Performance Analysis
Crystal Analysis of Jagged Edge
<![CDATA[
component delay (ns)
input latches 16.32
ls_try latches 14.52
xor 13.23
xor_tim 9.25
xor_add 9.61
adder (8-bit) 61.50
and (2-input) 9.05
and_comp 8.87
inverter 5.78
logic (boolean control) 9.35
or (2-input) 8.84
latch-buffer 18.85
fsm 235.22
]]>
Spice Analysis of Critical Subcircuit
The above crystal analysis showed the adder to be the critical path
subcircuit through the cell. Specifically, the longest path through the
adder is from the carry-in input of the low-order adder to the carry-out
output of the high-order adder. Thus, we used a Spice analysis of the most
pathological input combination to the adder -- one in which every carry and
output bit must flip as a result of the input change. The resulting Spice
analysis showed the following curve (the red curve shows the carry-in, while
the blue curve is the carry-out):
From this curve, we see a maximum delay of 35.5 ns for the adder. We thus expect a maximum frequency of roughly 25 MHz.