Today, there are effectively three methods to measure pass-band 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 converter’s bandwidth 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 ADC output-captured response 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 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.