# Designing two stage CE amplifier with negative feedback [closed]

I'm trying to design two stage ce amplifier with negative feedback using 2n2222 transistors. The circuit must have certain voltage gain, Rin, Rout, Vcc, low and high frequency filter. This is the circuit:

I am a noobie with electronics and I've no idea where to even start designing such amplifier. I find it especially hard to design this circuit with certain voltage gain, Rin and Rout. I can't really wrap my head around it.

Any help would be greatly appreciated.

## closed as too broad by Dmitry Grigoryev, awjlogan, RoyC, Scott Seidman, Elliot AldersonOct 17 '18 at 18:31

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Can you explain what you already understand and what specifically you don't? – Hearth Oct 15 '18 at 17:08
• I understand the basic ce amplifier, even two stage is fine. Things get confusing with negative feedback and the voltage gain, rin and rout requirements. I know how to calculate voltage gain and Rin/Rout values for this circuit. I really don't know how to start designing this circuit with the requirements. – J Jon Oct 15 '18 at 17:13
• With the capacitive feedback, you will either (1) have an oscillator, or (2) only have a voltage-gain of ONE. I suggest you remove C4 (across R7), and let the closed-loop gain be 1 + R7/R10. Enjoy the learning. – analogsystemsrf Oct 15 '18 at 17:39
• A robust biasing method places Vbase at 1/3 of VDD, and Vcollector at 2/3 of VDD. Select the base resistors to be 10X the emitter or collector resistances. Thus with 10Kohm in emiiter and collector, use 100K and 200K resistors to set Vbase to 1/3 of VDD. This guarantees you will be operating the transistors in the linear region, with collector voltage swing of +- 1/3 of VDD around the DC collector bias of 2/3 VDD. This biasing does require a high BETA, at least 50 or 100, to produce the expected Vcollecter. – analogsystemsrf Oct 15 '18 at 17:43
• C4 is supposed to act as high frequency filter if I'm not mistaken. – J Jon Oct 15 '18 at 17:44

Steps to solve this:

Draw the small signal equivalent circuit. From that you can derive the small signal parameters $$\R_{in}\$$, $$\R_{out}\$$ and the gain over frequency. $$\R_{in}\$$ and $$\R_{out}\$$ might depend on the $$\gm\$$ of the transistors so $$\R_{in}\$$ and $$\R_{out}\$$ will be expressed as the gm of one or more transistors and values of resistors.

This circuit has feedback which complicates things. You should know that circuits with feedback have a transfer of $$\A/(1+A\beta)\$$. You can just open the loop and then evaluate A and $$\\beta\$$ separately.

Then also realize what the relations are between the open loop $$\R_{out}\$$ and the closed loop $$\R_{out}\$$. Generally Rout will become much lower in closed loop (as the circuit "counteracts" any changes at the output).

Determine what components affect the behavior over frequency so look for RC time constants in the circuit, C1 and R6 is an example. Think what influence this RC circuit has (C1 shorts R6 at high frequencies) and what the crossover frequency of that RC is.

Yep, this is not easy! The steps should really have been explained in a course, book or class as this is not something you can figure out yourself. The question rises why a "Noobie" like yourself has to be able to solve this. It is not like you are ever going to need this unless you want to become a Analog circuit designer. And then you would have chosen to learn this yourself.

Oh, and this is not "designing"! This is dimensioning meaning, the circuit is there and you can only play with the component values. Also, I guess that even many Electrical Engineers with a Master's in Electrical Engineering would have a hard time to dimension this circuit properly. Most would just use a circuit simulator. Personally I would do the same but as I have a lot of experience (more than 25 years) in Analog design I can start with better initial values for the resistors and I also know what the effect is of changing certain (combinations of) resistors. So if for example the gain is too low, I immediately know what my options are to solve that. As a newbie, you lack that experience so you have to do this the hard way.