Comparator

A comparator is kind of like a “greater than or less than” block. It lets us compare two analog signals and give a digital output.

Definition

$$V_{out}=\{\begin{array}{l}{V}_{DD},V_{+}>V_{-}\\ V_{SS},V_{+}<V_{-}\end{array}$$

Example

A digital system with a light sensor for differentiating between night and day.

• Boolean 0 = 0 Volts, Boolean 1= 5 Volts
• Light sensor output voltage exceeds 2V during the day.

A comparator “slams” any input voltage below the $V_{ref}$ (which is 2V in this case) to zero, and anything above to $V_{out}$ (5V in this case).

• If $V_{ref}$ is connected to the negative terminal, any input voltage below it is $V_{SS}$
  • “Greater than” operation
• If $V_{ref}$ is connected to the positive terminal, any input voltage above it is $V_{SS}$
  • “Less than” operation