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FEATURES Single Supply Operation Low Supply Current: 700 A max Wide Gain Range: 1 to 1000 Low Offset Voltage: 150 V 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
IN(-) 2 IN(+) 3
Precision Single Supply Instrumentation Amplifier AMP04*
FUNCTIONAL BLOCK DIAGRAM
100k R GAIN 1 INPUT BUFFERS 8 VOUT 6
11k
11k
100k 5 REF
GENERAL DESCRIPTION
The AMP04 is specified over the extended industrial (-40C to +85C) 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)
RGAIN 1 -IN 2 +IN 3 V- 4 8 RGAIN
The 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 consumption, 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 addition to being easy to use, the AMP04 draws only 700 A of supply current. For high resolution data acquisition systems, laser trimming of low drift thin-film resistors limits the input offset voltage to under 150 V, 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.
*Protected by U.S. Patent No. 5,075,633.
8-Lead Narrow-Body SO (S Suffix)
RGAIN -IN +IN V- RGAIN
AMP-04
7 V+ 6 VOUT 5 REF
AMP-04
V+ VOUT REF
REV. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
AMP04-SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
Parameter Symbol
(VS = +5 V, VCM = +2.5 V, TA = +25 C unless otherwise noted)
Conditions Min AMP04E Typ Max Min AMP04F Typ Max Units
OFFSET VOLTAGE Input Offset Voltage Input Offset Voltage Drift Output Offset Voltage Output Offset Voltage Drift INPUT CURRENT Input Bias Current Input Bias Current Drift Input Offset Current Input Offset Current Drift
VIOS TCVIOS VOOS TCVoos IB TCIB IOS TCIOS
-40C TA +85C -40C TA +85C
30
0.5
150 300 3 1.5 3 30 30 50 65 5 10 8 4 4 3.0 0 55 75 80 80
300 600 6 3 6 50 40 60 10 15
V V V/C mV mV V/C nA nA pA/C nA nA pA/C G G V dB dB dB dB
-40C TA +85C -40C TA +85C
22 65 1 8 4 4
INPUT Common-Mode Input Resistance Differential Input Resistance Input Voltage Range VIN Common-Mode Rejection CMR
Common-Mode Rejection
CMR
Power Supply Rejection
PSRR
0 V VCM 3.0 V G=1 G = 10 G = 100 G = 1000 0 V VCM 2.5 V -40C TA +85C G=1 G = 10 G = 100 G = 1000 4.0 V VS 12 V -40C TA +85C G=1 G = 10 G = 100 G = 1000 G = 1 to 100 G = 1 to 100 -40C TA +85C G = 1000
0 60 80 90 90 80 100 105 105
3.0
55 75 85 85
50 70 75 75
dB dB dB dB
95 105 105 105 0.2 0.5 0.8 0.4 1 1000 0.005 0.015 0.025 30 4.0 3.8 2.0 30 15 4.2
85 95 95 95 0.75 1.0 0.75 1 1000
dB dB dB dB % % % V/V % % % ppm/C V V 2.5 30 15 mV mA mA
GAIN (G = 100 K/RGAIN) Gain Equation Accuracy
Gain Range Nonlinearity
G G = 1, RL = 5 k G = 10, RL = 5 k G = 100, RL = 5 k
Gain Temperature Coefficient OUTPUT Output Voltage Swing High
G/T VOH VOL
50 4.0 3.8
Output Voltage Swing Low Output Current Limit
RL = 2 k RL = 2 k -40C TA +85C RL = 2 k -40C TA +85C Sink Source
-2-
REV. A
AMP04
Parameter Symbol Conditions Min AMP04E Typ Max Min AMP04F Typ Max Units
NOISE Noise Voltage Density, RTI
eN
Noise Current Density, RTI Input Noise Voltage
iN eN p-p
f = 1 kHz, G = 1 f = 1 kHz, G = 10 f = 100 Hz, G = 100 f = 100 Hz, G = 1000 f = 100 Hz, G = 100 0.1 to 10 Hz, G = 1 0.1 to 10 Hz, G = 10 0.1 to 10 Hz, G = 100 G = 1, -3 dB
270 45 30 25 4 7 1.5 0.7 300 550 700 850
270 45 30 25 4 7 1.5 0.7 300 700 850
nV/Hz nV/Hz nV/Hz nV/Hz pA/Hz V p-p V p-p V p-p kHz A A
DYNAMIC RESPONSE Small Signal Bandwidth POWER SUPPLY Supply Current
BW ISY
-40C TA +85C
Specifications subject to change without notice.
