Linearity Testing of A/D Converters Using Selective Code Measurement

Measurement of integral non-linearity (INL) and differential non-linearity (DNL) of an A/D converter using the histogram method incurs large test time. This test time can be a significant percentage of the total test time, especially for high resolution and low sampling-speed A/D converters. This paper describes a test methodology for measuring the INL and DNL specifications of A/D converters by measuring a subset of the total set of code widths. This methodology is based on the fact that manufacturing variations in the electronic components of an A/D converter affect specific sets of codes in a similar manner. The proposed methodology measures code width parameters across such different sets of codes and estimates the A/D converter transfer function from the resulting information. A novel test generation methodology is presented for measuring the relevant code widths using a piecewise linear ramp that is designed to extract test information accurately from test data in minimal test time. The test procedure has been applied to different A/D converters and test time reduction of more than 75% has been achieved.