A SURVEY OF SEMICONDUCTOR DEVICES
A SURVEY OF SEMICONDUCTOR DEVICES
A SURVEY OF SEMICONDUCTOR DEVICES
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1. Fast intrinsic response?<br />
2. Fast circuit?<br />
V G<br />
“High-speed” device<br />
Parameters Considerations Speed fig-of-merit of FET<br />
Transit time Intrinsic, no capacitance gm/CG<br />
S-para. meas. (f T) No output capacitance, no runner g m/(C G+C ip)<br />
(fmax) Optimized load, no runner<br />
Ring oscillator Fan-out = 1, short runner gm/(CG+Cip+Cout)<br />
Real circuit Mult fan-outs, long runner, load capacitance g m/(C G+C ip+C out+C run+C lo)<br />
High intrinsic speed not sufficient (although necessary)!<br />
Critical parameters: gm, CG, Cdrain, etc.<br />
I<br />
Q<br />
C<br />
VL<br />
I I I<br />
Speed ≈ --- ≈ ---------- ≈ ----------- ≈<br />
Q CV<br />
L<br />
CV<br />
G<br />
g<br />
m<br />
------<br />
C<br />
38/39 K. Ng
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