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DVANCED
L
INEAR
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EVICES,
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NC.
ALD1721E/ALD1721
EPAD™ MICROPOWER OPERATIONAL AMPLIFIER
KEY FEATURES
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EPAD ( Electrically Programmable Analog Device)
User programmable V
OS
trimmer
Computer-assisted trimming
Rail-to-rail input/output
Compatible with standard EPAD Programmer
High precision through in-system circuit precision trimming
Reduces or eliminates V
OS
, PSRR, CMRR and TCV
OS
errors
System level “calibration” capability
Application Specific Programming mode
In-System Programming mode
Electrically programmable to compensate for
external component tolerances
Achieves 0.01pA input bias current and 35
µ
V
input offset voltage simultaneously
Compatible with industry standard pinout
BENEFITS
• Eliminates manual and elaborate
system trimming procedures
• Remote controlled automated trimming
• In-System Programming capability
• No external components
• No internal chopper clocking noise
• No chopper dynamic power dissipation
• Simple and cost effective
• Small package size
• Extremely small total functional
volume size
• Low system implementation cost
• Micropower and Low Voltage
GENERAL DESCRIPTION
The ALD1721E/ALD1721 is a monolithic rail-to-rail precision CMOS
operational amplifier with integrated user programmable EPAD (Electri-
cally Programmable Analog Device) based offset voltage adjustment. The
ALD1721E/ALD1721 operational amplifier is a direct replacement of the
ALD1701 operational amplifier, with the added feature of user-program-
mable offset voltage trimming resulting in significantly enhanced total
system performance and user flexibility. EPAD technology is an exclusive
ALD design which has been refined for analog applications where preci-
sion voltage trimming is necessary to achieve a desired performance. It
utilizes CMOS FETs as in-circuit elements for trimming of offset voltage
bias characteristics with the aid of a personal computer under software
control. Once programmed, the set parameters are stored indefinitely
within the device even after power-down. EPAD offers the circuit designer
a convenient and cost-effective trimming solution for achieving the very
highest amplifier/system performance.
The ALD1721E/ALD1721 operational amplifier features rail-to-rail input
and output voltage ranges, tolerance to over-voltage input spikes of
300mV beyond supply rails, capacitive loading up to 50pF, extremely low
input currents of 0.01pA typical, high open loop voltage gain, useful
bandwidth of 700KHz, slew rate of 0.7 V/µs, and low typical supply current
of 120 uA.
APPLICATIONS
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Sensor interface circuits
Transducer biasing circuits
Capacitive and charge integration circuits
Biochemical probe interface
Signal conditioning
Portable instruments
High source impedance electrode
amplifiers
Precision Sample and Hold amplifiers
Precision current to voltage converter
Error correction circuits
Sensor compensation circuits
Precision gain amplifiers
Periodic In-system calibration
System output level shifter
PIN CONFIGURATION
VE1
1
2
3
4
TOP VIEW
DA, PA, SA PACKAGE
2
8
7
6
5
VE2
V+
OUT
N/C
ORDERING INFORMATION
Operating Temperature Range
-55°C to +125°C
8-Pin
CERDIP
Package
ALD1721E DA
ALD1721 DA
0°C to +70°C
8-Pin
Small Outline
Package (SOIC)
ALD1721E SA
ALD1721 SA
0°C to +70°C
8-Pin
Plastic Dip
Package
ALD1721E PA
ALD1721 PA
-IN
+IN
V-
* Contact factory for industrial temperature range
© 1998 Advanced Linear Devices, Inc. 415 Tasman Drive, Sunnyvale, California 94089 -1706 Tel: (408) 747-1155 Fax: (408) 747-1286 http://www.aldinc.com
FUNCTIONAL DESCRIPTION
The ALD1721E/ALD1721 uses EPADs as in-circuit elements
for trimming of offset voltage bias characteristics. Each
ALD1721E/ALD1721 has a pair of EPAD-based circuits
connected such that one circuit is used to adjust V
OS
in one
direction and the other circuit is used to adjust V
OS
in the
other direction.
Functional Description of ALD1721E
While each of the EPAD devices is a monotonically adjust-
able programmable device, the V
OS
of the ALD1721E can be
adjusted many times in both directions. Once programmed,
the set V
OS
levels are stored permanently, even when the
device power is removed.
