AFE4403EVM: AFE4403 output waveform

Mohammad Akbar

Prodigy 50 points

Part Number: AFE4403EVM
Other Parts Discussed in Thread: AFE4403

Hello,

I have two thing to discuss:

1. I am using AFE4403 EVM, In the datasheet of AFE4403, it is mentioned that the output waveform is Inverted.

Can you make it clear that is it vertically (upside down) inverted or horizontally (left to right)? Or is it both?

2. The DC offset is keep on increasing and in the end clipping starts.

I tried all the solutions mentioned in the previous question regarding DC offset (like using isolation tape, using laptop running on battery etc.) but the issue is still there.

over 1 year ago

0 ChienChun Yang over 1 year ago

TI__Mastermind 19815 points

Hi,

1. would you be a bit more specific on what do you mean by inverted? particularly what you mean by "horizontally(Left to right) inverted"?

2. DC offset drift/increasing could be due to the current and the LED characteristics and thermal effects, which are the characteristics most LEDs often have, i.e. LED's DC light actually increases or fluctuates as the current starts driving and temperature increases. And photodiode + TIA could be very sensitive to that.

Could you attach some pictures?

For example, see if the DC offset drift/increases under other steady/stable DC light sources or low DC light environment.

What might be your LED current and ON time and pulse frequency? Try adjust them lower and also play around with the RF and CF.

e.g. "CF is adjusted to keep TIA time constant at 1/10th of sampling duration" and datasheet page 23

"The RF amplifier and the feedback capacitor (CF) form a low-pass filter for the input signal current. Always ensure that the low-pass filter RC time constant has sufficiently high bandwidth (as shown by Equation 1) because the input current consists of pulses. For this reason, the feedback capacitor is also programmable. Available CF values include: 5 pF, 10 pF, 25 pF, 50 pF, 100 pF, and 250 pF. Any combination of these capacitors can also be used."

Thanks

0 Mohammad Akbar over 1 year ago in reply to ChienChun Yang

Prodigy 50 points

1. Output data inversion:

In AFE4403 datasheet on page 79 and 80 is mentioned that the output is inverted "Note that this value is inverted when compared to waveforms shown in many publications." What does it mean?

I am attaching the standard PPG wave given in other text and output of AFE4403.

Standard PPG wave

Output wave of AFE4403

2. DC offset Drift:

The picture of DC_offset drift is given blow.

This drift is at the auto calibration of the GUI of AFE4403 EVM. I am using default setting of the GUI (e.g. Pulse Frequency = 500).

0 ChienChun Yang over 1 year ago in reply to Mohammad Akbar

TI__Mastermind 19815 points

Hi,

Regarding to "In AFE4403 datasheet on page 79 and 80 is mentioned that the output is inverted "Note that this value is inverted when compared to waveforms shown in many publications." What does it mean?"

I will get back to you in a day.

Thanks