ANALOG DEVICES OP 297 FPZ Datasheet

Dual Low Bias Current

FEATURES

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

APPLICATIONS

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

Precision Operational Amplifier

OP297

PIN CONFIGURATION

1

OUTA

2

–INA

+INA

A

3

4

Figure 1.

60

40

20

0

–20

INPUT CURRENT (pA)

–40

8

V+

OUTB

7

B

6

–INB

5

+INBV–

00300-001

V

= ±15V

S

V

= 0V

CM

I

–

B

IB+

I

OS

GENERAL DESCRIPTION

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.

Precision performance of the OP297 includes very low offset
(less than 50 V) and low drift (less than 0.6 V/°C). Open­loop 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 A.

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.

–60

–75 –50 –25 0 25 50 75 100 125

TEMPERATURE (° C)

00300-002

Figure 2. Low Bias Current over Temperature

400

1200 UNITS

300

200

NUMBER OF UNI TS

100

0

–100 –80 –60 –40 –20 0 20 40 60 80 100

INPUT OFFSET VOLTAGE (µV)

T

A

V

S

V

CM

= 25°C
= ±15V

= 0V

00300-003

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. G

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: [phone] www.analog.com
Fax: [phone] ©2008 Analog Devices, Inc. All rights reserved.

OP297

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1 

General Description ......................................................................... 1

Pin Configuration ............................................................................. 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Electrical Characteristics ............................................................. 3

Absolute Maximum Ratings ............................................................ 4

Thermal Resistance ...................................................................... 4

ESD Caution .................................................................................. 4

Typical Performance Characteristics ............................................. 5

Applications Information ................................................................ 9

REVISION HISTORY

4/08—Rev. F to Rev. G

Changes to Table 2 Conditions ....................................................... 3

Changes to Table 2 Power Supply Rejection Parameter .............. 3

Changes to Figure 5, Figure 6, Figure 7 ......................................... 5

Changes to Figure 16 ........................................................................ 6

Updated Outline Dimensions ....................................................... 13

Changes to Ordering Guide .......................................................... 14

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

AC Performance ............................................................................9

Guarding and Shielding ................................................................9

Open-Loop Gain Linearity ....................................................... 10

Application Circuits ....................................................................... 11

Precision Absolute Value Amplifier ......................................... 11

Precision Current Pump ............................................................ 11

Precision Positive Peak Detector .............................................. 11

Simple Bridge Conditioning Amplifier ................................... 11

Nonlinear Circuits ...................................................................... 12

Outline Dimensions ....................................................................... 13

Ordering Guide .......................................................................... 14

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. G | Page 2 of 16

OP297

SPECIFICATIONS

ELECTRICAL CHARACTERISTICS

@ VS = ±15 V, TA = 25°C, unless otherwise noted.

Table 1.

OP297E OP297F OP297G
Parameter Symbol Conditions Min Typ Max Min Typ Max Min Typ Max Unit

Input Offset Voltage VOS 25 50 50 100 80 200 µV
Long-Term Input Voltage

Stability
Input Offset Current IOS VCM = 0 V 20 100 35 150 50 200 pA
Input Bias Current IB VCM = 0 V +20 ±100 +35 ±150 +50 ±200 pA
Input Noise Voltage en
Input Noise Voltage Density en f
f
Input Noise Current Density in f
Input Resistance

Differential Mode RIN 30 30 30 MΩ

Common-Mode R
Large Signal Voltage Gain AVO V

Input Voltage Range

1

Common-Mode Rejection CMRR VCM = ±13 V 120 140 114 135 114 135 dB
Power Supply Rejection PSRR VS = ±2 V to

Output Voltage Swing V
R
Supply Current per Amplifier ISY No load 525 625 525 625 525 625 µA
Supply Voltage VS Operating range ±2 ±20 ±2 ±20 ±2 ±20 V
Slew Rate SR 0.05 0.15 0.05 0.15 0.05 0.15 V/µs
Gain Bandwidth Product GBWP AV = +1 500 500 500 kHz
Channel Separation CS V

Input Capacitance CIN 3 3 3 pF

1

Guaranteed by CMR test.