ELECTRICAL CHARACTERISTICS (V =
S
5 V, VCM = 0 V, TA = +25 C unless otherwise noted)
Min AMP04E Typ Max Min AMP04F Typ Max Units
Parameter
Symbol
Conditions
OFFSET VOLTAGE Input Offset Voltage Input Offset Voltage Drift Output Offset Voltage Output Offset Voltage Drift INPUT CURRENT Input Bias Current Input Bias Current Drift Input Offset Current Input Offset Current Drift INPUT Common-Mode Input Resistance Differential Input Resistance Input Voltage Range Common-Mode Rejection
VIOS TCVIOS VOOS TCVoos IB TCIB IOS TCIOS
-40C TA +85C -40C TA +85C
80
1
400 600 3 3 6 30 30 50 65 5 15 28 4 4 +12 -12 55 75 80 80
600 900 6 6 9 50 40 60 10 20
V V V/C mV mV V/C nA nA pA/C nA nA pA/C G G V dB dB dB dB
-40C TA +85C -40C TA +85C
17 65 2 28 4 4
VIN CMR
Common-Mode Rejection
CMR
Power Supply Rejection
PSRR
-12 V VCM +12 V G=1 G = 10 G = 100 G = 1000 -11 V VCM +11 V -40C TA +85C G=1 G = 10 G = 100 G = 1000 2.5 V VS 18 V -40C TA +85C G=1 G = 10 G = 100 G = 1000 -3-
-12 60 80 90 90 80 100 105 105
+12
55 75 85 85
50 70 75 75
dB dB dB dB
75 90 95 95
70 80 85 85
dB dB dB dB
REV. A
AMP04
Parameter Symbol Conditions Min AMP04E Typ Max Min AMP04F Typ Max Units
GAIN (G = 100 K/RGAIN) Gain Equation Accuracy
G = 1 to 100 G = 1000 G = 1 to 100 -40C TA +85C G G = 1, RL = 5 k G = 10, RL = 5 k G = 100, RL = 5 k 1
0.2 0.4
0.5 0.75 0.8 1000
0.75
% % % V/V % % % ppm/C V V
Gain Range Nonlinearity
1 0.005 0.015 0.025 50 +13 +12.5
1.0 1000
Gain Temperature Coefficient OUTPUT Output Voltage Swing High
G/T VOH VOL
0.005 0.015 0.025 30 +13 +12.5 -14.5 30 15 270 45 30 25 4 5 1 0.5 700 750 900 1100 +13.4
Output Voltage Swing Low Output Current Limit NOISE Noise Voltage Density, RTI
RL = 2 k RL = 2 k -40C TA +85C RL = 2 k -40C TA +85C Sink Source f = 1 kHz, G = 1 f = 1 kHz, G = 10 f = 100 Hz, G = 100 f = 100 Hz, G = 1000 f = 100 Hz, G = 100 0.1 to 10 Hz, G = 1 0.1 to 10 Hz, G = 10 0.1 to 10 Hz, G = 100 G = 1, -3 dB
30 15 270 45 30 25 4 5 1 0.5 700
-14.5 V mA mA nV/Hz nV/Hz nV/Hz nV/Hz pA/Hz V p-p V p-p V p-p kHz 900 1100 A A
eN
Noise Current Density, RTI Input Noise Voltage
iN eN p-p
DYNAMIC RESPONSE Small Signal Bandwidth POWER SUPPLY Supply Current
BW ISY
-40C TA +85C
Specifications subject to change without notice.
