Calibrating amplifiers and ADCs in SoCs

by M. Ganesh Raaja and Pushek Madaan, Cypress Semiconductor , TechOnline India - February 09, 2012

There is no such thing as an “ideal” converter in the real world, where systems have to contend with error that is introduced into the system and affects the ADC’s output. The most important errors, and the ones discussed in this article, are offset and gain errors.

In today’s world of mixed-signal systems, many applications require analog quantities – including but not limited to voltage, current, temperature, pressure, acceleration, pH, flow, and ECG – to be measured and processed. The field of uses ranges from lab and medical equipment operating in controlled environments to industrial equipment running under harsh operating conditions. The analog signals to be measured can range from a few micro-volts in ECG systems to thousands of volts in electricity generation plants.

Unfortunately, there is no such thing as an “ideal” converter in the real world, where systems have to contend with error that is introduced into the system and affects the ADC’s output. The most important errors, and the ones discussed in this article, are offset and gain errors.

This article begins with a mathematical representation of a practical system. It then looks at some widely used calibration methods used to eliminate offset and gain errors. Each of these methods has its own merits and disadvantages. These include:

• Two-point calibration
• Correlated double sampling
• Gain calibration by an external voltage reference
 
Depending upon the application, one or more of these methods can be combined to achieve maximum accuracy. The article concludes by putting the calibration concepts to test.

To read the article, which is presented as a pdf document, click here.


 
About the Authors:

Ganesh Raaja received his degree in Electronics and Communication Engineering from Motilal Nehru Government Polytechnic, Pondicherry. His expertise lies in developing with analog circuits, embedded systems, designing PCBs, and working with Assembly and C.

Pushek Madaan is currently working with Cypress Semiconductor India Pvt. Ltd. as a Senior Application Engineer. His interests are in designing embedded system applications in C and assembly languages, working with analog and digital circuits, developing GUIs in C# and, above all, enjoying adventure sports. Pushek can be reached at pmad@cypress.com.
 

Article Courtesy: Test & Measurement DesignLine

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