VOH, VOL, VIH, and VIL — Simple Explanation
These terms are used in digital electronics to describe what voltage a logic gate considers a 0 (LOW) or a 1 (HIGH).
Think of two people talking:
- The first gate is the sender.
- The second gate is the receiver.
The sender outputs a voltage and the receiver must correctly understand whether that voltage means HIGH (1) or LOW (0).
The Four Important Voltages
| Symbol | Meaning |
|---|---|
| VOH | Minimum guaranteed output voltage when output is HIGH |
| VOL | Maximum guaranteed output voltage when output is LOW |
| VIH | Minimum input voltage that will be accepted as HIGH |
| VIL | Maximum input voltage that will be accepted as LOW |
Easy Example (5V Logic)
Suppose:
- VOH = 4.4 V
- VOL = 0.4 V
- VIH = 2.0 V
- VIL = 0.8 V
If a gate outputs 4.4 V, the next gate sees it as HIGH because 4.4 V is greater than VIH (2.0 V).
If a gate outputs 0.4 V, the next gate sees it as LOW because 0.4 V is less than VIL (0.8 V).
Visual Diagram
How to Remember
O means Output.
- VOH → Output HIGH
- VOL → Output LOW
I means Input.
- VIH → Input recognized as HIGH
- VIL → Input recognized as LOW