@ V

= ±15 V, −40°C ≤ TA ≤ +85°C, unless otherwise noted.

S

0.1 0.1 0.1 µV/month

0.1 Hz to 10 Hz 0.5 0.5 0.5 V p-p

p-p

= 10 Hz 20 20 20 nV/√Hz

OUT

= 1000 Hz 17 17 17 nV/√Hz

OUT

= 10 Hz 20 20 20 fA/√Hz

OUT

500 500 500 GΩ

INCM

OUT

= 2 kΩ

R

L

= ±10 V,

2000 4000 1500 3200 1200 3200 V/mV

VCM ±13 ±14 ±13 ±14 ±13 ±14 V

120 130 114 125 114 125 dB

±20 V

R

OUT

= 10 kΩ ±13 ±14 ±13 ±14 ±13 ±14 V

L

= 2 kΩ ±13 ±13.7 ±13 ±13.7 ±13 ±13.7 V

L

= 20 V p-p,

OUT

= 10 Hz

f

OUT

150 150 150 dB

Table 2.

OP297E OP297F OP297G
Parameter Symbol Conditions Min Typ Max Min Typ Max Min Typ Max Unit

Input Offset Voltage VOS 35 100 80 300 110 400 V
Average Input Offset Voltage Drift TCVOS 0.2 0.6 0.5 2.0 0.6 2.0 V/°C
Input Offset Current IOS VCM = 0 V 50 450 80 750 80 750 pA
Input Bias Current IB VCM = 0 V +50 ±450 +80 ±750 +80 ±750 pA
Large Signal Voltage Gain AVO V

Input Voltage Range

1

VCM ±13 ±13.5 ±13 ±13.5 ±13 ±13.5 V

OUT

= 2 kΩ

R

L

= ±10 V,

Common-Mode Rejection CMRR VCM = ±13 114 130 108 130 108 130 dB
Power Supply Rejection PSRR VS = ±2.5 V to

±20 V

Output Voltage Swing V

RL = 10 kΩ ±13 ±13.4 ±13 ±13.4 ±13 ±13.4 V

OUT

Supply Current per Amplifier ISY No load 550 750 550 750 550 750 A
Supply Voltage VS Operating range ±2.5 ±20 ±2.5 ±20 ±2.5 ±20 V

1

Guaranteed by CMR test.

1200 3200 1000 2500 800 2500 V/mV

114 108 108 dB

Rev. G | Page 3 of 16

OP297

ABSOLUTE MAXIMUM RATINGS

Table 3.

Parameter Rating

Supply Voltage ±20 V
Input Voltage1 ±20 V
Differential Input Voltage1 40 V
Output Short-Circuit Duration Indefinite
Storage Temperature Range

Z-Suffix −65°C to +175°C
P-Suffix, S-Suffix −65°C to +150°C

Operating Temperature Range

OP297E (Z-Suffix) −40°C to +85°C
OP297F, OP297G (P-Suffix, S-Suffix) −40°C to +85°C

Junction Temperature

Z-Suffix −65°C to +175°C
P-Suffix, S-Suffix −65°C to +150°C

Lead Temperature (Soldering, 60 sec) 300°C

1

For supply voltages less than ±20 V, the absolute maximum input voltage is

equal to the supply voltage.

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.

THERMAL RESISTANCE

θJA is specified for worst-case mounting conditions, that is, θJA
is specified for device in socket for CERDIP and PDIP pack­ages; θ

is specified for device soldered to printed circuit board

JA

for the SOIC package.

