1. Resistance to Frequency Converter Amol Mupid Andrew Ricketts

2. Outline Original design Component parts Roadblock Modified design Buffer optimization Design specification Conclusion

3. 400  Chemiresistive Sensors RsRs R s : resistance of nanowire C : concentration of the gas A,α : constants that change with type of gas and temperature 350

4. Original design D CLK Q Qbar + - - + Rs V out R4 R1 R2 R3 C R5

5. Original design components Diode Spice simulation …but layout issues insurmountable

6. Original design components Zener Diode More simulations possible …but layout even more challenging

7. Modified design Key point is that what is desired is a way to control oscillations based on input voltage Voltage Controlled Oscillator (VCO) Buffer added to output to ensure rapid rise and fall of output square wave

8. VCO design LC tank oscillators Good phase noise with low power but tuning range is relatively low Output frequency may fall out of range due to process variations Spiral inductors occupy a lot of area, high cost and low yield issues. Ring oscillators Easy integration, high yield, low cost. Less chip area In-phase outputs

9. Single delay cell

10. Schematic of rectified VCO

11. Buffer optimization Initial single stage buffer Moved output close to binary Had difficulty clamping small swings about origin Double stage buffer Delay increase inconsequential Greatly improved clamping range

12. Layout of complete design

13. Period versus Vin change

14. Transistor sizing Core area 48.75 X162.6 = 7,926(um^2) TransistorWidth (um)Length (um) Mb111.00.6 Mp1,Mp25.160.6 Mp3,Mp45.160.6 Mn1,Mn23.00.6 MpInv18.00.6 MnInv6.00.6

15. Voltage dependant output periodicity

16. Power dissipation ( mW)

17. Resistance We want the Vcontrol be to be in between operable range => Rs*VDD/ (Rs+ R) has to be in between 3.3V and 5V Rs R Vcontrol

18. Resistance For max swing when Rs only increases R = (1.7 * Rs)/3.3 For max swing when Rs increases and decreases R = (1.1 * Rs)/3.9 For max swing when Rs only decreases R = (0.5 Rs)/4.5

19. Layout with pads

20. Layout simulation R = 11 KΩ Rs = 25 KΩ Per = 1.9 ns

21. Layout simulation R = 11 KΩ Rs = 40 KΩ Per = 2.35 ns

22. Layout simulation R = 11 KΩ Rs = 99 KΩ Per = 2.85 ns

23. Layout linearity (almost)

24. Conclusion The change in the sensor resistance can be detected in “ns” range and converted to square wave pulses This completely eliminates the need of ADC, huge potential resource savings. Successfully overcame practical design issues and produced desired results.

25. Thank You Questions??