ADS8686SEVM-PDK: Microvolt Signal Reading with ADS8686SEVM-PDK Board

Gozde Guvendi

Part Number: ADS8686SEVM-PDK
Other Parts Discussed in Thread: ADS8686S

Tool/software:

Hello,

We are attempting to read microvolt-level signals with the Texas Instruments ADS8686SEVM-PDK development board. I am attaching screenshots of the signal we send from the signal generator as well as the signal we read through the interface, along with an image of our test setup.

The signal we read from the interface appears with a DC offset. Is there a way to adjust the parameters in the GUI to resolve this, or is this issue only solvable through hardware modifications? Additionally, when we log the data, the Excel file shows values rounded to limits like 0, 1, and 2. How can we modify the format of this log file?

Lastly, do you have any source code available that would allow us to use a GUI similar to yours and transfer data from the registers to a PC via UART?

Thank you in advance for your support.

Best regards,

36dB_deneme_07_11_24_11_03_43.csv

2 months ago

0 Tom Hendrick 2 months ago

TI__Guru**** 175201 points

Hi Gozde,

Welcome to our e2e forum! I see what looks like a little bit of a negative offset in your signal generator screen shot, while the Time Domain Display looks like it has a positive offset. That may be from the offset error of the ADS8686S, either way, there is nothing in the GUI that can adjust that for you. Also, by the CSV file, I see that you are in the +/-10V input range. The values in column A are 'codes' - it's not actually rounding at all. With 260uVpp input and the +/-10V input range, you are only seeing ~3 codes in the conversion results. You might try changing the input range (under Device Configurations) to the +/-2.5V input range, which should give you a larger code spread - still very small in the end though. You can also right click on the graph and 'Export' the data to Excel - this will give you the voltage (rather than codes) you see in the graph.

0 Tom Hendrick 2 months ago in reply to Tom Hendrick

TI__Guru**** 175201 points

Here are some screen shots for you:

0 Gozde Guvendi 2 months ago

Prodigy 35 points

Hello Tom,

First of all, thank you very much for your quick response and informative answer. In addition, we would like to read digital data via the SPI interface of the ADS8686S board using an STM32 microcontroller. Is it possible to provide a source code for this process?

Best Regards.

0 Tom Hendrick 2 months ago in reply to Gozde Guvendi

TI__Guru**** 175201 points

Hi Gozde,

Unfortunately I do not have a source code example for you. I'll ask our SW team to put something into the creative backlog.

0 Gozde Guvendi 2 months ago in reply to Tom Hendrick

Prodigy 35 points

Hello Tom,

Did your software team give you any feedback?

Thank you.

0 Tom Hendrick 2 months ago in reply to Gozde Guvendi

TI__Guru**** 175201 points

No, not yet. I'll ping them again...

0 Gozde Guvendi 1 month ago in reply to Tom Hendrick

Prodigy 35 points

Hello Tom,

I would like to ask you one more question. When I connect 20 mV peak to peak sine input signal to ADS8686S board with SMA connector (AIN0 channel), the value I read from GUI comes with -7.5 mV offset. When I short the negative and positive ends of the input and read the float channel, the offset value I read is 0.2 mV. I see offset values above the offset error specified in the datasheet of the board when I plug the input signal. What are the improvements I can make on hardware and software to get rid of this offset?

Thank you.

0 Tom Hendrick 1 month ago in reply to Gozde Guvendi

TI__Guru**** 175201 points

Hi Gozde -

It is hard to say where the offset is coming from without knowing a little more about your signal source, perhaps its caused by some impedance issue and/or bias currents. What signal generator are you using? Are you feeding the inputs through an amplifier or direct connection to the SMA?

0 Gozde Guvendi 1 month ago in reply to Tom Hendrick

Prodigy 35 points

Hi Tom,

I use the function generator of the Rohde&Schwarz Oscilloscope (RTM3004). I am attaching the scope, device configuration, test setup and signal I took. How can I solve this negative offset problem?

0 Tom Hendrick 1 month ago in reply to Gozde Guvendi

TI__Guru**** 175201 points

Thank you!

Can you please remove the fly wires from the green terminal block and just double check the Sine wave on the scope as well to verify there is no offset (the display shows 0V, but please confirm).

0 Gozde Guvendi 1 month ago in reply to Tom Hendrick

Prodigy 35 points

Hello Tom,

I removed the cables and took a screen shot of the GUI but offset remains the same. And i also attached the signal I sent from oscilloscope. What is your opinion?