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FEATURE HIGH DC PRECISION 50 V max Offset Voltage 0.6 V/ C max Offset Drift 110 pA max Input Bias Current LOW NOISE 0.5 V p-p Voltage Noise, 0.1 Hz to 10 Hz LOW POWER 750 A Supply Current Available in 8-Lead Plastic Mini-DlP, Hermetic Cerdip and Surface Mount (SOIC) Packages Available in Tape and Reel in Accordance with EIA-481A Standard Single Version: AD705, Quad Version: AD704 PRIMARY APPLICATIONS Low Frequency Active Filters Precision Instrumentation Precision Integrators
Dual Picoampere Input Current Bipolar Op Amp AD706
CONNECTION DIAGRAM Plastic Mini-DIP (N) Cerdip (Q) and Plastic SOIC (R) Packages
AMPLIFIER 1 OUTPUT 1 -IN 2 IN 3 V-
4
AMPLIFIER 2
AD706
8 7 6 5
V OUTPUT -IN IN
TOP VIEW
The AD706 is offered in three varieties of an 8-lead package: plastic mini-DIP, hermetic cerdip and surface mount (SOIC). "J" grade chips are also available.
PRODUCT HIGHLIGHTS
PRODUCT DESCRIPTION
The AD706 is a dual, low power, bipolar op amp that has the low input bias current of a BiFET amplifier, but which offers a significantly lower IB drift over temperature. It utilizes superbeta bipolar input transistors to achieve picoampere input bias current levels (similar to FET input amplifiers at room temperature), while its IB typically only increases by 5x at 125C (unlike a BiFET amp, for which IB doubles every 10C for a 1000x increase at 125C). The AD706 also achieves the microvolt offset voltage and low noise characteristics of a precision bipolar input amplifier. Since it has only 1/20 the input bias current of an OP07, the AD706 does not require the commonly used "balancing" resistor. Furthermore, the current noise is 1/5 that of the OP07, which makes this amplifier usable with much higher source impedances. At 1/6 the supply current (per amplifier) of the OP07, the AD706 is better suited for today's higher density boards. The AD706 is an excellent choice for use in low frequency active filters in 12- and 14-bit data acquisition systems, in precision instrumentation and as a high quality integrator. The AD706 is internally compensated for unity gain and is available in five performance grades. The AD706J and AD706K are rated over the commercial temperature range of 0C to +70C. The AD706A and AD706B are rated over the industrial temperature range of -40C to +85C.
1. The AD706 is a dual low drift op amp that offers BiFET level input bias currents, yet has the low IB drift of a bipolar amplifier. It may be used in circuits using dual op amps such as the LT1024. 2. The AD706 provides both low drift and high dc precision. 3. The AD706 can be used in applications where a chopper amplifier would normally be required but without the chopper's inherent noise.
100
10
TYPICAL IB - nA
TYPICAL JFET AMP 1
0.1 AD706 0.01 -55
+25 +110 TEMPERATURE - C
+125
Figure 1. Input Bias Current vs. Temperature
REV. C
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: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 1997
AD706-SPECIFICATIONS (@ T = +25 C, V
A
CM
= 0 V and
Min
15 V dc, unless otherwise noted)
Min AD706K/B Typ Max 10 25 0.2 132 126 0.3 30 0.2 300 400 200 300 30 0.4 80 80 100 200 200 300 75 150 150 250 110 108 110 106 50 100 0.6 Units V V V/C dB dB V/Month pA pA pA/C pA pA pA pA pA/C pA pA V V pA pA dB dB dB dB dB
Parameter INPUT OFFSET VOLTAGE Initial Offset Offset vs. Temp, Average TC vs. Supply (PSRR) TMIN to TMAX Long Term Stability INPUT BIAS CURRENT1
Conditions
AD706J/A Typ Max 30 40 0.2 132 126 0.3 50 0.3 100 150 1.5
TMIN to TMAX VS = 2 V to 18 V VS = 2.5 V to 18 V 110 106
112 108
