Data Sheet AD8655/AD8656
Rev. E | Page 15 of 20
THEORY OF OPERATION
The AD8655/AD8656 amplifiers are voltage feedback, rail-to-rail
input and output precision CMOS amplifiers, which operate
from 2.7 V to 5.0 V of power supply voltage. These amplifiers
use the Analog Devices DigiTrim technology to achieve a higher
degree of precision than is available from most CMOS amplifiers.
DigiTrim technology, used in a number of Analog Devices
amplifiers, is a method of trimming the offset voltage of the
amplifier after it is packaged. The advantage of post-package
trimming is that it corrects any offset voltages caused by the
mechanical stresses of assembly.
The AD8655/AD8656 are available in standard op amp pinouts,
making DigiTrim completely transparent to the user. The input
stage of the amplifiers is a true rail-to-rail architecture, allowing
the input common-mode voltage range of the amplifiers to
extend to both positive and negative supply rails. The open-
loop gain of the AD8655/AD8656 with a load of 10 kΩ is
typically 110 dB.
The AD8655/AD8656 can be used in any precision op amp
application. The amplifier does not exhibit phase reversal for
common-mode voltages within the power supply. The AD8655/
AD8656 are great choices for high resolution data acquisition
systems with voltage noise of 2.7 nV/√Hz and THD + Noise of
–103 dB for a 2 V p-p signal at 10 kHz. Their low noise, sub-pA
input bias current, precision offset, and high speed make them
superb preamps for fast filter applications. The speed and output
drive capability of the AD8655/AD8656 also make them useful
in video applications.
