AD OP297FSZ

Dual Low Bias Current
Precision Operational Amplifier
OP297
PIN CONFIGURATION
Low offset voltage: 50 μV maximum
Low offset voltage drift: 0.6 μV/°C maximum
Very low bias current: 100 pA maximum
Very high open-loop gain: 2000 V/mV minimum
Low supply current (per amplifier): 625 μA maximum
Operates from ±2 V to ±20 V supplies
High common-mode rejection: 120 dB minimum
OUTA 1
8
V+
–INA 2
7
OUTB
+INA 3
6
–INB
V– 4
5
+INB
A
B
00300-001
FEATURES
Figure 1.
60
VS = ±15V
VCM = 0V
APPLICATIONS
40
INPUT CURRENT (pA)
20
IB–
0
IB+
–20
IOS
–60
–75
GENERAL DESCRIPTION
Precision performance of the OP297 includes very low offset,
under 50 μV, and low drift, below 0.6 μV/°C. Open-loop gain
exceeds 2000 V/mV, ensuring high linearity in every application.
Errors due to common-mode signals are eliminated by the
common-mode rejection of over 120 dB, which minimizes
offset voltage changes experienced in battery-powered systems.
The supply current of the OP297 is under 625 μA.
The OP297 uses a super-beta input stage with bias current
cancellation to maintain picoamp bias currents at all temperatures. This is in contrast to FET input op amps whose bias
currents start in the picoamp range at 25°C, but double for
every 10°C rise in temperature, to reach the nanoamp range
above 85°C. Input bias current of the OP297 is under 100 pA at
25°C and is under 450 pA over the military temperature range
per amplifier. This part can operate with supply voltages as low
as ±2 V.
–25
0
25
50
TEMPERATURE (°C)
75
100
125
Figure 2. Low Bias Current over Temperature
400
1200 UNITS
TA = 25°C
VS = ±15V
VCM = 0V
300
NUMBER OF UNITS
The OP297 is the first dual op amp to pack precision performance into the space saving, industry-standard 8-lead SOIC
package. The combination of precision with low power and
extremely low input bias current makes the dual OP297 useful
in a wide variety of applications.
–50
00300-002
–40
200
100
0
–100 –80
–60
–40
–20
0
20
40
INPUT OFFSET VOLTAGE (µV)
60
80
100
00300-003
Strain gage and bridge amplifiers
High stability thermocouple amplifiers
Instrumentation amplifiers
Photocurrent monitors
High gain linearity amplifiers
Long-term integrators/filters
Sample-and-hold amplifiers
Peak detectors
Logarithmic amplifiers
Battery-powered systems
Figure 3. Very Low Offset
Combining precision, low power, and low bias current, the
OP297 is ideal for a number of applications, including instrumentation amplifiers, log amplifiers, photodiode preamplifiers,
and long term integrators. For a single device, see the OP97; for
a quad device, see the OP497.
