What are interacting and non-interacting cascading stages?
If in a cascade of stages the input impedance of one stage is low enough to act as an appreciable shunt on the output impedance of the preceding stage the output impedance of the preceding stage the stages are said to interacting stages.
If in a cascade of stages the input impedance of one stage is high enough so that it will not be able to affect the output impedance of the preceding stage the stages are said to Non-interacting stages.
What is lower/upper cut-off frequency of non-interacting cascading stages?
For n Non-interacting stages with each stage having lower and upper cut-off frequencies as fl, fh the upper and lower cut-off frequencies are given as follows
fh” = fh*(2^(1/n)-1)^(1/2)
fl” = fl/(2^(1/n)-1)^(1/2)
What is the upper cut-off for interacting stages?
The upper cut-off frequency of n interacting stages with each stage having upper cut-off frequencies fh is
1/fh” = 1.1*((1/f1^2)+(1/f2^2)+……..+(1/fn^2))^(1/2)
Why amplifier gains will reduce at higher frequency?
At high frequencies internal feedback capacitance’s comes into picture. These capacitance’s introduce negative feedback from output to input which reduces the amplifier gain at high frequencies.