WAFER TEST LIMITS
Parameter
(VS = +5 V, VCM = +2.5 V, TA = +25 C unless otherwise noted)
Symbol Conditions Limit Units
OFFSET VOLTAGE Input Offset Voltage Output Offset Voltage INPUT CURRENT Input Bias Current Input Offset Current INPUT Common-Mode Rejection
VIOS VOOS IB IOS CMR 0 V VCM 3.0 V G=1 G = 10 G = 100 G = 1000 VS = 15 V, -12 V VCM +12 V G=1 G = 10 G = 100
300 3 40 10
V max mV max nA max nA max
55 75 80 80 55 75 80
dB min dB min dB min dB min dB min dB min dB min
Common-Mode Rejection
CMR
-4-
REV. A
AMP04
Parameter Symbol Conditions Limit Units
Power Supply Rejection
PSRR
G = 1000 4.0 V VS 12 V G=1 G = 10 G = 100 G = 1000 G = 1 to 100
80 85 95 95 95 0.75 4.0 2.5 900 700
dB min dB min dB min dB min dB min % max V min mV max A max A max
GAIN (G = 100 K/RGAIN) Gain Equation Accuracy OUTPUT Output Voltage Swing High Output Voltage Swing Low POWER SUPPLY Supply Current VOH VOL ISY
RL = 2 k RL = 2 k VS = 15
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 RATINGS 1
DICE CHARACTERISTICS
Supply 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 . . . . . . . . . . . . . . . . . . . . . . . . . . -65C to +175C P, S Package . . . . . . . . . . . . . . . . . . . . . . . . -65C to +150C Operating Temperature Range AMP04A . . . . . . . . . . . . . . . . . . . . . . . . . . -55C to +125C AMP04E, F . . . . . . . . . . . . . . . . . . . . . . . . . -40C to +85C Junction Temperature Range Z Package . . . . . . . . . . . . . . . . . . . . . . . . . . -65C to +175C P, S Package . . . . . . . . . . . . . . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering, 60 sec) . . . . . . . +300C
Package Type JA3 JC Units
8-Pin Cerdip (Z) 8-Pin Plastic DIP (P) 8-Pin SOIC (S)
148 103 158
16 43 43
C/W C/W C/W
NOTES 1 Absolute maximum ratings apply to both DICE and packaged parts, unless otherwise noted. 2 For supply voltages less than 18 V, the absolute maximum input voltage is equal to the supply voltage. 3 JA is specified for the worst case conditions, i.e., JA is specified for device in socket for cerdip, P-DIP, and LCC packages; JA is specified for device soldered in circuit board for SOIC package.
AMP04 Die Size 0.075 x 0.99 inch, 7,425 sq. mils. Substrate (Die Backside) Is Connected to V+. Transistor Count, 81.
ORDERING GUIDE Temperature Range VOS @ +5 V TA = +25 C Package Description Package Option
Model
AMP04EP AMP04ES AMP04FP AMP04FS AMP04FS-REEL AMP04FS-REEL7 AMP04GBC REV. A
XIND XIND XIND XIND XIND XIND +25C
150 V 150 V 300 V 300 V 150 V 150 V 300 V -5-
Plastic DIP SOIC Plastic DIP SOIC SOIC SOIC
N-8 SO-8 N-8 SO-8 SO-8 SO-8
AMP04
Input Common-Mode Voltage Below Ground APPLICATIONS Common-Mode Rejection
The 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. Instrumentation amplifiers are often judged by the common-mode rejection ratio, which is equal to 20 x 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, guaranteed to be greater than 90 dB at gains of 100 or greater. Input offsets attain very low temperature drift by proprietary lasertrimmed thin-film resistors and high gain amplifiers.
Input Common-Mode Range Includes Ground
Although not tested and guaranteed, the AMP04 inputs are biased in a way that they can amplify signals linearly with commonmode voltage as low as -0.25 volts below ground. This holds true over the industrial temperature range from -40C to +85C.
Extended Positive Common-Mode Range
The 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 illustrate, take for example the single supply, gain of 100 instrumentation 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. Consequently 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.
100k R GAIN IN(-) 2 INPUT BUFFERS IN(+) 3 1 8 VOUT 6
On the high side, other instrumentation amplifier configurations, 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 saturation. As a result, the AMP04 can accommodate much wider common-mode range than most instrumentation amplifiers.