VCM = 0 V VCM = 13.5 V vs. Temp, Average TC TMIN to TMAX TMIN to TMAX INPUT OFFSET CURRENT vs. Temp, Average TC TMIN to TMAX TMIN to TMAX MATCHING CHARACTERISTICS Offset Voltage TMIN to TMAX Input Bias Current2 TMIN to TMAX Common-Mode Rejection TMIN to TMAX Power Supply Rejection Crosstalk (Figure 19a) FREQUENCY RESPONSE Unity Gain Crossover Frequency Slew Rate INPUT IMPEDANCE Differential Common Mode INPUT VOLTAGE RANGE Common-Mode Voltage Common-Mode Rejection Ratio INPUT CURRENT NOISE INPUT VOLTAGE NOISE 13.5 VCM = 13.5 V TMIN to TMAX 0.1 Hz to 10 Hz f = 10 Hz 0.1 Hz to 10 Hz f = 10 Hz f = 1 kHz VO = 12 V RLOAD = 10 k TMIN to TMAX VO = 10 V RLOAD = 2 k TMIN to TMAX RLOAD = 10 k TMIN to TMAX Short Circuit Gain = +1 200 150 200 150 13 13 110 108 TMIN to TMAX @ f = 10 Hz RL = 2 k 106 106 106 104 VCM = 0 V VCM = 13.5 V VCM = 0 V VCM = 13.5 V VCM = 0 V VCM = 13.5 V
200 250
110 160
30 0.6 80 80
150 250 250 350 150 250 300 500
150
150
G = -1 TMIN to TMAX
0.8 0.15 0.15 40 2 300 2 14 132 128 3 50 0.5 17 15 2000 1500 1000 1000 14 14 15 10,000 13.5 114 108
0.8 0.15 0.15 40 2 300 2 14 132 128 3 50 0.5 17 15 400 300 300 200 13 13 2000 1500 1000 1000 14 14 15 10,000 1.0 22
MHz V/s V/s M pF G pF V dB dB pA p-p fA/Hz V p-p nV/Hz nV/Hz V/mV V/mV V/mV V/mV V V mA pF
22
OPEN-LOOP GAIN
OUTPUT CHARACTERISTICS Voltage Swing Current Capacitive Load Drive Capability
-2-
REV. C
AD706
Parameter POWER SUPPLY Rated Performance Operating Range Quiescent Current, Total TMIN to TMAX TRANSISTOR COUNT # of Transistors Conditions Min AD706J/A Typ Max 15 0.75 0.8 90 Min AD706K/B Typ Max 15 0.75 0.8 90 Units V V mA mA
2.0
18 1.2 1.4
2.0
18 1.2 1.4
NOTES l Bias current specifications are guaranteed maximum at either input. 2 Input bias current match is the difference between corresponding inputs (I B of -IN of Amplifier #1 minus I B of -IN of Amplifier #2).
VOS #1 VOS # 2
CMRR match is the difference between
VCM VOS #1
for amplifier #1 and
VCM VOS # 2
for amplifier #2 expressed in dB.
PSRR match is the difference between
VSUPPLY
for amplifier #l and
VSUPPLY
for amplifier #2 expressed in dB.
All min and max specifications are guaranteed. Specifications subject to change without notice.
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 V Internal Power Dissipation (Total: Both Amplifiers)2 . . . . . . . . . . . . . . . . . . . . 650 mW Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VS Differential Input Voltage3 . . . . . . . . . . . . . . . . . . . . +0.7 Volts Output Short Circuit Duration . . . . . . . . . . . . . . . . Indefinite Storage Temperature Range (Q) . . . . . . . . . -65C to +150C Storage Temperature Range (N, R) . . . . . . . -65C to +125C Operating Temperature Range AD706J/K . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +70C AD706A/B . . . . . . . . . . . . . . . . . . . . . . . . . -40C to +85C Lead Temperature (Soldering 10 secs) . . . . . . . . . . . . +300C
NOTES 1 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 Specification is for device in free air: 8-Lead Plastic Package: JA = 100C/Watt 8-Lead Cerdip Package: JA = 110C/Watt 8-Lead Small Outline Package: JA = 155C/Watt 3 The input pins of this amplifier are protected by back-to-back diodes. If the differential voltage exceeds 0.7 volts, external series protection resistors should be added to limit the input current to less than 25 mA.
ABSOLUTE MAXIMUM RATINGS l
ORDERING GUIDE
Model AD706AN AD706JN AD706KN AD706JR AD706JR-REEL AD706AQ AD706BQ AD706AR AD706AR-REEL
Temperature Range -40C to +85C 0C to +70C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Description Plastic DIP Plastic DIP Plastic DIP SOIC Tape and Reel Cerdip Cerdip SOIC Tape and Reel
Package Option* N-8 N-8 N-8 R-8 Q-8 Q-8 R-8
*N = Plastic DIP; Q = Cerdip, R = Small Outline Package.
METALIZATION PHOTOGRAPH
Dimensions shown in inches and (mm). Contact factory for latest dimensions.
