LMV796, LMV797
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SNOSAU9D – MARCH 2006 – REVISED MARCH 2013
LMV796/LMV796Q/LMV797 17 MHz, Low Noise, CMOS Input, 1.8V Operational Amplifiers
Check for Samples: LMV796, LMV797
FEATURES
DESCRIPTION
1
(Typical 5V Supply, Unless Otherwise Noted)
2
•
•
•
•
•
•
•
•
•
Input Referred Voltage Noise 5.8 nV/√Hz
Input Bias Current 100 fA
Unity Gain Bandwidth 17 MHz
Supply Current per Channel
– LMV796/LMV796Q 1.15 mA
– LMV797 1.30 mA
Rail-to-Rail Output Swing
– @ 10 kΩ Load 25 mV from Rail
– @ 2 kΩ Load 45 mV from Rail
Guaranteed 2.5V and 5.0V Performance
Total Harmonic Distortion 0.01% @ 1kHz, 600Ω
Temperature Range −40°C to 125°C
LMV796Q is an Automotive Grade Product that
is AEC-Q100 Grade 1 Qualified and is
Manufactured on an Automotive Grade Flow.
APPLICATIONS
•
•
•
•
•
•
Photodiode Amplifiers
Active Filters and Buffers
Low Noise Signal Processing
Medical Instrumentation
Sensor Interface Applications
Automotive
The LMV796/LMV796Q (Single) and the LMV797
(Dual) low noise, CMOS input operational amplifiers
offer a low input voltage noise density of 5.8 nV/√Hz
while consuming only 1.15 mA (LMV796/LMV796Q)
of quiescent current. The LMV796/LMV796Q and
LMV797 are unity gain stable op amps and have gain
bandwidth of 17 MHz. The LMV796/LMV796Q/
LMV797 have a supply voltage range of 1.8V to 5.5V
and can operate from a single supply. The
LMV796/LMV796Q/LMV797 each feature a rail-to-rail
output stage capable of driving a 600Ω load and
sourcing as much as 60 mA of current.
The LMV796/LMV796Q family provides optimal
performance in low voltage and low noise systems. A
CMOS input stage, with typical input bias currents in
the range of a few femtoAmperes, and an input
common mode voltage range, which includes ground,
make the LMV796/LMV796Q and the LMV797 ideal
for low power sensor applications.
The LMV796/LMV796Q/LMV797 are manufactured
using TI’s advanced VIP50 process. The LMV796/
LMV796Q are offered in 5–pin SOT-23 package. The
LMV797 is offered in 8–pin VSSOP package.
Typical Application
CF
100
+
V = 5.5V
IIN
CCM
CD
VB
+
+
VOUT
CIN = CD + CCM
VOUT
= - RF
IIN
VOLTAGE NOISE (nV/ Hz)
RF
V+ = 2.5V
10
1
1
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 1. Photodiode Transimpedance Amplifier
Figure 2. Input Referred Voltage Noise vs.
Frequency
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006–2013, Texas Instruments Incorporated
LMV796, LMV797
SNOSAU9D – MARCH 2006 – REVISED MARCH 2013
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings (1) (2)
Human Body Model
ESD Tolerance (3)
2000V
Machine Model
200V
Charge-Device Model
1000V
VIN Differential
±0.3V
Supply Voltage (V+ – V−)
6.0V
Input/Output Pin Voltage
V+ +0.3V, V− −0.3V
−65°C to 150°C
Storage Temperature Range
Junction Temperature (4)
+150°C
Soldering Information
(1)
(2)
(3)
(4)
Infrared or Convection (20 sec)
235°C
Wave Soldering Lead Temperature (10 sec)
260°C
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not ensured. For ensured specifications and the test
conditions, see the Electrical Characteristics tables.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
Human Body Model is 1.5kΩ in series with 100pF. Machine Model is 0Ω in series with 200pF.
The maximum power dissipation is a function of TJMAX, θJA. The maximum allowable power dissipation at any ambient temperature is PD
= (TJMAX - TA) / θJA. All numbers apply for packages soldered directly onto a PC Board.
Operating Ratings (1)
Temperature Range (2)
−40°C to 125°C
Supply Voltage (V+ – V−)
Package Thermal Resistance (θJA) (2)
(1)
(2)
−40°C ≤ TA ≤ 125°C
2.0V to 5.5V
0°C ≤ TA ≤ 125°C
1.8V to 5.5V
5-Pin SOT-23
180°C/W
8-Pin VSSOP
236°C/W
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is intended to be functional, but specific performance is not ensured. For ensured specifications and the test
conditions, see the Electrical Characteristics tables.
