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What are the voltage and current noise of the input end and in amplifier?

Latest Updated:12/01/2011

Question:

What are voltage noise referred to input (en) and current noise referred to input (in) of an operational amplifier?

Answer:

These characteristics are particularly important in audio pre-amplifiers, etc., in order to obtain a high gain from small signals. In the same way as there are two types of offset, two types of noise are generated in operational amplifiers: noise voltage and noise current. The noise that occurs in the input offset voltage is voltage noise referred to input and the noise that occurs in the input bias current is current noise referred to input. Because these values refer to input, they appear amplified at the output in the same way as the input offset voltage. Because the current noise referred to input is multiplied with the signal source resistance, it appears as voltage noise referred to input and is added to the voltage noise. Therefore, the larger the signal source resistance, the larger the noise that appears at the output.
Suitable Products
Operational Amplifiers
USB2.0 Host/Peripheral Controller
UPD720150