# Correction !!!!

Discussion in 'Homework Help' started by Nice, Jun 13, 2009.

1. ### Nice Thread Starter Member

Jun 13, 2009
19
0
Hi Guys

How can I have an amplifier with :

1- High gain
2- High input resistance
3- Low output resistance

Is it important to use multistage amplifier ??

2. ### mik3 Senior Member

Feb 4, 2008
4,846
69
How high is the gain?

What is the maximum operating frequency?

3. ### Nice Thread Starter Member

Jun 13, 2009
19
0
The input signal is 10mV

and the needed gain is 40V/V

The frequency is 1000Hz= 1khz

4. ### mik3 Senior Member

Feb 4, 2008
4,846
69
You can use an op amp in this case with good results.

5. ### Nice Thread Starter Member

Jun 13, 2009
19
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I should use BJT's or MOSFET's only !!!

6. ### Nice Thread Starter Member

Jun 13, 2009
19
0
Thank you for your response

7. ### mik3 Senior Member

Feb 4, 2008
4,846
69
Then you have to build a common emitter amplifier with a gain of 40V/V and then fed its output to the input of an emitter follower to achieve low output impedance.

8. ### bertus Administrator

Apr 5, 2008
18,336
3,514
Hello,

So you need a gain of 40 V/V.
What input resistance is required?
What output resistance is required?

Greetings,
Bertus

Jun 13, 2009
19
0

Rin > 40k

Rout < 1k

10. ### Nice Thread Starter Member

Jun 13, 2009
19
0

Can you please show me the connection

because I tried this configuration (CE-CC) in the PSpice & the gain is approximately = 1

11. ### Nice Thread Starter Member

Jun 13, 2009
19
0
Thank you guys..I appreciate what you are doing

12. ### bertus Administrator

Apr 5, 2008
18,336
3,514
Hello,

That could be made with a two stage amplifier.
At the input a mosfet for the high input resistance and gain.
Afther that an emmitter follower for the low output resistance.

Greetings,
Bertus

13. ### mik3 Senior Member

Feb 4, 2008
4,846
69
The gain of a CC is about 1.

The gain of a CE depends on Rc and Rin.

14. ### Nice Thread Starter Member

Jun 13, 2009
19
0

Also CE will give a high gain & input resistance !!!

15. ### Nice Thread Starter Member

Jun 13, 2009
19
0
The rule says:

The gain of a multistage amplifier is the gain product of each BJT

16. ### Audioguru Expert

Dec 20, 2007
10,385
1,140
So simply make a CE transistor with a gain of 40 followed by a CC transistor that has a gain of 1. The CE transistor has a high input impedance and the CC transistor has a low output impedance.

17. ### mik3 Senior Member

Feb 4, 2008
4,846
69
This is true about the voltage gain.

For the current gain you cannot simply multiply the individual current gains.

18. ### Nice Thread Starter Member

Jun 13, 2009
19
0

You are absolutely right..