The maximum power dissipation is a function of TJMAX, θJA. The maximum allowable power dissipation at any ambient temperature is PD
= (TJMAX - TA) / θJA. All numbers apply for packages soldered directly onto a PC Board.
2.5V Electrical Characteristics
Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 2.5V, V− = 0V, VCM = V+/2 = VO. Boldface limits apply
at the temperature extremes.
Symbol
Parameter
VOS
Input Offset Voltage
TC VOS
Input Offset Voltage Temperature Drift
Min
Conditions
(1)
LMV796/LMV796Q (3)
LMV797
Input Bias Current
VCM = 1.0V
(1)
(2)
(3)
(4)
(5)
2
Input Offset Current
(1)
Units
0.1
±1.35
±1.65
mV
μV/°C
−1.8
0.05
1
25
0.05
1
100
(4) (5)
−40°C ≤ TA ≤ 125°C
IOS
Max
(2)
−1.0
(3)
−40°C ≤ TA ≤ 85°C
IB
Typ
VCM = 1.0V (5)
10
pA
fA
Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using the
statistical quality control (SQC) method.
Typical values represent the parametric norm at the time of characterization.
Offset voltage average drift is determined by dividing the change in VOS by temperature change.
Positive current corresponds to current flowing into the device.
This parameter is specified by design and/or characterization and is not tested in production.
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2.5V Electrical Characteristics (continued)
Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 2.5V, V− = 0V, VCM = V+/2 = VO. Boldface limits apply
at the temperature extremes.
Symbol
CMRR
Min
Typ
80
75
94
2.0V ≤ V ≤ 5.5V, VCM = 0V
80
75
100
1.8V ≤ V+ ≤ 5.5V, VCM = 0V
80
98
Parameter
Common Mode Rejection Ratio
Conditions
0V ≤ VCM ≤ 1.4V
+
PSRR
CMVR
AVOL
Power Supply Rejection Ratio
Common Mode Voltage Range
Open Loop Voltage Gain
CMRR ≥ 60 dB
CMRR ≥ 55 dB
VOUT = 0.15V to 2.2V,
RLOAD = 2 kΩ to V+/2
IS
Supply Current per Amplifier
SR
Slew Rate
GBW
Gain Bandwidth
en
(1)
Units
dB
1.5
1.5
85
80
98
LMV797
82
78
92
88
84
110
25
75
82
RLOAD = 10 kΩ to V+/2
20
65
71
RLOAD = 2 kΩ to V+/2
30
75
78
RLOAD = 10 kΩ to V+/2
15
65
67
Sourcing to V−
VIN = 200 mV (6)
35
28
47
Sinking to V+
VIN = –200 mV (6)
7
5
15
V
dB
RLOAD = 2 kΩ to V+/2
Output Voltage Swing Low
Output Current
Max
dB
LMV796/LMV796Q
VOUT
IOUT
(2)
−0.3
-0.3
VOUT = 0.15V to 2.2V,
RLOAD = 10 kΩ to V+/2
Output Voltage Swing High
(1)
mV from
either rail
mA
LMV796/LMV796Q
0.95
1.30
1.65
LMV797
per channel
1.1
1.50
1.85
mA
AV = +1, Rising (10% to 90%)
8.5
AV = +1, Falling (90% to 10%)
10.5
14
MHz
Input Referred Voltage Noise Density
f = 1 kHz
6.2
nV/√Hz
in
Input Referred Current Noise Density
f = 1 kHz
0.01
pA/√Hz
THD+N
Total Harmonic Distortion + Noise
f = 1 kHz, AV = 1, RLOAD = 600Ω
0.01
%
(6)
V/μs
The short circuit test is a momentary test, the short circuit duration is 1.5ms.
5V Electrical Characteristics
Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 5V, V− = 0V, VCM = V+/2 = VO. Boldface limits apply at
the temperature extremes.
Symbol
Parameter
VOS
Input Offset Voltage
TC VOS
Input Offset Voltage Temperature Drift
(1)
(2)
(3)
Conditions
Min
(1)
Typ
Max
(1)
Units
0.1
±1.35
±1.65
mV
(2)
LMV796/LMV796Q (3)
−1.0
LMV797 (3)
−1.8
μV/°C
Limits are 100% production tested at 25°C. Limits over the operating temperature range are specified through correlations using the
statistical quality control (SQC) method.
