Electrical Engineering - Please Help me urgently

Author

Please Help me urgently

mavihot

2006-05-27, 10:21 am

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=2E Amplitude of the input voltage may vary between 10 mVpp and 50 mVpp.

2=2E 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=2E Output impedance of the ampli=AFer should be smaller than 2 k=AD.

4=2E 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...

TimPerry

2006-05-27, 12:21 pm

mavihot wrote:
> 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...

typically the input voltage is first amplified then rectified and filtered
to a fluctuating DC which is used to control a VCA (voltage controlled
amplifier)

these are commonly found in AM radio circuits.

Salmon Egg

2006-05-27, 4:21 pm

On 5/27/06 5:37 AM, in article
1148733431.065796.4680@y43g2000cwc.googlegroups.com, "mavihot"
<mavihot@gmail.com> wrote:

> 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...
>
How much are you willing to pay?

Bill
-- Ferme le Bush

Derek ^

2006-05-27, 5:21 pm

On Sat, 27 May 2006 10:34:40 -0400, "TimPerry"
<timperry@noaspamadelphia.net> wrote:

>

Such a device is called a compressor.

Example here:

http://freespace.virgin.net/ljmayes.mal/comp/comp.htm

and here

http://www.wireless.org.uk/circuits.htm

The use of a 1 transistor amplifier represents a fairly stringent
requirement. If it had a 2k collector load then it would have an
output impedance of < 2k. A voltage gain of 100 must be possible.

Probably the gain adjusting element would have to be on the input to
the amplifier to avoid it becoming overloaded, some sort of JFET or
LDR element such as in the examples above.

You'd have to get the gain in the AGC feedback loop right. I think
you'd have to build it to prove it, god only knows what the "gain" of
an led and a LDR glued into a plastic tube is.

>
>typically the input voltage is first amplified then rectified and filtered
>to a fluctuating DC which is used to control a VCA (voltage controlled
>amplifier)
>
>these are commonly found in AM radio circuits.

No.

The AGC in AM radios is driven by rectifying the carrier.

Rectifying the audio to drive the AGC could lead to distortion of
various kinds and other undesirable effects, which is apparently what
is required in the answer to this question. :-)

For this reason the use of compressors in broadcasting is avoided
whenever possible.

See also:

<http://216.239.59.104/search?q=cach...uk&ct=clnk&cd=3>

DG

TimPerry

2006-05-28, 2:21 am

Derek ^ wrote:
> On Sat, 27 May 2006 10:34:40 -0400, "TimPerry"
> <timperry@noaspamadelphia.net> wrote:
>
>
> Such a device is called a compressor.
>
> Example here:
>
> http://freespace.virgin.net/ljmayes.mal/comp/comp.htm
>
> and here
>
> http://www.wireless.org.uk/circuits.htm
>
> The use of a 1 transistor amplifier represents a fairly stringent
> requirement. If it had a 2k collector load then it would have an
> output impedance of < 2k. A voltage gain of 100 must be possible.
>
> Probably the gain adjusting element would have to be on the input to
> the amplifier to avoid it becoming overloaded, some sort of JFET or
> LDR element such as in the examples above.
>
> You'd have to get the gain in the AGC feedback loop right. I think
> you'd have to build it to prove it, god only knows what the "gain" of
> an led and a LDR glued into a plastic tube is.
>
>
> No.
>
> The AGC in AM radios is driven by rectifying the carrier.
>
> Rectifying the audio to drive the AGC could lead to distortion of
> various kinds and other undesirable effects, which is apparently what
> is required in the answer to this question. :-)

it has the effect of maintaining audio levels as the signal strength
fluctuates.
i feel pointing the poster in the direction of commonly available radio AGC
circuits may help provide an understanding of what is needed without actully
doing classwork for him.

>
> For this reason the use of compressors in broadcasting is avoided
> whenever possible.
>

you are either joking or you have no idea about audio processing in
broadcasting.
compressors are used at every stage of the broadcast airchain starting with
the mic preamp and more at the STL then finally whopping big AGC +
compression + limiting at the excitors.

a form of AGC is even used to control power output in most modern broadcast
transmitters.

Adrian C

2006-05-29, 12:21 pm

Salmon Egg wrote:
> <mavihot@gmail.com> wrote:

> How much are you willing to pay?

Probably not much, he is a student in a Turkish university....

--
Adrian C

Salmon Egg

2006-05-30, 2:21 am

On 5/29/06 8:06 AM, in article 4e0gvsF1bo1mjU1@individual.net, "Adrian C"
<email@here.invalid> wrote:

> Salmon Egg wrote:
>
>
> Probably not much, he is a student in a Turkish university....

Suppose a student wanted, and maybe even needed, my house. How much of a
price break should he expect?

Bill
-- Ferme le Bush

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