Appendix B
579
Distortion Characteristics
Distortion is usually measured by sourcing a sine wave. The analog
response is first captured and then analyzed in the frequency
domain. This means, the processed waveform is converted into its
spectrum using the FFT algorithm, and the calculations are based
on the frequency components.
NOTE Distortion Characteristics are defined and calculated in the same way
for DACs, ADCs and buffers.
Standard distortion measures are:
Distortion Measures
Total Harmonic Distortion
The total harmonic distortion (THD) compares the combined
power of the first N harmonics with the power of the input signal.
The THD is calculated as the ratio of the rms sum of the first N
harmonic components (typically up to the 5th harmonic) to the
rms value of a full-scale input signal.
THD is expressed in dB.
Calculation of THD
•Total harmonic distortion (THD)
•Signal-to-noise plus distortion (SND)
•Signal-to-noise ratio (SNR)
•Spurious free dynamic range (SFDR)
•Signal resolution
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