Resistance to Frequency Converter Amol Mupid Andrew Ricketts

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

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

Original design D CLK Q Qbar Rs V out R4 R1 R2 R3 C R5

Original design components Diode Spice simulation …but layout issues insurmountable

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

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

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

Single delay cell

Schematic of rectified VCO

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

Layout of complete design

Period versus Vin change

Transistor sizing Core area X162.6 = 7,926(um^2) TransistorWidth (um)Length (um) Mb Mp1,Mp Mp3,Mp Mn1,Mn MpInv MnInv6.00.6

Voltage dependant output periodicity

Power dissipation ( mW)

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

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

Layout with pads

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

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

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

Layout linearity (almost)

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.

Thank You Questions??