Rev. F
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
OP297
TABLE OF CONTENTS
Features .............................................................................................. 1
AC Performance ............................................................................9
Applications....................................................................................... 1
Guarding and Shielding................................................................9
General Description ......................................................................... 1
Open-Loop Gain Linearity ....................................................... 10
Pin Configuration............................................................................. 1
Applications..................................................................................... 11
Revision History ............................................................................... 2
Precision Absolute Value Amplifier......................................... 11
Specifications..................................................................................... 3
Precision Current Pump............................................................ 11
Electrical Characteristics............................................................. 3
Precision Positive Peak Detector.............................................. 11
Absolute Maximum Ratings............................................................ 4
Simple Bridge Conditioning Amplifier ................................... 11
Thermal Resistance ...................................................................... 4
Nonlinear Circuits...................................................................... 12
ESD Caution.................................................................................. 4
Outline Dimensions ....................................................................... 13
Typical Performance Characteristics ............................................. 5
Ordering Guide .......................................................................... 14
Applications Information ................................................................ 9
REVISION HISTORY
2/06—Rev. E to Rev. F
Updated Format..................................................................Universal
Changes to Features.......................................................................... 1
Deleted OP297 Spice Macro Model Section ................................. 9
Updated Outline Dimensions ....................................................... 13
Changes to Ordering Guide .......................................................... 14
7/03—Rev. D to Rev. E
Changes to TPCs 13 and 16 ............................................................ 4
Edits to Figures 12 and 14 ............................................................... 8
Changes to Nonlinear Circuits Section ......................................... 8
10/02—Rev. C to Rev. D
Edits to Figure 16...............................................................................6
10/02—Rev. B to Rev. C
Edits to Specifications .......................................................................2
Deleted Wafer Test Limits ................................................................3
Deleted Dice Characteristics............................................................3
Deleted Absolute Maximum Ratings..............................................4
Edits to Ordering Guide ...................................................................4
Updated Outline Dimensions....................................................... 12
Rev. F | Page 2 of 16
OP297
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
@ VS = ±15 V, TA = 25°C, unless otherwise noted.
Table 1.
OP297E
Parameter
Input Offset Voltage
Symbol
VOS
Conditions
Long-Term Input
Voltage Stability
Input Offset Current
Input Bias Current
Input Noise Voltage
Input Noise Voltage Density
IOS
IB
en p-p
en
VCM = 0 V
VCM = 0 V
0.1 Hz to 10 Hz
fO = 10 Hz
fO = 1000 Hz
fO = 10 Hz
Input Noise Current Density
Input Resistance
Differential Mode
Input Resistance
Common-Mode
Large Signal
Voltage Gain
Input Voltage Range 1
Common-Mode Rejection
Power Supply Rejection
Output Voltage Swing
in
RINCM
AVO
VCM
CMRR
PSRR
VO
ISY
VS
SR
GBWP
CS
Input Capacitance
CIN
VO = ±10 V
RL = 2 kΩ
VCM = ±13 V
VS = ±2 V to ±20 V
RL = 10 kΩ
RL = 2 kΩ
No Load
Operating Range
Typ
25
0.1
20
20
0.5
20
17
20
RIN
Supply Current per Amplifier
Supply Voltage
Slew Rate
Gain Bandwidth Product
Channel Separation
1
Min
2000
±13
120
120
±13
±13
±2
0.05
AV = +1
VO = 20 V p-p
fO = 10 Hz
OP297F
Max
50
Min
Typ
50
0.1
35
35
0.5
20
17
20
100
±100
OP297G
Max
100
Min
Typ
80
0.1
50
50
0.5
20
17
20
150
±150
Max
200
200
±200
Unit
μV
μV/mo
pA
pA
μV p-p
nV/√Hz
nV/√Hz
fA/√Hz
30
30
30
MΩ
500
500
500
GΩ
3200
±14
135
125
±14
±13.7
525
0.15
500
150
V/mV
V
dB
dB
V
V
μA
V
V/μs
kHz
dB
3
pF
4000
±14
140
130
±14
±13.7
525
1500
±13
114
114
±13
±13
625
±20
0.15
500
150
±2
0.05
3
3200
±14
135
125
±14
±13.7
525
1200
±13
114
114
±13
±13
625
±20
0.15
500
150
±2
0.05
3
625
±20
Guaranteed by CMR test.
@ VS = ±5 V, –40°C ≤ TA ≤ +85°C for OP297E/OP297F/OP297G, unless otherwise noted.
Table 2.
