the role of peaking capacitor

[lhlblue]

what is the role of a peaking capacitor in the circuit? just as the picture shows, Cp is a peaking capacitor, how can it influence the peaking behavior? in some paper, Cp = 3% of C1, is that right? how to choose the proper value of Cp? assuming that, in the following picture, C1=1nF, R1=10k.
thanks.

 

[barry]

I don't think that cap is going to give you any peaking; it WILL determine the maximum gain of your circuit as well as the cutoff frequency. (I'm assuming your opamp is just a buffer).

What do you mean "choose the proper value"? What do you want the circuit to do?

 

[Audioguru]

A peaking capacitor boosts high frequencies for a peak in the frequency response.
But Cp in your circuit does not peak, instead it cuts high frequencies if the source has some resistance.

C1 has nothing to do with peaking high frequencies. Its value determines the LOW frequency cutoff. If its value is very low then it is a highpass filter and cuts low frequencies (MAKING A PEAK AT A HIGH FREQUENCY).

 

[lhlblue]

maybe i uploaded a wrong circuit, the opamp is a current-fedback amplifier, and there is a feedback resistor between the output and the negatibe input, so can Cp be a peaking capacitor?
besides, i just want to know the basic role(or principle)of a peaking capacitor in circuit (no matter what kind of circuit).
thanks.

 

[Audioguru]

A series capacitor feeding a resistor to ground is a highpass filter that peaks high frequencies.

 

[barry]

A series capacitor feeding a resistor to ground is a highpass filter that peaks high frequencies.

I think you are mistaking "filtering" with "peaking"

 

[Audioguru]

A circuit normally has a drop in its high frequency response.
Adding a highpass filter extends the high frequency response.

Here is a circuit that uses two resistors to attenuate low frequencies -6dB. The peaking capacitor parallel to the series resistor bypasses it at high frequencies.
Then at a frequency that is -6db at a high frequency its response is is flat at the same high frequency when it has a peaking capacitor.