Typical values represent the parametric norm at the time of characterization.
Offset voltage average drift is determined by dividing the change in VOS by temperature change.
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5V Electrical Characteristics (continued)
Unless otherwise specified, all limits are specified for TA = 25°C, V+ = 5V, V− = 0V, VCM = V+/2 = VO. Boldface limits apply at
the temperature extremes.
−40°C ≤ TA ≤ 85°C
0.1
1
25
−40°C ≤ TA ≤ 125°C
0.1
1
100
(4) (5)
IB
Input Bias Current
VCM = 2.0V
IOS
Input Offset Current
VCM = 2.0V (5)
Common Mode Rejection Ratio
0V ≤ VCM ≤ 3.7V
80
75
100
2.0V ≤ V+ ≤ 5.5V, VCM = 0V
80
75
100
1.8V ≤ V+ ≤ 5.5V, VCM = 0V
80
98
CMRR
PSRR
CMVR
AVOL
10
Power Supply Rejection Ratio
Common Mode Voltage Range
Open Loop Voltage Gain
CMRR ≥ 60 dB
CMRR ≥ 55 dB
Output Voltage Swing High
85
80
97
LMV797
82
78
89
88
84
110
35
75
82
RLOAD = 10 kΩ to V+/2
25
65
71
LMV796/LM796Q
42
75
78
LMV797
45
80
83
20
65
67
+
RLOAD = 2 kΩ to V /2
Output Voltage Swing Low
RLOAD = 10 kΩ to V+/2
Output Current
Sourcing to V−
VIN = 200 mV (6)
45
37
60
Sinking to V+
VIN = –200 mV (6)
10
6
21
LMV796/LMV796Q
IS
Supply Current per Amplifier
LMV797per channel
1.40
1.75
1.30
1.70
2.05
6.0
9.5
AV = +1, Falling (90% to 10%)
7.5
11.5
mV from
either rail
mA
1.15
AV = +1, Rising (10% to 90%)
V
dB
RLOAD = 2 kΩ to V+/2
VOUT
IOUT
dB
4
4
LMV796/LMV796Q
VOUT = 0.3V to 4.7V,
RLOAD = 10 kΩ to V+/2
fA
dB
−0.3
-0.3
VOUT = 0.3V to 4.7V,
RLOAD = 2 kΩ to V+/2
pA
mA
SR
Slew Rate
GBW
Gain Bandwidth
17
MHz
en
Input Referred Voltage Noise Density
f = 1 kHz
5.8
nV/√Hz
in
Input Referred Current Noise Density
f = 1 kHz
0.01
pA/√Hz
THD+N
Total Harmonic Distortion + Noise
f = 1 kHz, AV = 1, RLOAD = 600Ω
0.01
%
(4)
(5)
(6)
4
V/μs
Positive current corresponds to current flowing into the device.
This parameter is specified by design and/or characterization and is not tested in production.
The short circuit test is a momentary test, the short circuit duration is 1.5ms.
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SNOSAU9D – MARCH 2006 – REVISED MARCH 2013
Connection Diagram
5
1
+
V
OUT A
-IN A
V
-
2
7
+
+
V
OUT B
2
+
+IN
8
1
-
OUTPUT
3
+IN A
4
-IN
V
Figure 3. 5-Pin SOT-23
Top View
-
3
4
+-
6
5
-IN B
+IN B
Figure 4. 8-Pin VSSOP
Top View
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Typical Performance Characteristics
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Supply Current vs. Supply Voltage (LMV796/LMV796Q)
Supply Current vs. Supply Voltage (LMV797)
2
2
1.6
1.6
SUPPLY CURRENT (mA)
SUPPLY CURRENT (mA)
125°C
125°C
25°C
1.2
0.8
-40°C
0.4
0
1.5
2.5
3.5
4.5
25°C
1.2
-40°C
0.8
0.4
0
1.5
5.5 6.0
2.5
3.5
+
4.5
5.5
6
+
V (V)
V (V)
Figure 5.
Figure 6.
