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AMP04EP-AMP04ES-AMP04FP-AMP04FS
Precision Single Supply Instrumentation Amplifier
REV.A
FUNCTIONAL BLOCK DIAGRAM
FEATURES
Single Supply Operation
Low Supply Current: 700 mA max
Wide Gain Range: 1 to 1000
Low Offset Voltage: 150 mV max
Zero-In/Zero-Out
Single-Resistor Gain Set
8-Pin Mini-DIP and SO packages
APPLICATIONS
Strain Gages
Thermocouples
RTDs
Battery Powered Equipment
Medical Instrumentation
Data Acquisition Systems
PC Based Instruments
Portable Instrumentation
Precision Single Supply
Instrumentation Amplifier
GENERAL DESCRIPTIONThe AMP04 is a single-supply instrumentation amplifier
designed to work over a +5 volt to ±15 volt supply range. It
offers an excellent combination of accuracy, low power con-
sumption, wide input voltage range, and excellent gain
performance.
Gain is set by a single external resistor and can be from 1 to
1000. Input common-mode voltage range allows the AMP04 to
handle signals with full accuracy from ground to within 1 volt of
the positive supply. And the output can swing to within 1 volt of
the positive supply. Gain bandwidth is over 700 kHz. In addi-
tion to being easy to use, the AMP04 draws only 700 μA of sup-
ply current.
For high resolution data acquisition systems, laser trimming of
low drift thin-film resistors limits the input offset voltage to
under 150 μV, and allows the AMP04 to offer gain nonlinearity
of 0.005% and a gain tempco of 30 ppm/°C.
A proprietary input structure limits input offset currents to less
than 5 nA with drift of only 8 pA/°C, allowing direct connection
of the AMP04 to high impedance transducers and other signal
sources.
*. Patent No. 5,075,633.The AMP04 is specified over the extended industrial (–40°C to
+85°C) temperature range. AMP04s are available in plastic and
ceramic DIP plus SO-8 surface mount packages.
Contact your local sales office for MIL-STD-883 data sheet
and availability.
PIN CONNECTIONS
8-Lead Epoxy DIP
(P Suffix)
8-Lead Narrow-Body SO
(S Suffix)
AMP04–SPECIFICATIONS
ELECTRICAL CHARACTERISTICSINPUT CURRENT
GAIN (G = 100 K/RGAIN)
OUTPUT
(VS = +5 V, VCM = +2.5 V, TA = +258C unless otherwise noted)
AMP04DYNAMIC RESPONSE
POWER SUPPLY
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICSINPUT CURRENT
(VS = 65 V, VCM = 0 V, TA = +258C unless otherwise noted)
AMP04OUTPUT
NOISE
DYNAMIC RESPONSE
POWER SUPPLY
Specifications subject to change without notice.
WAFER TEST LIMITSINPUT CURRENT
INPUT
(VS = +5 V, VCM = +2.5 V, TA = +258C unless otherwise noted)
OUTPUT
NOTE
Electrical tests and wafer probe to the limits shown. Due to variations in assembly methods and normal yield loss, yield after packaging is not guaranteed for standard
product dice. Consult factory to negotiate specifications based on dice lot qualifications through sample lot assembly and testing.
ABSOLUTE MAXIMUM RATINGS1Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±18 V
Common-Mode Input Voltage2 . . . . . . . . . . . . . . . . . .±18 V
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . .36 V
Output Short-Circuit Duration to GND . . . . . . . . . .Indefinite
Storage Temperature Range
Z Package . . . . . . . . . . . . . . . . . . . . . . . . . .–65°C to +175°C
P, S Package . . . . . . . . . . . . . . . . . . . . . . . .–65°C to +150°C
Operating Temperature Range
AMP04A . . . . . . . . . . . . . . . . . . . . . . . . . .–55°C to +125°C
AMP04E, F . . . . . . . . . . . . . . . . . . . . . . . . .–40°C to +85°C
Junction Temperature Range
Z Package . . . . . . . . . . . . . . . . . . . . . . . . . .–65°C to +175°C
P, S Package . . . . . . . . . . . . . . . . . . . . . . . .–65°C to +150°C
Lead Temperature Range (Soldering, 60 sec) . . . . . . .+300°C
NOTESAbsolute maximum ratings apply to both DICE and packaged parts, unless
otherwise noted.For supply voltages less than ±18 V, the absolute maximum input voltage is
equal to the supply voltage.θJA is specified for the worst case conditions, i.e., θJA is specified for device in
socket for cerdip, P-DIP, and LCC packages; θJA is specified for device
soldered in circuit board for SOIC package.
ORDERING GUIDE
DICE CHARACTERISTICSAMP04 Die Size 0.075 × 0.99 inch, 7,425 sq. mils.
Substrate (Die Backside) Is Connected to V+.
Transistor Count, 81.
