SBOA345 June   2021 ADC10D1000QML-SP , ADC12D1600QML-SP , ADC12D1620QML-SP , INA1620 , OPA132 , OPA134 , OPA1602 , OPA1604 , OPA1611 , OPA1612 , OPA1622 , OPA1632 , OPA1637 , OPA1641 , OPA1642 , OPA1644 , OPA1652 , OPA1654 , OPA1655 , OPA1656 , OPA1662 , OPA1664 , OPA1671 , OPA1677 , OPA1678 , OPA1679 , OPA1688 , OPA1692 , OPA2132 , OPA2134 , OPA4132 , OPA4134

 

  1.   Trademarks
  2. 1Thermal Noise
  3. 2Operational Amplifier Voltage Noise
    1. 2.1 Flicker Noise
    2. 2.2 Broadband Noise
  4. 3Operational Amplifier Current Noise
    1. 3.1 Taking a Deeper Look at Noise Sources
  5. 4Calculating Voltage Noise at the Output
  6. 5Summary

3.1 Taking a Deeper Look at Noise Sources

Using the OPA1656 and OPA1612 we can see how the different noise sources can affect the overall noise. Using excel we can plot out the voltage noise, current noise, and resistance noise vs resistance values. For this example, the frequency is set to 1kHz.

GUID-20201007-CA0I-TFNV-FFXJ-TLRBN6WZXBLL-low.gifFigure 3-2 OPA1656 Noise Curves
GUID-20201007-CA0I-XJM3-WZ36-NMLDXB5CPSD2-low.gifFigure 3-3 OPA1612 Noise Curves

As the source resistance increases, the overall noise of the OPA1612 will eventually dominate that of the OPA1656 due to the current noise. For this reason, it is paramount to understand the system and all its noise contributions before choosing an amplifier.

GUID-20201007-CA0I-HJ3G-MGDP-9BKR4JH3TZF7-low.gif Figure 3-4 Total Noise of OPA1656 vs OPA1612