Zero-Drift, Single-Supply, Rail-to-Rail
Input/Output Operational Amplifier
AD8628/AD8629/AD8630
Rev. I
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FEATURES
Lowest auto-zero amplifier noise
Low offset voltage: 1 μV
Input offset drift: 0.002 μV/°C
Rail-to-rail input and output swing
5 V single-supply operation
High gain, CMRR, and PSRR: 130 dB
Very low input bias current: 100 pA maximum
Low supply current: 1.0 mA
Overload recovery time: 50 μs
No external components required
Qualified for automotive applications
APPLICATIONS
Automotive sensors
Pressure and position sensors
Strain gage amplifiers
Medical instrumentation
Thermocouple amplifiers
Precision current sensing
Photodiode amplifiers
GENERAL DESCRIPTION
This amplifier has ultralow offset, drift, and bias current.
The AD8628/AD8629/AD8630 are wide bandwidth auto-zero
amplifiers featuring rail-to-rail input and output swing and low
noise. Operation is fully specified from 2.7 V to 5 V single supply
(±1.35 V to ±2.5 V dual supply).
The AD8628/AD8629/AD8630 provide benefits previously
found only in expensive auto-zeroing or chopper-stabilized
amplifiers. Using Analog Devices, Inc., topology, these zero-
drift amplifiers combine low cost with high accuracy and low
noise. No external capacitor is required. In addition, the AD8628/
AD8629/AD8630 greatly reduce the digital switching noise
found in most chopper-stabilized amplifiers.
With an offset voltage of only 1 µV, drift of less than 0.005 V/°C,
and noise of only 0.5 µV p-p (0 Hz to 10 Hz), the AD8628/
AD8629/AD8630 are suited for applications where error
sources cannot be tolerated. Position and pressure sensors,
medical equipment, and strain gage amplifiers benefit greatly
from nearly zero drift over their operating temperature range.
Many systems can take advantage of the rail-to-rail input and
output swings provided by the AD8628/AD8629/AD8630 to
reduce input biasing complexity and maximize SNR.
PIN CONFIGURATIONS
O
UT
1
V–
2
+IN
3
V+
5
–IN
4
AD8628
TOP VIEW
(Not to Scale)
02735-001
Figure 1. 5-Lead TSOT (UJ-5) and 5-Lead SOT-23 (RJ-5)
NC
1
–IN
2
+IN
3
V–
4
NC
8
V+
7
OUT
6
NC
5
NC = NO CONNECT
AD8628
TOP VIEW
(Not to Scale)
02735-002
Figure 2. 8-Lead SOIC_N (R-8)
OUT A
1
–IN A
2
+IN A
3
V–
4
V+
8
OUT B
7
–IN B
6
+IN B
5
AD8629
TOP VIEW
(Not to Scale)
02735-063
Figure 3. 8-Lead SOIC_N (R-8) and 8-Lead MSOP (RM-8)
1
–IN A
2
+IN A
3
V+
4
OUT D
14
–IN D
13
+IN D
12
V–
11
+IN B
5
+IN C
10
–IN B
6
–IN C
9
OUT B
OUT A
7
OUT C
8
AD8630
TOP VIEW
(Not to Scale)
02735-066
Figure 4. 14-Lead SOIC_N (R-14) and 14-Lead TSSOP (RU-14)
The AD8628/AD8629/AD8630 are specified for the extended
industrial temperature range (−40°C to +125°C). The AD8628
is available in tiny 5-lead TSOT, 5-lead SOT-23, and 8-lead
narrow SOIC plastic packages. The AD8629 is available in the
standard 8-lead narrow SOIC and MSOP plastic packages. The
AD8630 quad amplifier is available in 14-lead narrow SOIC and
14-lead TSSOP plastic packages. See the Ordering Guide for
automotive grades.
