[SOLVED] Need help with simple Class A amplifier desgin and simulation..

[tedzxavier]

Hi! Good day to everyone! Im a freshman student and i've been working on a project my teacher has given me last friday. He wants me to produce a schematic diagram and a simulation of a Class A amplifier that is a voltage-divider kinda looking with the emitter resistor being bypassed by a cap. The hard part here is the designing part to which i am a newbie. He wants the circuit to have a voltage gain of 4200 & a bandwidth of 20 kHz. The DC source should be 12 V. It's on me (or you) to decide whether BJT or a FET be used as long as the parameters mentioned above can be provided. Lastly, he instructed that if the gain found is less, one can use OP AMP (l have little knowledge on this) for it to be fixed. I will be truly grateful if anyone here can assist me on this problem...Thanks in advance!!!

 

[E-design]

It would be a lot of gain for a single stage BJT of FET to produce.
What is the required input and output impedance?

 

[goldsmith]

He wants the circuit to have a voltage gain of 4200

Hi
A single stage ? with collector resistor or active load ? if with usual load i need to confess that your teacher want that you bring him/her a miracle ! you can harvest that gain with op amp as well but BW will be reduced and noise factor will be increased . and also if you use a single stage active load to do it the result in practice will be so bad because of the limited BW and high value of noise .

What else do you need to hear ?
Best Wishes
Goldsmith

 

[BradtheRad]

Although a class A amplifier is a popular and useful project, there are a variety of factors involved when you want to optimize its performance.

The idea is for you to learn how the various concepts interact.
To do this you have to experiment with component values, and watch how it affects performance.

Aim for 100x gain first. Later you can add a second transistor to create a darlington or sziklai pair. (You can add an op amp but it will complicate matters by bringing in other concepts besides class A topology).

The assignment tells you to produce a simulation of your design. Consider using the one at:

www.falstad.com/circuit:

The professor does not want you to copy a design, however. You need to discover how to adjust the resistors at the bias and collector and emitter, in order to obtain the desired operation. Also the emitter capacitor.

Start with a high output impedance, to see whether that will help you get higher gain.

 

[tedzxavier]

Thank you for the replies!!! Im not tasked to buy components and make this project guys. My professor just wants the design or the schematic with the noise being ignored...And also, it's up to me/you to decide for both the output and input impedances..Im already making a headway with the values and etc,the hard part now is the simulation. I dont know if Orcad can produce graphs..I just downloaded orcad..hope it does...anyways, thank you guys..I appreciate all the comments!

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it's up to you to decide the input and output impedances

 

[goldsmith]

Thank you for the replies!!! Im not tasked to buy components and make this project guys. My professor just wants the design or the schematic with the noise being ignored...And also, it's up to me/you to decide for both the output and input impedances..Im already making a headway with the values and etc,the hard part now is the simulation. I dont know if Orcad can produce graphs..I just downloaded orcad..hope it does...anyways, thank you guys..I appreciate all the comments!

- - - Updated - - -

it's up to you to decide the input and output impedances

Hi again
First of all a thing about orcad : orcad is one of the most powerful softwares for simulations ! precise simulations . and it can easily draw graphs .
Ok , there iare no problem with impedances . but about number of stages . how much is the maximum allowed stages ? can you use three transistors or perhaps more ? or an auxiliary op amp ? if yes then it will be so easy .
Best Wishes
Goldsmith