[sdiy] How is the feedback loop of the exponential converter analysed?

[David Manley]

Hi Spiro,

I haven't seen a reply to your question, so I'll just point you in the 
general direction and hope that helps.  I'm sure one of the analog gurus 
will step up and correct me.  :-)

An opamp can affect not only the gain of a signal it is processing, but 
also its phase.  If the output phase is shifted over 180 degrees, that 
signal is feed back to the input, and the opamp has gain at that 
frequency then it will oscillate.  Look up 'gain and phase margin'.

The feedback path here is not trivial but maybe one of the gurus can 
offer a simplification that gives insight.  Playing around in Spice may 
give you some intuitive insights.

Here's a videoon gain and phase margin, but without knowing your 
background it may not help too much since it assumes some fundamental 
electrical engineering background:

     https://youtu.be/ThoA4amCAX4?t=483

I'm sure there are simpler descriptions out there I just didn't find 
them in a few minutes of searching.

-Dave