How are binary values represented in electronic circuits?
- The logic values can be represented as voltage levels below and above a predefined level known as the threshold
- In a positive logic system, voltage levels lower than the threshold represent logic
- In a negative logic system, it's the opposite
- In practice, voltage ranges for logic values are separated by a noise margin for increased reliability
Transistors
We use transistors to implement "switches" in electronic circuits.
NMOS Transistor
- One end (vss) is the source connected to ground. the other ends (vg and vdd) are the gate and drain
- When , the transistor is off, and acts as an open switch
- When , the transistor is on, and acts as a closed switch
PMOS Transistor
This diagram may be wrong.
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tri-state buffer
Tri-State Buffer
- Has one input , one output , and a control input
- If , then , else if , then the output is high-impedance state (aka logic Z, third state)
| e |
x |
f |
| 0 |
0 |
Z |
| 0 |
1 |
Z |
| 1 |
0 |
0 |
| 1 |
1 |
1 |