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ALD1721/ALD1721G
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PRECISION MICROPOWER CMOS OPERATIONAL AMPLIFIER
GENERAL DESCRIPTION
The ALD1721/ALD1721G is a monolithic CMOS micropower high slew
rate operational amplifier intended for a broad range of precision applica-
tions requiring exremely low input signal power. Input signal power is the
product of input offset voltage and input bias current, which represents the
minimum required power draw from the signal source in order to drive the
input of the operational amplifier. Input signal power is also a figure of
merit in source loading and its associated error, and is a measure of the
basic signal resolution possible through the operational amplifier for a
given signal source. For certain types of signal sources, signal loading
directly translates into a significant distortion or "interface noise equiva-
lent" term.
The ALD1721/ALD1721G is designed to set a new standard in low input
signal power requirements. The typical input loading at its input is 0.05 mV
offset voltage and 0.01 pA input bias current at 25C, resulting in 0.0005
fW input signal power draw. This input characteristic virtually eliminates
any loading effects on most types of signal sources, offering unparalled
accuracy and signal integrity and fidelity. Obviously, for capacitive and
high sensitivity, high impedance signal sources, the ALD1721/
ALD1721G is ideally suited. It is readily suited for +5V single supply (or
±1V
to
±5V)
systems, with low operating power dissipation, a traditional
strength of CMOS technology. It is offered with industry standard pin
configuration of
µA741
and ICL7611 types.
The ALD1721/ALD1721G can operate with rail to rail large signal input
and output voltages with relatively high slew rate. The input voltage can
be equal to or exceed the positive and negative supply voltages while the
output voltage can swing close to these supply voltage rails. This feature
significantly reduces the supply overhead voltage required to operate the
operational amplifier and allows numerous analog serial stages to oper-
ate in a low power supply environment. In addition, the device can
accommodate mixed applications where digital and analog circuits may
operate off the same power supply or battery. Finally, the output stage
can typically drive up to 50pF capacitive and 10KΩ resistive loads.
These features make the ALD1721/ALD1721G a versatile, micropower
high precision operational amplifier that is user friendly and easy to use
with virtually no source loading and zero input-loading induced source
errors. Additionally, robust design and rigorous screening make this
device especially suitable for operation in temperature-extreme environ-
ments and rugged conditions.
FEATURES & BENEFITS
• Lead Free - RoHS compatible
• Robust high-temperature operation
• Guaranteed extremely low input signal
power of 1.5 fW
• Input offset voltage of 0.05 mV typical
(0.15 mV max.)
• Low input bias currents of 0.01pA typical
(10pA max.)
• Rail to rail input and output voltage ranges
• All parameters specified for +5V single
supply or
±2.5V
dual supplies
• Unity gain stable, no compensation needed
• High voltage gain -- typically 100V/mV @
±2.5V(100dB)
• Drive as low as 10KΩ load
• Output short circuit protected
• Unity gain bandwidth of 0.7MHz
• Slew rate of 0.7V/µs
• Micro power dissipation
• Suitable for rugged, temperature-extreme
environments
APPLICATIONS
•
•
•
•
•
•
•
•
•
•
•
•
•
Voltage amplifier
Voltage follower/buffer
Charge integrator
Photodiode amplifier
Data acquisition systems
High performance portable instruments
Signal conditioning circuits
Sensor and transducer amplifiers
Low leakage amplifiers
Active filters
Sample/Hold amplifier
Picoammeter
Current to voltage converter
PIN CONFIGURATION
N/C
-IN
+IN
1
2
3
4
TOP
VIEW
TOP
VIEW
SAL, PAL, DA PACKAGES
* N/C pins are internally connected. Do not connect externally.
ORDERING INFORMATION
(“L” suffix denotes lead-free (RoHS))
0°C to +70°C
8-Pin
Small Outline
Package (SOIC)
ALD1721SAL
ALD1721GSAL
Operating Temperature Range
0°C to +70°C
-55°C to +125°C
8-Pin
Plastic Dip
Package
ALD1721PAL
ALD1721GPAL
8-Pin
CERDIP
Package
ALD1721DA
ALD1721GDA
8
2
7
6
5
N/C
V+
OUT
N/C
V-
* Contact factory for leaded (non-RoHS) or high temperature versions.
Rev 2.1 ©2011 Advanced Linear Devices, Inc. 415 Tasman Drive, Sunnyvale, CA 94089-1706 Tel: (408) 747-1155 Fax: (408) 747-1286
www.aldinc.com
Design & Operating Notes:
1. The ALD1721/ALD1721G CMOS operational amplifier uses a 3 gain
stage architecture and an improved frequency compensation
scheme to achieve large voltage gain, high output driving capability,
and better frequency stability. The ALD1721/ALD1721G is internally
compensated for unity gain stability. This compensation produces a
clean single pole roll off in the gain characteristics while providing for
more than 70 degrees of phase margin at the unity gain frequency,
reducing or eliminating low levels of oscillation or ringing with many
types of loading conditions.
