ANALOG DEVICES OP 297 FPZ Datasheet

Page 1
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: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2008 Analog Devices, Inc. All rights reserved.
Page 2
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
Page 3
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
Page 4
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
+
50k
50
1/2
OP297
+
CHANNEL SEPARATION = 20 l og
Figure 4. Channel Separation Test Circuit
2k
20V p-p @ 10Hz
V
1
V
2
V
1
V2/10000
00300-004
Rev. G | Page 4 of 16
Page 5
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
Page 6
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
Page 7
OP297
1k
100
10
TA = 25°C V
= ±2V TO ±15V
S
VOLTAGE
NOISE
CURRENT
NOISE
1k
100
10
0
RL = 10k 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
= 10k
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
Page 8
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
= 1M
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
Page 9
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
Page 10
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 = 10k
= ±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
Page 11
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 2k
R3
1k
1/2
OP297
+
7
0V < V
OUT
< 10V
R1
1k
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
10k
R1
10k
2
3
R4
10k
1/2
OP297
+
7
R2
V
IN
10k
Figure 32. Precision Current Pump
1
+15V
8
1/2
OP297
–15V
R5
100k
+
5
6
R5
V
IN
= = = 10mA/V
I
OUT
I
OUT
10mA MAX
V
IN
100
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.
1k
+15V
1N4148
2
OP297
1k
V
3
IN
+
RESET
1/2
1
1k
C
H
1k
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
Page 12
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
33k
6
1/2
I
OUT
OP297
5
MAT04E
9
R3
50k
+
–15V
R4 50k
I
REF
7
6
Q2
5
8
Q3
10
1
=
R2V
OUT
2
C1
R1
33k
V
IN
100pF
2
3
Figure 35. Squaring Amplifier
I
REF
V
+
T4
I
S4
7
V
OUT
14
13
Q4
12
R2
33k
C2
100pF
6
1/2
7
V
14
12
R4 50k
I
REF
OUT
00300-036
I
OUT
OP297
5
+
MAT04E
1
⎞ ⎟ ⎟ ⎠
R1
33k
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
50k
–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
Page 13
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°
0.015 (0.38)
0.008 (0.20)
Rev. G | Page 13 of 16
Page 14
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
Page 15
OP297
NOTES
Rev. G | Page 15 of 16
Page 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
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