[time-nuts] Software Sawtooth correction prerequisites?
Henk ten Pierick
henk at deriesp.demon.nl
Wed Aug 1 08:50:08 EDT 2007
On Aug 1, 2007, at 0:51, Dr Bruce Griffiths wrote:
> There is no theory to show that sigma delta modulators of order higher
> than 2 are actually unconditionally stable.
Yes, but with the Gerzon-Craven theory is is possible to predict
stability of noise shapers. My experience with Gerzon-Craven in a
number of noise shapers is very good, and upto 11th order (never
> Merely simulating the device is not conclusive proof that the
> will never saturate, albeit infrequently.
> Most implementations include saturation detection circuitry that
> the modulator should this occur.
We use feed-forward and graceful degradation. In this way saturated
noise shapers recover correct. In our application overdriven noise
shapers can not be avoided at input signal transients.
> If saturation isn't too frequent then for most purposes this is only a
> minor annoyance.
> However cascaded first order modulators as employed in the MASH
> technique are stable in theory and practice.
How to match analog circuits with digital circuits for the mash, that
is the question. How do you avoid leakage?
> However if one adopts a non linear control theory approach, one can
> actually design high order modulators that both stable in theory
> and in
Unconditionally? Do you have a link for me?
More information about the time-nuts