SNIU028E February 2016 – February 2025 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
Figure 8-2 shows a simplified model of the input circuit of UCD3138 ADC12.
Figure 8-2 ADC12 Input Impedance ModelThe first portion is a 16-to-1 multiplexer that selects the channel to be converted. The second portion is the sample and hold circuit that is controlled by the control block of ADC12. There are several factors to be considered in the ADC input path: the resistance of the CMOS switches and the capacitances associated with them; the leakage resistance, and the sample and hold capacitance.
The external components are also to be considered. Figure 8-3 shows the ADC input model of one channel containing the external circuit and the source impedance.
Figure 8-3 ADC Input Impedance Model Containing External Circuits