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Determining Minimum Acquisition Times for SAR ADCs, part 2


The input structure circuit of a successive-approximation register analog-to-digital converter (SAR ADC) in combination with the driving circuit forms a transfer function that can be used to determine minimum acquisition times for different types of applied input signals. This application report, which builds on Determining Minimum Acquisition Times for SAR ADCs When a Step Function is Applied to the Input (SBAA173), investigates the situation when a dc voltage is applied to the input. First, the input structure of the ADC is examined along with the driving circuit. Next, a simple method is derived for calculating the minimum acquisition time for SAR ADCs when the input is a dc voltage. This method will then be compared with the minimum acquisition time derived in the previous application report. Last of all, three different test cases are evaluated using both exact and approximated equations in order to support the derivations in this report.