# Homework Help: Differential amplifier

1. Apr 27, 2010

### yg2010

1. The problem statement, all variables and given/known data

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.

2. Relevant equations

so,

how to find Vd and Vcm?

2. Apr 27, 2010

### collinsmark

Hello yg2010,

Welcome to Physics Forums!

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.

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?

3. Apr 27, 2010

### yg2010

so Vd is equal to zero; Vcm is 0.5V. i think i have gotten it correctly. =) thanks!