Hi all, this looks like a great site and I look forward to being a member of it. My questions today are as follows.
This is part of an examination question. Basically, a diagram of a Sallen Key filter with 2 equal resistances and 2 capacitors was given. The gain of the amp is unity and it is assumed that this circuit is used to approximate a 3rd order Butterworth filter. Now I understand that this will give a transfer function with a quadratic term, basically a second order block to which another Sallen Key filter will be added to make it a 3rd order filter. The capacitances in the 2nd order block can be determined easily enough by comparing the transfer function of a second order B-worth filter. But how does one find the capacitance for the 1st order block added onto it? Does one compare the co-efficients of a 1st order B-worth to get it?
I can provide additional info if necessary.
Many thanks.
Dhana
This is part of an examination question. Basically, a diagram of a Sallen Key filter with 2 equal resistances and 2 capacitors was given. The gain of the amp is unity and it is assumed that this circuit is used to approximate a 3rd order Butterworth filter. Now I understand that this will give a transfer function with a quadratic term, basically a second order block to which another Sallen Key filter will be added to make it a 3rd order filter. The capacitances in the 2nd order block can be determined easily enough by comparing the transfer function of a second order B-worth filter. But how does one find the capacitance for the 1st order block added onto it? Does one compare the co-efficients of a 1st order B-worth to get it?
I can provide additional info if necessary.
Many thanks.
Dhana