OUTPUT A
1 8
+VS
-INPUT A
2 7
0.118 (3.00)
OUTPUT B
6
+INPUT A
3
-INPUT B +INPUT B
-VS
4
5
0.074 (1.88)
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD706 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
REV. C
-3-
AD706-Typical Characteristics(@ +25 C, V =
S
1000 SAMPLE SIZE: 3000 800
NUMBER OF UNITS
15 V, unless otherwise noted)
1000 SAMPLE SIZE: 2400 800
1000 SAMPLE SIZE: 5100 800
NUMBER OF UNITS
600
600
NUMBER OF UNITS
-160 -80 0 80 160 INPUT BIAS CURRENT - pA
600
400
400
400
200
200
200
0 -80 -40 0 40 80 INPUT OFFSET VOLTAGE - V
0
0 -120 -60 0 60 120 INPUT OFFSET CURRENT - pA
Figure 2. Typical Distribution of Input Offset Voltage
Figure 3. Typical Distribution of Input Bias Current
Figure 4. Typical Distribution of Input Offset Current
INPUT COMMON-MODE VOLTAGE LIMIT - Volts (REFERRED TO SUPPLY VOLTAGES)
VS -0.5 OUTPUT VOLTAGE - Volts p-p -1.0 -1.5
35 30 25 20 15 10 5 0 1k
100
OFFSET VOLTAGE DRIFT - V/ C
SOURCE RESISTANCE MAY BE EITHER BALANCED OR UNBALANCED
10
FOR INDUSTRIAL TEMPERATURE RANGE
1.5 1.0 0.5 -VS 0 5 10 15 SUPPLY VOLTAGE - Volts 20
1.0
100k 10k FREQUENCY - Hz
1M
0.1 1k
100k 1M 10M 10k SOURCE RESISTANCE -
100M
Figure 5. Input Common-Mode Voltage Range vs. Supply Voltage
Figure 6. Large Signal Frequency Response
Figure 7. Offset Voltage Drift vs. Source Resistance
200
4
60 40 20 0
POSITIVE IB
CHANGE IN OFFSET VOLTAGE - V
SAMPLE SIZE: 375 -55 C TO 125 C
160
NUMBER OF UNITS
3
120
2
80
INPUT BIAS CURRENT - pA
-20 -40 -60 -15
NEGATIVE IB
1
40
0 -0.8 -0.4 0 0.4 0.8 OFFSET VOLTAGE DRIFT - V/ C
0 0 1 2 3 4 WARM-UP TIME - Minutes 5
-10 -5 0 5 10 15 COMMON-MODE VOLTAGE - Volts
Figure 8. Typical Distribution of Offset Voltage Drift
Figure 9. Change in Input Offset Voltage vs. Warm-Up Time
Figure 10. Input Bias Current vs. Common-Mode Voltage
-4-
REV. C
AD706
1000 1000
VOLTAGE NOISE - nV/ Hz
CURRENT NOISE - fA/ Hz
100
100
0.5 V
100
10k
10
10
20M VOUT
1
1
10 100 FREQUENCY - Hz
1000
1
1
10 100 FREQUENCY - Hz
1000
0
5 TIME - Seconds
10
Figure 11. Input Noise Voltage Spectral Density
Figure 12. Input Noise Current Spectral Density
Figure 13. 0.1 Hz to 10 Hz Noise Voltage
1000
+160 +140
180 160 140
QUIESCENT CURRENT - A
900
+120
CMRR - dB
800
+125 C +25 C
+80 +60 +40
PSRR - dB
+100
120 100 80
+ PSRR - PSRR
700
-55 C
60 40 20 0.1
+20 0 0.1
600 0 5 10 15 SUPPLY VOLTAGE - Volts 20
1
10
100 1k 10k 100k 1M FREQUENCY - Hz
1
10
100 1k 10k 100k 1M FREQUENCY - Hz
Figure 14. Quiescent Supply Current vs. Supply Voltage
Figure 15. Common-Mode Rejection Ratio vs. Frequency
Figure 16. Power Supply Rejection Ratio vs. Frequency
10M
140
0 OUTPUT VOLTAGE SWING - Volts 30 60
PHASE
+VS
(REFERRED TO SUPPLY VOLTAGES)
OPEN-LOOP VOLTAGE GAIN - dB
120 100 80 60 40
GAIN
-0.5 -1.0 -1.5
OPEN-LOOP VOLTAGE GAIN
+25 C +125 C
90 120 150 180 210 240 10 100 1k 10k 100k 1M 10M FREQUENCY - Hz
1M
PHASE SHIFT - Degrees
-55 C
+1.5 +1.0 +0.5 -VS 0 5 10 15 SUPPLY VOLTAGE - Volts 20
20 0 -20 0.01 0.1
100k
1
2
4 6 8 10 LOAD RESISTANCE - k
100
1
