AN-940 데이터 시트보기 (PDF) - Analog Devices

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AN-940

Low Noise Amplifier Selection Guide for Optimal Noise Performance

Analog Devices 

Application Note

CONCLUSION

Consider all potential noise sources when evaluating an

amplifier’s noise performance for low noise design.

The key noise contribution of an op amp is dependent on

source resistance as follows:

 RS >> RS, OP; input-referred current noise dominates.

 RS = RS, OP; amplifier noise and resistor noise are equal

 RS << RS, OP; input-referred voltage noise dominates.

In summary, reduce or eliminate interference signals by

 Proper layout techniques to reduce parasitics.

 Proper ground techniques, such as isolating digital

and analog ground.

 Proper shielding.

AN-940

For resistive noise sources, use the following rules:

 Restrict bandwidth to only what is necessary.

 Reduce resistor value where possible.

 Use low noise resistors, such as bulk metal foil, wirewound,

and metal film technology resistors.

 Reduce the number of resistive noise sources where

possible.

 Use Figure 8 and Figure 9 to assist with the selection of

an Analog Devices low noise amplifier using the criteria

described in this application note.

For more information on noise, see the article, “Noise Opti-

mization in Sensor Signal Conditioning Circuit” available at

http://www.analog.com/noiseoptimization.

Rev. D | Page 9 of 12

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