OP297E
Parameter
Input Offset Voltage
Symbol
VOS
Average Input Offset
Voltage Drift
Input Offset Current
Input Bias Current
Large Signal Voltage Gain
TCVOS
IOS
IB
AVO
Input Voltage Range 1
Common-Mode Rejection
Power Supply Rejection
VCM
CMRR
PSRR
Output Voltage Swing
Supply Current per Amplifier
Supply Voltage
1
Conditions
VCM = 0 V
VCM = 0 V
VO = ±10 V
RL = 2 kΩ
Min
OP297F
Typ
35
Max
100
0.2
50
50
0.6
450
±450
Min
OP297G
Typ
80
Max
300
0.5
80
80
2.0
750
±750
Min
Typ
110
Max
400
Unit
μV
0.6
80
80
2.0
750
±750
μV/°C
pA
pA
3200
±13.5
130
1000
±13
108
2500
±13.5
130
800
±13
108
2500
±13.5
130
V/mV
V
dB
VO
VCM = ±13
VS = ±2.5 V
to ±20 V
RL = 10 kΩ
1200
±13
114
114
±13
0.15
±13.4
108
±13
0.15
±13.4
108
±13
0.3
±13.4
dB
V
ISY
VS
No Load
Operating Range
± 2.5
550
750
±20
Guaranteed by CMR test.
Rev. F | Page 3 of 16
550
±2.5
750
±20
550
±2.5
750
±20
μA
V
OP297
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter
Supply Voltage
Input Voltage1
Differential Input Voltage1
Output Short-Circuit Duration
Storage Temperature Range
Z Package
P, S Packages
Operating Temperature Range
OP297E (Z)
OP297F, OP297G (P, S)
Junction Temperature
Z Package
P, S Packages
Lead Temperature
(Soldering, 60 sec)
1
Rating
±20 V
±20 V
40 V
Indefinite
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.
−65°C to +175°C
−65°C to +150°C
THERMAL RESISTANCE
−40°C to +85°C
−40°C to +85°C
θJA is specified for worst-case mounting conditions, that is, θJA
is specified for device in socket for CERDIP and PDIP packages; θJA is specified for device soldered to printed circuit board
for the SOIC package.
−65°C to +175°C
−65°C to +150°C
300°C
Table 4. Thermal Resistance
For supply voltages less than ±20 V, the absolute maximum input voltage is
equal to the supply voltage.
Package Type
8-Lead CERDIP (Z-Suffix)
8-Lead PDIP (P-Suffix)
8-Lead SOIC (S-Suffix)
θJA
134
96
150
ESD 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 this product 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.
–
1/2
OP297
+
V1 20V p-p @ 10Hz
2kΩ
50kΩ
50Ω
–
1/2
OP297
V2
CHANNEL SEPARATION = 20 log
V1
V2/10000
Figure 4. Channel Separation Test Circuit
Rev. F | Page 4 of 16
00300-004
+
θJC
12
37
41
Unit
°C/W
°C/W
°C/W
OP297
TYPICAL PERFORMANCE CHARACTERISTICS
400
60
VS = ±15V
VCM = 0V
TA = 25°C
VS = ±15V
VCM = 0V
1200 UNITS
40
INPUT CURRENT (pA)
NUMBER OF UNITS
300
200
20
IB–
0
IB+
–20
IOS
100
–80
–60
–40 –20
0
20
40
INPUT OFFSET VOLTAGE (pA)
60
80
100
–60
–75
00300-005
0
–100
Figure 5. Typical Distribution of Input Offset Voltage
0
25
50
TEMPERATURE (°C)
75
100
125
60
TA = 25°C
VS = ±15V
VCM = 0V
1200 UNITS
VS = ±15V
VCM = 0V
40
INPUT CURRENT (pA)
200
150
100
50