AD8628/AD8629/AD8630
Rev. I | Page 2 of 24
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description......................................................................... 1
Pin Configurations........................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Electrical Characteristics—VS = 5.0 V....................................... 3
Electrical Characteristics—VS = 2.7 V....................................... 4
Absolute Maximum Ratings............................................................ 5
Thermal Characteristics .............................................................. 5
ESD Caution.................................................................................. 5
Typical Performance Characteristics ............................................. 6
Functional Description.................................................................. 14
1/f Noise....................................................................................... 14
Peak-to-Peak Noise .................................................................... 15
Noise Behavior with First-Order, Low-Pass Filter................. 15
Total Integrated Input-Referred Noise for First-Order Filter15
Input Overvoltage Protection................................................... 16
Output Phase Reversal............................................................... 16
Overload Recovery Time .......................................................... 16
Infrared Sensors.......................................................................... 17
Precision Current Shunt Sensor............................................... 18
Output Amplifier for High Precision DACs........................... 18
Outline Dimensions....................................................................... 19
Ordering Guide .......................................................................... 21
REVISION HISTORY
4/11—Rev. H to Rev. I
Updated Outline Dimensions....................................................... 19
Changes to Ordering Guide .......................................................... 21
4/10—Rev. G to Rev. H
Change to Features List.................................................................... 1
Change to General Description Section........................................ 1
Changes to Table 3............................................................................ 5
Updated Outline Dimensions Section......................................... 19
Changes to Ordering Guide .......................................................... 21
6/08—Rev. F to Rev. G
Changes to Features Section............................................................ 1
Changes to Table 5 and Figure 42 Caption ................................. 12
Changes to 1/f Noise Section and Figure 49 ............................... 14
Changes to Figure 51 Caption and Figure 55 ............................. 15
Changes to Figure 57 Caption and Figure 58 Caption .............. 16
Changes to Figure 60 Caption and Figure 61 Caption .............. 17
Changes to Figure 64...................................................................... 18
2/08—Rev. E to Rev. F
Renamed TSOT-23 to TSOT ............................................Universal
Deleted Figure 4 and Figure 6......................................................... 1
Changes to Figure 3 and Figure 4 Captions.................................. 1
Changes to Table 1............................................................................ 3
Changes to Table 2............................................................................ 4
Changes to Table 4............................................................................ 5
Updated Outline Dimensions....................................................... 19
Changes to Ordering Guide .......................................................... 20
5/05—Rev. D to Rev. E
Changes to Ordering Guide .......................................................... 22
1/05—Rev. C to Rev. D
Added AD8630 ...................................................................Universal
Added Figure 5 and Figure 6............................................................1
Changes to Caption in Figure 8 and Figure 9................................7
Changes to Caption in Figure 14.....................................................8
Changes to Figure 17.........................................................................8
Changes to Figure 23 and Figure 24................................................9
Changes to Figure 25 and Figure 26............................................. 10
Changes to Figure 31...................................................................... 11
Changes to Figure 40, Figure 41, Figure 42................................. 12
Changes to Figure 43 and Figure 44............................................. 13
Changes to Figure 51...................................................................... 15
Updated Outline Dimensions....................................................... 20
Changes to Ordering Guide.......................................................... 20
10/04—Rev. B to Rev. C
Updated Formatting...........................................................Universal
Added AD8629...................................................................Universal
Added SOIC and MSOP Pin Configurations................................1
Added Figure 48 ............................................................................. 13
Changes to Figure 62...................................................................... 17
Added MSOP Package................................................................... 19
Changes to Ordering Guide.......................................................... 22
10/03—Rev. A to Rev. B
Changes to General Description .....................................................1
Changes to Absolute Maximum Ratings........................................4
Changes to Ordering Guide.............................................................4
Added TSOT-23 Package .............................................................. 15
6/03—Rev. 0 to Rev. A
Changes to Specifications.................................................................3
Changes to Ordering Guide.............................................................4
Change to Functional Description............................................... 10
Updated Outline Dimensions....................................................... 15
10/02—Revision 0: Initial Version
AD8628/AD8629/AD8630
Rev. I | Page 3 of 24
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS—VS = 5.0 V
VS = 5.0 V, VCM = 2.5 V, TA = 25°C, unless otherwise noted.
Table 1.
