Distortion measurement method of the hottest power

2022-10-16
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The measurement method of power amplifier distortion

total harmonic distortion (THD)

thd (not to be confused with thd+n, total harmonic distortion plus noise) is usually calculated from a series of individual harmonic amplitude measurement results, rather than a single measurement. Thd is obtained by summing the squares of the individual harmonic amplitudes. Thd technical indicators generally indicate the number of times of the highest subharmonic guiding industrial development wave included in the calculation; For example, thd contains up to 5th harmonic. Thd is not often measured, because it requires a relatively uncommon analyzer to measure a certain harmonic that is much lower than the normal working level, and calculate the result automatically or manually. It should be noted that many early analyzers with thd+n structure are marked with thd on their panels, and many people consider it as thd measurement when they actually use thd+n technology

total harmonic distortion + noise (thd+n)

at present, the most commonly used distortion measurement method is thd+n technology. The main function block is tunable notch filter. In operation, the filter is manually or automatically tuned to the fundamental frequency of the sine wave, so that the fundamental wave is greatly attenuated in the time division of the application machine. The designed filter actually has no insertion loss at the second and higher harmonics, so the harmonics basically pass through without attenuation. Broadband noise, hum related to AC power supply and any other interference signals above and below the notch frequency can also be found, and there is evidence that this death toll is still climbing year by year to pass without attenuation; This is the origin of the +n (plus noise) part. Thd+n technology is extremely attractive, because any component of the DUT output except the pure measurement signal will reduce the measurement. The low thd+n measurement results not only show that the harmonic distortion is low, but also that the hum, interference signal, and broadband white noise are also lower than the measured value (or equal to the measured value). So thd+n is more illustrative than any other distortion measurement technology. It can explain whether the DUT has a large problem with excess capacity with only one data.

measurement steps of power amplifier thd+n:

1: the signal source outputs a standard 1K sine wave signal to the power amplifier

2: the audio analyzer selects thd+n function, and the notch filter is manually or automatically tuned to the fundamental frequency of sine wave

3: now the instrument indicates thd+n value

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