IB–
20
IB+
0
IOS
–80
–60
–40 –20
0
20
40
INPUT OFFSET VOLTAGE (pA)
60
80
100
–40
–15
00300-006
0
–100
Figure 6. Typical Distribution of Input Bias Current
±3
DEVIATION FROM FINAL VALUE (µV)
TA = 25°C
VS = ±15V
VCM = 0V
300
200
100
–80
–60
–40 –20
0
20
40
INPUT OFFSET VOLTAGE (pA)
60
80
100
10
15
TA = 25°C
VS = ±15V
VCM = 0V
±2
±1
0
00300-007
0
–100
–5
0
5
COMMON-MODE VOLTAGE (V)
Figure 9. Input Bias, Offset Current vs. Common-Mode Voltage
400
1200 UNITS
–10
00300-009
–20
0
1
2
3
4
TIME AFTER POWER APPLIED (Minutes)
Figure 10. Input Offset Voltage Warm-Up Drift
Figure 7. Typical Distribution of Input Offset Current
Rev. F | Page 5 of 16
5
00300-010
NUMBER OF UNITS
–25
Figure 8. Input Bias, Offset Current vs. Temperature
250
NUMBER OF UNITS
–50
00300-008
–40
OP297
1300
BALANCED OR UNBALANCED
VS = ±15V
VCM = 0V
1000
100
–55°C ≤ TA ≤ +125°C
1100
TA = +25°C
1000
TA = +25°C
100
1k
10k
100k
1M
10M
SOURCE RESISTANCE (Ω)
TA = –55°C
900
800
0
100
COMMON-MODE REJECTION (dB)
EFFECTIVE OFFSET VOLTAGE DRIFT (µV/°C)
10
1
100k
1M
10M
100M
SOURCE RESISTANCE (Ω)
120
100
80
60
1
100
1k
10k
FREQUENCY (Hz)
100k
1M
160
35
30
TA = 25°C
VS = ±15V
ΔVS = 10V p-p
TA = –55°C
POWER SUPPLY REJECTION (dB)
25
TA = +25°C
20
15
TA = +125°C
10
VS = ±15V
OUTPUT SHORTED
TO GROUND
5
0
–5
–10
–15
TA = +125°C
–20
TA = +25°C
–25
140
120
100
80
60
TA = –55°C
–30
0
1
2
3
TIME FROM OUTPUT SHORT (Minutes)
4
40
0.1
00300-013
SHORT-CIRCUIT CURRENT (mA)
10
Figure 15. Common-Mode Rejection Frequency
Figure 12. Effective TCVOS vs. Source Resistance
–35
±20
TA = 25°C
VS = ±15V
140
40
00300-012
10k
±15
160
BALANCED OR UNBALANCED
VS = ±15V
VCM = 0V
1k
±10
SUPPLY VOLTAGE (V)
Figure 14. Total Supply Current vs. Supply Voltage
Figure 11. Effective Offset Voltage vs. Source Resistance
0.1
100
±5
00300-015
10
TA = +125°C
1
10
100
1k
FREQUENCY (Hz)
10k
100k
Figure 16. Power Supply Rejection vs. Frequency
Figure 13. Short-Circuit Current vs. Time, Temperature
Rev. F | Page 6 of 16
1M
00300-016
10
1200
00300-014
TOTAL SUPPLY CURRENT (µA)
NO LOAD
00300-011
EFFECTIVE OFFSET VOLTAGE (µV)
10000
OP297
1000
VOLTAGE
NOISE
10
1
10
1
10
1
1000
100
FREQUENCY (Hz)
RL = 10kΩ
VS = ±15V
VCM = 0V
TA = +125°C
TA = +25°C
0
TA = –55°C
–15
–5
0
5
10
15
OUTPUT VOLTAGE (V)
Figure 17. Voltage Noise Density and Current Noise Density vs. Frequency
Figure 20. Differential Input Voltage vs. Output Voltage
10
35
TA = 25°C
VS = ±2V TO ±20V
30
OUTPUT SWING (V p-p)
TOTAL NOISE DENSITY (nV/√Hz)
–10
00300-020
CURRENT
NOISE
CURRENT NOISE DENSITY (fA/√Hz)
100
100
DIFFERENTIAL INPUT VOLTAGE (10µV/DIV)
TA = 25°C
VS = ±2V TO ±15V
00300-017
1
10Hz
1kHz
0.1
1kHz
25
TA = 25°C
VS = ±15V
AVCL = +1
1% THD
