public release v1.0HEADmain

1 files changed, 49 insertions, 0 deletions

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+function [RMS] = noiseimpulse2rms(IR,PSD,BW,DT)
+%NOISEIMPULSE2RMS Noise Impulse response to output-referred RMS value
+%   Convert impulse response of noise path filters to output-referred RMS value.
+%
+% The equivalent RMS output noise power is calculated by
+% 1. Converting the time-domain noise impulse response into a frequency-domain
+%    noise transfer function
+% 2. Integrating the squared noise transfer function up to the noise
+%    integration bandwidth.
+% 3. Scaling the input noise by the input noise PSD
+% 4. Returning the square-root of the result.
+%
+%   Inputs:
+%       IR  - Noise impulse response
+%       PSD - Noise power spectral density (PSD) in units of V^2/GHz
+%       BW  - Noise integration bandwidth in Hz
+%       DT  - Sampling interval in seconds
+%
+%   Outputs:
+%       rms - Noise RMS value in V
+
+%   Copyright 2020 The MathWorks, Inc.
+
+%Validate inputs
+validateattributes(IR,{'numeric'},{'vector','finite'},'NoiseIR2RMS','ir',1);
+validateattributes(PSD,{'numeric'},{'scalar','nonnegative'},'NoiseIR2RMS','psd',2);
+validateattributes(BW,{'numeric'},{'scalar','positive'},'NoiseIR2RMS','bw',3);
+validateattributes(DT,{'numeric'},{'scalar','positive'},'NoiseIR2RMS','dt',4);
+
+% Convert noise impulse response (IR) to transfer function (TF)
+tf = fft(IR);
+
+% Number of points in IR and TF
+num_pts = length(IR);
+
+% Frequency step
+df = (1 / DT) / num_pts;
+
+% Noise integration index, keep it below half of FFT frequency range
+i_bw = min(round(BW / df), num_pts/2 );
+
+% To calculate noise RMS
+% 1. Take magnitude of noise TF
+% 2. Square noise TF magnitude
+% 3. Integrate over noise BW (convert frequency step, df, to GHz)
+% 4. Scale by input noise PSD in V^2/GHz
+% 5. Take square root 
+RMS = sqrt(PSD * sum((df/1e9) * abs(tf(1:i_bw)).^2));
+end
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