Analog hardware fabric cost driven by composability not computation
Composability rather than computation sets the cost of an analog EML hardware fabric
Emerging TechnologiesHardware Architecture
Summary
The paper explores a special computing operation called eml that combines exponential and logarithm functions, which could replace traditional digital logic circuits in analog hardware. The authors show that individual components using this operation can be very energy efficient. However, building complex systems from these components is much less efficient due to the need for many amplifiers and limitations in the types of functions that can be performed. In other words, while the basic building block is promising, putting many together to form a working machine is costly and less practical.
What this means in practice
- •For analog circuit designers: Design energy-efficient components using eml operators that outperform digital counterparts in single operations.
- •For embedded systems engineers: Evaluate trade-offs of analog fabrics for computation when integrating with digital systems to optimize power and resource use.
Authors
C. Teuscher
Abstract
The operator eml(x, y) = exp(x) - ln(y) with the constant 1 generates the elementary functions, a continuous counterpart to NAND. Whether it yields a useful fabric had not been asked of hardware. We ask in network models, circuit simulation and SkyWater 130 nm layout. Four bipolar junctions evaluate the operator for 13 fJ, beating a width-matched digital datapath by 4-134x. The fabric assembled from them is not cheap: it loses to resource-matched baselines, and over the reals its grammar excludes trigonometry. Amplifiers holding those junctions' operating points take 74.5% of a cell's current, so a cell costs 3000 times what they spend. Extracted non-idealities cost 2.6x when a cell must hold a value and nothing when it need only be repeatable. Sharing them across cells recovers two of the three orders. The premise was that a universal primitive licenses a uniform machine. It survives in the primitive and fails in the machine.