Table 4. Thermal Resistance

Package Type θJA θ

Unit

JC

8-Lead CERDIP (Z-Suffix) 134 12 °C/W
8-Lead PDIP (P-Suffix) 96 37 °C/W
8-Lead SOIC (S-Suffix) 150 41 °C/W

ESD CAUTION

–

1/2

OP297

+

50kΩ

50Ω

–

1/2

OP297

+

CHANNEL SEPARATION = 20 l og

Figure 4. Channel Separation Test Circuit

2kΩ

20V p-p @ 10Hz

V

1

V

2

V

1

V2/10000

00300-004

Rev. G | Page 4 of 16

OP297

TYPICAL PERFORMANCE CHARACTERISTICS

NUMBER OF UNIT S

400

300

200

100

1200 UNITS

T

A

V

S

V

CM

= 25°C
= ±15V

= 0V

60

40

20

–

I

B

0

–20

INPUT CURRENT (p A)

–40

IB+

I

OS

V

S

V

CM

= ±15V

= 0V

0

–100 –80 –60 –40 –20 0 20 40 60 80 100

INPUT OFFSET VO LTAGE (µV)

Figure 5. Typical Distribution of Input Offset Voltage

250

1200 UNITS

200

150

100

NUMBER OF UNITS

50

0

–100 –80 –60 –40 –20 0 20 40 60 80 100

INPUT BIAS CURRENT (pA)

TA = 25°C
V

= ±15V

S

V

CM

Figure 6. Typical Distribution of Input Bias Current

400

1200 UNITS

300

TA = 25°C
V

= ±15V

S

V

CM

= 0V

= 0V

–60

0300-005

–75 –50 –25 0 25 50 75 100 125

TEMPERATURE ( °C)

00300-008

Figure 8. Input Bias, Offset Current vs. Temperature

60

= ±15V

V

S

V

= 0V

CM

40

I

–

B

20

0

INPUT CURRENT (p A)

–20

–40

00300-006

–15 –10 –5 0 5 10 15

COMMON-MODE VOLTAGE (V)

IB+

I

OS

00300-009

Figure 9. Input Bias, Offset Current vs. Common-Mode Voltage

±3

TA = 25°C
V

= ±15V

S

V

= 0V

CM

±2

200

NUMBER OF UNIT S

100

0

–100 –80 –60 –40 –20 0 20 40 60 80 100

INPUT OFFSET CURRENT ( pA)

Figure 7. Typical Distribution of Input Offset Current

00300-007

Rev. G | Page 5 of 16

±1

DEVIATION FROM FI NAL VALUE (µV)

0

01234 5

TIME AFT ER POWER APP LIED (Mi nutes)

Figure 10. Input Offset Voltage Warm-Up Drift

0300-010

OP297

10k

BALANCED OR UNBALANCED
V

= ±15V

S

V

= 0V

CM

1k

100

–55°C ≤ TA ≤ +125°C

EFFECTIVE OFFSET VOLTAGE (µV)

TA = +25°C

10

100 1k 10k 100k 1M

10 10M

SOURCE RESIST ANCE (Ω)

Figure 11. Effective Offset Voltage vs. Source Resistance

0300-011

1300

NO LOAD

TOTAL SUPPLY CURRENT (µA)

1200

1100

1000

900

800

0

±5 ±10 ±15

SUPPLY VOLTAGE (V)

= +125°C

T

A

= +25°C

T

A

TA = –55°C

Figure 14. Total Supply Current vs. Supply Voltage

±20

00300-014

100

BALANCED OR UNBALANCED
V

= ±15V

S

V

= 0V

CM

10

1

EFFECTIVE OFFSET VOLTAGE DRIFT (µV/°C)

0.1
100 100M

1k 10k 10 0k 1M 10M

SOURCE RESIST ANCE (Ω)

Figure 12. Effective TCVOS vs. Source Resistance

35

30

25

20

15

10

VS = ±15V

5

OUTPUT SHORTED

0

TO GROUND

–5

–10

–15

–20

SHORT-CIRCUIT CURRENT (mA)