VOS vs. VCM
0.5
VOS vs. VCM
0.6
+
V = 1.8V
0.55
0.45
+
V = 2.5V
125°C
0.5
0.4
0.45
0.3
VOS (mV)
VOS (mV)
-40°C
0.35
25°C
0.25
0.4
0.35
25°C
0.3
0.25
0.2
0.15
0.1
-0.3
-40°C
0.2
125°C
0.15
0
0.3
0.6
0.9
0.1
-0.3
1.2
Figure 7.
Figure 8.
VOS vs. VCM
VOS vs. Supply Voltage
+
0.45
0.4
0.4
-40°C
0.35
0.35
0.3
0.3
VOS (mV)
VOS (mV)
1.8
0.5
V = 5V
0.45
25°C
0.25
0.2
-40°C
0.25
25°C
0.2
0.15
0.15
125°C
0.1
125°C
0.1
0.05
0.05
0
0.6
1.5
2.4
3.3
4.2
1.5
2.5
3.5
4.5
5.5 6.0
+
VCM (V)
V (V)
Figure 9.
6
1.1
VCM (V)
0.5
0
-0.3
0.4
VCM (V)
Figure 10.
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Slew Rate vs. Supply Voltage
Input Bias Current vs. VCM
1.5
13
+
V = 5V
1
12
-40°C
FALLING
0
IBIAS (pA)
SLEW RATE (V/Ps)
0.5
11
10
9
-0.5
25°C
-1
-1.5
8
-2
RISING
7
-2.5
6
1.8
-3
2.3
2.8
3.3
3.8
4.3
4.8
0
5.3 5.5
1
2
+
V (V)
Figure 11.
4
Figure 12.
Input Bias Current vs. VCM
50
Sourcing Current vs. Supply Voltage
80
+
V = 5V
40
70
30
125°C
60
20
125°C
ISOURCE (mA)
IBIAS (pA)
3
VCM (V)
10
0
85°C
-10
-40°C
50
25°C
40
30
-20
20
-30
10
-40
0
-50
0
1
2
3
1
4
2
3
VCM (V)
4
5
6
V+ (V)
Figure 13.
Figure 14.
Sinking Current vs. Supply Voltage
Sourcing Current vs. Output Voltage
35
70
30
60
125°C
125°C
50
ISOURCE (mA)
ISINK (mA)
25
25°C
20
15
-40°C
10
-40°C
40
25°C
30
20
5
10
0
0
1
2
3
4
5
6
0
+
1
2
3
V (V)
VOUT (V)
Figure 15.
Figure 16.
4
5
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Sinking Current vs. Output Voltage
Positive Output Swing vs. Supply Voltage
40
30
RLOAD = 10 k:
35
VOUT FROM RAIL (mV)
125°C
25
ISINK (mA)
20
25°C
15
10
-40°C
5
125°C
25
25°C
20
-40°C
15
10
5
0
1.8
0
0
1
2
3
4
5
2.5
3.2
VOUT (V)
V (V)
Figure 17.
Figure 18.
5.3
6
Positive Output Swing vs. Supply Voltage
25
50
45
VOUT FROM RAIL (mV)
20
15
125°C
10
5
125°C
40
25°C
35
30
25
20
-40°C
15
10
RLOAD = 10 k:
0
1.8
2.5
3.2
5
3.9
4.6
5.3
RLOAD = 2 k:
0
1.8
2.5
3.2
6
+
V (V)
4.6
5.3
6
Figure 20.
Negative Output Swing vs. Supply Voltage
Positive Output Swing vs. Supply Voltage
100
50
-40°C
45
90
25°C
VOUT FROM RAIL (mV)
40
35
125°C
30
25
20
15
RLOAD = 600:
80
125°C
70
60
25°C
50
40
-40°C
30
20
10
5
3.9
+
V (V)
Figure 19.
VOUT FROM RAIL (mV)
4.6
Negative Output Swing vs. Supply Voltage
-40°C
10
RLOAD = 2 k:
0
1.8
2.5
3.2
3.9
4.6
5.3
6
0
1.8
+
2.5
3.2
3.9
4.6
5.3
6
+
V (V)
V (V)
Figure 21.
8
3.9
+
25°C
VOUT FROM RAIL (mV)
30
Figure 22.
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Negative Output Swing vs. Supply Voltage
Time Domain Voltage Noise
120
VS = ±2.5V
125°C
RLOAD = 600:
VCM = 0.0V
25°C
80
400 nV/DIV
VOUT FROM RAIL (mV)
100
-40°C
60
40
20
0
1.8
2.5
3.2
3.9
4.6
5.3
1S/DIV
6
+
V (V)
Figure 23.
