Please Help me urgently

[[email protected]]

Hello,
I can not handle a problem which is about AGC. Please help me about
that. The conditions are;
It is required to design and implement an AGC circuit
with the following specifcations:
1. Amplitude of the input voltage may vary between 10 mVpp and 50 mVpp.


2. Amplitude of the output voltage should be in the range 0.9 Vpp
and1.1 V
pp for the input signals with amplitudes stated above.


3. Output impedance of the ampli¯er should be smaller than 2 k­.


4. The circuit should be able to amplify the signals having frequencies

between 500 Hz and 10000 Hz.


The amplifer designed should be a single transistor amplifer in the
common-emitter form for BJT amplifers or common-source form for the
FET amplifers. However, it can be used extra transistors for making the

amplifer an adjustable gain amplifer.


And the AGC should be composed of 2 parts adjustable gain part and
feedback part.


Please help me urgently to design this problem. Thanks...

 

[Phil Hobbs]

Hello,
I can not handle a problem which is about AGC. Please help me about
that. The conditions are;
It is required to design and implement an AGC circuit
with the following specifcations:
1. Amplitude of the input voltage may vary between 10 mVpp and 50 mVpp.


2. Amplitude of the output voltage should be in the range 0.9 Vpp
and1.1 V
pp for the input signals with amplitudes stated above.


3. Output impedance of the ampli¯er should be smaller than 2 k­.


4. The circuit should be able to amplify the signals having frequencies

between 500 Hz and 10000 Hz.


The amplifer designed should be a single transistor amplifer in the
common-emitter form for BJT amplifers or common-source form for the
FET amplifers. However, it can be used extra transistors for making the

amplifer an adjustable gain amplifer.


And the AGC should be composed of 2 parts adjustable gain part and
feedback part.


Please help me urgently to design this problem. Thanks...

If you're waiting for us to do your homework for you, you're going to be
waiting quite awhile. On the other hand, if you've had a good try at it
and are just stuck on one or two things, your odds are better.
Posting from a real email account (not Gmail or hotmail) will improve
your odds further.

What have you actually done so far?

Cheers,

Phil Hobbs

 

[martin griffith]

On 27 May 2006 05:35:09 -0700, in sci.electronics.design

Hello,
I can not handle a problem which is about AGC. Please help me about
that. The conditions are;
It is required to design and implement an AGC circuit
with the following specifcations:
1. Amplitude of the input voltage may vary between 10 mVpp and 50 mVpp.


2. Amplitude of the output voltage should be in the range 0.9 Vpp
and1.1 V
pp for the input signals with amplitudes stated above.


3. Output impedance of the ampli¯er should be smaller than 2 k­.


4. The circuit should be able to amplify the signals having frequencies

between 500 Hz and 10000 Hz.


The amplifer designed should be a single transistor amplifer in the
common-emitter form for BJT amplifers or common-source form for the
FET amplifers. However, it can be used extra transistors for making the

amplifer an adjustable gain amplifer.


And the AGC should be composed of 2 parts adjustable gain part and
feedback part.


Please help me urgently to design this problem. Thanks...

try posting to sci.electronics.homework



martin

 

[mavihot]

Hello,
thanks to response my problem. I have spent a lot of time for this
problem, but I can not find a specific solution. I used a BJT for
amplification. Then connect a resistor to input, then I connect a JFET
other terminal of the resistor. And connect the JFET to the output. I
use JFET by using its property of it is a voltage controlled resistor.
By using this property and making a voltage division there. I adjust
the outout to neighbourhood of 1 Vpp. However one of the problem is
that I can not get a proper output, also the output is AC signal, but I
have to control JFET DC signal; this is one of the problem. I thought
that I can use a full wave rectifier to change AC signal to DC signal,
unfortunately I am working about 1 V , and diodes opening voltage is
about 0.7 V; so, it is not a proper way. If you give me your e-mail
address, I can send you our Multisim Simulation for this homework,
because I have worked a lot on it. Finally, the most important problem
is whether I am on the right way or not. This is very important. My
finals just finished and I have not had much time for this work. Please
help to design this work. If it is possible, I will be pleased about
that.
Thanks for your interests

 

[mavihot]

Hello,
Thanks, but I can not send it to sci.electronics.homework
Could you help me how can I send it?
Thanks again.

 

[Tom Bruhns]

Hint #1: for low distortion, keep the AC voltage across the JFET used
to control the gain as low as you reasonably can.

Hint #2: Have that JFET handle AC only, no DC, in order to offer a
reasonably linear resistance.

Hint #3: With a high load impedance, silicon diodes conduct enough to
offer significant rectification much below 0.7 volts.

Consider other topologies than you have so far. For example, consider
using the FET and a resistor to form a voltage divider, which then
feeds an amplifier stage. There are many ways you can solve this
problem. Don't invest too heavily in just one at first. Step back
from the problem and think of some different ways to do it, and then
weigh the pros and cons of each.

More later, after you mull that over.

Cheers,
Tom

 

[Bob]

Hello,
Thanks, but I can not send it to sci.electronics.homework
Could you help me how can I send it?
Thanks again.

I love it!

Bob

 

[mc]

Just to make explicit what others did not...

"sci.electronics.homework" does not exist.

In these forums, people are very unwilling to do students' homework for
them. Also, remember that your teacher may be here, too.

 

[Pooh Bear]

Hello,
I can not handle a problem which is about AGC. Please help me about
that. The conditions are;

< snip >

Design consultancy is easy to obtain. It involves paying money though.

Graham

 

[Rich Grise]

Hello,
I can not handle a problem which is about AGC. Please help me about
that.

Read fast:
http://www.google.com/search?q="automatic+gain+control"++circuit

Good Luck!
Rich

 

[Ken Smith]

Hint #1: for low distortion, keep the AC voltage across the JFET used
to control the gain as low as you reasonably can.

Also, apply some of the drain's AC voltage to the gate. You want to bring
the change of the RDS(on) with AC voltage near to zero.