5.3 Combinational Gates

• A combinational gate is an abstract representation of a circuit that satisfies two properties:

1. Its outputs are a function of its inputs alone.

2. It satisfies the static discipline.

5.2 Boolean Logic

5.1 Voltage Levels and Static Discipline

• To send a logical 0, the sender must produce an output voltage value that is less than VOL. Correspondingly, the receiver must interpret input voltages below VIL as a logical 0.
• Similarly, to send a logical 1, the sender must produce an output voltage value that is greater than VOH. Further, the receiver must interpret voltages above VIH as a logical 1.
• Noise Margin: The absolute value of the difference between the prescribed output voltage for a given logical value and the corresponding forbidden region voltage threshold for the receiver is called the noise margin for that logical value.
• NM0 = VIL − VOL
• NM1 = VOH − VIH
• The static discipline is a specification for digital devices. The static discipline requires devices to interpret correctly voltages that fall within the input thresholds (VIL and VIH). As long as valid inputs are provided to the devices, the discipline also requires the devices to produce valid output voltages that satisfy the output thresholds (VOL and VOH).