AMP04
APPLICATIONS
Common-Mode RejectionThe purpose of the instrumentation amplifier is to amplify the
difference between the two input signals while ignoring offset
and noise voltages common to both inputs. One way of judging
the device’s ability to reject this offset is the common-mode
gain, which is the ratio between a change in the common-mode
voltage and the resulting output voltage change. Instrumenta-
tion amplifiers are often judged by the common-mode rejection
ratio, which is equal to 20 × log10 of the ratio of the user-selected
differential signal gain to the common-mode gain, commonly
called the CMRR. The AMP04 offers excellent CMRR, guaran-
teed to be greater than 90 dB at gains of 100 or greater. Input
offsets attain very low temperature drift by proprietary laser-
trimmed thin-film resistors and high gain amplifiers.
Input Common-Mode Range Includes GroundThe AMP04 employs a patented topology (Figure 1) that
uniquely allows the common-mode input voltage to truly extend
to zero volts where other instrumentation amplifiers fail. To il-
lustrate, take for example the single supply, gain of 100 instru-
mentation amplifier as in Figure 2. As the inputs approach zero
volts, in order for the output to go positive, amplifier A’s output
(VOA) must be allowed to go below ground, to –0.094 volts.
Clearly this is not possible in a single supply environment. Con-
sequently this instrumentation amplifier configuration’s input
common-mode voltage cannot go below about 0.4 volts. In
comparison, the AMP04 has no such restriction. Its inputs will
function with a zero-volt common-mode voltage.
Figure 1.Functional Block Diagram
Input Common-Mode Voltage Below GroundAlthough not tested and guaranteed, the AMP04 inputs are bi-
ased in a way that they can amplify signals linearly with common-
mode voltage as low as –0.25 volts below ground. This holds
true over the industrial temperature range from –40°C to +85°C.
Extended Positive Common-Mode RangeOn the high side, other instrumentation amplifier configura-
tions, such as the three op amp instrumentation amplifier, can
have severe positive common-mode range limitations. Figure 3
shows an example of a gain of 1001 amplifier, with an input
common-mode voltage of 10 volts. For this circuit to function,
VOB must swing to 15.01 volts in order for the output to go to
10.01 volts. Clearly no op amp can handle this swing range
(given a +15 V supply) as the output will saturate long before it
reaches the supply rails. Again the AMP04’s topology does not
have this limitation. Figure 4 illustrates the AMP04 operating at
the same common-mode conditions as in Figure 3. None of the
internal nodes has a signal high enough to cause amplifier satu-
ration. As a result, the AMP04 can accommodate much wider
common-mode range than most instrumentation amplifiers.
Figure 3. Gain = 1001, Three Op Amp Instrumentation
Amplifier
Programming the GainThe gain of the AMP04 is programmed by the user by selecting
a single external resistor—RGAIN:
Gain = 100 kΩ/RGAIN
The output voltage is then defined as the differential input volt-
age times the gain.
VOUT = (VIN+ – VIN–) × Gain
In single supply systems, offsetting the ground is often desired
for several reasons. Ground may be offset from zero to provide
a quieter signal reference point, or to offset “zero” to allow a
unipolar signal range to represent both positive and negative
values.
In noisy environments such as those having digital switching,
switching power supplies or externally generated noise, ground
may not be the ideal place to reference a signal in a high accu-
racy system.
Often, real world signals such as temperature or pressure may
generate voltages that are represented by changes in polarity. In
a single supply system the signal input cannot be allowed to go
below ground, and therefore the signal must be offset to accom-
modate this change in polarity. On the AMP04, a reference in-
put pin is provided to allow offsetting of the input range.
The gain equation is more accurately represented by including
this reference input.
VOUT = (VIN+ – VIN–) × Gain + VREF
GroundingThe most common problems encountered in high performance
analog instrumentation and data acquisition system designs are
found in the management of offset errors and ground noise.
Primarily, the designer must consider temperature differentials
and thermocouple effects due to dissimilar metals, IR voltage
drops, and the effects of stray capacitance. The problem is
greatly compounded when high speed digital circuitry, such as
that accompanying data conversion components, is brought
into the proximity of the analog section. Considerable noise and
error contributions such as fast-moving logic signals that easily
propagate into sensitive analog lines, and the unavoidable noise
common to digital supply lines must all be dealt with if the accu-
racy of the carefully designed analog section is to be preserved.
Besides the temperature drift errors encountered in the ampli-
fier, thermal errors due to the supporting discrete components
should be evaluated. The use of high quality, low-TC compo-
nents where appropriate is encouraged. What is more important,
large thermal gradients can create not only unexpected changes
in component values, but also generate significant thermoelec-
tric voltages due to the interface between dissimilar metals such
as lead solder, copper wire, gold socket contacts, Kovar lead
frames, etc. Thermocouple voltages developed at these junc-
tions commonly exceed the TCVOS contribution of the
AMP04. Component layout that takes into account the power
dissipation at critical locations in the circuit and minimizes gra-
dient effects and differential common-mode voltages by taking
advantage of input symmetry will minimize many of these errors.
