Can't measure on higher bit rates.

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cmug
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Can't measure on higher bit rates.

Post by cmug » Fri May 18, 2018 6:04 pm

I can't measure on higher bit rates. Every value I use above 8 bit, the signals becomes weaker. The trouble starts at frequencies above circa 10 kHz.
Above 100kHz the line is nearly flat.

MacOS 10.13.5
1:10 probe
Mono MonoFramework-MDK-5.12.0.226.macos10.xamarin.universal
Picoscope software 6.12.9.64
Picoscope hardware 2206A

Martyn
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Re: Can't measure on higher bit rates.

Post by Martyn » Sat May 19, 2018 6:09 am

If you mean Resolution Enhancement to increase vertical resolution, then that is applying a moving average filter to the displayed data and will flatten signals.

Tool->ViewProperties will show the actual sample rates in use.

Pictures will help us understand the problem, as will psdata files
Martyn
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cmug
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Re: Can't measure on higher bit rates.

Post by cmug » Sun May 20, 2018 9:42 am

I make an screenshot movie. I hope this 'll help te explain.
You see if I use 8 Bit ; everything works as expected.
But if I change to an higher Bit range (here in this example 12 Bit) the signal becomes weaker when I change time/div as you see easily. IHO there is something wrong.
Another example: if I use 12 Bit and sweep an amplifier from a frequency range 1k to 100k I see as higher the frequency the weaker te signal. So I thought bad amplifier ; but it was limitation of my Picoscope in 12 Bit modus.
Can I only do this test in 8 Bit modus ?

https://cmug.stackstorage.com/s/iWoMfEuXGDFYoj0

(link works for several weeks after 5-2018)

cmug
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Re: Can't measure on higher bit rates.

Post by cmug » Sun May 20, 2018 5:21 pm

I studied your explanation.
https://www.picotech.com/library/oscill ... nhancement
I thought my equipment it was possible to measure at 12 bit. But if I understand correct, No it's not. I bought an 8 bit scope (2206A) and in some situations I can use an smart oversampling technic to simulate higher bitrates . But not in all situations.

Martyn
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Re: Can't measure on higher bit rates.

Post by Martyn » Mon May 21, 2018 6:44 am

That's correct.

In your video with 12bit resolution enhancement you are using a 256 sample moving average filter. As you change the timebase the number of cycles of the waveform across the screen increases and the number of samples covering a single cycle drops. Eventually meaning the 256 sample moving average covers more of a single cycle and so the level collapses.

The same effect occurs if you keep the timebase the same and increase the frequency.

With the deep memory scopes you can counter this effect by increasing the sampling rate at the same time, unfortunately the 2206a doesn't have the memory to allow this.
Martyn
Technical Support Manager

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