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Forum / Altium Designer / I am using ADC129 with ESp32 for collecting data of small ECG signal . Unwanted noise is facing of

I am using ADC129 with ESp32 for collecting data of small ECG signal . Unwanted noise is facing of

Atta Rehman , 12-17-2024, 07:35 PM

@ Robert Feranec .
I am using ADC129 with ESp32 for collecting data of small ECG signal .
Unwanted noise is facing of 9.76 HZ .
please suggest me solution to remove or possible reason of this 9.76 HZ noise removal .
i have no frequency on board operating at 9.76HZ .

Atta Rehman , 12-17-2024, 07:37 PM

Sir , As per your experience , Please suggest possible reason of low frequency noise reasons. respectful regard Arehamn

QDrives , 12-17-2024, 10:05 PM

What op-amp are you using?

Atta Rehman , 12-17-2024, 10:10 PM

ADS1299

QDrives , 12-17-2024, 10:20 PM

Not other external op-amp?
Ceramic capacitors (class II) or tantalum/electrolytic?
What about the regulator?
Jitter in the clock?

Atta Rehman , 12-17-2024, 10:43 PM

1. Inverting opamp for noise cancellation within ADC. as shown in figure data sheet figure 73.

Atta Rehman , 12-17-2024, 10:45 PM

2. using ceramic capacitors.
3. LDO's using for analog supply of ADC and digital of controller ESp32.

Atta Rehman , 12-17-2024, 10:46 PM

4. ADC internal clock is using , ADS1299 , 2.048MHz

Atta Rehman , 12-17-2024, 11:02 PM

power Spectral density of data , have harmonics of 9.76HZ

QDrives , 12-17-2024, 11:59 PM

I assume two separate LDO's, one for analog and one for digital?
https://www.youtube.com/watch?v=A9Kvst8hl0M

Atta Rehman , 12-18-2024, 10:11 AM

for digital +3.3V

Atta Rehman , 12-18-2024, 10:12 AM

for analog +/- 2.5V

QDrives , 12-18-2024, 03:44 PM

Do you get your values at 20Hz?
If so, 20 [M?] / 2.048 [MHz] = 9.765625

If you make your picture any smaller, you might as well not post them at all.
I see inductors and ferrite beads on the outputs. Remove them.
https://www.youtube.com/watch?v=HaLMjVkKYMw
https://www.youtube.com/watch?v=U5_61EJlytc

Atta Rehman , 12-18-2024, 04:33 PM

YES , power spectral density Values starts near 20HZ () ,

Atta Rehman , 12-18-2024, 04:34 PM

and repeats harmonics 9.76HZ multiples.

Atta Rehman , 12-18-2024, 04:35 PM

YES , i already removed FB with 0603 ohm jumper 0R resistor . .

Atta Rehman , 12-18-2024, 04:41 PM

" Do you get your values at 20Hz?
If so, 20 [M?] / 2.048 [MHz] = 9.765625 "

yes _ exactly starts from 20HZ and multiples of 9.76HZ .

Atta Rehman , 12-18-2024, 04:42 PM

why it starts from 20Hz. and get harmonics of 9.76Hz , as frequency is 2.048 MHz

QDrives , 12-18-2024, 05:05 PM

The 'frequency' you **see** starts at 40 / 2.048 [MHz] = 19.53125.
What settings do you have set for the SINC filter?
What sample rate (output SINC filter) are you using?

Atta Rehman , 12-18-2024, 07:42 PM

1. Respectfully , X axis is HZ , First Peak starts at 19.53 HZ than 9.76 multiples peaks. it should be in MHZ harmonics peaks are in HZ. Don't under stand _40 digit._
2. ADS1299 has fix **third order SINC** filter **. (not programmable ).
3. i am using **250 SPS** data rate .