Layout_Examples

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Unformatted text preview: 000000000000000000000000000 11111111111111111111111111 00000000000000000000000000 11111111111111 00000000000000 111111111111111111111111111 000000000000000000000000000 11111111111111111111111111 00000000000000000000000000 11111111111111 00000000000000 111111111111111111111111111 000000000000000000000000000 11111111111111111111111111 00000000000000000000000000 11111111111111 00000000000000 111111111111111111111111111 000000000000000000000000000 11111111111111111111111111 00000000000000000000000000 11111111111111 00000000000000 111111111111111111111111111 000000000000000000000000000 11111111111111111111111111 00000000000000000000000000 11111111111111 00000000000000 111111111111111111111111111 000000000000000000000000000 11111111111111 00000000000000 11111111111111 00000000000000 B (Metal) 11111111111111 00000000000000 Gate (Poly) Fig.2.15 All sources, drains and Gates connected. This has the same effective Gate width as one long and thin transistor. Another tip is to never terminate a long route (greater than ~100μm) with a diffusion region (transistor source-drain; e.g. a pass gate). Electromagnetic (transmission line) effects can cause signals to exceed VDD or drop below ground momentarily, potentially forward biasing the source/drain-substrate/well diode. Long distance signals should always end at the gate of a transistor instead. This can be accomplished by placing one or two inverters between the long wire and the pass gate (usually a MUX). Obviously, if only one inverter is inserted, the logic before or after the gate will have to be adjusted. 9 Note that it is needed to minimize the number of times a signal switches between routing layers. Contacts and vias have resistance that can be equal to fairly long metal lines. For this reason, poly may be a better choice than M1 for very short routes between gates. It is necessary to avoid driving one transistor through another. In other words, do not chain transistors together via their gates as shown in Fig.2.16. The combination of high poly sheet resistance and gate capacitance can cause...
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This document was uploaded on 01/14/2014.

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