AD8571ARZ-REEL7 Analog Devices Inc, AD8571ARZ-REEL7 Datasheet - Page 14

• Manufacturer Part Number: AD8571ARZ-REEL7
• Description: IC,Operational Amplifier,SINGLE,CMOS,SOP,8PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of AD8571ARZ-REEL7

• Amplifier Type: Chopper (Zero-Drift)
• Number Of Circuits: 1
• Output Type: Rail-to-Rail
• Slew Rate: 0.4 V/µs
• Gain Bandwidth Product: 1.5MHz
• Current - Input Bias: 10pA
• Voltage - Input Offset: 1µV
• Current - Supply: 850µA
• Current - Output / Channel: 30mA
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8571/AD8572/AD8574
FUNCTIONAL DESCRIPTION
The AD8571/AD8572/AD8574 are CMOS amplifiers that
achieve their high degree of precision through random frequency
auto-zero stabilization. The autocorrection topology allows the
AD857x to maintain its low offset voltage over a wide temperature
range, and the randomized auto-zero clock eliminates any inter-
modulation distortion (IMD) errors at the amplifier output.
The AD857x can run from a single-supply voltage as low as 2.7 V.
The extremely low offset voltage of 1 μV and no IMD products
allow the amplifier to be easily configured for high gains without
risk of excessive output voltage errors, which makes the AD857x
an ideal amplifier for applications requiring both dc precision
and low distortion for ac signals. The extremely small temperature
drift of 5 nV/°C ensures a minimum of offset voltage error over
its −40°C to +125°C temperature range. These combined features
make the AD857x an excellent choice for a variety of sensitive
measurement and automotive applications.
AMPLIFIER ARCHITECTURE
Each AD857x op amp consists of two amplifiers: a main amplifier
and a secondary amplifier that is used to correct the offset voltage
of the main amplifier. Both consist of a rail-to-rail input stage,
allowing the input common-mode voltage range to reach both
supply rails. The input stage consists of an NMOS differential
pair operating concurrently with a parallel PMOS differential
pair. The outputs from the differential input stages are combined in
another gain stage whose output is used to drive a rail-to-rail
output stage.
The wide voltage swing of the amplifier is achieved by using two
output transistors in a common-source configuration. The output
voltage range is limited by the drain-to-source resistance of
these transistors. As the amplifier is required to source or sink
more output current, the voltage drop across these transistors
increases due to their on resistance (R
voltage does not swing as close to the rail under heavy output
current conditions as it does with light output current. This is a
characteristic of all rail-to-rail output amplifiers. Figure 12 and
Figure 13 show how close the output voltage can get to the rails
with a given output current. The output of the AD857x is short-
circuit protected to approximately 50 mA of current.
The AD857x amplifiers have exceptional gain, yielding greater
than 120 dB of open-loop gain with a load of 2 kΩ. Because
the output transistors are configured in a common-source
configuration, the gain of the output stage, and thus the open-
loop gain of the amplifier, is dependent on the load resistance.
Open-loop gain decreases with smaller load resistances, which
is another characteristic of rail-to-rail output amplifiers.
DS
). Simply put, the output
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BASIC AUTO-ZERO AMPLIFIER THEORY
Autocorrection amplifiers are not a new technology. Various IC
implementations have been available for more than 15 years,
and some improvements have been made over time. The
AD857x design offers a number of significant performance
improvements over older versions while attaining a very
substantial reduction in device cost. This section offers a
simplified explanation of how the AD857x is able to offer
extremely low offset voltages and high open-loop gains.
As noted in the Amplifier Architecture section, each AD857x
op amp contains two internal amplifiers. One is used as the
primary amplifier, and the other as an autocorrection, or nulling,
amplifier. Each amplifier has an associated input offset voltage
that can be modeled as a dc voltage source in series with the
noninverting input. In Figure 50 and Figure 51, these are labeled
as V
denotes the primary amplifier. The open-loop gain for the +IN
and −IN inputs of each amplifier is given as A
also have a third voltage input with an associated open-loop
gain of B
There are two modes of operation determined by the action of
two sets of switches in the amplifier: an auto-zero phase and an
amplification phase.
V
V
V
V
IN+
IN–
IN+
IN–
OSA
and V
X
.
OSB
Figure 50. Auto-Zero Phase of the Amplifier
Figure 51. Output Phase of the Amplifier
, where A denotes the nulling amplifier and
ΦA
ΦA
1
ΦB
ΦB
V
V
OSA
OSA
+
+
A
A
A
A
V
V
V
V
OA
OA
OSB
OSB
–B
–B
+
+
A
A
V
V
NA
NA
ΦB
ΦB
ΦA
X
ΦA
. Both amplifiers
A
A
2
B
B
B
B
C
V
C
C
V
C
B
B
NB
M2
M1
M2
NB
M1
V
V
OUT
OUT
B