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HP Prime: Thermal Noise (Johnson-Nyquist Noise) - Eddie W. Shore - 02-18-2015 01:30 PM The following program calculates the RMS (root-mean-square) voltage of a resistor at a certain temperature. Thermal noise, also known as Johnson-Nyquist Noise is generated when the resistor has a temperature above absolute zero. The equation to calculate the voltage is: V = √(4*k*T*R*B) where k = Boltzmann’s Constant = 1.3806488 * 10^-23 J/K T = temperature in degrees Kelvin (K) R = resistance in ohms (Ω) B = noise bandwidth (Hz) This program also calculates the noise power in decibels. Yes, the power for most calculations for this application will be a negative quantity. (I did a double take when I first learned about noise power.) The equation for the noise power is: P = −198.599167802+10*LOG(T*B) where -198.599167802 = 10*LOG(k*1000) (see above) Example: R = 1040 Ω T = 300 K B = 19000 Hz Results: V = 5.721708 * 10^-7 V P = -131.040419 dB Code: Code: EXPORT THNOISE(R,T,B) Sources: John A. Ball. "Algorithms for RPN Calculators" John Wiley & Sons, Inc. New York. 1978. pg. 267 Johnson-Nyquist Noise. http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise Retrieved 2015-2-15 |