This is wrong?
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Progg70 said:
Hi Progg70,
Can you be a bit more specific? What exactly do you want? The gain of the amp? Closed loop, open loop? The gain of the feedback network itself? The gain of 12 you showed, what is that? The gain block, or the complete closed loop amp circuit? And if the latter, it's wrong.
Please think a moment and then formulate your question.
Jan Didden
My attempt
If the amplifier voltage gain is A and the feedback attenuation is B
The closed loop gain X = A / [ 1 + (A x B )]
The feedback factor is Y = A / X
The feedback factor in decibels = 20 x log( Y )
[note: this is base 10 log not natural log]
In your diagram, B = R2 / (R1 + R2)
Remember that in a real life amp A changes with frequency and the input impedance of the amp may alter the effective value of B. Any load on the amp output may also change the effective value of A.
If the amplifier voltage gain is A and the feedback attenuation is B
The closed loop gain X = A / [ 1 + (A x B )]
The feedback factor is Y = A / X
The feedback factor in decibels = 20 x log( Y )
[note: this is base 10 log not natural log]
In your diagram, B = R2 / (R1 + R2)
Remember that in a real life amp A changes with frequency and the input impedance of the amp may alter the effective value of B. Any load on the amp output may also change the effective value of A.
Hi,
have we sorted out what the 12 represented?
If open loop gain =12 =+21.58db
closed loop gain~=47/4.7+1=11=+20.83db. This is approximate because the accurate formula is quite complicated, particularly appropriate as closed loop gain approaches open loop gain.
feedback ratio is open loop gain - closed loop gain =21.58-20.83=0.75db. Hardly worth closing the loop, since all the advantages of closing the loop are proportional to the magnitude of the feedback factor.
The accurate formula for closed loop gain of an inverting amp is
Av=Rfb/[Rg+(Rfb+Rg)/A] where Rfb=the feedback resistor (47k)
Rg=lower leg resistor to common (4k7), A = open loop gain (x12)
what is the correction factor when non inverting is being used?
Just to check my arithmetic, I think the corrected closed loop gain is 5.22 (+14.35db) resulting in a feedback factor of 7.2db.
Am I close? or is it 6.22?
have we sorted out what the 12 represented?
If open loop gain =12 =+21.58db
closed loop gain~=47/4.7+1=11=+20.83db. This is approximate because the accurate formula is quite complicated, particularly appropriate as closed loop gain approaches open loop gain.
feedback ratio is open loop gain - closed loop gain =21.58-20.83=0.75db. Hardly worth closing the loop, since all the advantages of closing the loop are proportional to the magnitude of the feedback factor.
The accurate formula for closed loop gain of an inverting amp is
Av=Rfb/[Rg+(Rfb+Rg)/A] where Rfb=the feedback resistor (47k)
Rg=lower leg resistor to common (4k7), A = open loop gain (x12)
what is the correction factor when non inverting is being used?
Just to check my arithmetic, I think the corrected closed loop gain is 5.22 (+14.35db) resulting in a feedback factor of 7.2db.
Am I close? or is it 6.22?
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