Parameter Symbol Conditions Min Typ Max Unit
INPUT CHARACTERISTICS
Offset Voltage VOS
1 5 μV
−40°C ≤ TA ≤ +125°C 10 μV
Input Bias Current IB
AD8628/AD8629
30 100 pA
AD8630
100 300 pA
−40°C ≤ TA ≤ +125°C 1.5 nA
Input Offset Current IOS
50 200 pA
−40°C ≤ TA ≤ +125°C 250 pA
Input Voltage Range 0 5 V
Common-Mode Rejection Ratio CMRR VCM = 0 V to 5 V 120 140 dB
−40°C ≤ TA ≤ +125°C 115 130 dB
Large Signal Voltage Gain AVO R
L = 10 kΩ, VO = 0.3 V to 4.7 V 125 145 dB
−40°C ≤ TA ≤ +125°C 120 135 dB
Offset Voltage Drift ∆VOS/∆T −40°C TA ≤ +125°C 0.002 0.02 μV/°C
OUTPUT CHARACTERISTICS
Output Voltage High VOH R
L = 100 kΩ to ground 4.99 4.996 V
−40°C ≤ TA ≤ +125°C 4.99 4.995 V
RL = 10 kΩ to ground 4.95 4.98 V
−40°C ≤ TA ≤ +125°C 4.95 4.97 V
Output Voltage Low VOL R
L = 100 kΩ to V+ 1 5 mV
−40°C ≤ TA ≤ +125°C 2 5 mV
RL = 10 kΩ to V+ 10 20 mV
−40°C ≤ TA ≤ +125°C 15 20 mV
Short-Circuit Limit ISC ±25 ±50 mA
−40°C ≤ TA ≤ +125°C ±40 mA
Output Current IO
±30 mA
−40°C ≤ TA ≤ +125°C ±15 mA
POWER SUPPLY
Power Supply Rejection Ratio PSRR VS = 2.7 V to 5.5 V, −40°C ≤ TA ≤ +125°C 115 130 dB
Supply Current per Amplifier ISY V
O = VS/2 0.85 1.1 mA
−40°C ≤ TA ≤ +125°C 1.0 1.2 mA
INPUT CAPACITANCE CIN
Differential
1.5 pF
Common Mode
8.0 pF
DYNAMIC PERFORMANCE
Slew Rate SR RL = 10 kΩ 1.0 V/μs
Overload Recovery Time
0.05 ms
Gain Bandwidth Product GBP
2.5 MHz
NOISE PERFORMANCE
Voltage Noise en p-p 0.1 Hz to 10 Hz 0.5 μV p-p
0.1 Hz to 1.0 Hz 0.16 μV p-p
Voltage Noise Density en f = 1 kHz 22 nV/√Hz
Current Noise Density in f = 10 Hz 5 fA/√Hz
AD8628/AD8629/AD8630
Rev. I | Page 4 of 24
ELECTRICAL CHARACTERISTICS—VS = 2.7 V
VS = 2.7 V, VCM = 1.35 V, VO = 1.4 V, TA = 25°C, unless otherwise noted.
Table 2.
Parameter Symbol Conditions Min Typ Max Unit
INPUT CHARACTERISTICS
Offset Voltage VOS 1 5 μV
−40°C TA ≤ +125°C 10 μV
Input Bias Current IB
AD8628/AD8629 30 100 pA
AD8630 100 300 pA
−40°C TA ≤ +125°C 1.0 1.5 nA
Input Offset Current IOS 50 200 pA
−40°C TA ≤ +125°C 250 pA
Input Voltage Range 0 2.7 V
Common-Mode Rejection Ratio CMRR VCM = 0 V to 2.7 V 115 130 dB
−40°C TA ≤ +125°C 110 120 dB
Large Signal Voltage Gain AVO R
L = 10 kΩ, VO = 0.3 V to 2.4 V 110 140 dB
−40°C TA ≤ +125°C 105 130 dB
Offset Voltage Drift ∆VOS/∆T −40°C TA ≤ +125°C 0.002 0.02 μV/°C
OUTPUT CHARACTERISTICS
Output Voltage High VOH R
L = 100 kΩ to ground 2.68 2.695 V
−40°C TA ≤ +125°C 2.68 2.695 V
R
L = 10 kΩ to ground 2.67 2.68 V
−40°C TA ≤ +125°C 2.67 2.675 V
Output Voltage Low VOL R
L = 100 kΩ to V+ 1 5 mV
−40°C TA ≤ +125°C 2 5 mV
R
L = 10 kΩ to V+ 10 20 mV
−40°C TA ≤ +125°C 15 20 mV
Short-Circuit Limit ISC ±10 ±15 mA
