Example: core area 64 mm²; average net length 0.1 mm; 400K gates/mm², a=0.25.
Net capacitance = 0.1 mm × 1 fF/mm × 400K × 64 mm² = 2.5 nF.
Supply Voltage | Clock Freq | Static Power | Dynamic Power | Total Power |
(V) | (MHz) | (mW) | (mW) | (mW) |
0.8 | 100 | 40 | 24 | 64 |
1.35 | 100 | 67 | 68 | 135 |
1.35 | 200 | 67 | 136 | 204 |
1.8 | 100 | 90 | 121 | 211 |
1.8 | 200 | 90 | 243 | 333 |
1.8 | 400 | 90 | 486 | 576 |
Workstation microprocessors dissipate tens of Watts: hence cooling fans.
The table shows example power consumption for a circuit when clocked at different frequencies and voltages. The important thing to ensure is that the supply voltage must be sufficient for the clock frequency in use: too low a voltage means that signals do not arrive at D-type inputs in time to meet set up times.
Power consumption versus frequency is worse than linear: it goes with a power law.
In the past, chips were often core-bound or pad-bound. Pad-bound meant that the chip had too many I/O signals for its core logic area: the number of I/O's puts a lower bound on the perimeter of the chip.
Today's VLSI technology allows I/O pads in the middle of the chip and designs are commonly power-bound.
8: (C) 2008-16, DJ Greaves, University of Cambridge, Computer Laboratory. |