Problem in 3db freq. when using Open time constant method

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luckyyum

Joined Jun 18, 2011
1
It is the problem when i studying Sedra's Electric Circuit.
In common, 3db freq result in open time constant method
like
W=1/(C1R1+C2R2+....)

but, when dominant pole W1 and W2 are close,
W=1/√(W1^2+W2^2)

What is a criterion of close?
How much?
 
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