+10.00V
A
100k 200 50A 100k +5V VOA VOB R R
R
10.01
+15.01V R
+10.01V
B
Figure 3. Gain = 1001, Three Op Amp Instrumentation Amplifier
100k 0.1A
11k
11k
+10.00V - +10.01V +
100
+15V VOUT +10V
+10.01V 100A +15V 11k -15V 100.1A
100k 5 REF
Figure 1. Functional Block Diagram
-15V +11.111V
0.01V + VIN 0V -
VOB
VOUT
11k 100k
B
VOA
A
100k 0V
Figure 4. Gain = 1000, AMP04
20k -.094V 2127 5.2A 0.01V
100k
20k 4.7A 4.7A
Figure 2. Gain = 100 Instrumentation Amplifier
-6-
REV. A
AMP04
Programming the Gain
The gain of the AMP04 is programmed by the user by selecting a single external resistor--RGAIN: Gain = 100 k/RGAIN The output voltage is then defined as the differential input voltage times the gain. VOUT = (VIN+ - VIN-) x 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 accuracy 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 accommodate this change in polarity. On the AMP04, a reference input 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-) x Gain + VREF
Grounding
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 related 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 applications. The user is encouraged to maintain separate power and ground between the analog and digital systems wherever possible, joining only at the supply itself if necessary, and to observe careful grounding layout and bypass capacitor scheduling in sensitive areas.
Input Shield Drivers
The 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 accuracy of the carefully designed analog section is to be preserved. Besides the temperature drift errors encountered in the amplifier, thermal errors due to the supporting discrete components should be evaluated. The use of high quality, low-TC components where appropriate is encouraged. What is more important, large thermal gradients can create not only unexpected changes in component values, but also generate significant thermoelectric 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 junctions 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 gradient 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 contributions due to the coupling of stray voltages into sensitive areas, including high impedance amplifier inputs which benefit from such techniques as ground planes, guard rings, and shields. Careful circuit layout, including good grounding and REV. A -7-
High impedance sources and long cable runs from remote transducers 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 reduction 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 remain in proximity to the AMP04 and careful grounding and bypassing techniques should be observed.
1/2 OP-213
2
1
8
VOUT 6
3
1/2 OP-213
Figure 5. Cable Shield Drivers
AMP04
Compensating for Input and Output Errors
To 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 independent 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 x 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 specifications. Again, the gain influences the input error but not the output, and the equation is: TCVOS (RTO) = (TCVIOS x G) + TCVOOS In some applications the user may wish to define the error contribution 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 additional offset voltage when flowing through the signal source resistance. 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 commonmode voltage which can be rejected. The difference in bias current between the inputs, the offset current, generates a differential 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 inputs 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 Input
5 100k REF R GAIN IN(-) 2 INPUT BUFFERS IN(+) 3 1 8
CEXT
100k
6 VOUT 11k
11k
LP =
1 2 (100k) C EXT
Figure 6. Noise Band Limiting
a single-pole low-pass filter is produced. The cutoff frequency (fLP) follows the relationship: f LP = 1 2 (100 k) CEXT
Filtering can be applied to reduce wide band noise. Figure 7a shows a 10 Hz low-pass filter, gain of 1000 for the AMP04. Figures 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 F capacitor, the noise is reduced by about a factor of 4 as shown in Figure 7c.
+15V 100 7 2 1 86 3 5 4 -15V 0.15F
Figure 7a. 10 Hz Low-Pass Filter
5mV
100 90
10ms
The VREF input is used to set the system ground. For dual supply 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 pseudoground between the supplies. In any case, the REF input must be driven with low impedance.
Noise Filtering
10 0%
Unlike most previous instrumentation amplifiers, the output stage's inverting input (Pin 8) is accessible. By placing a capacitor across the AMP04's feedback path (Figure 6, Pins 6 and 8)
Figure 7b. Unfiltered AMP04 Output
-8-
REV. A
AMP04
1mV
100 90
2s
First, the potentiometer should be adjusted to cause the output to swing in the positive direction; then adjust it in the reverse direction, causing the output to swing toward ground, until the output just stops changing. At that point the output is at the saturation limit.
RG
10 0%
1 2 INPUT 3
AMP-04
8 7 6 5 OP-113 +5V OUTPUT
Figure 7c. 10 Hz Low-Pass Filtered Output
Power Supply Considerations
4
In dual supply applications (for example 15 V) if the input is connected to a low resistance source less than 100 , a large current may flow in the input leads if the positive supply is applied before the negative supply during power-up. A similar condition may also result upon a loss of the negative supply. If these conditions could be present in you system, it is recommended that a series resistor up to 1 k be added to the input leads to limit the input current. This condition can not occur in a single supply environment as losing the negative supply effectively removes any current return path.