fO = 1kHz
20
15
10
5
103
104
105
SOURCE RESISTANCE (Ω)
106
107
0
10
00300-018
0.01
102
10k
Figure 21. Output Swing vs. Load Resistance
Figure 18. Total Noise Density vs. Source Resistance
35
TA = –55°C
TA = +25°C
VS = ±15V
VO = ±10V
TA = 25°C
VS = ±15V
AVCL = +1
1% THD
fO = 1kHz
RL = 10kΩ
30
OUTPUT SWING (V p-p)
10000
TA = +125°C
1000
25
20
15
10
5
100 1
2
5 6 7 8 9 10
3
4
LOAD RESISTANCE (kΩ)
20
0
100
00300-019
OPEN-LOOP GAIN (V/mV)
100
1k
LOAD RESISTANCE (Ω)
00300-021
10Hz
1k
10k
FREQUENCY (Hz)
Figure 22. Maximum Output Swing vs. Frequency
Figure 19. Open-Loop Gain vs. Load Resistance
Rev. F | Page 7 of 16
100k
00300-022
VOLTAGE NOISE DENSITY (nV/√Hz)
1000
OP297
1000
100
VS = ±15V
CL = 30pF
RL = 1MΩ
60
PHASE
40
TA = 25°C
VS = ±15V
100
TA = –55°C
20
OUTPUT IMPEDANCE (Ω)
OPEN-LOOP GAIN (dB)
GAIN
PHASE SHIFT (Deg)
80
0
10
1
0.1
0.01
–20
10k
100k
FREQUENCY (Hz)
1M
10M
Figure 23. Open-Loop Gain, Phase vs. Frequency
TA = 25°C
VS = ±15V
AVCL = +1
VOUT = 100mV p-p
–EDGE
40
+EDGE
30
20
10
0
0
100
1000
LOAD CAPACITANCE (pF)
10000
00300-024
OVERSHOOT (%)
50
100
1k
10k
FREQUENCY (Hz)
100k
Figure 25. Open-Loop Output Impedance vs. Frequency
70
60
0.001
10
Figure 24. Small Signal Overshoot vs. Load Capacitance
Rev. F | Page 8 of 16
1M
00300-025
1k
00300-023
TA = +125°C
–40
100
OP297
APPLICATIONS INFORMATION
Extremely low bias current over a wide temperature range
makes the OP297 attractive for use in sample-and-hold
amplifiers, peak detectors, and log amplifiers that must operate
over a wide temperature range. Balancing input resistances is
unnecessary with the OP297. Offset voltage and TCVOS are
degraded only minimally by high source resistance, even
when unbalanced.
100
90
The input pins of the OP297 are protected against large differential voltage by back-to-back diodes and current-limiting resistors.
Common-mode voltages at the inputs are not restricted and can
vary over the full range of the supply voltages used.
10
0%
20mV
00300-028
5µs
Figure 28. Large Signal Transient Response (AVCL = 1)
The OP297 requires very little operating headroom about the
supply rails and is specified for operation with supplies as low as
2 V. Typically, the common-mode range extends to within 1 V
of either rail. The output typically swings to within 1 V of the
rails when using a 10 kΩ load.
NONINVERTING AMPLIFIER
UNITY-GAIN FOLLOWER
AC PERFORMANCE
–
–
The ac characteristics of the OP297 are highly stable over its full
operating temperature range. Unity gain small signal response is
shown in Figure 26. Extremely tolerant of capacitive loading on
the output, the OP297 displays excellent response with 1000 pF
loads (see Figure 27).