−40°C TA ≤ +125°C ±10 mA
Output Current IO ±10 mA
−40°C TA ≤ +125°C ±5 mA
POWER SUPPLY
Power Supply Rejection Ratio PSRR VS = 2.7 V to 5.5 V, −40°C ≤ TA ≤ +125°C 115 130 dB
Supply Current per Amplifier ISY V
O = VS/2 0.75 1.0 mA
−40°C TA ≤ +125°C 0.9 1.2 mA
INPUT CAPACITANCE CIN
Differential 1.5 pF
Common Mode 8.0 pF
DYNAMIC PERFORMANCE
Slew Rate SR RL = 10 kΩ 1 V/μs
Overload Recovery Time 0.05 ms
Gain Bandwidth Product GBP 2 MHz
NOISE PERFORMANCE
Voltage Noise en p-p 0.1 Hz to 10 Hz 0.5 μV p-p
Voltage Noise Density en f = 1 kHz 22 nV/√Hz
Current Noise Density in f = 10 Hz 5 fA/√Hz
AD8628/AD8629/AD8630
Rev. I | Page 5 of 24
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Rating
Supply Voltage 6 V
Input Voltage GND – 0.3 V to VS + 0.3 V
Differential Input Voltage1 ±5.0 V
Output Short-Circuit Duration to GND Indefinite
Storage Temperature Range −65°C to +150°C
Operating Temperature Range −40°C to +125°C
Junction Temperature Range −65°C to +150°C
Lead Temperature (Soldering, 60 sec) 300°C
ESD AD8628
HBM 8-Lead SOIC ±7000V
FICDM 8-Lead SOIC ±1500V
FICDM 5-Lead TSOT ±1000V
MM 8-Lead SOIC ±200V
ESD AD8629
HBM 8-Lead SOIC ±4000V
FICDM 8-Lead SOIC ±1000V
ESD AD8630
HBM 14-Lead SOIC ±5000V
FICDM 14-Lead SOIC ±1500V
FICDM 14-Lead TSSOP ±1500V
MM 14-Lead SOIC ±200V
1 Differential input voltage is limited to ±5 V or the supply voltage, whichever
is less.
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 CHARACTERISTICS
θJA is specified for worst-case conditions, that is, θJA is specified
for the device soldered in a circuit board for surface-mount
packages. This was measured using a standard two-layer board.
Table 4.
Package Type θJA θJC Unit
5-Lead TSOT (UJ-5) 207 61 °C/W
5-Lead SOT-23 (RJ-5) 230 146 °C/W
8-Lead SOIC_N (R-8) 158 43 °C/W
8-Lead MSOP (RM-8) 190 44 °C/W
14-Lead SOIC_N (R-14) 105 43 °C/W
14-Lead TSSOP (RU-14) 148 23 °C/W
ESD CAUTION
AD8628/AD8629/AD8630
Rev. I | Page 6 of 24
TYPICAL PERFORMANCE CHARACTERISTICS
INPUT OFFSET VOLTAGE (µV)
NUMBER OF AMPLIFIERS
180
160
140
120
100
80
60
40
20
0
–2.5 –1.5 –0.5 0.5 1.5 2.5
02735-003
V
S
= 2.7V
T
A
= 25°C
Figure 5. Input Offset Voltage Distribution
+85°C
+25°C
–40°C
VS = 5V
INPUT COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (pA)
60
40
50
30
10
20
0
012345
02735-004
6
Figure 6. AD8628 Input Bias Current vs. Input Common-Mode Voltage
150°C
125°C
INPUT COMMON-MODE VOLTAGE (V)
INPUT BIAS CURRENT (pA)
1500
500
1000
0
–1000
–500
–1500
012345
02735-005
6
VS = 5V
Figure 7. AD8628 Input Bias Current vs. Input Common-Mode Voltage
INPUT OFFSET VOLTAGE (µV)
NUMBER OF AMPLIFIERS
