Measuring the Power Efficiency of Subthreshold FPGAs for Implementing Portable Biomedial Applications

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Shahin Lotfabadi

Ryerson University

February, 2013

Abstract: Power is a significant design constraint for implementing efficient

portable biomedical applications. Operating transistors in the

subthreshold region can significantly reduce power consumption; it,

however, also reduces performance. While this performance reduction

can be significant in many applications, the low frequency nature of

biosignals makes subthreshold region a good candidate for implementing

biomedical applications. In this work, we investigate the feasibility

of designing a specialized FPGA for implementing portable biomedical

applications. In particular, we perform a case study on the

performance of the Burg algorithm, a widely used biomedical signal

processing algorithm, to deter- mine the minimum operating frequency

required for the processing of biosignals in real time. Based on the

requirement, the trade-off between power consumption and performance

is measured for FPGA routing resources operating in the subthreshold

region. It is found that operating FPGA routing resources in the

subthreshold region can significantly reduce power consumption while

allowing the Burg algorithm to operate in real time. For the 32 nm

Predictive Technology Model studied in this work, we observed a power

reduction of 197.7 times (which corresponds to a power-delay-product

reduction of 10.78 times) for operating FPGA routing tracks in the

subthreshold region under a supply voltage of 0.4 V. Under this

voltage, the FPGA can operate at 2.0 MHz while allowing signals to

propagate unregistered through 45 routing tracks. Furthermore, the 2.0

MHz operating frequency meets the realtime requirement of the Burg

algorithm for processing 20,000 samples per second.