Saturday, May 11, 2013

AVR120 8-bit Microcontrollers Application Note download ATMEL pdf datasheets

Application Note

 AVR120: Characterization and Calibration of the ADC on an AVR

• Understanding Analog to Digital Converter (ADC) characteristics
• Measuring parameters describing ADC characteristics
• Temperature, frequency and supply voltage dependencies
• Compensating for offset and gain error

1 Introduction
This application note explains various ADC (Analog to Digital Converter) characterization parameters given in the datasheets and how they effect ADC measurements. It also describes how to measure these parameters during application testing in production and how to perform run-time compensation for some of the measured deviations.
A great advantage with the Flash memory of the AVR is that calibration code can be replaced with application code after characterization. Therefore, no code space is consumed by calibration code in the final product.

2 Theory
Before getting into the details, some central concepts need to be introduced. The following section (General ADC concepts) can be skipped if quantization, resolution, and ADC transfer functions are familiar to the reader.

2.1 General ADC concepts
The ADC translates an analog input signal to a digital output value representing the size of the input relative to a reference. To get a better basis for describing a general ADC, this document distinguishes between ideal, perfect and actual ADCs.
An ideal ADC is just a theoretical concept, and cannot be implemented in real life. It has infinite resolution, where every possible input value gives a unique output from the ADC within the specified conversion range. An ideal ADC can be described mathematically by a straight-line transfer function, as shown in Figure 1.
Figure 1. Transfer function of an ideal ADC

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