Short note on Multifinger Transistor

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written 6.6 years ago by

teamques10 ★ 67k

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Wide x'tor are usually folded to reduce both S/D junction area and gate resistance
A simple folded structure such as fig.a may prove inadequate for very wide devices, necessitating the use of multiple fingers (fig.b)
As a rule of thumb, the width of each finger is chosen such that the resistance of the finger is less than ${gm}^-1$ associated with the finger .
In low noise, application, the gate resistance must be $\frac{1}{5}$ to $\frac{1}{10}$ of $\frac{1}{gm}$.
While the gate resistance can be reduced by decomposing the X'tor into more parallel fingers, the capacitance associated with the perimeter of S/D area.

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