Hello Guys,
Good day.
Our customer is using the ADS1114 to AC couple very low voltage signals (uV range). They are ware that the ADC does not provide the internal reference on an external pin. However, they want to reference their signal as close as possible to the voltage value of the internal reference so they do not create unnecessary common mode voltages. What is the value of the internal reference voltage?
Thanks in advance!
Art
Art,
The errors that you see from the common-mode changes don't come from the reference voltage, but rather the discharge point of the input sampling capacitors.
This is the simplified analog input circuit that you see for the ADS1114:
The periodic sampling of the input appears as a input impedance with a differential and common-mode input impedance. These input impedances vary with the PGA setting for the device. This is listed in the electrical characteristics table:
If your customer wants to minimize the common-mode input impedance contribution, they should center the input at about 0.7V above ground.
Joseph Wu
