--------------------FFT_SINE------------------------------- Using Excel to FFT signwaves ^ /|\ Signal = SIN(2*P()*Num/8) | __--S--__ | __S \S_ | _/ \_ _ _S/ _ _ _ _ _ _ _ _ _ \S _ _ _ _ _ _ _ _ _ _ _ \ | \_ _/ / | \__ __/ | S__ ___S | --S-- Num Samp FFt 0 0 0 1 .71 -4i 2 1 0 3 .71 0 4 0 0 5 -.71 0 6 -1 0 7 -.71 4i REAL MAGNITUDE ^ /|\ | \ | \ | /______\ | \ \ | \ | Nyq\__ | \ | \ | \_|____\ \|____/_____________\ -4j /______\ / @bin1 \ \ IMAGINARY MAGNITUDE \ Nyq\__ \ \ \______\ +4j \ / @bin7 _V J_OMEGA --------------------FFT_NYQ------------------------------ ^ /|\ Signal = SIN(2*P()*Num/8) S_ S S S | \ / \ / \ / \ | \ / \ / \ / \ _ _|_ _|_ _|_ _|_ _|_ _|_ _| _ \ _ _ _ \ | | | | | | | | | / | \ / \ / \ / \ / | \S/ \S/ \S/ \S/ | Num Samp FFt 0 1 0 Real \ 1 -1 0 Complex | 2 1 0 Complex | 8 data points in/out 3 -1 0 Complex | 4 1 8 Real / 5 -1 0 6 1 0 7 -1 4 ^ REAL MAGNITUDE ^ /|\ /|\ | | | \ | | \ | | \ | | \ | | \ | | Nyq\| | ^ \ | /|\ \ | | 8 at @bin4 \ | | \|___|_________________\ \ | / \ | IMAGINARY MAGNITUDE \ | Nyq\| \ \ \ \ _V J_OMEGA Bin_width Sample_rate/Number_Points_FFT F_max Sample_rate/2 RMS Signal A/SQRT(2) (FSR/2)/SQRT(2) 2^(n-1)*q/SQRT(2) RMS Noise Qn q/SQRT(12) SNR RMS_Signal/RMS_Noise 2^(n-1)*SQRT(6) SNR_pos_dB 20*log(2^(n-1)*SQRT(6)) 6.02*n + 1.76 (See Table 1) NOISE_FLOOR_neg_dB 6.02*n + 1.76 + 10*log(N/2) (See Table 1) 6.02*n +10*log(3*N/(PI*ENBW)) THD_neg_dB 20*log(SQRT(sum_of_Harm_squared) ) Note: HAR (-dB) SINAD_pos_dB -20*log( SQRT( SNR^2+THD^2 ) ) SINAD Singal to noise ratio and distortion ENOB Effective number of bits (SNR +Distort -1.76 +20*log(Amp_FS/Amp_Actual) )/6.02 fs Sampling Rate (Hz) fin Input Signal Frequency (Hz) FSR Full Scale (Input) Range of Sampling A/D Converter FS FSRi2 = Full Scale input of Sampling A/D Converter A Input Signal Amplitude FSR/2= OdB n Numberof Bitsof Resolution q LSB Size LSB Least Significant Bit N Numberof FFT Points N/2 Numberof Frequency Bins (real component) ENBW Equivalent noise bandwidth of window function. Blackman-Harris four-term Blackman-Harris window, ENBW= 2. ------------------------------------------------------------- --------------------FFT_COS------------------------------ ^ /|\ Signal = SIN(2*P()*Num/8) S--__ __-- | \S_ __S | \_ _/ | \S S/ | \_ _/ | \__ __/ | S__ ___S |_ _ _ _ _ _ _ _ _ _--S-- _ _ _ _ _ \ | / Num Samp FFt 0 2 8 1 1.71 4 2 1 0 3 .29 0 4 0 0 5 .29 0 6 1 0 7 1.71 4 REAL MAGNITUDE ^ /|\ | \ | \ ^ 8 at @bin0 \ /|\ \ ^ | Nyq\_ /|\| \ | | \ | | \| | ^ 4 at @bin1 \ |/|\ \|_|_________________\ \ | / \| IMAGINARY MAGNITUDE \ \ ^ Nyq\_ /|\ 4 at @bin7 \ | \ | \| \ _V J_OMEGA Theoretical Noise Floor_dB (Table 1) FFT Points 12Bits 14Bits 16Bits 1024 101 113 125 2048 104 116 128 4096 107 119 131 8192 110 122 134 16384 113 125 137 32768 116 128 140 SNR_dB 74.0 86.0 98.1 FFT _ _ _ _ _ _ _ _ _ _ _ _ OdB Spurious | ^ Free Dyn | | Fundamental | SNR Range | | at_max_signal v |__\ |--|---------------------------RMS_Noise_Level / | | | 3rd Harmonic | _| | __| 5rd Harmonic |/ \/\__|/\/ |_/\/ ----------- Ave Noise Level |______________________________\ (Noise Floor) ^ ^ ^ ^ ^ ^ /