The ALD1721E provides the user with an operational ampli-
fier that can be trimmed with user application-specific pro-
gramming or in-system programming conditions. User appli-
cation-specific circuit programming refers to the situation
where the Total Input Offset Voltage of the ALD1721E can be
trimmed with the actual intended operating conditions.
The ALD1721E is pre-programmed at the factory under
standard operating conditions for minimum equivalent input
offset voltage. It also has a guaranteed offset voltage
program range, which is ideal for applications that require
electrical offset voltage programming.
For example, an application circuit may have +6V and -2.5V
power supplies, and the operational amplifier input is biased
at +0.7V, and the average operating temperature is at 55
°
C.
The circuit can be wired up to these conditions within an
environmental chamber, and the ALD1721E can be inserted
into a test socket connected to this circuit while it is being
electrically trimmed. Any error in V
OS
due to these bias
conditions can be automatically zeroed out. The Total V
OS
error is now limited only by the adjustable range and the
stability of V
OS
, and the input noise voltage of the operational
amplifier. Therefore, this Total V
OS
error now includes V
OS
as V
OS
is traditionally specified; plus the V
OS
error contribu-
tions from PSRR, CMRR, TCV
OS
, and noise. Typically this
total V
OS
error term (V
OST
) is approximately
±35µV
for the
ALD1721E.
The V
OS
contribution due to PSRR, CMRR, TCV
OS
and
external components can be large for operational amplifiers
without trimming. Therefore the ALD1721E with EPAD trim-
ming is able to provide much improved system performance
by reducing these other sources of error to provide signifi-
cantly reduced V
OST.
In-System Programming refers to the condition where the
EPAD adjustment is made after the ALD1721E has been
inserted into a circuit board. In this case, the circuit design
must provide for the ALD1721E to operate in normal mode
and in programming mode. One of the benefits of in-system
programming is that not only is the ALD1721E offset voltage
from operating bias conditions accounted for, any residual
errors introduced by other circuit components, such as resis-
tor or sensor induced voltage errors, can also be corrected.
In this way, the “in-system” circuit output can be adjusted to
a desired level eliminating other trimming components.
Functional Description of ALD1721
The ALD1721 is pre-programmed at the factory under stan-
dard operating conditions for minimum equivalent input offset
voltage. The ALD1721 offers similar programmable features
as the ALD1721E, but with more limited offset voltage pro-
gram range. It is intended for standard operational amplifier
applications where little or no electrical programming by the
user is necessary.
USER PROGRAMMABLE Vos FEATURE
Each ALD1721E/ALD1721 has two pins named VE1 and
VE2 which are internally connected to an internal offset bias
circuit. VE1/VE2 have initial typical values of 1.2 /1.7 Volt.
The voltage on these pins can be programmed using the ALD
E100 EPAD Programmer and the appropriate Adapter Mod-
ule. The useful programming range of VE1 and VE2 is 1.2
Volt to 3.0 Volts. VE1 and VE2 pins are programming pins,
used during programming mode. The Programming pin is
used during electrical programming to inject charge into the
internal EPADs. Increases of VE1 decrease the offset volt-
age while increases of VE2 increase the offset voltage of the
operational amplifier. The injected charge is permanently
stored and determines the offset voltage of the operational
amplifier. After programming, VE1 and VE2 terminals must
be left open to settle on a voltage determined by internal bias
currents.
During programming, the voltages on VE1 or VE2 are in-
creased incrementally to set the offset voltage of the opera-
tional amplifier to the desired V
OS
. Note that desired V
OS
can
be any value within the offset voltage programmable ranges,
and can be either zero, a positive value or a negative value.
This V
OS
value can also be reprogrammed to a different
value at a later time, provided that the useful VE1 or VE2
programming voltage range has not been exceeded. VE1 or
VE2 pins can also serve as capacitively coupled input pins.
Internally, VE1 and VE2 are programmed and connected
differentially. Temperature drift effects between the two
internal offset bias circuits cancel each other and introduce
less net temperature drift coefficient change than offset
voltage trimming techniques such as offset adjustment with
an external trimmer potentiometer.
While programming, V+, VE1 and VE2 pins may be alter-
nately pulsed with 12V (approximately) pulses generated by
the EPAD Programmer. In-system programming requires the
ALD1721E/ALD1721 application circuit to accommodate
these programming pulses. This can be accomplished by
adding resistors at certain appropriate circuit nodes. For
more information, see Application Note AN1700.
2
Advanced Linear Devices
ALD1721E/ALD1721
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