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Unformatted text preview: tPlus and use electronic rulers to
measure this layout. The people who get high grades on this assignment are the ones who
are fairly careful about modeling parasitics in the layout.
2. (Reduction of CMOS Propagation Delay in Long Buses.) Consider again the prior
problem. Answer the following questions about the circuit:
(a) Will it speed up the circuit to break the wire into two lengths and use a buﬀer (consisting
of two cascaded inverters) in between the two lengths? In order to determine the answer,
you must assume minimal wiring distance between the two static inverters making up
the buﬀer. Also, you must recalculate all wiring delays for the ﬁrst wire segment and
the second wire segment. If it pays to break the wire into two lengths, how much shorter
will the new propagation delay be? Do not forget to include the eﬀect of the new buﬀer.
(b) Would it be even better to break the wire into three lengths?
3. (Static CMOS Decoder Design.) Design a logic schematic, a transistor schematic, a
sticks diagram, and a circuit layout (using the rules established in Assignment III) for a
three-input, eight-output decoder. Use only CMOS transmission gates, pass transistors, and
inverters. Important hint: Use a regular gate matrix layout style for this design. Use pchannel MOSFET’s to realize the conditions for decoding each output (pulling it to logic 1)
when it is selected. Use a weak n-channel MOSFET transistor on each output to pull it down
to logic 0 when it is not being decoded. Turn in the following items: a logic schematic (generated by Cadence), logic simulation results for all possible input combinations (generated
by Cadence), a transistor schematic (generated by Cadence), analog simulation results for
all possible input combinations (generated by Spectre), a layout (generated by Caden...
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- Fall '08