What is wrong with my FFT code?

I have this code, the plot looks correct but the values don’t come out right. I even tested an ideal sine wave, but it’s the same. which means the code is wrong, but I can’t figure out which part of the code is wrong. it looks correct to me. please help me out;

% Parameters
N = 8192; % Number of samples for FFT
fs = 10e9; % Sampling frequency (10 GHz)
harmonics = 3; % Number of harmonics to consider

% Extract 8192 samples from OUTPUT (assuming OUTPUT is already defined)
x = OUTPUT(1:N);

% Normalize data to unit magnitude
x = x / max(abs(x));

% Perform FFT
X = fft(x);

% Frequency axis
f_axis = (0:N-1) * fs / N; % Frequency axis from 0 to fs

% Remove DC component
X(1) = 0;

% Find dominant frequency component
[~, max_idx] = max(abs(X)); % Find the index of the maximum magnitude

% Calculate estimated signal frequency
f_signal = f_axis(max_idx); % Frequency corresponding to the maximum magnitude

% Calculate SNR correctly
signal_power = abs(X(max_idx))^2; % Power of the signal tone
noise_power = sum(abs(X).^2) – signal_power; % Total noise power (excluding signal tone)
SNR = 10*log10(signal_power / noise_power); % Signal-to-Noise Ratio in dB

% Calculate ENOB
ENOB = (SNR – 1.76) / 6.02;

% Calculate SFDR
SFDR_power = max(abs(X))^2; % Power of the largest spurious component (excluding DC)
SFDR = 10*log10(SFDR_power / signal_power); % Spurious Free Dynamic Range in dB

% Calculate THD correctly
THD_power = sum(abs(X(2:end)).^2); % Total harmonic distortion power (excluding signal and DC)
THD = 10*log10(THD_power / signal_power); % Total harmonic distortion in dB

% Plot FFT magnitude spectrum (folded, centered around fs/2)
figure;
plot(f_axis / 1e6, 20*log10(abs(X) / N)); % Plot in MHz and dB
xlabel(‘Frequency (MHz)’);
ylabel(‘Magnitude (dB/Hz)’);
title(‘FFT Magnitude Spectrum’);
grid on;
xlim([0 fs/2/1e6]); % Limit x-axis to 0 to fs/2 in MHz

% Mark signal tone and harmonics on the plot
hold on;
plot(f_signal / 1e6, 20*log10(abs(X(max_idx)) / N), ‘ro’, ‘MarkerSize’, 10, ‘LineWidth’, 2); % Mark signal tone
for i = 1:harmonics
harmonic_freq = i * f_signal;
[~, harmonic_bin] = min(abs(f_axis – harmonic_freq)); % Find nearest bin index
plot(f_axis(harmonic_bin) / 1e6, 20*log10(abs(X(harmonic_bin)) / N), ‘go’, ‘MarkerSize’, 10, ‘LineWidth’, 2); % Mark harmonics
end
hold off;

% Create legend for ENOB, SNR, SFDR, THD without identifiers
legend_str = {[‘ENOB: ‘, num2str(ENOB), ‘ bits’], [‘SNR: ‘, num2str(SNR), ‘ dB’], …
[‘SFDR: ‘, num2str(SFDR), ‘ dB’], [‘THD: ‘, num2str(THD), ‘ dB’]};
legend(legend_str, ‘Location’, ‘best’, ‘AutoUpdate’, ‘off’); % AutoUpdate off to prevent adding previous legend entries

% Display results
disp([‘Estimated Signal Tone Frequency: ‘, num2str(f_signal / 1e6), ‘ MHz’]);
disp([‘ENOB: ‘, num2str(ENOB), ‘ bits’]);
disp([‘SNR: ‘, num2str(SNR), ‘ dB’]);
disp([‘SFDR: ‘, num2str(SFDR), ‘ dB’]);
disp([‘THD: ‘, num2str(THD), ‘ dB’]);I have this code, the plot looks correct but the values don’t come out right. I even tested an ideal sine wave, but it’s the same. which means the code is wrong, but I can’t figure out which part of the code is wrong. it looks correct to me. please help me out;

% Parameters
N = 8192; % Number of samples for FFT
fs = 10e9; % Sampling frequency (10 GHz)
harmonics = 3; % Number of harmonics to consider

% Extract 8192 samples from OUTPUT (assuming OUTPUT is already defined)
x = OUTPUT(1:N);

% Normalize data to unit magnitude
x = x / max(abs(x));

% Perform FFT
X = fft(x);

% Frequency axis
f_axis = (0:N-1) * fs / N; % Frequency axis from 0 to fs

% Remove DC component
X(1) = 0;

% Find dominant frequency component
[~, max_idx] = max(abs(X)); % Find the index of the maximum magnitude

% Calculate estimated signal frequency
f_signal = f_axis(max_idx); % Frequency corresponding to the maximum magnitude

% Calculate ENOB
ENOB = (SNR – 1.76) / 6.02;

% Calculate SFDR
SFDR_power = max(abs(X))^2; % Power of the largest spurious component (excluding DC)
SFDR = 10*log10(SFDR_power / signal_power); % Spurious Free Dynamic Range in dB

% Calculate THD correctly
THD_power = sum(abs(X(2:end)).^2); % Total harmonic distortion power (excluding signal and DC)
THD = 10*log10(THD_power / signal_power); % Total harmonic distortion in dB

% Display results
disp([‘Estimated Signal Tone Frequency: ‘, num2str(f_signal / 1e6), ‘ MHz’]);
disp([‘ENOB: ‘, num2str(ENOB), ‘ bits’]);
disp([‘SNR: ‘, num2str(SNR), ‘ dB’]);
disp([‘SFDR: ‘, num2str(SFDR), ‘ dB’]);
disp([‘THD: ‘, num2str(THD), ‘ dB’]); I have this code, the plot looks correct but the values don’t come out right. I even tested an ideal sine wave, but it’s the same. which means the code is wrong, but I can’t figure out which part of the code is wrong. it looks correct to me. please help me out;

% Parameters
N = 8192; % Number of samples for FFT
fs = 10e9; % Sampling frequency (10 GHz)
harmonics = 3; % Number of harmonics to consider

% Extract 8192 samples from OUTPUT (assuming OUTPUT is already defined)
x = OUTPUT(1:N);

% Normalize data to unit magnitude
x = x / max(abs(x));

% Perform FFT
X = fft(x);

% Frequency axis
f_axis = (0:N-1) * fs / N; % Frequency axis from 0 to fs

% Remove DC component
X(1) = 0;

% Find dominant frequency component
[~, max_idx] = max(abs(X)); % Find the index of the maximum magnitude

% Calculate estimated signal frequency
f_signal = f_axis(max_idx); % Frequency corresponding to the maximum magnitude

% Calculate ENOB
ENOB = (SNR – 1.76) / 6.02;

% Calculate SFDR
SFDR_power = max(abs(X))^2; % Power of the largest spurious component (excluding DC)
SFDR = 10*log10(SFDR_power / signal_power); % Spurious Free Dynamic Range in dB

% Calculate THD correctly
THD_power = sum(abs(X(2:end)).^2); % Total harmonic distortion power (excluding signal and DC)
THD = 10*log10(THD_power / signal_power); % Total harmonic distortion in dB

Cart

Cart