Today, there are effectively three methods to measure passband flatness:
- The fundamental frequency response measurement method, which is typically used when collecting the input/output network and converter bandwidth response together.
- The vector network analyzer (VNA) method, which uses a VNA to collect only the bandwidth of the converter response, enabling a precise and accurate measurement of just the converter. This method effectively deembeds the analog input/output network connections [1-3].
- The input pulse method, which uses a high-frequency pulse generator to input a high-frequency square wave. In this method, the user effectively inputs a pure pulse response and cross-correlates the output-captured response of the ADC vs. an ideal square wave. Add a bit of math into the mix, and a user can effectively extract the bandwidth of the converter.
This series focuses only on the fundamental frequency response measurement method as this applies to both ADCs and DACs, using devices from Texas Instruments (TI) as our example test cases. The first installment focuses on ADCs and the second installment discusses DACs. This document offers guidance on how to set up and test bandwidth for both ADCs and DACs in real and bypass mode for the ADC, and with complex digital features enabled such as DDCs and DUCs for the AFE.