+
+
1/2
OP297
1/2
OP297
MINI-DIP
BOTTOM VIEW
INVERTING AMPLIFIER
8
1
A
100
–
90
1/2
OP297
B
00300-029
+
Figure 29. Guard Ring Layout and Considerations
10
10
0%
5µs
00300-026
GUARDING AND SHIELDING
20mV
Figure 26. Small Signal Transient Response (CLOAD = 100 pF, AVCL = 1)
100
90
10
20mV
5µs
00300-027
0%
To maintain the extremely high input impedances of the
OP297, care is taken in circuit board layout and manufacturing.
Board surfaces must be kept scrupulously clean and free of
moisture. Conformal coating is recommended to provide a
humidity barrier. Even a clean PC board can have 100 pA of
leakage currents between adjacent traces, so guard rings should
be used around the inputs. Guard traces operate at a voltage
close to that on the inputs, as shown in Figure 29, to minimize
leakage currents. In noninverting applications, the guard ring
should be connected to the common-mode voltage at the
inverting input. In inverting applications, both inputs remain at
ground, so the guard trace should be grounded. Guard traces
should be placed on both sides of the circuit board.
Figure 27. Small Signal Transient Response (CLOAD = 1000 pF, AVCL = 1)
Rev. F | Page 9 of 16
The OP297 has both an extremely high gain of 2000 V/mV
minimum and constant gain linearity. This enhances the
precision of the OP297 and provides for very high accuracy in
high closed-loop gain applications. Figure 30 illustrates the
typical open-loop gain linearity of the OP297 over the military
temperature range.
RL = 10kΩ
VS = ±15V
VCM = 0V
TA = +125°C
TA = +25°C
0
TA = –55°C
–15
–10
–5
0
5
10
OUTPUT VOLTAGE (V)
Figure 30. Open-Loop Linearity of the OP297
Rev. F | Page 10 of 16
15
00300-030
OPEN-LOOP GAIN LINEARITY
DIFFERENTIAL INPUT VOLTAGE (10µV/DIV)
OP297
OP297
APPLICATIONS
PRECISION ABSOLUTE VALUE AMPLIFIER
PRECISION POSITIVE PEAK DETECTOR
The circuit in Figure 31 is a precision absolute value amplifier
with an input impedance of 30 MΩ. The high gain and low
TCVOS of the OP297 ensure accurate operation with microvolt
input signals. In this circuit, the input always appears as a
common-mode signal to the op amps. The CMR of the OP297
exceeds 120 dB, yielding an error of less than 2 ppm.
In Figure 33, the CH must be of polystyrene, Teflon®, or
polyethylene to minimize dielectric absorption and leakage.
The droop rate is determined by the size of CH and the bias
current of the OP297.
1kΩ
+15V
1N4148
C2
0.1µF
2
R3
1kΩ
R1
1kΩ
3
1/2
OP297
+
4
1
6
D2
1N4148
C3
0.1µF
+
1kΩ
1/2
OP297
+
RESET
1kΩ
7
1/2
OP297
+
R4
10kΩ
Figure 34 shows a simple bridge conditioning amplifier using
the OP297. The transfer function is
ΔR ⎞ R F
VOUT = VREF ⎛⎜
⎟
R
⎝ + ΔR ⎠ R
The REF43 provides an accurate and stable reference voltage for
the bridge. To maintain the highest circuit accuracy, RF should
be 0.1% or better with a low temperature coefficient.
R6
10kΩ
1
2
IOUT
10mA
4
R + ΔR
8
1/2
OP297
–
6
6
100Ω
= 10mA/V
–15V
00300-032
R5
VIN
3
–
1/2
OP297
1
VOUT
+
5
5
=
RF
REF43
+15V
7
0.1µF
15V
+
3
–
VOUT
2N930
VREF
2
+
7
SIMPLE BRIDGE CONDITIONING AMPLIFIER
R3
10kΩ
R2
10kΩ
1/2
OP297
Figure 33. Precision Positive Peak Detector
R2
2kΩ
Maximum output current of the precision current pump shown
in Figure 32 is ±10 mA. Voltage compliance is ±10 V with
±15 V supplies. Output impedance of the current transmitter
exceeds 3 MΩ with linearity better than 16 bits.
