CMOS Logic Gates

• CMOS (complementary metal-oxide-semiconductor) technology is used predominantly to create digital circuitry.
• The fundamental building blocks of CMOS circuits are P-type and N-type MOSFET transistors.
• A P-type MOSFET can be modeled as a switch that is closed when the input voltage is low (0 V) and open when the input voltage is high (5 V).
• A N-type MOSFET can be modeled as a switch that is closed when the input voltage is high (5 V) and open when the input voltage is low (0 V).
• The basic idea for CMOS technology is to combine P-type and N-type MOSFETs such that there is never a conducting path from the supply voltage (5 V) to ground.
• As a consequence, CMOS circuits consume very little energy.

  

Figure 3.1: P-type and N-type MOSFETS.