ADS1292R: Saturation?

Hello Seonjo,

Welcome to our forum and thank you for your post!

Most likely, the input common-mode voltage range is violated. Please see the Input Common-Mode section of the datasheet on page 22.

Are you applying the input sine wave as a single-ended signal on INxP only (INxN = GND) or is the sine wave differential (INxP and INxN are driven, out of phase)? In your images, it looks like you are driving a single-ended sine wave with 100 mV of DC offset voltage. As you increase the differential peak-to-peak voltage, you will eventually exceed the negative supply rail and the PGA output will clip on one side.

Best regards,

Hi Seonjo,

Good to hear from you again, I hope you're well.

To confirm, you're operating from a unipolar 3.3V supply for AVDD?

What is your reference voltage?

Keep in mind that the input signal must be within the common-mode limits of the PGA. This can be seen on pg 22 of the datasheet, equation 6. 

With this in mind, I'm not surprised that you're seeing saturation when the input signal is being driven below ground. 

Try centering your input signal to mid supply (3.3/2 = 1.65V) and swinging the sine wave around that 1.65V. 

The maximum amplitude that can be input to the device can be seen on pg 22 of the datasheet, equation 7.