- Laptops, PDA, cell-phones, etc —obvious!
- For microprocessors in personal computers, every watt above 40W adds $1 to manufacturing cost.
- Approx 25% of operating expense of server farm goes to energy bills.
- Sandia Labs had to build a special sub-station when they took delivery of Teraflops massively parallel supercomputer (over 9000 Pentium Pros)
- High-speed microprocessors today can run so hot that they will damage themselves—Athlon reliability problems, Pentium 4 processor thermal throttling
- Future power viruses: cell phone viruses cause cell phone to run in full power mode
- Power minimization is usually about heat removal.
- Energy minimization is usually about battery life or energy costs.
Power = Switching Power+Shortcircuit Power+Leakage Power
Dynamic power = Switching Power+Shortcircuit Power
Static Power = Leakage Power
- Dynamic Power dependent upon clock speed
- Switching Power useful —charges/discharges transistors
- Short Circuit Power not useful —both N and P transistors are on
- Static Power independent of clock speed
- Leakage Power not useful —leaks around transistor
- Roughly 20% of signals switch during a clock cycle.
- Need to take glitches into account when calculating activity factor. Glitches increase the activity factor.
- Equations for dynamic power contain clock speed and activity factor.
- Analog
- Parameters to work with:
- capacitance for example, Silicon on Insulator (SOI)
- resistance for example, copper wires
- voltage low-voltage circuits
- Techniques:
- dual-VDD Two different supply voltages: high voltage for performance-critical portions of design, low voltage for remainder of circuit. Alternatively, can vary voltage over time: high voltage when running performance-critical software and low voltage when running software that is less sensitive to performance.
- dual-Vt Two different threshold voltages: transistors with low threshold voltage for performance-critical portions of design (can switch more quickly, but more leakage power), transistors with high threshold voltage for remainder of circuit (switches more slowly, but reduces leakage power).
- exotic circuits Special flops, latches, and combinational circuitry that run at a high frequency while minimizing power
- adiabatic circuits Special circuitry that consumes power on 0 - 1 transitions, but not 1 - 0 transitions. These sacrifice performance for reduced power.
- clock trees Up to 30% of total power can be consumed in clock generation and clock tree
- Digital
- Parameters to work with:
- capacitance (number of gates)
- activity factor
- clock frequency
- Techniques:
- multiple clocks Put a high speed clock in performance-critical parts of design and a low speed clock for remainder of circuit
- clock gating Turn off clock to portions of a chip when it's not being used
- data encoding Gray coding vs one-hot vs fully encoded vs ...
- glitch reduction Adjust circuit delays or add redundant circuitry to reduce or eliminate glitches.
- asynchronous circuits Get rid of clocks altogether....
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