Analysis for minimum overall ‘gain’

Thread Starter

artmaster547

Joined Jan 6, 2016
410
Hi All

I have a phase shift oscillator, and would like to find the minimum overall gain required from component tolerances given, I am using LTSpice, I would like to ask what kind of method should I take? Since I believe it's possible to do this just using LT Spice and I think I don't need to derive any equations but I may be wrong
thanks
Art
 

ramancini8

Joined Jul 18, 2012
473
Lets assume that four components can change value enough to change frequency. Hold three component values constant while cycling one component value through its possible range, then plot the worst case transfer function values (gains) versus the component value. After four tries you can see the effect of one variable on gain four different times. Assuming that a range of component values exists, then a worst case value also exists, but where in the range does it exist--- finding this point is the object of finding worst case solution. Finding the worst case solution involves crafty thinking, good circuit knowledge, 256 tries with graph matching, or a big fast computer. Circuit analysis programs are approximations, so it is chancy to depend on their solutions unless 3 or so programs agree.

Unless you are doing this for a very high volume production job it is usually easier to add feedback that keeps the gain constant.

The phase shift of the amplifier(s) can be critical in this design, so the amplifier 3dB BW >> 50 signal frequency.
 

Thread Starter

artmaster547

Joined Jan 6, 2016
410
Lets assume that four components can change value enough to change frequency. Hold three component values constant while cycling one component value through its possible range, then plot the worst case transfer function values (gains) versus the component value. After four tries you can see the effect of one variable on gain four different times. Assuming that a range of component values exists, then a worst case value also exists, but where in the range does it exist--- finding this point is the object of finding worst case solution. Finding the worst case solution involves crafty thinking, good circuit knowledge, 256 tries with graph matching, or a big fast computer. Circuit analysis programs are approximations, so it is chancy to depend on their solutions unless 3 or so programs agree.

Unless you are doing this for a very high volume production job it is usually easier to add feedback that keeps the gain constant.

The phase shift of the amplifier(s) can be critical in this design, so the amplifier 3dB BW >> 50 signal frequency.
Yes thank you so much I feel so inexperienced with designing circuits can you give me any recommendations/advice to become more proficient?
 
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