Figure 24.
Input Referred Voltage Noise vs. Frequency
Overshoot and Undershoot vs. CLOAD
100
70
OVERSHOOT AND UNDERSHOOT %
+
VOLTAGE NOISE (nV/ Hz)
V = 5.5V
V+ = 2.5V
10
1
US%
60
50
OS%
40
30
20
10
0
1
10
1k
100
10k
20
0
100k
40
FREQUENCY (Hz)
100
120
Figure 25.
Figure 26.
THD+N vs. Peak-to-Peak Output Voltage (VOUT)
THD+N vs. Peak-to-Peak Output Voltage (VOUT)
0
0
+
V = 1.2V
+
V = 2.75V
-20 V = -2.75V
AV = +2
-40
-
-20 V = -0.6V
AV = +2
THD+N (dB)
-40
THD+N (dB)
80
60
CLOAD (pF)
-60
RLOAD = 600:
-80
-60
RLOAD = 600:
-80
-100
-100
-120
RLOAD = 100 k:
RLOAD = 100 k:
-120
0.02
0.2
2
-140
0.02
0.2
OUTPUT AMPLITUDE (V)
OUTPUT AMPLITUDE (V)
Figure 27.
Figure 28.
2
4
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
THD+N vs. Frequency
THD+N vs. Frequency
0.006
0.006
0.005
0.004
THD+N (%)
0.004
RL = 100 k:
0.003
0.002 V+ = 1.2V
+
0.003
V = 2.5V
-
V = 2.5V
0.002
VO = 4 VPP
AV = +2
-
V = 0.6V
0.001 VO = 0.9 VPP
0.001
AV = +2
0
10
RL = 100 k:
100
1k
10k
0
10
100k
100
Figure 29.
CL = 50 pF
GAIN (dB)
GAIN
40
CL = 100 pF
100
80
80
80
60
60
60
40
20
20
0
CL = 20 pF
-20
CL = 50 pF
-40
CL = 100 pF
-60
1k
10k
100k
1M
10M
PHASE
100
GAIN (dB)
CL = 20 pF
120
120
PHASE (°)
100
60
40
GAIN
20
20
0
0
0
-20
-20
-40
-40
-60
100M
-20
-40
RLOAD = 600: 10 k: 10 M:
-60
10k
100k
-60
100M
10M
FREQUENCY (Hz)
Figure 31.
Figure 32.
Crosstalk Rejection
160
CROSSTALK REJECTION RATION (dB)
OUTPUT IMPEDANCE (:)
1M
FREQUENCY (Hz)
100
10
1
0.1
100
1k
10k 100k
1M
10M 100M
140
120
100
80
60
40
20
0
1k
FREQUENCY (Hz)
10k
100k
1M
10M
100M
FREQUENCY (Hz)
Figure 33.
10
100
40
Closed Loop Output Impedance vs. Frequency
0.01
10
100k
Open Loop Gain and Phase with Resistive Load
120
PHASE
80
10k
Figure 30.
Open Loop Gain and Phase with Capacitive Load
120
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
PHASE (°)
THD+N (%)
RL = 600:
0.005
RL = 600:
Figure 34.
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Large Signal Transient Response, AV = +1
10 mV/DIV
200 mV/DIV
Small Signal Transient Response, AV = +1
INPUT = 20 mVPP
INPUT = 1 VPP
f = 200 kHz
f = 1 MHz
+
+
V = 2.5V
V = 2.5V
800 ns/DIV
Figure 35.
Figure 36.
Small Signal Transient Response, AV = +1
Large Signal Transient Response, AV = +1
10 mV/DIV
200 mV/DIV
200 ns/DIV
INPUT = 20 mVPP
f = 1 MHz
INPUT = 1 VPP
f = 200 kHz
+
V = 5V
+
V = 5V
200 ns/DIV
800 ns/DIV
Figure 37.
Figure 38.
Phase Margin vs. Capacitive Load (Stability)
Phase Margin vs. Capacitive Load (Stability)
50
50
RLOAD = 600:
RLOAD = 600:
40
RLOAD = 10 k:
30
20
RLOAD = 10 M:
10
0
PHASE MARGIN (°)
PHASE MARGIN (°)
40
RLOAD = 10 k:
30
20
RLOAD = 10 M:
10
0
+
+
V = 2.5V
-10
10
V = 5V
100
1000
-10
10
100
1000
CLOAD (pF)
CLOAD (pF)
Figure 39.
