BJT and MOSFET are both transistor families, but this route focuses on MOSFETs because modern digital CMOS logic is MOSFET-based.
BJT is still useful as a contrast.
BJT First Model
BJT stands for bipolar junction transistor.
Its three terminals are:
- base
- collector
- emitter
In a simplified view, a small base current helps control a larger collector-emitter current.
That makes BJT commonly introduced as current-controlled.
MOSFET First Model
MOSFET stands for metal-oxide-semiconductor field-effect transistor.
Its main terminals are:
- gate
- source
- drain
- body
In a simplified view, gate voltage controls whether a channel exists between source and drain.
That makes MOSFET commonly introduced as voltage-controlled.
Why the Distinction Matters
For a developer trying to understand digital hardware, the MOSFET path is the direct one:
- MOSFET gate voltage controls a channel
- NMOS and PMOS behave as complementary switches
- CMOS gates use pull-up and pull-down networks
- output voltages become logical states
BJT logic exists historically and in some specialized contexts, but it is not the main physical path to modern CMOS processors and memory.
Boundary
“Current-controlled” and “voltage-controlled” are first mental models, not full device physics.
The durable distinction is:
BJT helps show that transistor families differ. MOSFET is the central device for the CMOS digital logic path this route follows.