Offset Nulling in Dual Supply
+5V 100 50k
Figure 9. Offset Adjust for Single Supply Applications
Alternative Nulling Method
Offset may be nulled by feeding a correcting voltage at the VREF pin (Pin 5). However, it is important that the pin be driven with a low impedance source. Any measurable resistance will degrade the amplifier's common-mode rejection performance as well as its gain accuracy. An op amp may be used to buffer the offset null circuit as in Figure 8.
RG
An alternative null correction technique is to inject an offset current into the summing node of the output amplifier as in Figure 10. This method does not require an external op amp. However the drawback is that the amplifier will move off its null as the input common-mode voltage changes. It is a less desirable nulling circuit than the previous method.
V+
V-
100k R GAIN IN(-) 2 INPUT BUFFERS IN(+)
1 - INPUT + 2 3 4 V- REF
1
8
VOUT 6
3
AMP-04
V+
8 7 6 5 +5V +5V OUTPUT +5V 50k
11k
11k
100k
-5V * OP-90 FOR LOW POWER OP-113 FOR LOW DRIFT -5V
*
5mV ADJ RANGE
100
5
50k -5V
REF
Figure 10. Current Injection Offsetting Is Not Recommended
Figure 8. Offset Adjust for Dual Supply Applications
Offset Nulling in Single Supply
Nulling the offset in single supply systems is difficult because the adjustment is made to try to attain zero volts. At zero volts out, the output is in saturation (to the negative rail) and the output voltage is indistinguishable from the normal offset error. Consequently the offset nulling circuit in Figure 9 must be used with caution.
REV. A
-9-
AMP04
APPLICATION CIRCUITS Low Power Precision Single Supply RTD Amplifier
Figure 11 shows a linearized RTD amplifier that is powered off a single +5 volt supply. However, the circuit will work up to 36 volts without modification. The RTD is excited by a 100 A constant current that is regulated by amplifier A (OP295). The 0.202 volts reference voltage used to generate the constant current is divided down from the 2.500 volt reference. The AMP04 amplifies the bridge output to a 10 mV/C output coefficient.
R3 BALANCE 500 R1 26.7k R2 26.7k 3 7 1 86 R9 50 +5V R8 383 100 R10 FULL-SCALE ADJ VOUT 04.00V (0C TO 400C)
To calibrate, either immerse the RTD into a zero-degree ice bath or substitute an exact 100 resistor in place of the RTD. Then adjust bridge BALANCE potentiometer R3 for a 0 volt output. Note that a 0 volt output is also the negative output swing limit of the AMP04 powered with a single supply. Therefore, be sure to adjust R3 to first cause the output to swing positive and then back off until the output just stop swinging negatively. Next, set the LINEARITY ADJ. potentiometer to the midrange. Substitute an exact 247.04 resistor (equivalent to 400C temperature) in place of the RTD. Adjust the FULL-SCALE potentiometer for a 4.000 volts output. Finally substitute a 175.84 resistor (equivalent to 200C temperature), and adjust the LINEARITY ADJ potentiometer for a 2.000 volts at the output. Repeat the full-scale and the half-scale adjustments as needed. When properly calibrated, the circuit achieves better than 0.5C accuracy within a temperature measurement range from 0C to 400C.
