9.1.4 Single-Ended Inputs

Although the ADS1018 has two differential inputs, the device can measure four single-ended signals. Figure 20 shows a single-ended connection scheme. The ADS1018 is configured for single-ended measurement by configuring the mux to measure each channel with respect to ground. Data are then read out of one input based on the selection in the Config register. The single-ended signal can range from 0 V up to positive supply or +FS, whichever is lower. Negative voltages cannot be applied to this circuit because the ADS1018 can only accept positive voltages with respect to ground. The ADS1018 does not lose linearity within the input range.

The ADS1018 offers a differential input voltage range of ±FS. The single-ended circuit shown in Figure 20, however, only uses the positive half of the ADS1018 FS input voltage range because differentially negative inputs are not produced. Because only half of the FS range is used, one bit of resolution is lost. For optimal noise performance, use differential configurations whenever possible. Differential configurations maximize the dynamic range of the ADC and provide strong attenuation of common-mode noise.

NOTE: Digital pin connections omitted for clarity.

Figure 20. Measuring Single-Ended Inputs

The ADS1018 also allows AIN3 to serve as a common point for measurements by adjusting the mux configuration. AIN0, AIN1, and AIN2 can all be measured with respect to AIN3. In this configuration, the ADS1018 operates with inputs where AIN3 serves as the common point. This ability improves the usable range over the single-ended configuration because negative differential voltages are allowed when GND < V_(AIN3) < VDD; however, common-mode noise attenuation is not offered.