I'm just reading the book "Microelectronic Circuits Fifth Edition" by Sedra/Smith about frequency response for amplifiers. An example shows how to find the DC-gain of an amplifier. The transfer function is (equation #1), which is on the form (equation #2).
The write then uses K as the DC-gain when s-->0 in the transfer function (equation 3). But K is not the DC-gain, but a constant. The DC-gain is the result from (equation 3), when K is known. Right? And how to find K then? One must be known...?
I thought that was a good book, im still using it for my circuits class.
i think what K is used for in that sense is a Load Resistance.
so, for instance a High Pass RL filter is H(s) = S / S + (R/L)
if there is a load resistance placed over the inductur than the transfer function changes so then so must H(S) = (Rl/R + Rl) S / S + (Rl/ R + Rl)( R/l)
lets simplify and make k = ( Rl / R + Rl)
and then finally.
H(s) = KS/ S + Wc : Wc = KR/L the cut off freq
Then K is not a constant so much as it just depends on the circuit.