Precision 4-20 mA Loop Transmitter With Noninteractive Trim
C3 0.1F
C1 0.47F
AMP-04
2 5 4 RTD 100 R4 100 1 1/2 OP-295 2
A
+5V 3 R7 121k 8 7 4 1/2 OP-295 6
B
5 50k LINEARITY ADJ. (@1/2 FS)
0.202V R SENSE 1k R5 1.02k 2.5V 6 OUT REF-43 GND 4 IN 2 R6 11.5k
+5V C2 0.1F
NOTES: ALL RESISTORS 0.5%, 25 PPM/C ALL POTENTIOMETERS 25 PPM/C
Figure 12 shows a full bridge strain gage transducer amplifier circuit that is powered off the 4-20 mA current loop. The AMP04 amplifies the bridge signal differentially and is converted to a current by the output amplifier. The total quiescent current drawn by the circuit, which includes the bridge, the amplifiers, and the resistor biasing, is only a fraction of the 4 mA null current that flows through the current-sense resistor RSENSE. The voltage across RSENSE feeds back to the OP90's input, whose common-mode is fixed at the current summing reference voltage, thus regulating the output current. With no bridge signal, the 4 mA null is simply set up by the 50 k NULL potentiometer plus the 976 k resistors that inject an offset that forces an 80 mV drop across RSENSE. At a 50 mV full-scale bridge voltage, the AMP04 amplifies the voltage-to-current converter for a full-scale of 20 mA at the output. Since the OP90's input operates at a constant 0 volt common-mode voltage, the null and the span adjustments do
Figure 11. Precision Single Supply RTD Thermometer Amplifier
The RTD is linearized by feeding a portion of the signal back to the reference circuit, increasing the reference voltage as the temperature increases. When calibrated properly, the RTD's nonlinearity error will be canceled.
Figure 12. Precision 4-20 mA Loop Transmitter Features Noninteractive Trims
-10-
REV. A
AMP04
not interact with one another. Calibration is simple and easy with the NULL adjusted first, followed by SPAN adjust. The entire circuit can be remotely placed, and powered from the 4-20 mA 2-wire loop.
4-20 mA Loop Receiver Single Supply Programmable Gain Instrumentation Amplifier
At the receiving end of a 4-20 mA loop, the AMP04 makes a convenient differential receiver to convert the current back to a usable voltage (Figure 13). The 4-20 mA signal current passes through a 100 sense resistor. The voltage drop is differentially amplified by the AMP04. The 4 mA offset is removed by the offset correction circuit.
+15V IN4002 4-20mA 4-20mA TRANSMITTER 7 1k 100 1% 1k
WIRE RESISTANCE
Combining with the single supply ADG221 quad analog switch, the AMP04 makes a useful programmable gain amplifier that can handle input and output signals at zero volts. Figure 15 shows the implementation. A logic low input to any of the gain control ports will cause the gain to change by shorting a gainset resistor across AMP04's Pins 1 and 8. Trimming is required at higher gains to improve accuracy because the switch ONresistance becomes a more significant part of the gain-set resistance. The gain of 500 setting has two switches connected in parallel to reduce the switch resistance.
+5V TO +30V
100k 0.15F 1 86 VOUT 0-1.6V FS -0.400V 2 -15V 6 OP-177 GAIN CONTROL
10F
13
5 ADG221 4 11 200 6 200 14 715 3 10.9k
+
0.1F 10 9
- +
4-20mA
3
AMP-04
2 5 4
7 GAIN OF 500 8 15 GAIN OF 100 16 2 GAIN OF 10 WR RG 1
+-
POWER SUPPLY
3 10k
27k -15V
-
AD589
+
12 RG V+
100k 0.22F 8 7 6 +5V TO +30V VOUT
Figure 13. 4-to-20 mA Line Receiver
Low Power, Pulsed Load-Cell Amplifier
1 - INPUT + 2 3 4
Figure 14 shows a 350 load cell that is pulsed with a low duty cycle to conserve power. The OP295's rail-to-rail output capability allows a maximum voltage of 10 volts to be applied to the bridge. The bridge voltage is selectively pulsed on when a measurement is made. A negative-going pulse lasting 200 ms should be applied to the MEASURE input. The long pulse width is necessary to allow ample settling time for the long time constant of the low-pass filter around the AMP04. A much faster settling time can be achieved by omitting the filter capacitor.
+12V 1k 330 1/2 OP-295 10k OUT 10V IN REF-01 GND
V-
REF
5
AMP-04
0.1F
Figure 15. Single Supply Programmable Gain Instrumentation Amplifier
The switch ON resistance is lower if the supply voltage is 12 volts or higher. Additionally the overall amplifier's temperature coefficient also improves with higher supply voltage.