100
80
90
60
70
40
50
10
20
30
0
–2.5 –1.5 –0.5 0.5 1.5 2.5
02735-006
V
S
= 5V
V
CM
= 2.5V
T
A
= 25°C
Figure 8. Input Offset Voltage Distribution
V
S
= 5V
T
A
= –40°C TO +125°C
TCVOS (nV/°C)
NUMBER OF AMPLIFIERS
7
6
5
4
3
2
1
0
02468
10
02735-007
Figure 9. Input Offset Voltage Drift
LOAD CURRENT (mA)
OUTPUT VOLTAGE (mV)
1k
100
10
1
0.1
0.01
0.0001 0.001 0.10.01 1 10
02735-008
V
S
= 5V
T
A
= 25°C
SOURCE
SINK
Figure 10. Output Voltage to Supply Rail vs. Load Current
AD8628/AD8629/AD8630
Rev. I | Page 7 of 24
LOAD CURRENT (mA)
OUTPUT VOLTAGE (mV)
1k
100
10
1
0.1
0.01
0.0001 0.001 0.10.01 1 10
02735-009
V
S
= 2.7V
SOURCE
SINK
Figure 11. Output Voltage to Supply Rail vs. Load Current
V
S
= 5V
V
CM
= 2.5V
T
A
= –40°C TO +150°C
TEMPERATURE (°C)
INPUT BIAS CURRENT (pA)
1500
1150
900
450
100
0
–50 0 25–25 50 75 100 125 150 175
02735-010
Figure 12. AD8628 Input Bias Current vs. Temperature
TA = 25
°
C
5V
2.7V
TEMPERATURE (°
C
)
SUPPLY CURRENT (µA)
1250
1000
750
500
250
0
–50 0 50 150100 200
02735-011
Figure 13. Supply Current vs. Temperature
T
A
= 25°C
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
1000
800
600
400
200
0
012 4536
02735-012
Figure 14. Supply Current vs. Supply Voltage
FREQUENCY (Hz)
OPEN-LOOP GAIN (dB)
60
40
20
–20
0
10k 100k 1M 10M
02735-013
45
90
135
180
225
0
PHASE SHIFT (Degrees)
VS = 2.7V
CL = 20pF
RL =
ФM = 45°
GAIN
PHASE
Figure 15. Open-Loop Gain and Phase vs. Frequency
FREQUENCY (Hz)
OPEN-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–30
10k 100k 1M 10M
02735-014
45
90
135
180
225
0
PHASE SHIFT (Degrees)
V
S
= 5V
C
L
= 20pF
R
L
=
Φ
M
= 52.
GAIN
PHASE
Figure 16. Open-Loop Gain and Phase vs. Frequency
AD8628/AD8629/AD8630
Rev. I | Page 8 of 24
FREQUENCY (Hz)
CLOSED-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–30
1k 10k 100k 1M 10M
02735-015
V
S
= 2.7V
C
L
= 20pF
R
L
= 2k
A
V
= 100
A
V
= 10
A
V
= 1
Figure 17. Closed-Loop Gain vs. Frequency
FREQUENCY (Hz)
CLOSED-LOOP GAIN (dB)
70
60
50
40
30
20
0
–10
–20
10
–30
1k 10k 100k 1M 10M
02735-016
V
S
= 5V
C
L
= 20pF
R
L
= 2k
A
V
= 100
A
V
= 10
A
V
= 1
Figure 18. Closed-Loop Gain vs. Frequency
FREQUENCY (Hz)
OUTPUT IMPEDANCE ()
300
270
240
210
180
150
90
60
30
120
0
100 1k 10k 100k 1M 10M 100M
02735-017
AV = 100
AV = 10
AV = 1
VS = 2.7V
Figure 19. Output Impedance vs. Frequency
FREQUENCY (Hz)
OUTPUT IMPEDANCE ()
300
270
240
210
180
150
90
60
30
120
0
100 1k 10k 100k 1M 10M 100M
02735-018
AV = 100
AV = 1
AV = 10
VS = 5V
Figure 20. Output Impedance vs. Frequency
V
S
= ±1.35V
C
L
= 300pF
R
L
=
A
V
= 1
TIME (4µs/DIV)
VOL
T
AGE (500mV/DIV)
02735-019
0V
