PMOS and NMOS

Timeline

Timeline

2025-12-26

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This article introduces the basic principles and characteristics of two types of field-effect transistors: PMOS and NMOS. It points out that NMOS uses a positive voltage to control conduction, with current flowing from the drain (D) to the source (S), making it suitable for use as a low-side switch; PMOS uses a negative voltage to control conduction, with current flowing from the source (S) to the drain (D), making it suitable for use as a high-side switch. Additionally, the article illustrates the structural differences between the two through schematic diagrams: PMOS uses an N-type semiconductor as the substrate, with the source and drain doped with P-type impurities to form P+ regions; NMOS uses P-type silicon as the substrate, with the source and drain doped with N-type impurities to form N+ regions.

PMOS and NMOS

• S: Source

• D: Drain

• G: Gate

• NMOS: Usepositive voltageto control conduction, current flows fromdrain (D) → source (S), suitable forlow-side switch。

• PMOS: Usenegative voltageto control conduction, current flows fromsource (S) → drain (D), suitable forhigh-side switch。

NMOS transistor

NMOS transistor

PMOS Structure Schematic

The figure above is a schematic diagram of PMOS. The substrate is an N-type semiconductor (majority carriers are electrons), and the source (Source) and drain (Drain) are doped with P-type impurities (such as boron B), forming P+ regions.

NMOS Structure Schematic

The figure above is a schematic diagram of NMOS. The substrate is P-type silicon (majority carriers are holes), and the source (Source) and drain (Drain) are doped with N-type impurities (such as phosphorus P), forming N+ regions.

References

[1]

PMOSandNMOSworking principle

[2]

NMOS and PMOS the difference（easy to understand）

Reference Bilibili video: