9.1.6 Establishing Proper Limits on the Absolute Input Voltage

The ADS1219 can be used to measure various types of input signal configurations: single-ended, pseudo-differential, and fully differential signals. However, configuring the device properly for the respective signal type is important.

Signals where the negative analog input is fixed and referenced to analog ground (V_AINN = 0 V) are commonly called single-ended signals. The absolute input voltages of the ADS1219 can be as low as 100 mV below AGND and as large as 100 mV above AVDD. Using the gain of 4 is still possible in this configuration. Measuring a 0-mA to 20-mA or 4-mA to 20-mA signal across a load resistor of 100 Ω referenced to GND is a typical example. The ADS1219 can directly measure the signal across the load resistor using the internal 2.048-V reference and gain = 1.

Signals where the negative analog input (AIN_N) is fixed at a voltage other the 0 V are referred to as pseudo-differential signals.

Fully differential signals in contrast are defined as signals having a constant common-mode voltage where the positive and negative analog inputs swing 180° out-of-phase but have the same amplitude.

The ADS1219 can measure pseudo-differential and fully differential signals.

Signals where both the positive and negative inputs are always ≥ 0 V are called unipolar signals. These signals can in general be measured with the ADS1219. A signal is called bipolar when either the positive or negative input can swing below 0 V. Bipolar signals cannot be measured with the ADS1219.