Switching Energy Estimates
This page contains background information regarding the switching energy estimates so important to designing energy-efficient data paths.
Register Read/Write Energy Estimates by Process Node
Note: Values are approximate and may vary by foundry and implementation
| Register | 28/22nm (fJ) | 16/14/12nm (fJ) | 7/6/5nm (fJ) | 3nm (fJ) | 2nm (fJ) |
|---|---|---|---|---|---|
| Read bit | 2.5 - 3.5 | 1.8 - 2.3 | 0.9 - 1.2 | 0.6 - 0.8 | 0.4 - 0.6 |
| Write bit | 3.0 - 4.0 | 2.0 - 2.8 | 1.1 - 1.5 | 0.7 - 1.0 | 0.5 - 0.8 |
Notes:
- Values assume typical operating conditions (TT corner, nominal voltage, 25°C)
- Energy includes both dynamic and short-circuit power
- Leakage power not included
- Values are for basic register operations without additional clock tree or routing overhead
- Advanced nodes (3nm, 2nm) are based on early estimates and projections
Register file energy estimates
All values in femtojoules per bit (fJ/bit)
| Operation | Size | 28/22nm | 16/14/12nm | 7/6/5nm | 3nm | 2nm |
|---|---|---|---|---|---|---|
| Read | ||||||
| 32-entry | 8.5 - 10.5 | 6.00 - 7.50 | 3.20 - 4.00 | 2.25 - 2.80 | 1.57 - 1.95 | |
| 64-entry | 12.0 - 14.0 | 8.50 - 10.00 | 4.50 - 5.50 | 3.15 - 3.85 | 2.21 - 2.70 | |
| 128-entry | 16.0 - 18.0 | 11.00 - 13.00 | 6.00 - 7.00 | 4.20 - 4.90 | 2.95 - 3.45 | |
| Write | ||||||
| 32-entry | 10.0 - 12.0 | 7.00 - 8.50 | 3.80 - 4.60 | 2.65 - 3.25 | 1.85 - 2.28 | |
| 64-entry | 14.0 - 16.0 | 10.00 - 11.50 | 5.20 - 6.20 | 3.65 - 4.35 | 2.55 - 3.05 | |
| 128-entry | 18.0 - 20.0 | 13.00 - 15.0 | 7.00 - 8.00 | 4.90 - 5.60 | 3.45 - 3.95 |
Notes:
- All values in femtojoules per bit (fJ/bit)
- Assumes typical operating conditions (TT corner, nominal voltage, 25°C)
- Includes decoder, wordline, and bitline energy
- Includes local clock distribution
- Includes both dynamic and short-circuit power
- Values represent single read port, single write port configuration
Integer Arithmetic and Logic Unit Switching Energy Estimates
| Unit Type | Bit Size | 28/22nm (pJ) | 16/14/12nm (pJ) | 7/6/5nm (pJ) | 3nm (pJ) | 2nm (pJ) |
|---|---|---|---|---|---|---|
| CPU ALU | ||||||
| 8-bit | 0.45 - 0.65 | 0.30 - 0.43 | 0.20 - 0.29 | 0.13 - 0.19 | 0.09 - 0.13 | |
| 16-bit | 0.90 - 1.30 | 0.60 - 0.86 | 0.40 - 0.58 | 0.26 - 0.38 | 0.18 - 0.26 | |
| 24-bit | 1.35 - 1.95 | 0.90 - 1.30 | 0.60 - 0.87 | 0.39 - 0.57 | 0.27 - 0.40 | |
| 32-bit | 1.80 - 2.60 | 1.20 - 1.73 | 0.80 - 1.16 | 0.52 - 0.76 | 0.36 - 0.53 | |
| 40-bit | 2.25 - 3.25 | 1.50 - 2.16 | 1.00 - 1.45 | 0.65 - 0.95 | 0.45 - 0.66 | |
| 48-bit | 2.70 - 3.90 | 1.80 - 2.60 | 1.20 - 1.74 | 0.78 - 1.14 | 0.54 - 0.79 | |
| 56-bit | 3.15 - 4.55 | 2.10 - 3.03 | 1.40 - 2.03 | 0.91 - 1.33 | 0.63 - 0.92 | |
| 64-bit | 3.60 - 5.20 | 2.40 - 3.47 | 1.60 - 2.32 | 1.04 - 1.52 | 0.72 - 1.05 | |
| GPU ALU | ||||||
| 8-bit | 0.60 - 0.85 | 0.40 - 0.57 | 0.27 - 0.38 | 0.17 - 0.25 | 0.12 - 0.17 | |
| 16-bit | 1.20 - 1.70 | 0.80 - 1.14 | 0.53 - 0.76 | 0.35 - 0.50 | 0.24 - 0.35 | |
