Anti-pop Res. -> impadence calc.?

[Phorhas]

Hello... I was wondering... to calculate the input impadance of a stage with pull-down resitors should the formula be:1/ (Rp||Rin*C*2*3.14)?

oh, and - where can I get good info on inverting BJT/FET gain stages' output impadence?

Best Regards,
Dan.

[Phorhas]

oh - I forgot, what's the formula if there's a series resistor, before or after Cin?

(is the R after Cin this => 1/(Rp||[Rs+Rin]C*2*3.14) ?

thanx again

[R.G.]

... to calculate the input impadance of a stage with pull-down resitors should the formula be:1/ (Rp||Rin*C*2*3.14)?

Not exactly. The input impedance of a stage with pull down resistors is just Rp||(Rin+j*2*pi*f*C) where j is the imaginary operator, square root of -1.

As long as 2*pi*f*C is less than a tenth of Rin (that is, above the low frequency rolloff point) then you can ignore C and call it Rp||Rin.

oh - I forgot, what's the formula if there's a series resistor, before or after Cin?

Then it's Zin= Rp|| (Rs+Rin). It doesn't matter whether it's in front of or after the cap, and the cap doesn't matter either with the same reasoning as above.

Most people are uncomfortable with this, but you may reverse the order of any R, C, or L series combinations with no effect whatsoever at the ends of the string. That is, R=>C is the same result as C=>R at the ends of the series combination. If you look at the middle points of the series string, order matters, but for purely series strings, order makes no difference at all.

[Hal]

what does || mean?

[mindwave_21]

in parallel
so R1//R2 or R1||R2=(R1*R2)/(R1+R2)

[Phorhas]

Thank you very much R.G.