1. Robust Low Power VLSI R obust L ow P ower VLSI CORDIC Implementation for a battery-less Body sensor Node L. Patricia Gonzalez G. Dept. of Electrical Engineering, University of Virginia January 20, 2015

2. Robust Low Power VLSI Body Sensor Nodes: A Power Challenge 2 http://www.fitbit.com/home 0 1 7 http://www.samsung.c om/us/mobile/wearabl e-tech Battery Life (days) http://time.com/3318655/apple-watch-2/ …

3. Robust Low Power VLSI Outline  Our BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 3

4. Robust Low Power VLSI Outline  The BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 4

5. Robust Low Power VLSI The Ultra Low Power Challenge 5 Sensor Analog Front End Digital Logic TX RX ADC Power Management Microcontroller Control / Processing / Interfaces Zhang, et. al. UVA 2014[1] 20 μW 50 μW

6. Robust Low Power VLSI 1. Optimum Energy : Subthreshold 6 VDD [V] Energy per cycle [J] Eleakage Subthreshold Region

7. Robust Low Power VLSI 2. Saving Energy : Hardware Accelerators 7 MCU 100 - 3000 clock cycles CORDIC Applications QRS Detection Gait Speed Estimation Blood Pressure Accelerator 13-15 clock cycles Coordinate Rotation Digital Computer

8. Robust Low Power VLSI Outline  The BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 8

9. Robust Low Power VLSI 9 x y

10. Robust Low Power VLSI CORDIC: Shifter and Adders 10 Multiplexer >> Xreg +/- Multiplexer >> Yreg +/- Multiplexer Zreg +/-

11. Robust Low Power VLSI Our CORDIC implementation  Re-use the data path to calculate 11 functions.  Increment the convergence range. 11 Multiplexer >> Xreg +/- Multiplexer >> Yreg +/- Multiplexer Zreg +/-

12. Robust Low Power VLSI Outline  The BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 12

13. Robust Low Power VLSI Data Path Re-use 13 y y x Walther, 1971. A Unified algorithm for elementary functions

14. Robust Low Power VLSI Outline  The BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 14

15. Robust Low Power VLSI Increase the range of convergence  Extra iterations.  Adjust the binary point 15 OperationConventional CORDIC Proposed Enhancements 1,2,3,…,n-3,-2,-1,1,2,3,…,n Xiaobo Hu, 1991

16. Robust Low Power VLSI Accuracy vs. Range Tradeoff 16

17. Robust Low Power VLSI Outline  The BSN Challenges  CORDIC  CORDIC Modifications  Data Path Re-use  Increment the Range of Convergence  Results 17

18. Robust Low Power VLSI 18 Multiplexer >> Xreg +/- Multiplexer >> Yreg +/- Multiplexer Zreg +/- New Hardware Conventional Data path ROM for Multiplexer >> Multiplexer i i i i Function Decoder From BSN

19. Robust Low Power VLSI Body Sensor Node 19 Klinefelter, A et. al. 2015 [2]

20. Robust Low Power VLSI Minimum Energy Point - Results 20 Frequency : 8KHz – 7.18 MHz Energy per cycle @ 0.5V – 348KHz : 1.1pJ

21. Robust Low Power VLSI Comparison Table 21 CORDIC [3] This Work Error Superior limit for the Convergence range 20 Cosine

22. Robust Low Power VLSI E per Cycle (Epc) VDD Subthreshold 22 Applications QRS Detection Gait Speed Estimation Blood Pressure Accelerators MCUAccelerator 3000 clock cycles 12-15 clock cycles Sensor Analog Front End Digital Logic TX RX ADC BSN Zhang, et. al. UVA 2014[1] Low Power Challenge!

23. Robust Low Power VLSI R obust L ow P ower VLSI Thanks

24. Robust Low Power VLSI Unified Algorithm for elementary functions 24 Walther, 1971. A Unified algorithm for elementary functions -

25. Robust Low Power VLSI ECG Algorithm Example 25 Low Pass Filter Arc Length Transform Adaptive Threshold & Local Search W. Zong, 2003, A robust open source algorithm to detect onset duration of QRS complexes.

26. Robust Low Power VLSI Table for CORDIC Functions 26 J. Kwong, 2010, Low Voltage Embedded biomedical processor. Thesis