–25

–30

–35

01234

TIME FROM OUTPUT SHORT (Minutes)

TA = –55°C

TA = +25°C

TA = +125°C

TA = +125°C

TA = +25°C

TA = –55°C

Figure 13. Short-Circuit Current vs. Time, Temperature

160

140

120

100

80

COMMON-MO DE REJECTIO N (dB)

60

40

0300-012

1 10 100 1k 10k 100k 1M

FREQUENCY (Hz)

TA = 25°C
V

= ±15V

S

00300-015

Figure 15. Common-Mode Rejection vs. Frequency

160

140

120

100

80

60

POWER SUPPLY REJECTI ON (dB)

40

20

00300-013

1 10 100 1k 10k 100k 1M

0.1
FREQUENCY (Hz)

TA = 25°C
V

= ±15V

S

ΔV

= 10V p-p

S

00300-016

Figure 16. Power Supply Rejection vs. Frequency

Rev. G | Page 6 of 16

OP297

1k

100

10

TA = 25°C
V

= ±2V TO ±15V

S

VOLTAGE

NOISE

CURRENT

NOISE

1k

100

10

0

RL = 10kΩ
V

= ±15V

S

V

= 0V

CM

TA = +125°C

TA = +25°C

TA = –55°C

1

10M

CURRENT NOISE DENSITY (fA/ √Hz)

00300-017

DIFFERENTIAL INPUT VOLTAGE (10µV/DIV)

–15

Figure 20. Differential Input Voltage vs. Output Voltage

35

TA = 25°C
V

= ±15V

S

30

A

VCL

1% THD

f

= 1kHz

OUT

25

20

15

10

OUTPUT SWING (V p-p)

5

0

10 100 1k 10k

00300-018

VOLTAGE NOISE DENSI TY (nV/ √Hz)

1

11

10 100 k

FREQUENCY (Hz)

Figure 17. Voltage Noise Density and Current Noise Density vs. Frequency

10

TA = 25°C

= ±2V TO ±20V

V

S

1

10Hz

1kHz

1M100k10k1k100

TOTAL NOISE DENSITY (nV/√Hz)

0.01

0.1

1kHz

10Hz

SOURCE RESISTANCE (Ω)

Figure 18. Total Noise Density vs. Source Resistance

10k

TA = –55°C

TA = +25°C

TA = +125°C

1k

VS = ±15V
V

= ±10V

OUT

35

30

25

20

15

–10 –5 0 5 10 15

= +1

OUTPUT VOLT AGE (V)

LOAD RESISTANCE (Ω)

Figure 21. Output Swing vs. Load Resistance

TA = 25°C
V

= ±15V

S

A

= +1

VCL

1% THD

f

= 1kHz

OUT

R

= 10kΩ

L

00300-020

00300-021

OPEN-LOOP GAIN (V/mV)

100

1

432

LOAD RESIST ANCE (kΩ)

Figure 19. Open-Loop Gain vs. Load Resistance

51020

87659

0300-019

Rev. G | Page 7 of 16

10

OUTPUT SWING (V p-p)

5

0

100 1k 10k 100k

FREQUENCY (Hz)

Figure 22. Maximum Output Swing vs. Frequency

00300-022

OP297

100

80

GAIN

60

PHASE

40

20

OPEN-LOOP GAIN (dB)

0

–20

–40

1k 10k 100k 1M 10M100

FREQUENCY (Hz)

Figure 23. Open-Loop Gain, Phase vs. Frequency

70

TA = 25°C
V

= ±15V

S

60

A

= +1

VCL

V

= 100mV p-p

OUT

50

40

30

OVERSHOOT (%)

20

–EDGE

VS = ±15V
C
R

TA = –55°C

TA = +125°C

+EDGE

= 30pF

L

= 1MΩ

L

90

135

180

225

270

PHASE SHIFT (Degrees)

00300-023

1k

TA = 25°C
V

= ±15V

S

100

10

1

0.1

OUTPUT IMPEDANCE (Ω)

0.01

0.001
100 1k 10k 100k 1M10

FREQUENCY (Hz)

00300-025

Figure 25. Open-Loop Output Impedance vs. Frequency

10

0

10 100

LOAD CAPACITANCE ( pF)

1k 10k

Figure 24. Small Signal Overshoot vs. Load Capacitance

0300-024

Rev. G | Page 8 of 16

OP297

G

A

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 TCV

OS

are
degraded only minimally by high source resistance, even
when unbalanced.

