AFE5801: Issu with Static PGA above about 10dB

Hello Fabrice,

Are you able to set any test pattern mode for example ramp pattern and able to capture the test patterns?

Hi Praveen,

Yes, test pattern work fine, I can set ramp and everything is okay.

If I use a regular pur sin wave on AFE input, it seems to work as expected when I set input to DC, and the issue append when I'm in AC coupled mode.

I'm working at 250 kHz with a sampling frequency of 6 MHz.

Thanks for your support.

Hi Fabrice,

I do not follow your statement:

"If I use a regular pur sin wave on AFE input, it seems to work as expected when I set input to DC, and the issue append when I'm in AC coupled mode."

Can you please clarify?

• What is your board input configuration?
• Is the input signal AC coupled or DC coupled? If DC coupled, do you ensure that you use the VCM output from the device to set the CM level of the input signal?

Hi,

Sorry for that.

My design is composend of 8 diff op amp which are dc bias with Vcm and that feed the AFE5801 with a 500 kHz signal.

My plan, was to direct input signal (AC+DCbias) on AFE5801, using the AC coupling parameter bit (High pass filter) to remove the small amount of residual DC voltage that may be an issue for high gain.

It doesnt work.

So during my investigation I decided to add a series capacitor at AFE5801 inputs to remove DC and set the parameter bit to DC not to use the High pas filter of AFE5801.

It work.

What I do not understand is why I don't succeed with the AFE5801 incorporated high pass filter even if both diff input are DC bias with Vcm voltage and signal magnitude is in the good range (+/- 1Vpp).

thanks for your help.

Fabrice

Hi Fabrice,

Can you please attach some waveforms to explain what you mean by "it does not work" with direct input signal (AC+DCbias) on AFE5801 and using the AC coupling parameter bit (High pass filter)?

Also, did you still notice the original issue with the coarse gain setting?