Figure 40.
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Typical Performance Characteristics (continued)
Unless otherwise specified, TA = 25°C, V– = 0, V+ = Supply Voltage = 5V, VCM = V+/2.
Negative PSRR vs. Frequency
-20
-20
-40
NEGATIVE PSRR (dB)
POSITIVE PSRR (dB)
Positive PSRR vs. Frequency
0
-40
-60
1.8V
-80
-60
+
V = 1.8V
-80
-100
+
V = 5.5V
5.5V
-100
10
-120
10k
1k
100
1M
100k
10
10M
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 41.
Figure 42.
CMRR vs. Frequency
Input Common Mode Capacitance vs. VCM
25
120
+
V = 5V
100
20
+
V = 2.5V
CCM (pF)
CMRR (dB)
80
+
V = 5V
60
15
10
40
5
20
0
0
10
100
1k
10k
100k
1M
0
Figure 43.
12
1
2
3
4
VCM (V)
FREQUENCY (Hz)
Figure 44.
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APPLICATION INFORMATION
ADVANTAGES OF THE LMV796/LMV797
Wide Bandwidth at Low Supply Current
The LMV796 and LMV797 are high performance op amps that provide a unity gain bandwidth of 17 MHz while
drawing a low supply current of 1.15 mA. This makes them ideal for providing wideband amplification in portable
applications.
Low Input Referred Noise and Low Input Bias Current
The LMV796/LMV797 have a very low input referred voltage noise density (5.8 nV/√Hz at 1 kHz). A CMOS input
stage ensures a small input bias current (100 fA) and low input referred current noise (0.01 pA/√Hz). This is very
helpful in maintaining signal fidelity, and makes the LMV796 and LMV797 ideal for audio and sensor based
applications.
Low Supply Voltage
The LMV796 and the LMV797 have performance specified at 2.5V and 5V supply. The LMV796 family is
specified to be operational at all supply voltages between 2.0V and 5.5V, for ambient temperatures ranging from
−40°C to 125°C, thus utilizing the entire battery lifetime. The LMV796 and LMV797 are also specified to be
operational at 1.8V supply voltage, for temperatures between 0°C and 125°C. This makes the LMV796 family
ideal for usage in low-voltage commercial applications.
RRO and Ground Sensing
Rail-to-rail output swing provides maximum possible dynamic range at the output. This is particularly important
when operating at low supply voltages. An innovative positive feedback scheme is used to boost the current drive
capability of the output stage. This allows the LMV796 and the LMV797 to source more than 40 mA of current at
1.8V supply. This also limits the performance of the LMV796 family as comparators, and hence the usage of the
LMV796 and the LMV797 in an open-loop configuration is not recommended. The input common-mode range
includes the negative supply rail which allows direct sensing at ground in single supply operation.
Small Size
The small footprint of the LMV796 and the LMV797 package saves space on printed circuit boards, and enables
the design of smaller electronic products, such as cellular phones, pagers, or other portable systems. Long
traces between the signal source and the op amp make the signal path susceptible to noise. By using the
physically smaller LMV796 or LMV797 package, the op amp can be placed closer to the signal source, reducing
noise pickup and increasing signal integrity.
CAPACITIVE LOAD TOLERANCE
The LMV796 and LMV797 can directly drive 120 pF in unity-gain without oscillation. The unity-gain follower is the
most sensitive configuration to capacitive loading. Direct capacitive loading reduces the phase margin of
amplifiers. The combination of the amplifier’s output impedance and the capacitive load induces phase lag. This
results in either an underdamped pulse response or oscillation. To drive a heavier capacitive load, the circuit in
Figure 45 can be used.
In Figure 45, the isolation resistor RISO and the load capacitor CL form a pole to increase stability by adding more
phase margin to the overall system. The desired performance depends on the value of RISO. The bigger the RISO
resistor value, the more stable VOUT will be. Increased RISO would, however, result in a reduced output swing and
short circuit current.