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.

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 k load.

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).

100

90

100

90

10

0%

20mV

Figure 28. Large Signal Transient Response (A

5µs

VCL

= +1)

0300-028

GUARDING AND SHIELDING

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 PCB can have 100 pA of leakage currents
between adjacent traces, therefore 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.

UNITY-GAIN FOLLOWER

NONINVERTIN

MPLIFIER

10

10

0%

20mV 5µs

Figure 26. Small Signal Transient Response (C

100

90

10

0%

20mV

Figure 27. Small Signal Transient Response (C

= 100 pF, A

L

5µs

= 1000 pF, A

L

VCL

VCL

00300-026

= +1)

00300-027

= +1)

Rev. G | Page 9 of 16

–

1/2

OP297

+

INVERTING AMPLIFIER

8

–

1/2

OP297

+

B

Figure 29. Guard Ring Layout and Considerations

–

1/2

OP297

+

MINI-DIP

BOTTOM VIEW

1

A

00300-029

OP297

OPEN-LOOP GAIN LINEARITY

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

= ±15V

V

S

= 0V

V

CM

0

DIFFERENTIAL INPUT VOLTAGE (10µV/DIV)

–15

–10 –5 0 5 10 15

TA = +125°C

TA = +25°C

TA = –55°C

OUTPUT VOLT AGE (V)

Figure 30. Open-Loop Linearity of the OP297

00300-030

Rev. G | Page 10 of 16

OP297

V

APPLICATION CIRCUITS

PRECISION ABSOLUTE VALUE AMPLIFIER

The circuit in Figure 31 is a precision absolute value amplifier
with an input impedance of 30 MΩ. The high gain and low
TCV

of the OP297 ensure accurate operation with microvolt

OS

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.

+15V

C2

0.1µF

5

6

R2
2kΩ

R3

1kΩ

–

1/2

OP297

+

7

0V < V

OUT

< 10V

R1

1kΩ

C1

30pF

8

2

–

1/2

–15V

4

C3

0.1µF

1

V

IN

+

OP297

3

D1
1N4148

D2

1N4148

Figure 31. Precision Absolute Value Amplifier

PRECISION CURRENT PUMP

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 M with linearity better than 16 bits. R1 through R4
should be matched resistors.

R3

10kΩ

R1

10kΩ

2

–

3

R4

10kΩ

1/2

OP297

+

7

R2

V

IN

10kΩ

Figure 32. Precision Current Pump

1

+15V

8

1/2

OP297

–15V

R5

100kΩ

+

–

5

6

R5

V

IN

= = = 10mA/V

I

OUT

I

OUT

10mA MAX

V

IN

100Ω

00300-032

00300-031

PRECISION POSITIVE PEAK DETECTOR

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 C

and the bias

H

current of the OP297.

1kΩ

+15V

1N4148

2

–

OP297

1kΩ

V

3

IN

+

RESET

1/2

1

1kΩ

C

H

1kΩ

2N930

Figure 33. Precision Positive Peak Detector

6

–

OP297

5

+

1/2

–15V

0.1µF

0.1µF

7

V

OUT

SIMPLE BRIDGE CONDITIONING AMPLIFIER

Figure 34 shows a simple bridge conditioning amplifier using
the OP297. The transfer function is

R

R

Δ

V

REF

6

–

OP297

5

+

Δ+

1/2

⎞
⎟

RR

⎠

R + ΔR

8

4

F

R

should

F

R

F

2

–

1/2

1

V

ΔR

OUT

R

F

R

00300-034

OP297

3

+

7

V

= V

OUT

REF

R + ΔR

OUT

⎝

⎛

VV

=

⎜

REF

The REF43 provides an accurate and stable reference voltage for
the bridge. To maintain the highest circuit accuracy, R
be 0.1% or better with a low temperature coefficient.