Figure 21. Large Signal Transient Response
V
S
= ±2.5V
C
L
= 300pF
R
L
=
A
V
= 1
TIME (5µs/DIV)
VOLTAGE (1V/DIV)
0V
02735-020
Figure 22. Large Signal Transient Response
AD8628/AD8629/AD8630
Rev. I | Page 9 of 24
V
S
= ±1.35V
C
L
= 50pF
R
L
=
A
V
= 1
TIME (4µs/DIV)
VOLTAGE (50mV/DIV)
0V
02735-021
Figure 23. Small Signal Transient Response
V
S
= ±2.5V
C
L
= 50pF
R
L
=
A
V
= 1
TIME (4µs/DIV)
VOLTAGE (50mV/DIV)
0V
02735-022
Figure 24. Small Signal Transient Response
CAPACITIVE LOAD (pF)
OVERSHOOT (%)
100
90
80
70
60
50
30
20
10
40
0
110100
02735-023
1k
OS–
OS+
V
S
= ±1.35V
R
L
= 2k
T
A
= 25°C
Figure 25. Small Signal Overshoot vs. Load Capacitance
CAPACITIVE LOAD (pF)
OVERSHOOT (%)
80
70
60
50
30
20
10
40
0
110100
02735-024
1k
OS–
OS+
V
S
= ±2.5V
R
L
= 2k
T
A
= 25°C
Figure 26. Small Signal Overshoot vs. Load Capacitance
TIME (2µs/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-025
V
S
= ±2.5V
A
V
= –50
R
L
= 10k
C
L
= 0pF
CH1 = 50mV/DIV
CH2 = 1V/DIV
Figure 27. Positive Overvoltage Recovery
TIME (10µs/DIV)
VOLTAGE (V)
V
OUT
0V
0V
V
IN
02735-026
V
S
= ±2.5V
A
V
= –50
R
L
= 10k
C
L
= 0pF
CH1 = 50mV/DIV
CH2 = 1V/DIV
Figure 28. Negative Overvoltage Recovery
AD8628/AD8629/AD8630
Rev. I | Page 10 of 24
TIME (200µs/DIV)
VOLTAGE (1V/DIV)
0V
02735-027
V
S
= ±2.5V
V
IN
= 1kHz @ ±3V p-p
C
L
= 0pF
R
L
= 10k
A
V
= 1
Figure 29. No Phase Reversal
FREQUENCY (Hz)
CMRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-028
V
S
= 2.7V
Figure 30. CMRR vs. Frequency
FREQUENCY (Hz)
CMRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-029
V
S
= 5V
Figure 31. CMRR vs. Frequency
FREQUENCY (Hz)
PSRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-030
V
S
= ±1.35V
+PSRR
–PSRR
Figure 32. PSRR vs. Frequency
FREQUENCY (Hz)
PSRR (dB)
140
120
100
80
60
40
0
–20
–40
20
–60
100 1k 10k 100k 1M 10M
02735-031
V
S
= ±2.5V
+PSRR
–PSRR
Figure 33. PSRR vs. Frequency
FREQUENCY (Hz)
OUTPUT SWING (V p-p)
3.0
2.5
2.0
1.5
1.0
0.5
0
100 1k 10k 100k 1M
02735-032
V
S
= 2.7V
R
L
= 10k
T
A
= 25°C
A
V
= 1
Figure 34. Maximum Output Swing vs. Frequency
AD8628/AD8629/AD8630
Rev. I | Page 11 of 24
FREQUENCY (Hz)
OUTPUT SWING (V p-p)
5.5
2.5
3.0
3.5
4.0
4.5
5.0
2.0
1.5
1.0
0.5
0
100 1k 10k 100k 1M
02735-033
V
S
= 5V
R
L
= 10k
T
A
= 25°C
A
V
= 1
Figure 35. Maximum Output Swing vs. Frequency
TIME (µs)
VOLTAGE (µV)
0.60
0.45
0.30
0.15
–0.15
–0.30
–0.45
0
–0.60
012345678910
02735-034
V
S
= 2.7V
Figure 36. 0.1 Hz to 10 Hz Noise
TIME (µs)
VOLTAGE (µV)
0.60
0.45
0.30
0.15
–0.15
–0.30
–0.45
0
–0.60
012345678910
02735-035
V
S
= 5V
Figure 37. 0.1 Hz to 10 Hz Noise
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
