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lam58
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Hello I'm a bit stuck on this.
The question states that the non ideal op amp (pictured below) in open loop conditions has an input resistance of 400kΩ, an output resistance of 2kΩ and a voltage gain of 500,000.
I then asks to find the voltage gain, the voltage at the negative input terminal and the input and output resistances when the supply voltage is 50mV. So for the first part finding the gain I assumed V at positive terminal (Vp) = 0.
Thus Vo = A(Vp-Vn) => Vn = Vo/A.
Also [tex]\frac{V_{s}-V_{n}}{R_{s}} = \frac{V_{n}-V{o}}{R_f}[/tex]
Then using Vn = Vo/A
[tex]\frac{R_f}{R_s} (V_s + \frac{V_o}{A}) = V_o (\frac{-1}{A}-1)[/tex]
[tex]\Rightarrow \frac{V_s}{V_o} + A = \frac{(-1/A)-1}{R_f/R_s}[/tex]
[tex]\Rightarrow \frac{V_o}{V_s} = \frac{(R_f/R_s)}{(-1/A)-1} - \frac{1}{A}[/tex]
Putting in the values given:
gain = [tex]\frac{320k/8k}{(1/500k)-1} - \frac{1}{500,000} = -39.999922[/tex]
From this I got [tex]V_o = - 1.9999961[/tex], [tex]V_n = 49.76v[/tex]
However, here I don't know if the above is correct and how to find the input and output resistances. Any help would be much appreciated. :)
EDIT Just realiased how to find input resistance and output resistances using my first equation.
Is the working above correct though?
The question states that the non ideal op amp (pictured below) in open loop conditions has an input resistance of 400kΩ, an output resistance of 2kΩ and a voltage gain of 500,000.
I then asks to find the voltage gain, the voltage at the negative input terminal and the input and output resistances when the supply voltage is 50mV. So for the first part finding the gain I assumed V at positive terminal (Vp) = 0.
Thus Vo = A(Vp-Vn) => Vn = Vo/A.
Also [tex]\frac{V_{s}-V_{n}}{R_{s}} = \frac{V_{n}-V{o}}{R_f}[/tex]
Then using Vn = Vo/A
[tex]\frac{R_f}{R_s} (V_s + \frac{V_o}{A}) = V_o (\frac{-1}{A}-1)[/tex]
[tex]\Rightarrow \frac{V_s}{V_o} + A = \frac{(-1/A)-1}{R_f/R_s}[/tex]
[tex]\Rightarrow \frac{V_o}{V_s} = \frac{(R_f/R_s)}{(-1/A)-1} - \frac{1}{A}[/tex]
Putting in the values given:
gain = [tex]\frac{320k/8k}{(1/500k)-1} - \frac{1}{500,000} = -39.999922[/tex]
From this I got [tex]V_o = - 1.9999961[/tex], [tex]V_n = 49.76v[/tex]
However, here I don't know if the above is correct and how to find the input and output resistances. Any help would be much appreciated. :)
EDIT Just realiased how to find input resistance and output resistances using my first equation.
Is the working above correct though?
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