R1
10kΩ
–
–15V
PRECISION CURRENT PUMP
IOUT =
5
0V < VOUT < 10V
Figure 31. Precision Absolute Value Amplifier
VIN
6
1
CH
–
–15V
VIN
1/2
OP297
0.1µF
–
8
1/2
OP297
+
7
VOUT = VREF
RF
ΔR
R + ΔR R
4
Figure 34. A Simple Bridge Condition Amplifier Using the OP297
Figure 32. Precision Current Pump
Rev. F | Page 11 of 16
00300-034
VIN
8
–
5
D1
1N4148
00300-031
2
C1
30pF
VIN
1kΩ 3
–
00300-033
+15V
OP297
R2
33kΩ
NONLINEAR CIRCUITS
C2
100pF
⎛I
VT 1ln⎜⎜ IN
⎝ I S1
⎞
⎛I
⎟ + VT 2 ln⎜ IN
⎟
⎜I
⎠
⎝ S2
⎞
⎛I
⎟ = VT 3ln⎜ O
⎟
⎜I
⎠
⎝ S3
⎞
⎛I
⎟ + VT 4 ln⎜ REF
⎟
⎜ I
⎠
⎝ S4
6
IO
Q1
⎞
⎟
⎟
⎠
VIN
2 ln IIN = ln IO + ln IREF = ln (IO × IREF)
I REF
⎛ R2
VOUT = ⎜⎜
⎝ I REF
⎞⎛ VIN ⎞ 2
⎟⎜
⎟⎝ R1 ⎟⎠
⎠
+
1
8
Q3
10
9
R3
50kΩ
4
R4
50kΩ
–15V
An important consideration for the squaring circuit is that a
sufficiently large input voltage can force the output beyond the
operating range of the output op amp. Resistor R4 can be
changed to scale IREF or R1; R2 can be varied to keep the output
voltage within the usable range.
(VIN )(I REF )
VOUT = R2
Unadjusted accuracy of the square root circuit is better than
0.1% over an input voltage range of 100 mV to 10 V. For a
similar input voltage range, the accuracy of the squaring circuit
is better than 0.5%.
R1
C2
100pF
R2
33kΩ
6
IO
1
Q1
3
+
Q3
10
8
4
V–
VOUT
+
MAT04E
8
C1
100pF V+
1/2
OP297
7
7
Q2
6
5
–
5
–
1/2
OP297
1
IREF
9
14
13
Q4
12
R3
50kΩ
R4
50kΩ
–15V
00300-035
2
3
8
1/2
OP297
7
14
Q4
12
In these circuits, IREF is a function of the negative power supply.
To maintain accuracy, the negative supply should be well regulated. For applications where very high accuracy is required, a
voltage reference can be used to set IREF.
A similar analysis made for the square root circuit of Figure 36
leads to its transfer function
2
–
13
Figure 36. Square Root Amplifier
Op Amp A2 forms a current-to-voltage converter, which gives
VOUT = R2 × IO. Substituting (VIN/R1) for IIN and the above
equation for IO yields
VIN
2
MAT04E
1
Q2
5
VOUT
+
V–
(I )2
= IN
R1
33kΩ
R1
33kΩ
3
Exponentiating both sides of the equation leads to
IO
6
V+
7
IREF
3
C1
100pF
All the transistors of the MAT04 are precisely matched and at
the same temperature, so the IS and VT terms cancel, where
5
–
1/2
OP297
Figure 35. Squaring Amplifier
Rev. F | Page 12 of 16
00300-036
Due to its low input bias currents, the OP297 is an ideal log
amplifier in nonlinear circuits such as the square and square
root circuits shown in Figure 35 and Figure 36. Using the
squaring circuit of Figure 35 as an example, the analysis begins
by writing a voltage loop equation across Transistor Q1,
Transistor Q2, Transistor Q3, and Transistor Q4.
