Thermal noise of resistor – Calculator

Thermal noise of passive components makes big influence on overall noise performance. Values of passive components should be carefully evaluated, especially in case of low noise design. Otherwise, you will not be able to take advantage of low noise performance of active components.

RMS value of thermal noise generated by resistor within Δf frequency range could be calculated by formula:

Vn=√(4*Kb*T*R* Δf) (V)

Where Kb is Boltzmann constant: Kb = 1.380?6504e-23 (joules/kelvin),
T is absolute temperature in kelvin,
R is resistance in Ohm and Δf is frequency range in Hz

This calculator will help you to evaluate noise performance of resistors.

Thermal Noise Calculator

100.0 Ohm resistor at 25.0 °C within 20.0 Hz to 20000.0 Hz frequency band will have :

Noise Spectral Density = 1.283185e-9 V/√Hz or 1.2832 nV/√Hz

Noise within desired bandwidth = 1.813790e-7 V or 0.1814 uV

Dynamic range re 1V RMS = 134.8 dBV

Dynamic range re 3V RMS = 144.4 dB

Dynamic range re 10V RMS = 154.8 dB

As a comparison, here is noise data for some commonly used low noise operational amplifiers:

Part Number

Input Noise Density

LME49713 1.9nV/√Hz National Semiconductor
LM4562 2.7nV/√Hz National Semiconductor
LME49990 0.9nV/√Hz National Semiconductor
OPA1611 1.1nV/√Hz Texas Instruments
OPA211 1.1nV/√Hz Texas Instruments
OPA827 4nV/√Hz Texas Instruments
AD797 0.9nV/√Hz Analog Devices
AD8597 1.1nV/√Hz Analog Devices
LT1028 0.85nV/√Hz Linear Technology
LT1115 0.9nV/√Hz Linear Technology


4 Responses to Thermal noise of resistor – Calculator

  1. Jackinnj says:

    The recent samples of SSM2019 from Analog Devices measure just under 1.0nV/RtHz.

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  3. steve says:

    any change to bandwidth high limit still gives 20khz result ie 1.28nv/hz

  4. Eugene says:

    Yes, and this is how it should be. Because it is Noise Spectral Density. Bandwidth changes “Noise within desired bandwidth”.