The output waveform is as follows. It looks quite good. But the measured THD is quite bad. I added the component 'fourier' in analogLib to measure THD. The result is as follows:
Harm: Absolute Absolute Relative Relative
Magnitude Phase Magnitude Phase
1: 276.589 mV 50.4506 Deg 0.000 dB 0 Deg <- normalizer
2: 43.0674 uV 16.6644 Deg -76.154 dB -33.7862 Deg
3: 161.77 uV 125.855 Deg -64.659 dB 75.4046 Deg
4: 5.56332 mV 92.6739 Deg -33.930 dB 42.2232 Deg
5: 82.87 uV 160.102 Deg -70.469 dB 109.652 Deg
6: 4.03262 mV -10.6745 Deg -36.725 dB -61.1252 Deg
7: 167.665 uV -40.5823 Deg -64.348 dB -91.033 Deg
8: 37.2955 uV -177.267 Deg -77.404 dB -227.718 Deg
9: 27.7985 mV 21.0579 Deg -19.956 dB -29.3927 Deg
10: 333.301 uV 87.8913 Deg -58.380 dB 37.4407 Deg
Total harmonic distortion = 10.354 % (-19.6978 dB).
Is there something wrong with the measurement, it should not be so high. somebody told me that I do not need to care about the even harmonics because " If you do fourier transform of a signal ranging from say, -V to +V ( i.e., differential), you will find that the output spectrum will be devoid of any even harmonics." . Is that true?
thanks for any advice.