MEASURE 2N3904 50k +12V 7 3 1 8 350 1N4148
0.22F
AMP-04
2 5 4
6
VOUT
Figure 14. Pulsed Load Cell Bridge Amplifier
REV. A
-11-
AMP04
120 BASED ON 300 UNITS 3 RUNS TA = +25C VS = +5V VCM = 2.5V
120 BASED ON 300 UNITS 3 RUNS TA = +25C VS = 15V VCM = 0V NUMBER OF UNITS 80
100
100
NUMBER OF UNITS
80
60
60
40
40
20
20
0 -200 -160 -120
-80 -40 0 40 80 120 INPUT OFFSET VOLTAGE - V
160
200
0 -0.5
-0.4
-0.3
-0.2 -0.1 0 0.1 0.2 0.3 INPUT OFFSET VOLTAGE - mV
0.4
0.5
Figure 16. Input Offset (VIOS) Distribution @ +5 V
Figure 17. Input Offset (VIOS) Distribution @ 15 V
120 300 UNITS VS = +5V VCM = 2.5V
120 300 UNITS VS = 15V VCM = 0V NUMBER OF UNITS 80
100
100
NUMBER OF UNITS
80
60
60
40
40
20
20
0 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 TCV IOS - V/ C
0 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 TCV IOS - V/C
Figure 18. Input Offset Drift (TCVIOS) Distribution @ +5 V
Figure 19. Input Offset Drift (TCVIOS) Distribution @ 15 V
120 BASED ON 300 UNITS 3 RUNS TA = +25C VS = +5V VCM = 2.5V
NUMBER OF UNITS
120 BASED ON 300 UNITS 3 RUNS TA = +25C VS = 15V VCM = 0V
100
100
NUMBER OF UNITS
80
80
60
60
40
40
20
20
0 -2.0
0
-1.6
-1.2
-0.8 -0.4 0 0.4 0.8 OUTPUT OFFSET - mV
1.2
1.6
2.0
-5
-4
-3
-2
-1 0 1 2 OUTPUT OFFSET - mV
3
4
5
Figure 20. Output Offset (VOOS) Distribution @ +5 V
Figure 21. Output Offset (VOOS) Distribution @ 15 V
-12-
REV. A
AMP04
120 300 UNITS VS = +5V VCM = 0V
120 300 UNITS VS = 15V VCM = 0V
NUMBER OF UNITS
0 2 4 6 8 10 12 14 16 18 20
100
100
NUMBER OF UNITS
80
80
60
60
40
40
20
20
0 TCV OOS - V/ C
0 2 4 6 8 10 12 14 16 18 20 22 24 TCV OOS - V/ C
Figure 22. Output Offset Drift (TCVOOS) Distribution @ +5 V
Figure 23. Output Offset Drift (TCVOOS) Distribution @ 15 V
5.0 VS = +5V
+OUTPUT SWING - Volts
15.0 14.5 14.0 13.5 13.0 12.5 -14.6 -14.7 -14.8 -14.9 -15.0 -15.1 -50
RL = 100k RL = 100k
VS = +5V
OUTPUT VOLTAGE SWING - Volts
4.8
RL = 10k
4.6 RL = 100k 4.4
RL = 2k
-OUTPUT SWING - Volts
RL = 2k
4.2 RL = 2k 4.0 RL = 10k
RL = 10k
3.8 -50
RL = 100k -25 0 25 50 75 100
-25
0 25 50 TEMPERATURE - C
75
100
TEMPERATURE - C
Figure 24. Output Voltage Swing vs. Temperature @ +5 V
Figure 25. Output Voltage Swing vs. Temperature @ +15 V
40 35 VS = +5V, VCM = 2.5V VS = 15V, VCM = 0V
8 VS = +5V, VCM = 2.5V INPUT OFFSET CURRENT - nA VS = 15V , VCM = 0V 6
INPUT BIAS CURRENT - nA
30 25 20 15 10 5 0 -50 VS = 15V VS = +5V
4
VS = +5V 2
VS = 15V
-25
0
25
50
75
100
TEMPERATURE - C
0 -50
-25
0
25
50
75
100
TEMPERATURE - C
Figure 26. Input Bias Current vs. Temperature
Figure 27. Input Offset Current vs. Temperature
REV. A
-13-
AMP04
50 G = 100 40 30 G = 10 20 10 G=1 0 TA = +25C VS = 15V
120 TA = +25C G=1
100
OUTPUT IMPEDANCE -
VOLTAGE GAIN - dB
