Errors and Error Budget Analysis in Instrumentation Amplifier Applications

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INTRODUCTION This application note describes a systematic approach to calculating the overall error in an instrumentation amplifier (in amp) application. We will begin by describing the primary sources of error (e.g., offset voltage, CMRR, etc.) in an in amp. Then, using data sheet specifications and practical examples, we will compare the accuracy of various in amp solutions (e.g., discrete vs. integrated, three op amp integrated vs. two op amp integrated). Because instrumentation amplifiers are most often used in low speed precision applications, we generally focus on dc errors such as offset voltage, bias current and low frequency noise (primarily at harmonics of the line frequency of either 50 Hz or 60 Hz). We must also estimate the errors that will result from sizable changes in temperature due the rugged and noisy environment in which many in amps find themselves. It is also important to remember that the effect of particular error sources will vary from application to

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