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Analog Electronics Workshop Noise

Analog Electronics Workshop Noise. Rev 1.1. Intrinsic Noise The Amplifier and Resistors Generate Noise. What is Spectral Density?. Voltage, Current, or Resistor Noise: Which dominates? . Noise Current Analogous to I B MOS (fA/rtHz) Bipolar (pA/rtHz). Noise Voltage Analogous to V OS.

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Analog Electronics Workshop Noise

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  1. Analog Electronics WorkshopNoise Rev 1.1

  2. Intrinsic NoiseThe Amplifier and Resistors Generate Noise

  3. What is Spectral Density?

  4. Voltage, Current, or Resistor Noise: Which dominates? Noise Current Analogous to IB MOS (fA/rtHz) Bipolar (pA/rtHz) Noise Voltage Analogous to VOS

  5. What is the Spectral Density for Thermal Noise (from Resistors) Noise Spectral Density vs. Resistance en density = √ (4kTKR) Noise Spectral Density vs. Resistance nV/rt-Hz Resistance (Ohms)

  6. Resistor vs. Amp Voltage Noise Resistor Noise Density Resistor enr> Op-Amp en 13nV/rtHz > 4.5nV/rtHz

  7. Amp Current Noise vs. Amp Voltage Noise Voltage Noise env> Current Noise as Voltage eni 4.5nV/rtHz > 0.0025nV/rtHz

  8. In the Data Sheet Low Frequency Noise on Scope Low Frequency Region 1/f Broadband Region

  9. Convert Spectral Density to RMS Convert RMS to Peak-to-Peak

  10. Adding noise sourcesTotal Noise Equation (Current or Voltage) enT = √[(en1/f)2 + (enBB)2] where: enT =Total rms Voltage Noise in volts rms en1/f = 1/f voltage noise in volts rms enBB = Broadband voltage noise in volts rms

  11. where: fP = roll-off frequency of pole or poles fBF = equivalent brickwall filter frequency Real Filter Correction vs Brickwall Filter

  12. AC Noise Bandwidth Ratios for nth Order Low-Pass Filters BWn = (fH)(Kn) Effective Noise Bandwidth Real Filter Correction vs Brickwall Filter

  13. Broadband Noise Equation eBB BWn = (fH)(Kn) where: BWn = noise bandwidth for a given system fH = upper frequency of frequency range of operation Kn = “Brickwall” filter multiplier to include the “skirt” effects of a low pass filter enBB = (eBB)(√[BWn]) where: enBB = Broadband voltage noise in volts rms eBB = Broadband voltage noise density ; usually in nV/√Hz BWn = Noise bandwidth for a given system

  14. en1/f = (e1/f@1Hz)(√[ln(fH/fL)]) where: en1/f = 1/f voltage noise in volts rms over frequency range of operation e1/f@1Hz = voltage noise density at 1Hz; (usually in nV) fH = upper frequency of frequency range of operation (Use BWn as an approximation for fH) fL = lower frequency of frequency range of operation e1/f@1Hz = (e1/f@f)(√[f]) where: e1/f@1Hz = normalized noise at 1Hz (usually in nV) e1/f@f = voltage noise density at f ; (usually in nV/√Hz) f = a frequency in the 1/f region where noise voltage density is known 1/f Noise Equation(see appendix for derivation) e1/f@1Hz

  15. When does 1/f Noise Dominate Rule of Thumb: Broadband noise dominates if BW > 10 x ff

  16. Simple Hand Calculation (is broadband or 1/f dominant?)

  17. Simple Hand Calculation (is voltage or current noise dominant?)

  18. Simple Hand Calculation (is voltage or current noise dominant?)

  19. Simple Hand Calculation(Ignores current, resistor, and flicker noise)

  20. Calculation Simulation Measurement

  21. How to Reduce Noise • Select a low noise amplifier • Consider both current and voltage noise • Consider low and high frequency noise • Select the appropriate feedback resistors • Low Resistance for low noise • Limit the bandwidth

  22. Links to Additional Reading Noise Article Series (www.en-genius.net) Tech-note Zone Operational Amplifier Noise: Techniques and Tips for Analyzing and Reducing Noise by Art Kay Published January 27, 2012 | ISBN-10: 0750685255

  23. Noise Lab • Simulation • Calculation • Measurement

  24. Ex 5.1: Hand Calculations 1. Determine the total rms and peak-to-peak output noise. Note: the switches are as shown (SW3 open, SW2 to GND).

  25. Ex 5.1 Solution to Hand Calc

  26. Ex 5.1 Solution to Hand Calc

  27. Ex 5.1: Noise Schematic Two copies of the same two stage amplifier is on the board. Each two stage amplifier has four jumpers to configure the circuit.

  28. Ex 5.1: Amplifier I/O PCB Setup U0 = OPA2211 U1 = OPA2188 Note for this experiment Rin will be shorted. For the next experiment Rin will be connected between input and GND.

  29. Ex 5.1: Instrument Setup The instrument setup above will configure the signal source and scope for the circuit below so that we can see the bandwidth limitations. Use the curser to determine the bandwidth (-3dB).

  30. Ex 5.1: Expected Results 1. Use the cursors on the myDAQ and Tina Spice tool to measure the slew rate (rise / run).

  31. Ex 5.2: Hand Calculations 1. Determine the total rms and peak-to-peak output noise. Note: the switches are as shown (SW3 closed, SW2 to GND). C1 & R8 form a filter.

  32. Ex 5.2 Solution to Hand Calc

  33. Ex 5.2 Solution to Hand Calc

  34. Ex 5.2: Noise PCB Setup U0 = OPA211 U1 = OPA277 Note for this experiment Rin will be shorted. For the next experiment Rin will be connected between input and GND.

  35. Ex 5.2: Instrument Setup The instrument setup above will configure the signal source and scope for the circuit below so that we can see the bandwidth limitations. Use the curser to determine the bandwidth (-3dB).

  36. Ex 5.1: Expected Results 1. Fill in table below. How effective is the filter in reducing noise?

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