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Everyday App Note: How to Perform a Noise Analysis on Any Op Amp Circuit

Sam Sattel

everyday-app-note-series

Everyday App Note: How to Perform a Noise Analysis on Any Op Amp Circuit

Noise is random in the realm of electronics, and that makes it all the more dangerous for sensitive components like op-amps. So how are you going to achieve an acceptable signal-to-noise ratio with something so volatile? Today’s Everyday App Note from Texas Instruments walks you through noise types, characteristics, and how to perform noise analysis on any op-amp circuit.

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Types of Noise Covered

This app note first covers the types of noise found in electronic circuits. The five types of common noise sources include:

  • Shot noise
  • Thermal noise
  • Flicker noise
  • Burst noise
  • Avalanche noise

Shot noise occurs whenever an electric charge crosses over a barrier like a PN junction. This event causes a current pulse which can be measured with its mean-square variation as shown below:

shot-noise-formula

Here, q is the charge and df is the differential frequency. It’s important to note that shot noise is independent of temperature and has a constant value when plotted. With values for each type of noise in this app note you’ll be able to calculate shot, thermal, flicker, burst, and avalanche noise in your circuit.

Noise Characteristics Covered

This app note also dives into the details of noise characteristics. For example, noise spectra defines how noise is spread over the frequency spectrum based on voltage power density and noise power density. To calculate the noise spectra of flicker noise, you can use the following equation:

flicker-noise-formula

Other noise characteristics covered in this app note includes:

  • Multiple noise sources
  • Integrating noise
  • Equivalent noise bandwidth

Op Amp Circuit Noise Model

Lastly, this app note covers a noise model used by op amp manufacturers to measure the noise characteristics of a device. There are two components of this model. A voltage source is placed in series with a positive input and noiseless op amp. A current source is placed between each input and ground. Both of these interact with a noiseless op amp. Put together, the op amp noise model looks like the figure below:

op-amp-noise-model

Using this model, it’s possible to perform a number of op amp noise calculations for several op amp configurations including:

  • Inverting op amps
  • Non-inverting op amps
  • Differential op amps

Download This App Note

As we all know, noise is an accepted variable in the world of electronics. But with too much noise, unexpected behavior can occur in your circuit. With the techniques presented in this app note, you’ll be ready to perform noise analysis on any op amp. It’s time to get that signal-to-noise ratio in line!

Download the Noise Analysis in Operational Amplifier Circuits app note now.

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