Please answer what should it be the value of Vs (-0.0036V) and please explain th

Question

Please answer what should it be the value of Vs (-0.0036V) and please explain the reason.

Resistors used in the voltage divider for op amp power supply R_1 = R_2 = 5.6 k ohm R_f = 50 k ohm. Determine the value of R_i required for a gain of 10. Ground both inputs and measure Y_out Determine V_s. The actual used value of R_f middot R_f = 56 k ohm. For a gain of 10, the value of R_i required: R_i = 5.6 k ohm. Measured V_in = 36m V = 0.036V implies V_s = -V_in(R_i/R_f) = -0.036(V)(5600 ohm/56000 ohm) = -0.0036(V) What should it be and why? If it isn't what you expect, why might that be?

Explanation / Answer

For an ideal opamp, it should be -0.0036V. However, in practice, the Vbe values of the input transistors in the opamp differ. THis will result in an offset voltage. This is called output offset voltage. and it can be measured by grounding the inputs and measuring the output voltage. Theoretically, when the inputs are grounded ( or 0V ), the output should be 0V. However we will observe some voltage ( this is what is measured in the beggining of item b above ). The output of the inverter will vary by this offset voltage. Hence you will not find Vs=-0.0036V.

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