Figure 17. Open-Loop Gain vs. Load Resistance vs. Load Resistance
Figure 18. Open-Loop Gain and Phase Shift vs. Frequency
Figure 19. Output Voltage Swing vs. Supply Voltage
REV. C
-5-
AD706
-80 1000
CLOSED-LOOP OUTPUT IMPEDANCE -
100
-100
CROSSTALK - dB
10
AV = -1000
-120
1
AV = + 1
0.1
-140
0.01
IOUT = +1mA
-160 10
0.001 100 1k FREQUENCY - Hz 10k 100k 1 10 100 1k FREQUENCY - Hz 10k 100k
Figure 20a. Crosstalk vs. Frequency
+VS 0.1 F
Figure 21. Magnitude of Closed-Loop Output Impedance vs. Frequency
RF +VS
2
1/2 AD706
3 4
VOUT #1 1 20V p-p 0.1 F RL 2k 8 0.1 F VOUT
SINE WAVE GENERATOR -VS
1/2 AD706
VIN 4 RL 2k
CL
20k +VS 1F 2.21k 6 8 0.1 F VOUT #2 7
0.1 F SQUARE WAVE INPUT -VS
1/2 AD706
5
Figure 22a. Unity Gain Follower (For Large Signal Applications, Resistor RF Limits the Current Through the Input Protection Diodes)
V #2 CROSSTALK = 20 LOG10 OUT -20dB VOUT #1
Figure 20b. Crosstalk Test Circuit
Figure 22b. Unity Gain Follower Large Signal Pulse Response, RF = 10 k, CL = 1,000 pF
Figure 22c. Unity Gain Follower Small Signal Pulse Response, RF = 0 , CL = 100 pF
Figure 22d. Unity Gain Follower Small Signal Pulse Response, RF = 0 , CL = 1000 pF
-6-
REV. C
AD706
10k +VS
+
10k VIN
0.1 F VOUT RL 2.5k
-
8
1/2 AD706
+
SQUARE WAVE INPUT
4
CL
0.1F -VS
Figure 23a. Unity Gain Inverter Connection
Figure 23b. Unity Gain Inverter Large Signal Pulse Response, CL = 1,000 pF
Figure 23c. Unity Gain Inverter Small Signal Pulse Response, CL = 100 pF
Figure 23d. Unity Gain Inverter Small Signal Pulse Response, CL = 1000 pF
Figure 24 shows an in-amp circuit that has the obvious advantage of requiring only one AD706, rather than three op amps, with subsequent savings in cost and power consumption. The transfer function of this circuit (without RG) is:
increases with gain, once initial trimming is accomplished--but CMR is still dependent upon the ratio matching of Resistors R1 through R4. Resistor values for this circuit, using the optional gain resistor, RG, can be calculated using:
R4 VOUT = (VIN #1 - VIN #2 ) 1+ R3
for R1 = R4 and R2 = R3 Input resistance is high, thus permitting the signal source to have an unbalanced output impedance.
RG (OPTIONAL) R1 49.9k +VS 0.1 F
2
R1= R4 = 49.9 k 49.9 k R2 = R3 = 0.9 G -1 99.8 k RG = 0.06 G
where G = Desired Circuit Gain
R2
R3
R4 49.9k
Table I provides practical 1% resistance values. (Note that without resistor RG, R2 and R3 = 49.9 k/G-1.)
Table I. Operating Gains of Amplifiers A1 and A2 and Practical 1% Resistor Values for the Circuit of Figure 24
- +
8
1/2
AD706
1 5
RP*
3
A1
1/2
-
A2
7
Circuit Gain
OUTPUT 0.1 F
Gain of A1 Gain of A2 11.00 4.01 3.00 2.00 1.11 1.01 1.001 1.10 1.33 1.50 2.00 10.10 101.0 1001
R2, R3 499 k 150 k 100 k 49.9 k 5.49 k 499 49.9
R1, R4 49.9 k 49.9 k 49.9 k 49.9 k 49.9 k 49.9 k 49.9 k
VIN#1
1k RP*
AD706
6
+
-VS
4
VIN#2
1k VOUT = (VIN#1 - VIN#2) (1+ R4 ) + ( 2R4 ) R3 RG FOR R1 = R4, R2 = R3
*OPTIONAL INPUT PROTECTION RESISTOR FOR GAINS GREATER THAN 100 OR INPUT VOLTAGES EXCEEDING THE SUPPLY VOLTAGE.
