AFE5801: how to remove the sine wave

Hi,

Did customer probe the input of AFE and confirm if same kind of signal is seen at the device input too? I am thinking that input is proper and due to third order LPF in the device, the output is looking like above picture.

Regards,

Shabbir 

Hi Shabbir,

Thank you for the support.

With the device low pass filter disabled, that is, the register address 0x07[3, 2] is set to 11, but the issue remains unchanged. The customer tested the input of the AFE and the measured waveform was a 200-kHz, 200-mV square wave, as produced by the signal generator.

Here is the waveform after the data is imported into the matlab, and you can see that one other waveform is overlaid in the square wave:

Thanks and regards,

Cherry

Hi,

Can you please ask customer to change the frequency and share the output waveform same as above? It will be good to see how device behaves with square wave signal frequency of 1MHz, 5MHz and 10kHz. Based on the observation across frequency, we can try to find possible root cause.

Thanks!

Regards,

Shabbir

Hi Shabbir,

In the previous experiment, the customer tested square waves of different frequencies, and their output waveforms were similar to those of 200 kHz, with only different frequencies.

Since AC coupling is used to emulate a signal single-ended input, INP is connected to the signal source, and INM is connected to AGND through 100 nF. The square wave signal cannot be AC coupled in its peak valley, so change the test waveform to Gamma waveform as shown.

The AFE output waveform was tested at 100 mV/200 kHz, 200 mV/200 kHz, and 200 mV/500 kHz without waveform input.

As you can see from the above testing, the waveform should have flattened at 2048, which is 0 of the ADC range, but all three sets of tests have varying degrees of overshoot, where 200 mV overshoot is larger than 100 mV at 200 kHz, there appears to be an internal capacitor being discharged, and oscillations with no waveform input are also coupled in the overshoot portion.

At 500 kHz, the capacitor discharge should have welcomed the next waveform before it is finished, so it does not overshoot to 2150 at 200 kHz, but it goes to the next waveform at 2100.

The customer would like to know how to make the acquired waveform the same as the incoming waveform? (Internal AC/DC register is set to DC, register 0x07[1] = 1)

Thanks and regards,

Cherry

Hi Shabbir,

I am also supporting this user. He said that when he was debugging AFE58801, when he selected AC/DC function, he mistakenly set register 0x07[0] to 1, that is, all the last four bits of 0x07 were set to 1, and found that there was some help with the output waveform. But the chip manual does not give a specific explanation of 0x07[0], and he wants to know what is the main function of this register bit? Could you please provide a detailed description of the register bit

Best Regards,

Amy Luo