ADS1299: 250 uVpp noise floor of unknown origin

Hi Brian, 

I have plotted it's histogram and Power spectrum  (figures 1 and 2). I have tried to avoid power line noise by using an unplugged laptop and moving away/turning off any other electronics and fluorescent lights nearby.

You can see this noise is even present when measuring stuff like the Test signal generated internally. (Figure 3).

I also selected components according to the datasheet's recommendations so maybe my PCB design is wrong in some way or a component is damaged. I will try soldering another prototype and test results but it would save me a lot of work if this one could be fixed.

Thanks a lot for your time Brian,

Pablo

Hi Pablo

I know it's an old post, but i have your problem with ads1299

my board work good with ads1294 but with ads1299 i have gussain noise :|

this is my test signal screen shot, as you can see registers setting is ok and internal reference has been turned on.

can you fix your problem?

Thanksssss.

Hi Brian Pisani,

This is MCU code:

for(j=0;j<3;j++)
{
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
SPI2->DR=0;
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_RXNE) == RESET);
data_info[j]=(SPI2->DR);
} 
for(i=0;i<8;i++)
{
for(j=0;j<3;j++)
{
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
SPI2->DR=0;
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_RXNE) == RESET);
data_info[j]=(SPI2->DR);

}
if(i<NumberOfChannels)
{
data[writerSeek++]=data_info[2];
data[writerSeek++]=data_info[1];
data[writerSeek++]=data_info[0];
}
}

firstly, i read STAT and ignore it then read channel data and write it in a buffer and then convert MSB first  data to LSB first and send it to computer.
 

this is computer code:

	for (int j = 0; j < numberOfChannels; j++)
                        {
                            Int32 sampleData = 0;
                            for (int k = 0; k < 3; k++)
                            {
                                sampleData += Convert.ToInt32(received[j * 3 + k] << (8 * k));
                            }
							if ((sampleData & 0x1 << 23) > 0)
                                   sampleData |= -16777216;
                                plotDataY[j].Add(Convert.ToDouble(sampleData)  * gainFactor);
								/*
									gainFactor=4.5/(2^23-1)*1000000/2=0.5364/2
								*/
                            }
						}

Also AVSS=-2.5 , AVDD=2.5 and DVDD=3.3

I think this problem pertain to IC or PCB.

This signal is recorded with ADS1294 with same PCB(approximately).