Figure 45. Isolation of CL to Improve Stability
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INPUT CAPACITANCE AND FEEDBACK CIRCUIT ELEMENTS
The LMV796 family has a very low input bias current (100 fA) and a low 1/f noise corner frequency (400 Hz),
which makes it ideal for sensor applications. However, to obtain this performance a large CMOS input stage is
used, which adds to the input capacitance of the op amp, CIN. Though this does not affect the DC and low
frequency performance, at higher frequencies the input capacitance interacts with the input and the feedback
impedances to create a pole, which results in lower phase margin and gain peaking. This can be controlled by
being selective in the use of feedback resistors, as well as, by using a feedback capacitance, CF. For example, in
the inverting amplifier shown in Figure 46, if CIN and CF are ignored and the open loop gain of the op amp is
considered infinite then the gain of the circuit is −R2/R1. An op amp, however, usually has a dominant pole, which
causes its gain to drop with frequency. Hence, this gain is only valid for DC and low frequency. To understand
the effect of the input capacitance coupled with the non-ideal gain of the op amp, the circuit needs to be
analyzed in the frequency domain using a Laplace transform.
CF
R2
R1
+
VIN
CIN
+
+
-
-
AV = -
VOUT
VIN
=-
VOUT
R2
R1
Figure 46. Inverting Amplifier
For simplicity, the op amp is modeled as an ideal integrator with a unity gain frequency of A0 . Hence, its transfer
function (or gain) in the frequency domain is A0/s. Solving the circuit equations in the frequency domain, ignoring
CF for the moment, results in an expression for the gain shown in Equation 1.
-R2/R1
(s) =
1+
s2
s
+
§ A0 R 1
§ A0
¨
¨C R
© R1 + R2
© IN 2
§
¨
©
VIN
§
¨
©
VOUT
(1)
It can be inferred from the denominator of the transfer function that it has two poles, whose expressions can be
obtained by solving for the roots of the denominator and are shown in Equation 2.
-1
2CIN
1
1
+
r
R1
R2
§1
1
+
¨
R2
© R1
§
¨
©
P1,2 =
2
-
4 A0CIN
R2
(2)
Equation 2 shows that as the values of R1 and R2 are increased, the magnitude of the poles, and hence the
bandwidth of the amplifier, is reduced. This theory is verified by using different values of R1 and R2 in the circuit
shown in Figure 45 and by comparing their frequency responses. In Figure 47 the frequency responses for three
different values of R1 and R2 are shown. When both R1 and R2 are 1 kΩ, the response is flattest and widest;
whereas, it narrows and peaks significantly when both their values are changed to 10 kΩ or 30 kΩ. So it is
advisable to use lower values of R1 and R2 to obtain a wider and flatter response. Lower resistances also help in
high sensitivity circuits since they add less noise.
14
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15
AV = -1
10
GAIN (dB)
5
0
-5
R1, R2 = 30 k:
-10
R1, R2 = 10 k:
-15
R1, R2 = 1 k:
-20
-25
10k
100k
1M
10M
100M
FREQUENCY (Hz)
Figure 47. Gain Peaking Caused by Large R1, R2
A way of reducing the gain peaking is by adding a feedback capacitance CF in parallel with R2. This introduces
another pole in the system and prevents the formation of pairs of complex conjugate poles which cause the gain
to peak. Figure 48 shows the effect of CF on the frequency response of the circuit. Adding a capacitance of 2 pF
removes the peak, while a capacitance of 5 pF creates a much lower pole and reduces the bandwidth
excessively.
20
R1, R2 = 30 k:
10
CF = 0 pF
AV = -1
GAIN (dB)
0
CF = 5 pF
-10
CF = 2 pF
-20
-30
-40
10k
100k
1M
10M
FREQUENCY (Hz)
Figure 48. Gain Peaking Eliminated by CF
AUDIO PREAMPLIFIER WITH BAND PASS FILTERING
With low input referred voltage noise, low supply voltage and current, and a low harmonic distortion, the LMV796
family is ideal for audio applications. Its wide unity gain bandwidth allows it to provide large gain for a wide range
of frequencies and it can be used to design a preamplifier to drive a load of as low as 600Ω with less than 0.01%
distortion. Two amplifier circuits are shown in Figure 49 and Figure 50. Figure 49 is an inverting amplifier, with a
10 kΩ feedback resistor, R2, and a 1kΩ input resistor, R1, and hence provides a gain of −10. Figure 50 is a noninverting amplifier, using the same values of R1and R2, and provides a gain of 11. In either of these circuits, the
coupling capacitor CC1 decides the lower frequency at which the circuit starts providing gain, while the feedback
capacitor CF decides the frequency at which the gain starts dropping off. Figure 51 shows the frequency
response of the inverting amplifier with different values of CF.