| 24-bit | 1.80 - 2.55 | 1.20 - 1.71 | 0.80 - 1.14 | 0.52 - 0.75 | 0.36 - 0.52 | |
| 32-bit | 2.40 - 3.40 | 1.60 - 2.28 | 1.07 - 1.52 | 0.69 - 1.00 | 0.48 - 0.70 | |
| 40-bit | 3.00 - 4.25 | 2.00 - 2.85 | 1.33 - 1.90 | 0.86 - 1.25 | 0.60 - 0.87 | |
| 48-bit | 3.60 - 5.10 | 2.40 - 3.42 | 1.60 - 2.28 | 1.04 - 1.50 | 0.72 - 1.04 | |
| 56-bit | 4.20 - 5.95 | 2.80 - 3.99 | 1.87 - 2.66 | 1.21 - 1.75 | 0.84 - 1.21 | |
| 64-bit | 4.80 - 6.80 | 3.20 - 4.56 | 2.13 - 3.04 | 1.38 - 2.00 | 0.96 - 1.38 | |
| DSP ALU | ||||||
| 8-bit | 0.55 - 0.75 | 0.37 - 0.53 | 0.25 - 0.35 | 0.16 - 0.23 | 0.11 - 0.16 | |
| 16-bit | 1.10 - 1.50 | 0.73 - 1.00 | 0.49 - 0.70 | 0.32 - 0.46 | 0.22 - 0.32 | |
| 24-bit | 1.65 - 2.25 | 1.10 - 1.50 | 0.73 - 1.05 | 0.48 - 0.69 | 0.33 - 0.48 | |
| 32-bit | 2.20 - 3.00 | 1.47 - 2.00 | 0.98 - 1.40 | 0.63 - 0.92 | 0.44 - 0.64 | |
| 40-bit | 2.75 - 3.75 | 1.83 - 2.50 | 1.22 - 1.75 | 0.79 - 1.15 | 0.55 - 0.80 | |
| 48-bit | 3.30 - 4.50 | 2.20 - 3.00 | 1.47 - 2.10 | 0.95 - 1.38 | 0.66 - 0.96 | |
| 56-bit | 3.85 - 5.25 | 2.57 - 3.50 | 1.71 - 2.45 | 1.11 - 1.61 | 0.77 - 1.12 | |
| 64-bit | 4.40 - 6.00 | 2.93 - 4.00 | 1.96 - 2.80 | 1.27 - 1.84 | 0.88 - 1.28 |
Notes:
- Values are approximate switching energy in picojoules (pJ)
- Represents typical dynamic switching energy per operation
- Accounts for:
- Arithmetic data path logic operations
- Typical instruction mix for each design point
Floating-Point Unit Switching Energy Estimates
| Unit Type | Bit Size | 28/22nm (pJ) | 16/14/12nm (pJ) | 7/6/5nm (pJ) | 3nm (pJ) | 2nm (pJ) |
|---|---|---|---|---|---|---|
| CPU FPU | ||||||
| 8-bit | 1.20 - 1.70 | 0.80 - 1.14 | 0.53 - 0.76 | 0.35 - 0.50 | 0.24 - 0.35 | |
| 16-bit | 1.80 - 2.60 | 1.20 - 1.73 | 0.80 - 1.16 | 0.52 - 0.76 | 0.36 - 0.53 | |
| 32-bit | 3.60 - 5.20 | 2.40 - 3.47 | 1.60 - 2.32 | 1.04 - 1.52 | 0.72 - 1.05 | |
| 64-bit | 7.20 - 10.40 | 4.80 - 6.93 | 3.20 - 4.64 | 2.08 - 3.04 | 1.44 - 2.10 | |
| GPU FPU | ||||||
| 8-bit | 1.60 - 2.30 | 1.07 - 1.53 | 0.71 - 1.02 | 0.46 - 0.66 | 0.32 - 0.46 | |
| 16-bit | 2.40 - 3.40 | 1.60 - 2.28 | 1.07 - 1.52 | 0.69 - 1.00 | 0.48 - 0.70 | |
| 32-bit | 4.80 - 6.80 | 3.20 - 4.56 | 2.13 - 3.04 | 1.38 - 2.00 | 0.96 - 1.38 | |
| 64-bit | 9.60 - 13.60 | 6.40 - 9.13 | 4.27 - 6.08 | 2.76 - 4.00 | 1.92 - 2.76 | |
| DSP FPU | ||||||
| 8-bit | 1.40 - 2.00 | 0.93 - 1.33 | 0.62 - 0.89 | 0.40 - 0.58 | 0.28 - 0.40 | |
| 16-bit | 2.20 - 3.00 | 1.47 - 2.00 | 0.98 - 1.40 | 0.63 - 0.92 | 0.44 - 0.64 | |
| 32-bit | 4.40 - 6.00 | 2.93 - 4.00 | 1.96 - 2.80 | 1.27 - 1.84 | 0.88 - 1.28 | |
| 64-bit | 8.80 - 12.00 | 5.87 - 8.00 | 3.91 - 5.60 | 2.54 - 3.68 | 1.76 - 2.56 |
Notes:
- Values are approximate switching energy in picojoules (pJ)
- 8-bit FPU estimates based on IEEE fp8 standard
- Represents typical dynamic switching energy per operation
- Accounts for:
- Arithmetic logic operations
- Floating-point operations (for FPU)
- Typical instruction mix for each design point