MT-083 TUTORIAL

Comparators
COMPARATOR BASICS
A comparator is similar to an op amp. It has two inputs, inverting and non-inverting and an output (see Figure 1). But it is specifically designed to compare the voltages between its two inputs. Therefore it operates in a non-linear fashion. The comparator operates open-loop, providing a two-state logic output voltage. These two states represent the sign of the net difference between the two inputs (including the effects of the comparator input offset voltage). Therefore, the comparator's output will be a logic "1" if the input signal on the non-inverting input exceeds the signal on the inverting input (plus the offset voltage, Vos) and a logic "0" for the opposite case. A comparator is normally used in applications where some varying signal level is compared to a fixed level (usually a voltage reference). Since it is, in effect, a 1-bit analog-to-digital converter (ADC), the comparator is a basic element in all ADCs. (See MT-011 for details of comparator operation as an ADC building block).