Input Common-Mode Resistance MOS Diff. Pair

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jegues

Joined Sep 13, 2010
733
How did they come up with that expression for \(R_{icm}\)?

Here's what I came up with,

\(R_{icm} = \frac{v_{id}}{i_{b}}\)

\(i_{e} = \frac{v_{id}}{\frac{R_{E} + r_{e}}{2} + R_{EE}}\)

\(i_{e} = (\beta + 1)i_{b}\)

\(\Rightarrow R_{icm} = (\beta + 1)( \frac{R_{E} + r_{e}}{2} + R_{EE})\)

Am I doing this incorrectly?
 

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The Electrician

Joined Oct 9, 2007
2,790
ro is across the collector-emitter.

The expression in the book appears to be correct with one exception; where they have β they should have β+1. That being the case, I don't think your expression is correct.

You also have RE and REE; what is RE?
 
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