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CF
R1
1 k:
CC1
R2
10 k:
+
VIN
CC2
-
-
+
RB1
V
+
+
-
VOUT
RB2
R2
= -10
R1
AV = -
Figure 49. Inverting Audio Preamplifier
+
V
RB1
CC2
+
VIN
RB2
-
+
-
+
R2
10 k:
-
VOUT
CF
R1
1 k:
CC1
AV = 1 +
R2
R1
= 11
Figure 50. Non-inverting Audio Preamplifier
25
CF = 10 pF
20
15
CF = 1 nF
GAIN (dB)
10
CF = 100 pF
5
0
-5
-10
-15
-20
1
10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 51. Frequency Response of the Inverting Audio Preamplifier
TRANSIMPEDANCE AMPLIFIER
CMOS input op amps are often used in transimpedance applications as they have an extremely high input
impedance. A transimpedance amplifier converts a small input current into a voltage. This current is usually
generated by a photodiode. The transimpedance gain, measured as the ratio of the output voltage to the input
current, is expected to be large and wide-band. Since the circuit deals with currents in the range of a few nA, low
noise performance is essential. The LMV796/LMV797 are CMOS input op amps providing wide bandwidth and
low noise performance, and are hence ideal for transimpedance applications.
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Usually, a transimpedance amplifier is designed on the basis of the current source driving the input. A
photodiode is a very common capacitive current source, which requires transimpedance gain for transforming its
miniscule current into easily detectable voltages. The photodiode and the amplifier’s gain are selected with
respect to the speed and accuracy required of the circuit. A faster circuit would require a photodiode with lesser
capacitance and a faster amplifier. A more sensitive circuit would require a sensitive photodiode and a high gain.
A typical transimpedance amplifier is shown in Figure 52. The output voltage of the amplifier is given by the
equation VOUT = −IINRF. Since the output swing of the amplifier is limited, RF should be selected such that all
possible values of IIN can be detected.
The LMV796/LMV797 have a large gain-bandwidth product (17 MHz), which enables high gains at wide
bandwidths. A rail-to-rail output swing at 5.5V supply allows detection and amplification of a wide range of input
currents. A CMOS input stage with negligible input current noise and low input voltage noise allows the
LMV796/LMV797 to provide high fidelity amplification for wide bandwidths. These properties make the
LMV796/LMV797 ideal for systems requiring wide-band transimpedance amplification.
CF
RF
IIN
CCM
CD
VB
+
+
VOUT
CIN = CD + CCM
VOUT
= - RF
IIN
Figure 52. Photodiode Transimpedance Amplifier
As mentioned earlier, the following parameters are used to design a transimpedance amplifier: the amplifier gainbandwidth product, A0; the amplifier input capacitance, CCM; the photodiode capacitance, CD; the
transimpedance gain required, RF; and the amplifier output swing. Once a feasible RF is selected using the
amplifier output swing, these numbers can be used to design an amplifier with the desired transimpedance gain
and a maximally flat frequency response.
An essential component for obtaining a maximally flat response is the feedback capacitor, CF. The capacitance
seen at the input of the amplifier, CIN, combined with the feedback capacitor, RF, generate a phase lag which
causes gain-peaking and can destabilize the circuit. CIN is usually just the sum of CD and CCM. The feedback
capacitor CF creates a pole, fP in the noise gain of the circuit, which neutralizes the zero in the noise gain, fZ,
created by the combination of RF and CIN. If properly positioned, the noise gain pole created by CF can ensure
that the slope of the gain remains at 20 dB/decade till the unity gain frequency of the amplifier is reached, thus
ensuring stability. As shown in Figure 53, fP is positioned such that it coincides with the point where the noise
gain intersects the op amp’s open loop gain. In this case, fP is also the overall −3 dB frequency of the
transimpedance amplifier. The value of CF needed to make it so is given by Equation 3. A larger value of CF
causes excessive reduction of bandwidth, while a smaller value fails to prevent gain peaking and instability.
CF =
1 + 1 + 4SRFCINA0
2SRFA0
(3)
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GAIN
OP AMP
OPEN LOOP
GAIN
fZ =
fP =
NOISE GAIN WITH NO CF
1
2S RFCIN
NOISE GAIN WITH CF
A0
2S RF(CIN+CF)
fP
fZ
A0
FREQUENCY
Figure 53. CF Selection for Stability
Calculating CF from Equation 3 can sometimes return unreasonably small values (