Frequency response of rc coupled amp

[amaresh92]

greetings,

At high frequency (more than 20kHz) the reactance of capacitor is very small and act as short circuit.this increase the loading of next stage.whats the meaning of increse of loading in next stage?

RC coupled two stage amplifier circuit is here-:
http://electron1.eng.kuniv.edu.kw/334/modified/exp4/rc-coupled.htm

advanced thanks.

 

[vk6kro]

The gain of the first stage depends on the 10 K load resistor, but in parallel with this is the coupling capacitor in series with the input capacitance of the second stage.

Although this is a FET, this capacitance will probably be quite large due to Miller Effect.

At high frequencies, the reactance of the coupling capacitor should be negligible, so they are saying the main effect will be the input capacitance of the second stage.

That is a very clever use of a cheap IC. How much gain did you get?

 

[amaresh92]

The gain of the first stage depends on the 10 K load resistor, but in parallel with this is the coupling capacitor in series with the input capacitance of the second stage.

Although this is a FET, this capacitance will probably be quite large due to Miller Effect.

At high frequencies, the reactance of the coupling capacitor should be negligible, so they are saying the main effect will be the input capacitance of the second stage.

That is a very clever use of a cheap IC. How much gain did you get?

but the frequency will be same for second stage input capacitor also so its reactance also will be less?

 

[vk6kro]

[PLAIN]http://dl.dropbox.com/u/4222062/effect%20of%20Miller%20C.PNG

You can see that 0.1 uF has very little effect on the total capcitance across the load resistor. It is still almost 500 pF. This is a guessed value for the Miller capacitance.
However if you made the 0.1 uF capacitor 1000 pf, the total capacitance would only be 333 pf

This capacitance affects the gain of the first stage. It reduces the gain at higher frequencies when the reactance of the capacitance becomes smaller so the effective load is smaller.

 

[gnurf]

Not that it changes anything, but according to standard OCD behavior I have to point out that the coupling caps in the schematic are 0.1μF, and not 1μF.

 

[vk6kro]

I believe they have tablets for that.

Yes, the capacitors in the diagram are 0.1 µF. I like to put a leading zero in such values so the dot can't get lost or carelessly neglected like I did.

I can't actually find the quote increase the loading of next stage in the text, though, so I'm not quite sure what the question is.
Just skirting around it until it gets explained a bit clearer.