Instrumentation Amplifier Noise Analysis

# Instrumentation Amplifier Noise Analysis

## Instrumentation Amplifier Noise Analysis

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##### Presentation Transcript

1. Instrumentation Amplifier Noise Analysis

2. Short Review of 3 Amp INA

3. Three Stage IA

4. Real World Input to Mathematical Model

5. Analyze the Input and Output Separately

6. Split Input Stage in Half

7. Use Superposition on Output Amp

8. Gain For Three Amp IA

9. Noise Model of 3 Amp INA

10. Complex Noise Model

11. The Complex Model is Simplified

12. The Input amplifier dominates at High Gain

13. Two Ways to represent INA Spectral Density Calculated using graphs and formula Taken directly from the graph

14. Hand Analysis of 3 Amp INA

15. Find the total RMS Noise Voltage at the Output

16. Look at Noise Sources: Bridge, INA333, Reference Buffer

17. Noise Equivalent Model for Reference Pin Buffer

18. Reference buffer

19. The reference voltage directly adds to the output noise

20. The bridge generates: thermal noise, in x R_bridge

21. Noise From Bridge / Current Sources

22. Combine all the noise sources

23. Rule of 3x

24. Bandwidth from Data Sheet For G = 100 20dB/decade 1st order Kn = 1.57

25. Calculate RMS Output Noise for INA333 From Voltage Noise

26. Simulation of 3 Amp INA

27. Simulate the Circuit

28. Using Tina Spice

29. Noise Spectral Density at the Output

30. Total RMS Noise at the Output

31. Why doesn’t calculation match simulation exactly? Bandwidth from Data Sheet and simulated bandwidth is different. The roll-off was approximated as first order in the calculations. Simulation shows that it is not first order.

32. Reduce Noise Using Averaging Circuit

33. Averaging Circuit

34. Noise in Averaging Circuit

35. Averaging Circuit with INA333

36. Experiment with 20 Parallel INA333 20 INA333 amps in parallel (jumper selectable) Socketed Gain Set Resistors OPA333 Averaging Circuit

37. Standard Noise Measurement Precautions Linear Power Source Steel Paint Can for Shielding

38. Total Output Noise vs Number of Amplifiers Being Averaged

39. Measured vs simulated spectral density

40. References • [1] Hann, Gina. "Selecting the right op amp - Electronic Products." Electronic Products Magazine – Component and Technology News. 21 Nov. 2008. Web. 09 Dec. 2009. <http://www2.electronicproducts.com/Selecting_the_right_op_amp-article-facntexas_nov2008-html.aspx>. • Henry W. Ott, Noise Reduction Techniques in Electronics Systems, John Wiley and Sons Acknowledgments: • R. Burt, Technique for Computing Noise based on Data Sheet Curves, General Noise Information • T. Green, General Information • B. Trump, General Information • Matt Hann, General INA information and review Noise Article Series (www.en-genius.net) http://www.en-genius.net/site/zones/audiovideoZONE/technical_notes/avt_022508

41. Thank You for Your Interest in INA Noise – Calculation and Measurement