2. The ALD1721/ALD1721G has complementary p-channel and n-
channel input differential stages connected in parallel to accomplish
rail to rail input common mode voltage range. With different ranges
of common mode input voltage, one or both of the two differential
stages is active. The transition between the two input stages takes
place at about 1.5V below the positive supply voltage. Input offset
voltage trimming on the ALD1721/ALD1721G is made when the
input voltage is symmetrical to the supply voltages, this internal
transition switching does not affect a variety of applications such as
an inverting amplifier or non-inverting amplifier with a gain larger
than 2.5 (5V operation), where the common mode voltage does not
make excursions above this switching point. If the operational
amplifier is connected as a unity gain buffer, and full input and/or
output rail to rail range is used, then provision should be made to
allow for slight input offset voltage variations. Likewise the output
has push-pull(source-sink) output stages working in tandem to
provide full (see note 4) rail to rail output. In addition, the source and
sink currents are designed to provide symmetrical drives to the load.
3. The input bias and offset currents are essentially input protection
diode reverse bias leakage currents, and are typically less than
0.01pA at room temperature. This low input bias current assures
that the analog signal from the source will not be distorted by input
bias currents. Normally, this extremely high input impedance of
greater than 10
14
Ω
would be limited by the source impedance which
would limit the node impedance. However, for applications where
source impedance is also very high, it may be necessary to limit
noise and hum pickup through proper ground shielding.
4. The output stage consists of class AB complementary output drivers,
capable of driving a low resistance load to either supply rail. The
output voltage swing is limited by the drain to source on-resistance
of the output transistors as determined by the bias circuitry, and the
value of the load resistor. When connected in the voltage follower
configuration, the oscillation resistant feature, combined with the rail
to rail input and output feature, makes an effective analog signal
buffer for medium to high source impedance sensors, transducers,
and other circuit networks.
5. The ALD1721/ALD1721G operational amplifier has been designed
to provide static discharge protection. Internally, the design has
been carefully implemented to minimize latch up. However, care
must be exercised when handling the device to avoid strong static
fields that may degrade a diode junction, causing increased input
leakage currents. The user is advised to power up the circuit before,
or simultaneously with any input voltages applied, and to limit input
voltages not to exceed 0.3V of the power supply voltage levels at all
times, including during power up and power down cycles.
6. The ALD1721/ALD1721G, with its micropower operation, offers
benefits in reduced power supply requirements, less noise coupling
and current spikes, less thermally induced drift, better overall reli-
ability due to lower self heating, and lower input bias current. It
requires practically no warm up time as the chip junction heats up to
0.1°C or less above ambient temperature under most operating
conditions.
7. The ALD1721/ALD1721G has an internal design architecture that
provides robust high temperature operation. Contact factory for
custom screening versions.
TYPICAL PERFORMANCE CHARACTERISTICS
SUPPLY CURRENT AS A FUNCTION
OF SUPPLY VOLTAGE
500
INPUTS GROUNDED
OUTPUT UNLOADED
COMMON MODE INPUT VOLTAGE RANGE
AS A FUNCTION OF SUPPLY VOLTAGE
±7
±6
+25°C
SUPPLY CURRENT (µA)
400
300
COMMON MODE INPUT
VOLTAGE RANGE (V)
-25°C
T
A
= -55°C
200
100
0
0
±1
±2
±3
±4
SUPPLY VOLTAGE (V)
±5
±6
+125°C
+70°C
±5
±4
±3
±2
±1
0
0
T
A
= 25°C
±1
±2
±3
±4
±5
±6
±7
SUPPLY VOLTAGE (V)
OPEN LOOP VOLTAGE GAIN AS A
FUNCTION OF LOAD RESISTANCE
1000
INPUT BIAS CURRENT AS A FUNCTION
OF AMBIENT TEMPERATURE
1000
INPUT BIAS CURRENT (pA)
OPEN LOOP VOLTAGE
GAIN (V/mV)
100
10
V
S
=
±2.5V
100
1.0
10
V
S
=
±2.5V
T
A
= 25°C
1
10K
100K
1M
10M
0.1
0.01
-50
-25
0
25
50
75
100
125
LOAD RESISTANCE (Ω)
AMBIENT TEMPERATURE (°C)
ALD1721/ALD1721G
Advanced Linear Devices
4 of 9
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