1.10 1.33 1.50 2.00 10.1 101.0 1001
Figure 24. A Two Op-Amp Instrumentation Amplifier
Furthermore, the circuit gain may be fine trimmed using an optional trim resistor, RG. Like the three op-amp circuit, CMR REV. C -7-
For a much more comprehensive discussion of in-amp applications, refer to the Instrumentation Amplifier Applications Guide-- available free from Analog Devices, Inc.
AD706
R1 1M INPUT R2 1M C2 C1
3+
C3 R3 1M R4 1M C4 0.1 F
+VS 0.1 F
5+ 8
1/2
AD706
2- 4
1
1/2
*WITHOUT THE NETWORK, PINS 1 & 2, AND 6 & 7 OF THE AD706 ARE TIED TOGETHER. CAPACITORS C1 & C2 ARE SOUTHERN ELECTRONICS MPCC, POLYCARB 5%, 50 VOLT
AD706
6-
7
OUTPUT
R5 2M
C5 0.01 F OPTIONAL BALANCE RESISTOR NETWORKS*
R6 2M
C6 0.01 F
Figure 25. A 1 Hz, 4-Pole Active Filter
Figure 25 shows the AD706 in an active filter application. An important characteristic of the AD706 is that both the input bias current, input offset current and their drift remain low over most of the op amp's rated temperature range. Therefore, for most applications, there is no need to use the normal balancing resistor. Adding the balancing resistor enhances performance at high temperatures, as shown by Figure 26.
OFFSET VOLTAGE OF FILTER CIRCUIT (RTI) - V
A 1 Hz, 4-Pole, Active Filter
180
120
WITHOUT OPTIONAL BALANCE RESISTOR, R3
60
0
WITH OPTIONAL BALANCE RESISTOR, R3
-60
-120
-180
-40
0
+40 +80 TEMPERATURE - C
+120
Figure 26. VOS vs. Temperature Performance of the 1 Hz Filter
Table II. 1 Hz, 4-Pole, Low Pass Filter Recommended Component Values
Desired Low Pass Response Bessel Butterworth 0.1 dB Chebychev 0.2 dB Chebychev 0.5 dB Chebychev 1.0 dB Chebychev
Section 1 Frequency (Hz) 1.43 1.00 0.648 0.603 0.540 0.492
Q 0.522 0.541 0.619 0.646 0.705 0.785
Section 2 Frequency (Hz) 1.60 1.00 0.948 0.941 0.932 0.925
Q 0.806 1.31 2.18 2.44 2.94 3.56
C1 ( F) 0.116 0.172 0.304 0.341 0.416 0.508
C2 ( F) 0.107 0.147 0.198 0.204 0.209 0.206
C3 ( F) 0.160 0.416 0.733 0.823 1.00 1.23
C4 ( F) 0.0616 0.0609 0.0385 0.0347 0.0290 0.0242
PRINTED IN U.S.A.
0.0196 (0.50) x 45 0.0099 (0.25) 8 0 0.0500 (1.27) 0.0160 (0.41)
NOTE Specified Values are for a -3 dB point of 1.0 Hz. For other frequencies simply scale capacitors C1 through C4 directly, i.e.: for 3 Hz Bessel response, C1 = 0.0387 F, C2 = 0.0357 F, C3 = 0.0533 F, C4 = 0.0205 F.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
Cerdip (Q-8)
0.005 (0.13) MIN
8
Plastic Mini-DIP (N-8)
0.430 (10.92) 0.348 (8.84)
8 5
SOIC (R-8)
0.1968 (5.00) 0.1890 (4.80)
8 5
0.055 (1.4) MAX
5
0.310 (7.87) 0.220 (5.59)
1 4
0.280 (7.11) 0.240 (6.10)
1 4
0.2440 (6.20) 0.2284 (5.80)
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93)
1
4
0.1574 (4.00) 0.1497 (3.80)
PIN 1 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)
PIN 1 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93)
0.060 (1.52) 0.015 (0.38) 0.130 (3.30) MIN SEATING PLANE
PIN 1
0.102 (2.59) 0.094 (2.39)
0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.100 0.070 (1.78) SEATING PLANE 0.014 (0.36) (2.54) 0.030 (0.76) BSC
15 0
0.015 (0.38) 0.008 (0.20)
0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC
0.015 (0.381) 0.008 (0.204)
0.0098 (0.25) 0.0040 (0.10) 0.0500 0.0192 (0.49) SEATING (1.27) 0.0138 (0.35) 0.0098 (0.25) PLANE BSC 0.0075 (0.19)
-8-
REV. C
C1429b-2-12/97
-VS

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