hi
in Saxena thesis(INDIRECT FEEDBACK COMPENSATION TECHNIQUES FOR MULTI-STAGE
OPERATIONAL AMPLIFIERS) is written that t_s =.35/f_un for a 90 degree phase margin,where t-s is 99.9% settling time and
f_un is unitary frequency.
how can this relation be obtained ?
thanks
I think it is wrong. 90° phase margin means simple RC behaviour. For an RC filter the 99.9% settling means the exponential part is
exp(-t_s/T) = 0.001, thus
t_s = -ln(0.001)*T, where T is 1/(2*pi*f_un).
From above relations the t_s = -ln(0.001)/(2*pi*f_un) ~ 1.1/f_un, where [f_un] is Hz.