High accuracy circuitry can experience considerable error con-
signal routing practice to minimize stray coupling and ground
loops is recommended. Leakage currents can be minimized by
using high quality socket and circuit board materials, and by
carefully cleaning and coating complete board assemblies.
As mentioned above, the high speed transition noise found in
logic circuitry is the sworn enemy of the analog circuit designer.
Great care must be taken to maintain separation between them
to minimize coupling. A major path for these error voltages will
be found in the power supply lines. Low impedance, load re-
lated variations and noise levels that are completely acceptable
in the high thresholds of the digital domain make the digital
supply unusable in nearly all high performance analog applica-
tions. The user is encouraged to maintain separate power and
ground between the analog and digital systems wherever pos-
sible, joining only at the supply itself if necessary, and to ob-
serve careful grounding layout and bypass capacitor scheduling
in sensitive areas.
Input Shield DriversHigh impedance sources and long cable runs from remote trans-
ducers in noisy industrial environments commonly experience
significant amounts of noise coupled to the inputs. Both stray
capacitance errors and noise coupling from external sources can
be minimized by running the input signal through shielded
cable. The cable shield is often grounded at the analog input
common, however improved dynamic noise rejection and a re-
duction in effective cable capacitance is achieved by driving the
shield with a buffer amplifier at a potential equal to the voltage
seen at the input. Driven shields are easily realized with the
AMP04. Examination of the simplified schematic shows that the
potentials at the gain set resistor pins of the AMP04 follow the
inputs precisely. As shown in Figure 5, shield drivers are easily
realized by buffering the potential at these pins by a dual, single
supply op amp such as the OP213. Alternatively, applications
with single-ended sources or that use twisted-pair cable could
drive a single shield. To minimize error contributions due to
this additional circuitry, all components and wiring should re-
main in proximity to the AMP04 and careful grounding and by-
passing techniques should be observed.
Figure 5. Cable Shield Drivers
AMP04
Compensating for Input and Output ErrorsTo achieve optimal performance, the user needs to take into
account a number of error sources found in instrumentation
amplifiers. These consist primarily of input and output offset
voltages and leakage currents.
The input and output offset voltages are independent from one
another, and must be considered separately. The input offset
component will of course be directly multiplied by the gain of
the amplifier, in contrast to the output offset voltage that is in-
dependent of gain. Therefore, the output error is the dominant
factor at low gains, and the input error grows to become the
greater problem as gain is increased. The overall equation for
offset voltage error referred to the output (RTO) is:
VOS (RTO) = (VIOS × G) + VOOS
where VIOS is the input offset voltage and VOOS the output offset
voltage, and G is the programmed amplifier gain.
The change in these error voltages with temperature must also
be taken into account. The specification TCVOS, referred to the
output, is a combination of the input and output drift specifica-
tions. Again, the gain influences the input error but not the out-
put, and the equation is:
TCVOS (RTO) = (TCVIOS × G) + TCVOOS
In some applications the user may wish to define the error con-
tribution as referred to the input, and treat it as an input error.
The relationship is:
TCVOS (RTI) = TCVIOS + (TCVOOS / G)
The bias and offset currents of the input transistors also have an
impact on the overall accuracy of the input signal. The input
leakage, or bias currents of both inputs will generate an addi-
tional offset voltage when flowing through the signal source re-
sistance. Changes in this error component due to variations with
signal voltage and temperature can be minimized if both input
source resistances are equal, reducing the error to a common-
mode voltage which can be rejected. The difference in bias cur-
rent between the inputs, the offset current, generates a differen-
tial error voltage across the source resistance that should be
taken into account in the user’s design.
In applications utilizing floating sources such as thermocouples,
transformers, and some photo detectors, the user must take care
to provide some current path between the high impedance in-
puts and analog ground. The input bias currents of the AMP04,
although extremely low, will charge the stray capacitance found
in nearby circuit traces, cables, etc., and cause the input to drift
erratically or to saturate unless given a bleed path to the analog
common. Again, the use of equal resistance values will create a
common input error voltage that is rejected by the amplifier.
Reference InputThe VREF input is used to set the system ground. For dual sup-
ply operation it can be connected to ground to give zero volts
out with zero volts differential input. In single supply systems it
could be connected either to the negative supply or to a pseudo-
ground between the supplies. In any case, the REF input must
be driven with low impedance.
Noise Filteringa single-pole low-pass filter is produced. The cutoff frequency
(fLP) follows the relationship:
Filtering can be applied to reduce wide band noise. Figure 7a
shows a 10 Hz low-pass filter, gain of 1000 for the AMP04. Fig-
ures 7b and 7c illustrate the effect of filtering on noise. The
photo in Figure 7b shows the output noise before filtering. By
adding a 0.15 μF capacitor, the noise is reduced by about a
factor of 4 as shown in Figure 7c.