45
30
15
60
0
0 0.5 1.0 1.5 2.0 2.5
02735-036
V
S
= 2.7V
NOISE AT 1kHz = 21.3nV
Figure 38. Voltage Noise Density at 2.7 V from 0 Hz to 2.5 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
45
30
15
60
0
0 5 10 15 20 25
02735-037
V
S
= 2.7V
NOISE AT 10kHz = 42.4nV
Figure 39. Voltage Noise Density at 2.7 V from 0 Hz to 25 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
45
30
15
60
0
0 0.5 1.0 1.5 2.0 2.5
02735-038
V
S
= 5V
NOISE AT 1kHz = 22.1nV
Figure 40. Voltage Noise Density at 5 V from 0 Hz to 2.5 kHz
AD8628/AD8629/AD8630
Rev. I | Page 12 of 24
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
45
30
15
60
0
0 5 10 15 20 25
02735-039
V
S
= 5V
NOISE AT 10kHz = 36.4nV
Figure 41. Voltage Noise Density at 5 V from 0 Hz to 25 kHz
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
45
30
15
60
0
05
02735-040
10
V
S
= 5V
Figure 42. Voltage Noise Density at 5 V from 0 Hz to 10 kHz
V
S
= 2.7V TO 5V
T
A
= –40°C TO +125°C
TEMPERATURE (°C)
POWER SUPPLY REJECTION (dB)
150
130
120
140
110
100
90
60
70
80
50
–50 0 25–25 50 75 100 125
02735-041
Figure 43. Power Supply Rejection vs. Temperature
TEMPERATURE (°C)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
150
100
50
0
–50
–100
–50 25 50 750–25 100 125 150 175
02735-042
V
S
= 2.7V
T
A
= –40°C TO +150°C
I
SC
I
SC
+
Figure 44. Output Short-Circuit Current vs. Temperature
TEMPERATURE (°C)
OUTPUT SHORT-CIRCUIT CURRENT (mA)
150
100
50
0
–50
–100
–50 25 50 750–25 100 125 150 175
02735-043
V
S
= 5V
T
A
= –40°C TO +150°C
I
SC
I
SC
+
Figure 45. Output Short-Circuit Current vs. Temperature
TEMPERATURE (°C)
OUTPUT-TO-RAIL VOLTAGE (mV)
1k
100
10
1
0.1
–50 25 50 750–25 100 125 150 175
02735-044
V
S
= 5V
V
CC
– V
OH
@ 1k
V
CC
– V
OH
@ 10k
V
CC
– V
OH
@ 100k
V
OL
– V
EE
@ 1k
V
OL
– V
EE
@ 10k
V
OL
– V
EE
@ 100k
Figure 46. Output-to-Rail Voltage vs. Temperature
AD8628/AD8629/AD8630
Rev. I | Page 13 of 24
TEMPERATURE (°C)
OUTPUT-TO-RAIL VOLTAGE (mV)
1k
100
10
1
0.1
–50 25 50 750–25 100 125 150 175
02735-045
V
S
= 2.7V
V
CC
– V
OH
@ 1k
V
CC
– V
OH
@ 10k
V
CC
– V
OH
@ 100k
V
OL
– V
EE
@ 1k
V
OL
– V
EE
@ 10k
V
OL
– V
EE
@ 100k
Figure 47. Output-to-Rail Voltage vs. Temperature
FREQUENCY (Hz)
CHANNEL SEPA
R
A
TION (dB)
140
120
100
80
60
40
20
0
1k 10k 100k 1M 10M
02735-062
V
OUT
V
IN
28mV p-p
–2.5V
+2.5V
R1
10k
V–
V+
+
V+
V–
AB
R2
100
V
S
= ±2.5V
Figure 48. AD8629/AD8630 Channel Separation vs. Frequency
AD8628/AD8629/AD8630
Rev. I | Page 14 of 24
FUNCTIONAL DESCRIPTION
The AD8628/AD8629/AD8630 are single-supply, ultrahigh
precision rail-to-rail input and output operational amplifiers.
