[hpsdr] THD in Op Amps

[Marco IK1ODO]

At 18.51 27/09/2006, you wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>Wrong forum perhaps, but since Steve brought this up:
>
>All of these Data sheets seem to indicate that the various op amps indicate
>lowest THD at some high output, perhaps 3v, and increases above and below
>that level.  Not sure I understand, (am sure that I don't), are they running
>in some non-class A mode such that the device works best with some high
>output or is there some inherent distortion that is "diluted" out by the
>stronger signal?  Several of the single ended "very low distortion" amps
>have almost no THD at the optimum level and look much worse beyond that.
>
>Thanks,
>
>N0UU

Hello Lawrence,
we are talking about very, very low THD levels. As I understand it at 
higher output levels the distortion becomes more noticeable (output 
transistors approaching saturation, etc) and at lower levels the 
noise dominates the THD spectrum. It is always "THD+noise" since it 
is very hard to separate the two things at this low level.
73 - Marco IK1ODO



 1159382162.0