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Applications of MOS Transistors in Digital Integrated Circuits (1). Section 15.1. ADD an Instance of NMOS. NMOS transistor. A Simple Switching Circuit. variable DC voltage. Threhold Voltage. Threshold voltage of T0. Design variable. Library Setup. A Primitive Inverter Circuit. Large VDS
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Applications of MOS Transistors in Digital Integrated Circuits (1) Section 15.1
ADD an Instance of NMOS NMOS transistor
A Simple Switching Circuit variable DC voltage
Threhold Voltage Threshold voltage of T0
Design variable Library Setup
A Primitive Inverter Circuit Large VDS SATURATION Small VDS :Triode
Determine Region of Operation OFF SATURATION TRIODE
Determine Kn and Vth Need to select drain terminal in order to get current
Derivation • ID=0.5 unCox(W/L)(VGS-VTH)2 • Find VTH • SQRT(2ID/(unCoxW/L))=VGS-VTH • The VGS that yields 0 LHS is the threshold voltage • SQRT(ID)=SLOPE(VGS-VTH) • SLOPE=SQRT(0.5 unCox(W/L)) • This example: W/L=2um/1um=2 • SLOPE=SQRT(unCox)
To Calculate Kn,find SQRT(ID) The x interscept gives Vth Vth (this method)=150 mV Vth(Cadence)=164 mV
Find Kn=W/LunCox SQRT(ID) dSQRT(ID)/dVGS This curve implies that unCox depends on VGS!
Noise Margin Noise Margin: the maximum amount of noise at the input that can be tolerated before the output is affected significantly. attenuating attenuating amplifying dVout/dVGS NML NMH dVout/dVGS=small signal gain
Inverter In the Presence of Noise Relatively clean output 400 mV peak to peak noise Time Scaling Factor
Inverter In the Presence of More Noise 1 V peak to peak of noise
Noisy Input Relatively Clean Output
Adding a Capacitor to the Output RC time constant
Ring Oscillator 1nF oscillation