Slide 1
A transistor controls a conducting path
A transistor can control current through a circuit. In a field-effect transistor, an electric field changes how easily a semiconductor channel conducts.
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The controlled current receives energy from the surrounding circuit’s power supply. Amplification does not mean the transistor creates energy; it uses an input signal to regulate supplied energy.
Slide 2
Gate voltage changes conduction between source and drain
In an insulated-gate design, the gate sits near the channel between source and drain terminals. Changing gate voltage alters how charge moves through that channel.
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The gate’s insulation can keep steady input current very small, but the gate still has capacitance. Changing its voltage requires moving charge, which matters when switching rapidly.
Slide 3
Real on/off states still have resistance and leakage
Digital circuits use transistors to create strongly conducting and weakly conducting states. Real devices still have resistance when on and some leakage when off.
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These nonideal properties contribute to power dissipation. Treating a transistor as a perfect switch is useful for logic design, but insufficient for calculating temperature and battery use.
Slide 4
Charging the next stage takes time
A transistor must charge or discharge capacitance in the circuit it drives. That process takes time and limits how quickly the next stage receives a valid signal.
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A larger transistor can supply more current but also adds capacitance. Increasing device size therefore creates a tradeoff rather than an unlimited route to faster circuits.
Slide 5
Connected switches can implement logic and memory
Networks of transistors implement logic operations by connecting inputs to output states. Combining these operations supports arithmetic, memory and control.
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The usefulness comes from predictable composition: one circuit’s output must satisfy another’s input requirements. Reliable computing depends on those electrical agreements as well as the abstract logic.
Sources
- Computation Structures: CMOS Technology
MIT OpenCourseWare