A High-Resolution Error Plotter for Analog-to-Digital Converters

This paper describes an automatic error plotting system for analog-to-digital converters (ADC's) which measures the static errors of the device under test at every quantization band edge (QBE) and displays them in graphical form. A quantization band edge is defined as any ADC input voltage which produces two adjacent output codes, each with 50-percent probability. The error of the ADC is then defined as the difference between the actual and nominal values of a QBE. A feedback loop which seeks each QBE is central to the system. Sample plots show the ability of the system to display common types of ADC errors and to display error signatures that often point to specific ADC problems. Resolution, accuracy, and (to a large extent) speed of the system depend on the digital voltmeter chosen as a standard. In a typical case, a 2000 point plot can be made in two minutes with a resolution and accuracy exceeding the weight of the ADC's least significant bit by an order of magnitude.