# NPN PNP coupling capacitor

#### michael1978

Mar 17, 2012
388
Hi, can somebody explain me how this circuits works? please, i dont understand input capacitor and C2 and C3. Thanks

#### michael1978

Mar 17, 2012
388
Hi, can somebody explain me how this circuits works? please, i dont understand input capacitor and C2 and C3. ThanksView attachment 40862
Hi i know input is input, and pnp emitter is to ground, but this C2 make it complicate for me.
so i ask with little words how does work?

#### duke37

Jan 9, 2011
5,364
What is the pupose of the circuit?
It looks to me to be a RF amplifier with Q! setting the current through Q2. The capacitors are to bypass RF current so to smooth the supply.
What are the component values?

#### michael1978

Mar 17, 2012
388
What is the pupose of the circuit?
It looks to me to be a RF amplifier with Q! setting the current through Q2. The capacitors are to bypass RF current so to smooth the supply.
What are the component values?
Hello, Duke, sorry for late answer, this is an form of bisasing on RF DESIGN

#### AnalogKid

Jun 10, 2015
2,892
Q1, R1, R2, and R5 form a constant current source to bias Q4 into its linear operating region without lowering the circuit's input impedance. C2 and C3 are bypass/decoupling capacitors to prevent the input RF signal from modulating the bias current and possibly forming an oscillator.

ak

Last edited:

#### michael1978

Mar 17, 2012
388
Q1, R1, R2, and R5 form a constant current source to bias Q4 into its linear operating region without lowering the circuit's input impedance. C2 and C3 are bypass/decoupling capacitors to prevent the input RF signal from modulating the bias current and possibly forming an oscillator.

ak
Thanks a lot man , now i understand.

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