One of the problems we have when evaluating very nonlinear circuits such as sigma delta dacs is that modulator behavior is not always easily understood from looking at typical FFT measurements. For instance, its possible for a dac to reproduce a periodic-steady-state (PSS) sine wave in a way that measures pretty well. However an amplitude modulated sine wave, or else maybe the sum of some fixed amplitude sine waves (multitone test signal) may have an amplitude modulation envelope as viewed in the time domain. In some cases we refer to the amplitude envelope modulation of summed sine waves as "beat notes."
Anyway, it turns out there is way to acquire a dataset as is done for a typical audio FFT, but then perform a different type of calculation to find the amplitude envelope. The envelope could then be compared with the envelope of the digital test signal in order to evaluate any error in amplitude envelope reproduction.
The calculations are described in more detail in the attached files.
Anyway, it turns out there is way to acquire a dataset as is done for a typical audio FFT, but then perform a different type of calculation to find the amplitude envelope. The envelope could then be compared with the envelope of the digital test signal in order to evaluate any error in amplitude envelope reproduction.
The calculations are described in more detail in the attached files.
