chenzhenyuchch: Shared IOUT/AIN Pin Many RTD system designers use sigma-delta ADCs with integrated mux and excitation currents that allow multiple channel measurements and flexible routing of the excitation currents to each sensor. An ADC such as the AD7124 allows a single pin to operate simultaneously as an excitation current and an analog input pin (see Figure 4). Sharing pins between IOUT and AIN will only require two pins per 3-wire RTD sensor, which increases the channel count. However, in this configuration, a large value of the resistor R in the antialiasing or electromagnetic interference (EMI) filtering can add errors to the RTD resistance value as R is in series with the RTD—thus, limited R values can be used. That’s why it is usually recommended to have a dedicated pin for each excitation current source to avoid possible errors across RTD measurements.