Need to design a Common Emitter amplifier using a single BJT with below specifications;

DC power supply - 12V
Loaded voltage gain - 25 minimum
Minimum loading on amplifier output- 5k
Minimum input impedance - 50k
Maximum output impedance - 100
3dB frequency response - 300Hz to 10kHz
Input voltage range - 0.4V pp or so on..

Need to select suitable low cost transistor with current gain around 200-700.

 

MOD NOTE: Moved to Homework Help.

 

You need to show your best attempt to get as far as you can.

Do you even have a basic circuit topology laid out?

 

It sounds more like like you want someone else to design it for you.

Les.

 

One small hint: With respect to the required input impedance, it seems to be necessary to use negative signal feeedback (Re not or only partial bridged wit a capacitor).

 

I am stuck at achieving input impedance. Here I maintain Iq=20mA. At this current, R1, and R2 will be around 22k and 7.4k. Also since emitter resistance is also impact for the input impedance, I am having issue with achieving 50k input impedance. Could you please help me to get required input impedance ?

 

Hi DS.
Please post your LTSpice asc file.
E

 

Please find my LTSpice asc file

 

Hi DC,
For an input of 0.4Vppk and gain of 25, assuming that Collector swing is going to be 10Vppk??

What will the transistor collector current have to be, approx??
So that Vc is approx VDC/2
E

 

Hi, If use 10Vpkpk output, then to maintain Vc at Vcc/2, it is need to have Ic=60mA current. it is little higher current. therefore, I have reduce the input signal voltage upto 0.05Vppk. Then Vc is maintained around 75% of Vcc. At that situation, Ic is around 20mA. As well as, to maintain the voltage gain, I have taken RE1 = 3.4 ohm. But the problem is, with that much small RE1 resistance, It is difficult to maintain input impedance around 50k. Can you suggest me any method that can maintain input impedance around 50k!

 

Hi DC.
If you maintain Ic quiescent at 20mA, this gives a Vc of 10V
So how can Vc swing 10Vppk?
[0.4ppk *25= 10Vppk]

The Gain of an amp is Vin/Vout
E

Check this link.
https://www.electronics-tutorials.ws/amplifier/input-impedance-of-an-amplifier.html

Added:
Maximum output impedance - 100
Check this value of 100 Ohms is correct

 

I am stuck at achieving input impedance. Here I maintain Iq=20mA. At this current, R1, and R2 will be around 22k and 7.4k. Also since emitter resistance is also impact for the input impedance, I am having issue with achieving 50k input impedance. Could you please help me to get required input impedance ?

One possible option is to use one single resistor between the VDC source and the base.
I know that this is not the best solution as far as DC operating point stability is concerned (if compared with the classical voltage divider at the base). However - since there are no corresponding requirements...

 

One possible option is to use one single resistor between the VDC source and the base.
I know that this is not the best solution as far as DC operating point stability is concerned (if compared with the classical voltage divider at the base). However - since there are no corresponding requirements...

Even use one single resistor, Still, Zin = Rb||beta*(Re1+re), emitter resistor reflection is coming. then equivalent impedance get reduced

 

I have reduce the input signal voltage upto 0.05Vppk.

Hi,
If you reduce the input signal to 0.05Vppk you are not following the requirement of the tutor's specification.
It states 0.4Vppk input, with an overall Gain of 25.

E

 

Even use one single resistor, Still, Zin = Rb||beta*(Re1+re), emitter resistor reflection is coming. then equivalent impedance get reduced

Example: For beta=200 and Re1=0.5k we get Rb||100k.

 

Hi DC.
I appreciate that you are asking for guidance on setting the BJT amp input Impedance to 50k, but you seem to be ignoring the specified requirement of your tutor regarding the Vin at 0.4Vppk and an overall Gain of 25.

Have you confirmed that you have posted the correct details of the specification?
E