Differential Amplifier: Calculating Common Mode Gain and Rejection Ratio

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SUMMARY

The discussion focuses on calculating the common-mode gain and common-mode rejection ratio (CMRR) of a differential amplifier with a differential gain (Ad) of 20,000. When a 1V signal is applied to the input terminals connected together, the output signal is 0.05V. The common-mode gain (Acm) is derived from the relationship V0 = Ad*Vd + Acm*Vcm, leading to the conclusion that Vd is 0V and Vcm is 0.5V, confirming the calculations for Acm and CMRR.

PREREQUISITES
  • Understanding of differential amplifiers and their configurations
  • Familiarity with the concepts of differential gain (Ad) and common-mode gain (Acm)
  • Knowledge of common-mode rejection ratio (CMRR) calculations
  • Basic principles of signal processing in electronics
NEXT STEPS
  • Study the derivation of common-mode gain in differential amplifiers
  • Learn about the implications of CMRR in real-world applications
  • Explore the effects of noise on differential amplifier performance
  • Investigate different configurations of differential amplifiers and their characteristics
USEFUL FOR

Electronics students, engineers designing signal processing circuits, and anyone interested in understanding differential amplifier performance metrics.

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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