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© Motorola, Inc., 2003
AN2438/D
2/2003
ADC Definitions
and Specifications
Application Note
By: J. Feddeler and Bill Lucas
8/16 Bit Division Systems Engineering
Austin, Texas
Introduction
This application note will help users of analog-to-digital converters (ADC)
understand common terminologies used in the electronics industry to define
ADC operation and performance. There are many terms and parameters used
to define the performance of ADC’s. Included in this document are common
definitions, numerical specifications, differences, and issues with the
definitions. By understanding the terminology used to specify various ADC
parameters, a systems designer can better understand how to obtain the
greatest overall system performance, based on the various performance
features of any given ADC system.
Terms and Definitions
The following terms are used in the electronics industry to define ADC
operation.
Measurement Units There are several terms commonly used to measure ADC performance.
Improper or inconsistent use of terms may result in confusion and or
misinterpretation of performance. Common measurement units in use in the
industry are described here (The following examples assume a 10-bit, 5.12-V
ADC with an ideal 2.56-V conversion at $200):
• Volts (V) — The error voltage is the difference between the input voltage
that converts to a given code and the ideal input voltage for the same
code. When the error is measured in volts, it is related to the actual
voltages and is not normalized to or dependent on the input range or
voltage supply. This measure is useful for fixed error sources such as
offset but does not relate well to the observed error.
• Least Significant Bits (LSB) — A least significant bit (LSB) is a unit of
voltage equal to the smallest resolution of the ADC. This unit of measure
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