OP297
OUTLINE DIMENSIONS
0.400 (10.16)
0.365 (9.27)
0.355 (9.02)
8
1
5
4
0.280 (7.11)
0.250 (6.35)
0.240 (6.10)
0.005 (0.13)
MIN
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
PIN 1
0.100 (2.54)
BSC
0.210
(5.33)
MAX
0.150 (3.81)
0.130 (3.30)
0.115 (2.92)
8
0.060 (1.52)
MAX
1
4
0.100 (2.54) BSC
0.015 (0.38)
GAUGE
PLANE
SEATING
PLANE
0.014 (0.36)
0.010 (0.25)
0.008 (0.20)
0.430 (10.92)
MAX
0.005 (0.13)
MIN
5
0.310 (7.87)
0.220 (5.59)
0.195 (4.95)
0.130 (3.30)
0.115 (2.92)
0.015
(0.38)
MIN
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
0.055 (1.40)
MAX
0.320 (8.13)
0.290 (7.37)
0.405 (10.29) MAX
0.060 (1.52)
0.015 (0.38)
0.200 (5.08)
MAX
0.150 (3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.070 (1.78)
0.060 (1.52)
0.045 (1.14)
0.023 (0.58)
0.014 (0.36)
0.070 (1.78)
0.030 (0.76)
SEATING
PLANE
15°
0°
0.015 (0.38)
0.008 (0.20)
COMPLIANT TO JEDEC STANDARDS MS-001-BA
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS.
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 37. 8-Lead Plastic Dual In-Line Package [PDIP]
P-Suffix (N-8)
Dimensions shown in inches and (millimeters)
Figure 38. 8-Lead Ceramic Dual In-Line Package [CERDIP]
Z-Suffix (Q-8)
Dimensions shown in inches and (millimeters)
5.00 (0.1968)
4.80 (0.1890)
8
4.00 (0.1574)
3.80 (0.1497) 1
5
1.27 (0.0500)
BSC
0.25 (0.0098)
0.10 (0.0040)
6.20 (0.2440)
4 5.80 (0.2284)
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
COPLANARITY
SEATING 0.31 (0.0122)
0.10
PLANE
0.50 (0.0196)
× 45°
0.25 (0.0099)
8°
0.25 (0.0098) 0° 1.27 (0.0500)
0.40 (0.0157)
0.17 (0.0067)
COMPLIANT TO JEDEC STANDARDS MS-012-AA
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 39. 8-Lead Standard Small Outline Package (SOIC)
Narrow Body
S-Suffix (R-8)
Dimensions shown in millimeters and (inches)
Rev. F | Page 13 of 16
OP297
ORDERING GUIDE
Model
OP297EZ
Temperature Range
−40°C to +85°C
Package Description
8-Lead CERDIP
Package Options
Q-8
OP297FP
OP297FPZ 1
OP297FS
OP297FS-REEL
OP297FS-REEL7
OP297FSZ1
OP297FSZ-REEL1
OP297FSZ-REEL71
OP297GP
OP297GPZ1
OP297GS
OP297GS-REEL
OP297GS-REEL7
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
8-Lead PDIP
8-Lead PDIP
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
8-Lead PDIP
8-Lead PDIP
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
N-8
N-8
R-8
R-8
R-8
R-8
R-8
R-8
N-8
N-8
R-8
R-8
R-8
OP297GSZ1
OP297GSZ-REEL1
OP297GSZ-REEL71
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
8-Lead SOIC
8-Lead SOIC
8-Lead SOIC
R-8
R-8
R-8
1
Z = PB-free part.
Rev. F | Page 14 of 16
OP297
NOTES
Rev. F | Page 15 of 16
OP297
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
C00300-0-2/06(F)
Rev. F | Page 16 of 16