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What is the common mode input voltage range of operational amplifier?

Latest Updated:12/01/2011

Question:

What is the common mode input voltage range of an operational amplifier?

Answer:

This is the range of input voltage within which an operational amplifier or comparator will operate correctly. If the common mode input voltage range is exceeded, the output will be saturated to either V+ or V-, and normal operation will no longer be possible.

An example using the uPC4558 is shown below.

Concept of common mode input voltage range
VBE (about 0.7 V) is required for the transistors to operate.



V+-VICM(+)=VF1+VCE(sat) ≤1V (TA=25°C)
V--VICM(-)=VF4+VF3+VCE(sat)-VF2 ≤1V (TA=25°C)

(1) When common mode input voltage is exceeded



The shaded sections show the area in which the common mode input voltage range has been exceeded. In the uPC4558, this has caused the output to be saturated to V+.

(2) When power supply voltage is changed
When V ±= ±15V, the common mode input voltage range is shown in the data sheet to be TYP ±14 V. However, because the common mode input voltage range is actually in the range of V-+1V to V+-1V, if the power supply voltage is lowered, the common mode input voltage range also becomes narrower.

Suitable Products
Comparators