Analog Comparator vs. Digital Comparator: Key Differences

This page compares analog comparators to digital comparators, outlining the key differences between the two.

Analog Comparator

Definition: An analog comparator is a circuit that compares two analog voltage inputs and generates an output based on which input is greater or lesser than the other. As shown in Figure 1, it’s essentially an amplifier without feedback, typically resulting in higher gain.

The analog comparator compares two input voltages, Vin0 (at the positive terminal) and Vin1 (at the negative terminal), and produces an output (Vout) based on their relationship.

• When Vin0 > Vin1: Vout is equal to +V supply.
• When Vin0 < Vin1: Vout is equal to -V supply.

In microcontroller-based designs, Ground (GND) is often considered the -V supply, while Vcc (supply voltage) is considered the +V supply. This is because a negative supply is often not readily available in such systems.

Digital Comparator

Definition: A digital comparator is a combinational circuit that compares digital binary inputs and produces different outputs indicating the relationship between these inputs. It’s also known as a magnitude comparator.

Digital comparators come in various types depending on the number of inputs:

• 1-bit comparator
• 2-bit comparator
• 4-bit comparator

1-Bit Comparator

A 1-bit comparator has two inputs, A and B. Its output typically consists of three binary variables indicating the conditions A > B, A = B, and A < B.

2-Bit Comparator

A 2-bit comparator has four inputs (A1, A0) and (B1, B0) and three outputs (E, G, and L).

• E: Equals 1 when the two input numbers are equal.
• G: Equals 1 when A > B.
• L: Equals 1 when A < B.

Based on Karnaugh Maps (K-Maps) and truth tables, we can derive the following equations for a 2-bit comparator:

• E = A’1A’0B’1B’0 + A’1A0B’1B0 + A1A0B1B0 + A1A’0B1B’0 or E = (( A0 ⊕ B0) + ( A1 ⊕ B1))’
• G = A1B’1 + A0B’1B’0 + A1A0B’0
• L = A’1B1 + A’1A’0B0 + A’0B1B0