Posted: March 13th, 2017

Op-Amp Noise Theory

The purpose of this lab is to learn to use Multisim to analyze noise in op-amp circuits. Students will capture screenshots of the noise spectral density curves which will provide a visual relationship of the output noise voltage versus frequency.

Read the document on configuring a noise analysis in Multisim. Week 7 – Configuring Noise Analysis in Multisim.pdf Following the instructions in pdf, construct the inverting Op-Amp circuit shown in figure 1. Run the simulation to measure the gain of the Op-Amp and record the values of R1 and R2 and the measured gain in the table below. (Use 5% tolerance for R1 and R2) Voltage gain (Av) R1 (5% tolerance) R2 (5% tolerance) Measured Voltage gain (Av) 1 1KΩ 5 1KΩ 10 1KΩ 12 1KΩ For the gain of 5 in the table above, run the noise analysis to obtain the results for noise voltage for R1 and R2. (Note: You need to run this noise analysis for the circuit with the gain of 5 only) Plot the noise spectrum density curve across frequency range of 100 Hz to 1 GHz. (Note: If your Multisim version does not support this option then try to download the trial version of Multisim Power Pro edition from NI website). Answer the following questions: Does the measured gain values match the given values? If not, explain why they are different? From the noise spectral density curve, explain the effect of increasing the frequency on the noise voltage. Is the voltage gain of the Op-Amp dependent on frequency? Please explain.

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