsinterleave (according to pages 75 and 76 of the PicoScope 3000 Series (A API) Programmer's Guide) and the relation of this two to the samplefrequency. Could you explain this better or in another way ? Do you have a timing diagram to show this relation ?

Many thanks in advance.

With kind regards

Pierre

Gerry
PICO STAFF
PICO STAFF
Posts: 900
Joined: Mon Aug 11, 2014 11:14 am

Re: ETS mode

Post by Gerry »

Hi PierreH,

In Extended Time Sampling (ETS) mode a 50 sample waveform cycle would consist of one sample from 50 consecutive waveform cycles captured in Real-Time Sample (RTS) mode. In the resulting ETS waveform cycle, ETS sample point 1 would be RTS sample point 1 from RTS waveform cycle 1, ETS sample point 2 would be RTS sample point 2 from RTS waveform cycle 2, and so on. (there is a good visual explanation of this here: https://www.picotech.com/download/manua ... nswers.pdf)
So, etsinterleave is the number of RTS waveform cycles used to donate one sample point towards the ETS waveform cycle, and etscycles is the number of ETS waveform cycles that will be constructed.

In order to compare the phases of 2 frequencies, stepping 200Hz at a time, you would need to hold the two analog frequencies constant for the total number of RTS cycles that you would need to construct your ETS waveform, So, for example, if you want 3 ETS waveforms constructed then etscycles will be 3, and if you want to use (or interleave) 50 sample points from from 50 RTS cycles then you would need an etsinterleave of 50, and you would need to hold the frequencies constant before performing a step increase of 200Hz for a total number of 3 x 50 = 150 cycles, each time.

If you apply this and still get strange results then could you describe what you mean by strange results.

Regards,

Gerry
Gerry
Technical Specialist

PierreH
User
User
Posts: 2
Joined: Tue Nov 29, 2016 6:36 pm

Re: ETS mode

Post by PierreH »

Hi Gerry,

Thanks for your reaction.

The picture was fine. I got the idea behind ETS.

I tried your advise for etscycles and etsinterleave. See the codedetail below.
etsCycles = 3;
etsInterleave = 50;

status = ps3000aSetEts(unit.handle, PS3000A_ETS_SLOW, etsCycles, etsInterleave, &sampleTimePicoseconds);

After debugging this piece of code, I got a status 13, which means according to page 144 of the Programmer's Guide for the Picoscope 3000 :
PICO_INVALID_PARAMETER A parameter value is not valid

On page 76 of this manual the following text about etscycles and etsinterleave is found:

etsCycles, the number of cycles to store: the driver then selects etsInterleave
cycles to give the most uniform spread of samples. Range: between two and five
times the value of etsInterleave, and not more than the etsCycles value returned
by ps3000aGetMaxEtsValues.
etsInterleave, the number of waveforms to combine into a single ETS capture. The
maximum allowed value for the selected device is returned by
ps3000aGetMaxEtsValues in the etsInterleave argument.

My conclusion from this text is, that etscycles shoud be larger than etsinterleave, which -in my opinion- is in contrast with your explanation.

So, where is my misunderstanding.

With kind regards

Pierre

Mmm22
User
User
Posts: 2
Joined: Mon Jun 15, 2020 9:21 am

Re: ETS mode

Post by Mmm22 »

Hi Gerry,
Isn't what you described here a STS mode rather than ETS? Is there any difference?

Gerry
PICO STAFF
PICO STAFF
Posts: 900
Joined: Mon Aug 11, 2014 11:14 am

Re: ETS mode

Post by Gerry »

Hi Pierre,

I'm answering your query this late because I'm responding to Mmm22, who has brought to my attention that this post was unanswered.

CORRECTION MADE NOVEMBER 5th 2020
The values I used as an example were wrong. The Real-Time cycles used to donate 1 sample to the ETS waveform are the ETScycles, and the resulting ETS waveform created is the ETSinterleave. So apologies for the misunderstanding. Also, in case of any further confusion, in my example I mention the RTS waveform donating 1 sample per cycle. This was just for illustration of the example used. The RTS waveform can donate more than 1 sample to the ETS waveform.

Hi Mmm22,

What is being discussed on this post is ETS mode, which is Extended Time Sampling, a method of increasing the effective sample rate for repetitive signals captured in Real-Time Scopes, such as the PicoScope 2000 to PicoScope 6000 series (see here: https://www.picotech.com/library/oscill ... e-sampling).

STS mode, which is Sequential Time Sampling, uses a similar technique but for Sampling scopes, such as the 9000 series see here: https://www.picotech.com/download/manua ... aSheet.pdf, under Multiple sampling modes - Sequential time sampling (STS) mode.

Regards,

Gerry
Gerry
Technical Specialist

Mmm22
User
User
Posts: 2
Joined: Mon Jun 15, 2020 9:21 am

Re: ETS mode

Post by Mmm22 »

Hi Gerry,
I still cannot get what is the difference between ETS and STS. Both use delays to have more samples/s than the real sampling rate.

Gerry
PICO STAFF
PICO STAFF
Posts: 900
Joined: Mon Aug 11, 2014 11:14 am

Re: ETS mode

Post by Gerry »

Hi Mmm22,

The techniques are essentially based on the same thing. The difference is where the term is used.

Our Sampling Scopes can't give you a waveform plot from just one cycle of a waveform, because they don't perform the reconstruction of the waveform from all of the samples of a waveform gathered in real time. They only gather a fixed number of data points for each cycle, using STS Mode (Sequential Time Sampling), which results in a smaller phase increment for the specific sample points, giving them a much higher effective sample rate (so they are used, for instance, for checking the integrity of cables, looking at fast edges, jitter/phase noise and eye diagrams). We use the term Sequential because acquiring each data sample in sequential cycles is the fundamental method of operation of these Picoscopes (Sequential Time Sampling is actually short for Sequential Equivalent-Time Sampling, describing sampling where the Equivalent-Time points of a waveform are built up from Sequential Cycles).
We use the term ETS mode (Extended Time Sampling), instead, for our Real-Time PicoScopes, which normally just sample data without discarding samples from cycles, and then reconstruct the waveform from all of the real time collected samples. In ETS Mode, it is Extending the Time between each sample point, (which again, results in a smaller phase increment, extending the limit of how fast you can effectively sample the data). The use of ETS Mode increases the effective sample rate of the PicoScope but is limited when measuring certain aspects of signal integrity, because the hardware is not designed to optimally work in this Mode, and at these sample rates (so Real-Time PicoScopes that employ ETS mode have much larger Jitter/phase noise relative to Sampling PicoScopes that employ STS Mode).

Regards,

Gerry
Gerry
Technical Specialist

Post Reply