Multistage using BJT

Thread Starter

Communications Student

Joined May 3, 2007
10
Plz guys I need ur help, I have a project,I need to design a multistage amplifier using BJT whith a voltage gain 100, and Rload=1Kohm, and it will operates in the frequency range from o to 5Mhz

Any ideas????
 

Thread Starter

Communications Student

Joined May 3, 2007
10
Thankss soo much 03GTS and Mozikluv, and I'll begin to work it out wiz the configuration tht u attached Moz, and I appreciate ur efforts o3GTS hoppin u find ur handout
 

Thread Starter

Communications Student

Joined May 3, 2007
10
Ok moderator I'm sorry but really I didn't mean to be tht lazy and tht dependent on others, so as it's my very first time to post in here, don't be too harsh on me ;)

So guys plz I need ur help, those are the values I computed based upon the pdf file above attached by Mozikluv:

R1=6oo ohm, R2=R3=50 kohm, R4=95kohm,R5=483.33 ohm,R7 =7.1 kohm
Problem is I can't compute R6,plus in the second BJT I have very small base current : I base=1.5 micro A, I collector= I emitter = 0,45mA (as I took hFE=300) , and also I don't know the values of the capacitors:((((((((((((((((
 

mozikluv

Joined Jan 22, 2004
1,437
am attaching formulas to help you out.

why is your R7 value higher than your load value (R8).

Review your emitter bypass cap. lesson

biasing your second Q (pnp) is practically the same as your first Q

moz:)
 

Attachments

Thread Starter

Communications Student

Joined May 3, 2007
10
Thankss so much MOz for ur kindess and ur help, I'll work it out today with the help of ur formulas, plus I asked my teacher assistant today at college, he told me tht i have to buy the BJT first, adn measure its hFE using the Avo-meter and not just assume it any value in my design.
 

Thread Starter

Communications Student

Joined May 3, 2007
10
in the formulas u sent me : Av = Vo/Vs = gm1 gm2(R4||rπ2 ) (R7||R8 ) ( R2/(R2 +R1))
Input resistance = R1||R2||r pi 1

how would i compute gm which is the differentiation of Id over Vgs ( JFET) while the required project and the configuration u attached is a BJT ??
and can I use anozer BJT other than 2N3904 and 2N3906 ??
 
The pdf attached contains a 2-stage CE BJTS with gain=10 and Rl=10k and a very good Q-point position.
I have a question, What is the advantage of putting the so called "swamping resistance" in the emitter side of the CE BJT amplifiers???
 

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Thread Starter

Communications Student

Joined May 3, 2007
10
Omar megane, the pdf u sent me is MORE THAN PERFECT AND VERYY USEFUL, REALLY THANK U SOOO MUCH :)

the advantage of putting the so called "swamping resistance" in the emitter side of the CE BJT amplifiers is tht in the DC analysis, it will help to get a good q point in the active region, and as we don't want this resistance in the AC analysis, as it will decrease the gain, we put a by pass capacitor in parallel wiz it which will act as short circuit in AC and open circuit in DC

hope I can help as u did :)
 
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