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Reducing Amplifier Offset to Maintain Dynamic Range, Part 1 of 2

For many applications where a high gain is needed, an amplifier with low offset voltage and drift is required. This is especially true as supply voltages continue to decrease, driven by reductions in IC process geometries and the desire for longer battery lifetimes. As supply voltages decrease, a constant offset voltage causes a reduction in the dynamic range of the system. In order to maintain dynamic range, the offset voltage needs to decrease along with the supply voltage.

Output dynamic range of an amplifier is the range, usually given in dB, between the smallest and largest useful output levels. The lowest useful level is limited by noise, while the largest is limited most often by distortion. The ratio of these two is quoted as the amplifier dynamic range. More precisely, if S is the maximum allowed signal power and N is the noise power, the dynamic range DR is DR = (S + N) /N.

This article, presented in two parts, analyzes the effects of offset as well as the various techniques used to minimize it, and their key attributes. It also looks at a new technique which offers additional advantages in overcoming this problem.

Part 1 , click here.

Part 2 will be posted soon after Part 1.

About the author
James Nolan is a senior technical staff engineer at Microchip Technology Inc. He has been with Microchip since November of 1993, when he joined the company as a mixed-signal design engineer. He has over 20 years of industry experience in analog and mixed-signal design and development. Mr. Nolan holds a BS from the University of Nebraska, and a MS from the University of Texas in Austin, TX.

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