The typical offset voltage of less than 1 µV allows these amplifiers
to be easily configured for high gains without risk of excessive
output voltage errors. The extremely small temperature drift
of 2 nV/°C ensures a minimum offset voltage error over their
entire temperature range of −40°C to +125°C, making these
amplifiers ideal for a variety of sensitive measurement applica-
tions in harsh operating environments.
The AD8628/AD8629/AD8630 achieve a high degree of precision
through a patented combination of auto-zeroing and chopping.
This unique topology allows the AD8628/AD8629/AD8630 to
maintain their low offset voltage over a wide temperature range
and over their operating lifetime. The AD8628/AD8629/AD8630
also optimize the noise and bandwidth over previous generations
of auto-zero amplifiers, offering the lowest voltage noise of any
auto-zero amplifier by more than 50%.
Previous designs used either auto-zeroing or chopping to add
precision to the specifications of an amplifier. Auto-zeroing
results in low noise energy at the auto-zeroing frequency, at the
expense of higher low frequency noise due to aliasing of wideband
noise into the auto-zeroed frequency band. Chopping results in
lower low frequency noise at the expense of larger noise energy
at the chopping frequency. The AD8628/AD8629/AD8630
family uses both auto-zeroing and chopping in a patented ping-
pong arrangement to obtain lower low frequency noise together
with lower energy at the chopping and auto-zeroing frequencies,
maximizing the signal-to-noise ratio for the majority of
applications without the need for additional filtering. The
relatively high clock frequency of 15 kHz simplifies filter
requirements for a wide, useful noise-free bandwidth.
The AD8628 is among the few auto-zero amplifiers offered in
the 5-lead TSOT package. This provides a significant improvement
over the ac parameters of the previous auto-zero amplifiers. The
AD8628/AD8629/AD8630 have low noise over a relatively wide
bandwidth (0 Hz to 10 kHz) and can be used where the highest
dc precision is required. In systems with signal bandwidths of
from 5 kHz to 10 kHz, the AD8628/AD8629/AD8630 provide
true 16-bit accuracy, making them the best choice for very high
resolution systems.
1/f NOISE
1/f noise, also known as pink noise, is a major contributor to
errors in dc-coupled measurements. This 1/f noise error term
can be in the range of several µV or more, and, when amplified
with the closed-loop gain of the circuit, can show up as a large
output offset. For example, when an amplifier with a 5 µV p-p
1/f noise is configured for a gain of 1000, its output has 5 mV of
error due to the 1/f noise. However, the AD8628/AD8629/AD8630
eliminate 1/f noise internally, thereby greatly reducing output errors.
The internal elimination of 1/f noise is accomplished as follows.
1/f noise appears as a slowly varying offset to the AD8628/AD8629/
AD8630 inputs. Auto-zeroing corrects any dc or low frequency
offset. Therefore, the 1/f noise component is essentially removed,
leaving the AD8628/AD8629/AD8630 free of 1/f noise.
One advantage that the AD8628/AD8629/AD8630 bring to
system applications over competitive auto-zero amplifiers is their
very low noise. The comparison shown in Figure 49 indicates
an input-referred noise density of 19.4 nV/√Hz at 1 kHz for
the AD8628, which is much better than the Competitor A
and Competitor B. The noise is flat from dc to 1.5 kHz, slowly
increasing up to 20 kHz. The lower noise at low frequency is
desirable where auto-zero amplifiers are widely used.
02735-046
MK AT 1kHz FOR ALL 3 GRAPHS
FREQUENCY (kHz)
VOLTAGE NOISE DENSITY (nV/Hz)
120
105
90
75
60
45
30
15
0
042861012
COMPETITOR A
(89.7nV/Hz)
COMPETITOR B
(31.1nV/Hz)
AD8628
(19.4nV/Hz)
Figure 49. Noise Spectral Density of AD8628 vs. Competition