how to determine the type of feedback,and calculate the feedback factor β simply?

[urian]

how to determine the type of feedback,and calculate the feedback factor β simply?

Hi,there
In gray's book,there are four types of feedback,such as series-shunt,series-series,shunt-series,shunt-shunt.
But in a practical circuit,i.e,switched-capacitor circuit,how to find the feedback type since there is no current through the capacitor,or when to find the feedback type,we use impedance 1/jωc to replace the capacitor,and use it as a resistor?
Furthemore,is there simple way to calculate to feedback factor β,like inspection in SC circuit?
In gray's book,it is so tedious to calculate the β using two-port method.
Anyway,I hate capacitors! They make things so different and difficult for me to understand! :-(

Best regards
urian

 

[FvM]

Re: how to determine the type of feedback,and calculate the feedback factor β simply?

Obviously Gray as well as other analog design text books are only touching the SC topic and don't claim to provide an exact theory. You surely noticed, that feedback factor, stability and similar properties aren't discussed here related to SC circuits. Strictly spoken, SC circuits are time-discrete and can't be handled with time-continuous descriptions, or at best in a rough estimation, if the characteristic frequencies are considerably lower than the sampling rate.

 

[urian]

Re: how to determine the type of feedback,and calculate the feedback factor β simply?

Hi,FvM
Like a charge re-distribution sample circuit comprising of Cs and Cf capacitors,the β is found by (1/Cs) / (1/Cs+1/Cf)=Cf/Cs+Cf in many papers.It seems that they treat the capacitors using their impedance as resistors.So where do the method derive from?