Differential Amplifier: Calculating Common Mode Gain and Rejection Ratio

AI Thread Summary
A differential amplifier with a differential gain of 20,000 is used to amplify electrocardiogram signals. When the input terminals are connected together and a 1V signal is applied, the output is 0.05V, indicating a common-mode gain that needs to be calculated. The discussion clarifies that with the terminals connected, the differential voltage (Vd) is zero, while the common-mode voltage (Vcm) is 0.5V. Participants emphasize the importance of verifying the equation used for calculations to ensure consistency with coursework definitions. The conversation concludes with confirmation of the values for Vd and Vcm, aiding in the calculation of common-mode gain and rejection ratio.
yg2010
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Homework Statement



a differential amplifier with differential gain Ad = 20000, is used for amplifying signals obtained from an electrocardiogram. If the input terminals are connected together and 1V signal is applied to them, an output signal of 0.05V results. Calculate the common-mode-gain of the amplifier and the common mode rejection ratio.


Homework Equations



so,
V0 = Ad*Vd + Acm*Vcm

how to find Vd and Vcm?
 
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Hello yg2010,

Welcome to Physics Forums!

yg2010 said:
so,
V0 = Ad*Vd + Acm*Vcm

You might want to check the above equation, and make sure it is consistent with your coursework's definition of Ad and Acm. Depending on how they are defined in your coursework, you might have missed a factor of 1/2 in there somewhere.

how to find Vd and Vcm?

The problem statement says, "If the input terminals are connected together..." What does that tell you about Vd?

The problem statement also says, "...and 1V signal is applied to them..." What does that tell you about Vcm?
 
so Vd is equal to zero; Vcm is 0.5V. i think i have gotten it correctly. =) thanks!
 

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