T
The Phantom
It was recently asked:
"Is there any www-resource which gives values (or simple ways to
calculate
the values) for the harmonic distortion of various step-approximations
to
sine waves, e.g. 8-bit, 10-bit,..."
The OP mentions "8-bit", which suggests a 256 step approximation to a
sine wave. One responder said:
"Simply as you find it ...
8 bits can be no cleaner than one part in 256 parts. Therefore THD
=1/256th or 1/2%
12 bits is one part in 4096 parts = 0.025%
ect ect"
This is not quite true; if it were then a simple square wave (with two
voltages, +V and -V, and zero, would have a distortion no lower than
50%. But in fact, with the proper pulse width, the distortion can be
as low as 28%.
The THD for a 257 (total) stepped approximation to a single frequency
sine wave, without dither, is around .32%
Another responder and myself discussed the case of fewer steps, such
as a power frequency inverter might generate. A commercial product
generating such a waveform exists:
http://www.xantrex.com/support/docdisplay.asp?prod=105&did=250
On alt.binaries.schematics.electronic, I have posted a method for
answering the OP's question.
"Is there any www-resource which gives values (or simple ways to
calculate
the values) for the harmonic distortion of various step-approximations
to
sine waves, e.g. 8-bit, 10-bit,..."
The OP mentions "8-bit", which suggests a 256 step approximation to a
sine wave. One responder said:
"Simply as you find it ...
8 bits can be no cleaner than one part in 256 parts. Therefore THD
=1/256th or 1/2%
12 bits is one part in 4096 parts = 0.025%
ect ect"
This is not quite true; if it were then a simple square wave (with two
voltages, +V and -V, and zero, would have a distortion no lower than
50%. But in fact, with the proper pulse width, the distortion can be
as low as 28%.
The THD for a 257 (total) stepped approximation to a single frequency
sine wave, without dither, is around .32%
Another responder and myself discussed the case of fewer steps, such
as a power frequency inverter might generate. A commercial product
generating such a waveform exists:
http://www.xantrex.com/support/docdisplay.asp?prod=105&did=250
On alt.binaries.schematics.electronic, I have posted a method for
answering the OP's question.