15

REF43

4

Figure 34. Simple Bridge Condition Amplifier Using the OP297

00300-033

Rev. G | Page 11 of 16

OP297

NONLINEAR CIRCUITS

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.

⎞

V lnlnlnln

T1

⎞

⎞

⎛

I

IN

⎟

⎜

⎟

⎜

I

S1

⎠

⎝

⎛

I

IN

⎟

⎜

V

+

T2

⎟

⎜

I

S

2

⎠

⎝

⎛

I

OUT

⎟

⎜

V

=

T3

⎟

⎜

I

S3

⎠

⎝

All the transistors of the MAT04 are precisely matched and at
the same temperature, so the I

2ln

I

IN

= lnI

OUT

+ lnI

and VT terms cancel, where

S

REF

= ln(I

OUT

× I

REF

)

Exponentiating both sides of the equation leads to

2

()

I

I

OUT

IN

=

I

REF

Op Amp A2 forms a current-to-voltage converter, which gives
V

= R2 × I

OUT

equation for I

V

OUT

. Substituting (VIN/R1) for IIN and the previous

OUT

yields

OUT

2

⎞

⎛
⎜

=

⎜
⎝

V

R2

⎛

⎞

IN

⎟

⎜

⎟

I

⎝

REF

⎠

R1

⎟
⎠

A similar analysis made for the square root circuit of Figure 36
leads to its transfer function

()( )

IV

1

Q1

3

V+

8

–

1/2

OP297

+

4

V–

R1

REFIN

C2

100pF

R2

33kΩ

6

–

1/2

I

OUT

OP297

5

MAT04E

9

R3

50kΩ

+

–15V

R4
50kΩ

I

REF

7

6

Q2

5

8

Q3

10

1

=

R2V

OUT

2

C1

R1

33kΩ

V

IN

100pF

2

3

Figure 35. Squaring Amplifier

⎛

I

REF

⎜

V

+

T4

⎜

I

S4

⎝

7

V

OUT

14

13

Q4

12

R2

33kΩ

C2

100pF

6

–

1/2

7

V

14

12

R4
50kΩ

I

REF

OUT

00300-036

I

OUT

OP297

5

+

MAT04E

1

⎞
⎟
⎟
⎠

R1

33kΩ

V

IN

C1

100pF

2

3

V+

8

–

1/2

OP297

+

4

V–

Q1

3

7

6

Q2

5

10

1

13

Q4

8

9

Q3

R3

50kΩ

–15V

Figure 36. Square Root Amplifier

In these circuits, I

is a function of the negative power supply.

REF

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 I

REF

.

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 I

or R1; R2 can be varied to keep the output

REF

voltage within the usable range.

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%.

00300-035

Rev. G | Page 12 of 16

OP297

OUTLINE DIMENSIONS

0.400 (10.16)

0.365 (9.27)

0.355 (9.02)

0.210 (5.33)

0.150 (3.81)

0.130 (3.30)

0.115 (2.92)

0.022 (0.56)

0.018 (0.46)

0.014 (0.36)

MAX

8

1

0.100 (2.54)

0.070 (1.78)

0.060 (1.52)

0.045 (1.14)

BSC

5

4

0.280 (7.11)

0.250 (6.35)

0.240 (6.10)

0.015
(0.38)
MIN

SEATING
PLANE

0.005 (0.13)
MIN

0.060 (1.52)
MAX

0.015 (0.38)
GAUGE

PLANE

0.325 (8.26)