80 VS = 15V
60 40
VS = +5V 20 0
-10 -20 100
1k
10k FREQUENCY - Hz
100k
1M
10
100
1k FREQUENCY - Hz
10k
100k
Figure 28. Closed-Loop Voltage Gain vs. Frequency
Figure 29. Closed-Loop Output Impedance vs. Frequency
120 TA = +25C COMMON-MODE REJECTION - dB G = 100 80 VS = 15V VCM = 2V P-P
120 TA = +25C VS = 15V VCM = 2V P-P
COMMON-MODE REJECTION - dB
100k
100
110 100 90
60 G = 10 40 20 0
80 70 60
G=1
-20 1 10 100 1k FREQUENCY - Hz 10k
50 1 10 100 VOLTAGE GAIN - G 1k
Figure 30. Common-Mode Rejection vs. Frequency
Figure 31. Common-Mode Rejection vs. Voltage Gain
140 TA = +25C VS = 15V
POWER SUPPLY REJECTION - dB
140 TA = +25C VS = 15V V S = 1V G = 100
POWER SUPPLY REJECTION - dB
120 G = 100 100
V S = 1V
120 100
80 60
G = 10
80 G = 10 60
40 G=1 20
40 G=1 20
0 10 100 1k 10k FREQUENCY - Hz 100k 1M
0 10 100 1k 10k FREQUENCY - Hz 100k 1M
Figure 32. Positive Power Supply Rejection vs. Frequency
Figure 33. Negative Power Supply Rejection vs. Frequency
-14-
REV. A
AMP04
1k TA = +25C VS = 15V = 100Hz 100 VOLTAGE NOISE - nV/ Hz 100 1k TA = +25C VS = 15V = 1kHz
VOLTAGE NOISE - nV/ Hz
10
10
1 1 10 100 VOLTAGE GAIN - G 1k
1 1 10 100 VOLTAGE GAIN - G 1k
Figure 34. Voltage Noise Density vs. Gain
Figure 35. Voltage Noise Density vs. Gain, f = 1 kHz
140 TA = +25C VS = 15V G = 100
100 90
20mV
1s
VOLTAGE NOISE DENSITY - nV/ Hz
120 100
80 60 40 20 0 1 10 100 FREQUENCY - Hz 1k 10k
VS = 15V, GAIN = 1000, 0.1 TO 10 Hz BANDPASS
10 0%
Figure 36. Voltage Noise Density vs. Frequency
Figure 37. Input Noise Voltage
1200
16 14 VS = 15V 12 10 8 6 4 TA = +25C VS = 15V
1000
SUPPLY CURRENT - A
800
600
400
VS = +5V
200 2 0 -50 0 10 100 1k LOAD RESISTANCE - 10k 100k
-25
0
25
50
75
100
TEMPERATURE - C
Figure 38. Supply Current vs. Temperature
Figure 39. Maximum Output Voltage vs. Load Resistance
REV. A
-15-
OUTPUT VOLTAGE - V
AMP04
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic DIP (N-8)
C1720-24-10/92
0.195 (4.95) 0.115 (2.93)
8
5 0.280 (7.11) 0.240 (6.10)
1
4 0.070 (1.77) 0.045 (1.15)
0.430 (10.92) 0.348 (8.84) 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93)
0.325 (8.25) 0.300 (7.62)
0.015 (0.381) TYP
0.130 (3.30) MIN 0.100 (2.54) BSC SEATING PLANE 0- 15
0.015 (0.381) 0.008 (0.204)
0.022 (0.558) 0.014 (0.356)
8-Lead Cerdip (Q-8)
0.005 (0.13) MIN 0.055 (1.4) MAX
8
5 0.310 (7.87) 0.220 (5.59)
1
4 0.070 (1.78) 0.030 (0.76)
0.405 (10.29) MAX 0.200 (5.08) MAX 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN
0.320 (8.13) 0.290 (7.37)
0.200 (5.08) 0.125 (3.18)
0.015 (0.38) 0.008 (0.20)
0.023 (0.58) 0.014 (0.36)
0-15 0.100 (2.54) BSC SEATING PLANE
8-Lead Narrow-Body SO (S0-8)
-16-
REV. A
PRINTED IN U.S.A.

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