ADC gain or attenuation in hardware vs. gain or attenuation in Waveforms

[Phil_D]

I see in the documentation that the ADG612 gain switch between high gain and low gain to the ADC.  I see in Waveforms Spectrum analyzer that there are many gain options: 0.01x, 0.1x, 1x, 10x, 100x.

Which hardware gain setting is used in Waveforms for those gain settings?

Thanks!

[Fa-b]

Hi @Phil_D,

Where do you see ADG612? OpenScope MZ uses TS3A5017 to switch between 4 gains (0.075, 0.125, 0.25, 1). And as far as I can see from the schematic there is no gain switch for the OpenLogger.

Are you sure you are asking your question in the correct (sub-)forum?

 

Regards

Fabian

[Phil_D]

Thanks for the response @Fa-b!

I see the reference to ADG612 in the Analog Discovery 2 Reference Manual:

https://reference.digilentinc.com/reference/instrumentation/analog-discovery-2/reference-manual

And it's this section that also mentions just the two gain settings, low gain at 0.019 and high gain at 0.212, basically a factor of 10 apart.

[Phil_D]

Just to be clear on the setup in case I did post this in the wrong place, I'm using:

-Analog Discovery 2

-Waveforms Beta Version 3.11.2 64-bit Qt5.9.7 Windows 7 SP 1

-I'm using the Waveforms Spectrum Analyzer tool a lot, along with the API calls for the ADC. I do also look at the Waveforms scope for troubleshooting.

[JColvin]

Hi @Phil_D,

The post was one level deeper forum wise than it needed to be, so I've moved it to where @attila will be looking for questions. I'm not certain if there is more to it, but based on the Oscilloscope section of the reference manual, it appears that the high gain is used when the difference between the positive and negative inputs are less than 7V, though I'm not certain how the Spectrum Analyzer tool calculates/determines what to use before-hand when selecting the attenuation.

Thanks,
JColvin

[attila]

Hi @Phil_D

The gain switch is adjusted automatically based on the selected scope range.
At 500mV/div (5Vpk2pk ~0.3mV resolution) or lower the high gain is used with  and above this the low gain (50Vpk2pk w ~3mV resolution).
In case you specify trigger level out of the screen (5Vpk2pk) or offset higher/lower than +/- 2.5V the low gain will be used for the trigger source channel. This will be noted on the screen with red warning text.

The attenuation is a different thing.
This option lets you specify the external attenuation or amplification on the signals which enter the scope inputs and the data is scaled accordingly.
Like, if you use a 10x scope probe, the scope input will actually get 1/10th of the original signal, but specifying 10x attenuation the signal is scaled to show values on the probe. In this case the 500mV/div (5Vpk2pk) low/high gain limit moves up to 5V/div (50Vpk2pk) and the low gain up to 50V/div
If you have an external 100x amplifier on the scope input you can specify 0.01x attenuation. With this you will have 5mV/div (50mVpk2pk ~0.003mV resolution) for high gain.

[Phil_D]

Thanks @attila!

If I'm using the API functions (from Waveforms SDK reference manual) to configure and acquire data from the ADCs, can I set the high/low gain or the high/low attenuation? Are there specific functions to do this, or do these things happen automatically based on input signal level, even when using the API?

 

[attila]

Hi @Phil_D

Actually this gain selection happens in the library behind the API/SDK which is also used the application.

The high gain is selected when the Range is equal or lower than 5V (pk2pk), Offset is withing +/- 2.5V and also if the trigger on a channel is selected the level of this is withing 5V pk2pk range. This 5V/2.5V should be multiplied with the attenuation when used.

After applying the AnalogIn configuration you can use the FDwfAnalogInChannelRangeGet to see the exact ADC range and FDwfAnalogInChannelOffsetGet for offset.