0.310 (7.87)

0.300 (7.62)

0.430 (10.92)
MAX

0.195 (4.95)

0.130 (3.30)

0.115 (2.92)

0.014 (0.36)

0.010 (0.25)

0.008 (0.20)

CONTROLL ING DIMENS IONS ARE IN INCHES; MILLIMETER DI MENSIONS
(IN PARENTHESES) ARE ROUNDED-OF F INCH EQUI VALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRI ATE FOR USE IN DESIGN.
CORNER LEADS MAY BE CONFIGURED AS WHOL E OR HALF LEADS.

COMPLIANT TO JEDEC STANDARDS MS-001

070606-A

Figure 37. 8-Lead Plastic Dual In-Line Package [PDIP]

P-Suffix (N-8)

Dimensions shown in inches and (millimeters)

0.005 (0.13)

0.200 (5.08)
MAX

0.200 (5.08)

0.125 (3.18)

0.023 (0.58)

0.014 (0.36)

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 38. 8-Lead Ceramic Dual In-Line Package [CERDIP]

Dimensions shown in inches and (millimeters)

0.055 (1.40)

MIN

0.100 (2.54) BSC

0.405 (10.29) MAX

MAX

58

14

0.070 (1.78)

0.030 (0.76)

Z-Suffix (Q-8)

0.310 (7.87)

0.220 (5.59)

0.060 (1.52)

0.015 (0.38)

0.150 (3.81)
MIN

SEATING
PLANE

0.320 (8.13)

0.290 (7.37)

15°

0°

0.015 (0.38)

0.008 (0.20)

Rev. G | Page 13 of 16

OP297

4.00 (0.1574)

3.80 (0.1497)

0.25 (0.0098)

0.10 (0.0040)

COPLANARITY

0.10

CONTROLL ING DIMENSI ONS ARE IN MILLIMETERS; INCH DI MENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRI ATE FOR USE IN DESIGN.

5.00 (0.1968)

4.80 (0.1890)

85

1

1.27 (0.0500)

SEATING

PLANE

COMPLIANT TO JEDEC STANDARDS MS-012-A A

BSC

6.20 (0.2441)

5.80 (0.2284)

4

1.75 (0.0688)

1.35 (0.0532)

0.51 (0.0201)

0.31 (0.0122)

0.25 (0.0098)

0.17 (0.0067)

0.50 (0.0196)

0.25 (0.0099)

8°
0°

1.27 (0.0500)

0.40 (0.0157)

45°

012407-A

Figure 39. 8-Lead Standard Small Outline Package [SOIC_N]

Narrow Body

S-Suffix (R-8)

Dimensions shown in millimeters and (inches)

ORDERING GUIDE

Model Temperature Range Package Description Package Options

OP297EZ −40°C to +85°C 8-Lead CERDIP Q-8 (Z-Suffix)
OP297FP −40°C to +85°C 8-Lead PDIP N-8 (P-Suffix)
OP297FPZ
OP297FS −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297FS-REEL −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297FS-REEL7 −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297FSZ
OP297FSZ-REEL
OP297FSZ-REEL7
OP297GP −40°C to +85°C 8-Lead PDIP N-8 (P-Suffix)
OP297GPZ
OP297GS −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297GS-REEL −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297GS-REEL7 −40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)
OP297GSZ
OP297GSZ-REEL
OP297GSZ-REEL7

1

Z = RoHS Compliant Part.

1

−40°C to +85°C 8-Lead PDIP N-8 (P-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

1

−40°C to +85°C 8-Lead PDIP N-8 (P-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

1

−40°C to +85°C 8-Lead SOIC_N R-8 (S-Suffix)

Rev. G | Page 14 of 16

OP297

NOTES

Rev. G | Page 15 of 16

OP297

NOTES

©2008 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D00300-0-4/08(G)

Rev. G | Page 16 of 16