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Explain CMOS inverter characteristics mentioning all regions of operations
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  • CMOS inverter configuration is called Complementary MOS (CMOS). The circuit topology is complementary push-pull.
  • That is for high input, the nMOS transistor drives (pulls down) the output node while the pMOS transistor acts as the load, and for low input the pMOS transistor drives (pulls up) the output node while the nMOS transistor acts as the load.

  • From the diagram,
  • VGS,n = Vin and VDS,n = Vout
  • VGS,p = Vin – VDD and VDS,p = Vout – VDD
  • The current equations are given as-

  • The voltage conditions are given as follows. For this examine the operating modes of nMOS and pMOS as function of input and output voltage.

A typical CMOS inverter voltage transfer characteristic with different operating regions is as shown below.

Region Vin Vout nMOS pMOS
A Vin < VT0,n VOH Cutoff Linear
B VIL High ≈ VOH Saturation Linear
C Vth Vth Saturation Saturation
D VIH Low ≈ VOL Linear Saturation
E greater than (VDD + VT0,p) VOL Linear Cutoff
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