62 lines
2.4 KiB
Markdown
62 lines
2.4 KiB
Markdown
---
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tags:
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- logic-gates
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- binary
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- electronics
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---
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# Transistors
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A digital circuit requires that electrical phenomena be treated as discrete
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rather than continuous values.
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Although a given voltage at a point in the circuit can vary widely, in order to
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represent the binary states of 'on' and 'off' we need it to remain fixed within
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certain narrow parameters. This is achieved with transistors.
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Transistors are an electrical component that is capable of controlling the flow
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of current in the manner of a switch where the 'off' and 'on' states are
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represented by [voltage](Voltage.md) values within set parameters.
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There are different types of transistors but the simplest for the purposes of
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explanation are **bipolar junction transistors**.
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The pins:
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- C: collector
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- B: base
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- E: emitter
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Applying a small amount of current at the base allows a larger current to flow
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from the collector to the emitter. Applying current to the base is like turning
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the switch on. Removing this current is like turning the switch off.
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This happens because of how current and voltage interact in a transistor. The
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small base current controls the larger collector-emitter current through a
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process called current amplification.
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When a small voltage is applied to the base, it allows a small current to flow
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from the base to the emitter. This base current triggers a much larger current
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to flow from the collector to the emitter. Think of it like a water valve: a
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small turn of the handle (base current) can control a large flow of water
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(collector-emitter current). The transistor amplifies this effect, allowing a
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tiny input signal to control a much larger output.
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## Transistors and logic gates
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We can combine transistors to create logic gates. A logic gate is a combination
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of transistors arranged such that the logical function is embodied by the
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characteristic input and output voltages to the transistor.
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For example to create an [AND](Logic_gates.md#and-gate) gate we would have two
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voltage inputs going into two transistors that are connected in sequence. The
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two transistors create a continuous line going from the collector of one to the
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emitter of the other. If either voltage input is low then the voltage of the
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combined line is low (equivalent to the circuit being broken) and there is no
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current flowing.
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// Add example of OR gate created with transistors
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