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Resistance to Frequency Converter
Amol Mupid
Andrew Ricketts
Outline Original design
Component parts Roadblock
Modified design Buffer optimization
Design specification Conclusion
400
Chemiresistive Sensors
αACsR1=
Rs
Rs : 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
Vout
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
Transistor sizing
Core area 48.75 X162.6 = 7,926(um^2)
Transistor Width (um) Length (um)
Mb1 11.0 0.6
Mp1,Mp2 5.16 0.6
Mp3,Mp4 5.16 0.6
Mn1,Mn2 3.0 0.6
MpInv 18.0 0.6
MnInv 6.0 0.6
Voltage dependant output periodicity
0
0.5
1
1.5
2
2.5
3
period(NS)
frequency(GHz)
3.3V3.5V4V4.5V5V
Power dissipation ( mW)
0
5
10
15
20
25
30
max power avg power rms power
3.3v3.5V4V4.5V5V
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
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??