5.6 Transistors in digital circuits

Transistors!digital circuits and

Transistors play a few important roles in digital circuits, acting as

• Active elements of the output stage
• Logical elements (especially inside logic gates)
• Switching elements for supplying power (section 4.3.11) and converting logic levels

In this section, we will consider more closely the most commonly used types of transistor in digital circuits: the bipolar junction transistor (BJT)Transistors!bipolar junction transistors (BJTs) and the metal-oxide-semiconductor field-effect transistor (MOSFET)Transistors!metal-oxide-semiconductor field-effect transistors (MOSFETs). The BJT-based logic families, transistor-transistor logic (TTL),Transistor-transistor (TTL) logic family have been largely supplanted by MOSFET-based logic familiesComplementary metal-oxide-semiconductor (CMOS) logic families (complementary metal-oxide-semiconductor, or CMOS) under different names like the popular HC(T)Complementary metal-oxide-semiconductor (CMOS) logic families!HC(T) and LVC/LVXComplementary metal-oxide-semiconductor (CMOS) logic families!LVC/LVX families. However, the TTL terminology remains relevant, and some CMOS …