20 μA Maximum, Rail-to-Rail I/O,
Zero Input Crossover Distortion Amplifiers
AD8505/AD8506/AD8508
FEATURES
V– 2
AD8505
5
The AD8505/AD8506/AD8508 are specified for both the industrial
temperature range of −40°C to +85°C and the extended industrial
temperature range of −40°C to +125°C. The AD8505 single amplifier is available in a tiny 5-lead SOT-23 and a 6-ball WLCSP
packages. The AD8506 dual amplifier is available in 8-lead MSOP
and 8-ball WLCSP packages. The AD8508 quad amplifier is
available in 14-lead TSSOP and 14-ball WLCSP packages. The
AD8505/AD8506/AD8508 are members of a growing series of
zero crossover distortion op amps offered by Analog Devices,
Inc., including the ADA4505-1/ADA4505-2/ADA4505-4, that
operate from a single 1.8 V to 5 V supply or from dual ±0.9 V to
±2.5 V power supplies.
NC
B1
B2
+IN
–IN
C1
C2
AD8505
4
–IN
Figure 1. 5-Lead SOT-23 (RJ-5)
Figure 2. 6-Ball WLCSP (CB-6-7)
BALL A1
CORNER
–IN A 2
+IN A 3
AD8506
TOP VIEW
(Not to Scale)
V– 4
8
V+
7
OUT B
6
–IN B
5
+IN B
OUT B
V+
OUT A
A1
A2
A3
–IN B
–IN A
B1
B3
+IN B
V–
+IN A
C1
C2
C3
AD8506
06900-002
OUT A 1
Figure 3. 8-Lead MSOP (RM-8)
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
Figure 4. 8-Ball WLCSP (CB-8-2)
BALL A1
CORNER
OUTD
OUTA
A1
A2
A3
–IND
V–
+INA
B1
–INA
B2
+IND
B3
+INB
OUT A
1
14 OUT D
–IN A
2
13 –IN D
+INC
V+
+IN A
3
12 +IN D
D1
D2
D3
V+
4
–INC
OUTC
OUTB
+IN B
5
E1
E2
E3
–IN B
6
9
–IN C
OUT B
7
8
OUT C
AD8508
C1
TOP VIEW
11 V–
(Not to Scale)
10 +IN C
Figure 5. 14-Lead TSSOP (RU-14)
06900-045
This combination of features makes the AD8505/AD8506/AD8508
amplifiers ideal choices for battery-powered applications because
they minimize errors due to power supply voltage variations over
the lifetime of the battery and maintain high CMRR even for a railto-rail input op amp. Remote battery-powered sensors, handheld
instrumentation, consumer equipment, hazard detection (for
example, smoke, fire, and gas), and patient monitors can benefit
from the features of the AD8505/AD8506/AD8508 amplifiers.
V–
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
NC = NO CONNECT
GENERAL DESCRIPTION
The AD8505/AD8506/AD8508 are single, dual, and quad micropower amplifiers featuring rail-to-rail input/output swings while
operating from a single 1.8 V to 5 V power supply or from dual
±0.9 V to ±2.5 V power supplies. Using a new circuit technology,
these amplifiers offer zero input crossover distortion (excellent
PSRR and CMRR performance) and low bias current while
operating with a supply current of less than 20 μA per amplifier.
This amplifier family offers the lowest noise in its power class.
A2
V+
TOP VIEW
(Not to Scale)
+IN 3
V+
A1
06900-100
OUT 1
OUT
06900-001
Pressure and position sensors
Remote security
Bio sensors
IR thermometers
Battery-powered consumer equipment
Hazard detectors
BALL A1
INDICATOR
C3
–INB
AD8508
TOP VIEW
(BALL SIDE DOWN)
Not to Scale
06900-104
APPLICATIONS
PIN CONFIGURATIONS
06900-051
PSRR: 100 dB minimum
CMRR: 105 dB typical
Very low supply current: 20 μA per amplifier maximum
1.8 V to 5 V single supply or ±0.9 V to ±2.5 V dual supply
Rail-to-rail input/output
Low noise: 45 nV/√Hz at 1 kHz
2.5 mV offset voltage maximum
Very low input bias current: 1 pA typical
Figure 6. 14-Ball WLCSP (CB-14-1)
Rev. E
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 ©2007–2010 Analog Devices, Inc. All rights reserved.
AD8505/AD8506/AD8508
TABLE OF CONTENTS
Features .............................................................................................. 1
ESD Caution...................................................................................5
Applications ....................................................................................... 1
Typical Performance Characteristics ..............................................6
General Description ......................................................................... 1
Theory of Operation ...................................................................... 13
Pin Configurations ........................................................................... 1
Applications Information .............................................................. 15
Revision History ............................................................................... 2
Pulse Oximeter Current Source ............................................... 15
Specifications..................................................................................... 3
Electrical Characteristics—1.8 V Operation ............................ 3
Four-Pole, Low-Pass Butterworth Filter for Glucose
Monitor ........................................................................................ 16
Electrical Characteristics—5 V Operation................................ 4
Outline Dimensions ....................................................................... 17
Absolute Maximum Ratings............................................................ 5
Ordering Guide .......................................................................... 20
Thermal Resistance ...................................................................... 5
REVISION HISTORY
5/10—Rev. D to Rev. E
Added AD8505, 6-Ball WLCSP Package ......................... Universal
Changes to Large-Signal Voltage Gain Parameter (Table 1) ....... 4
Changes to Large-Signal Voltage Gain Parameter (Table 2) ....... 5
Changes to Table 4 ............................................................................ 6
Updated Outline Dimensions ....................................................... 19
Changes to Ordering Guide .......................................................... 21
10/09—Rev. C to Rev. D
Added AD8505, 5-Lead SOT-23 Package ....................... Universal
Changes to General Description, Added Figure 1 ....................... 1
Moved Electrical Characteristics—1.8 V Operation Section,
Changes to Supply Current per Amplifier Parameter, Table 1 ..... 3
Moved Electrical Characteristics—5 V Operation Section,
Changes to Supply Current per Amplifier Parameter, Table 2 ..... 4
Changes to Thermal Resistance Section and Table 4................... 5
Changes to Figure 20 and Figure 23 ............................................... 8
Updated Outline Dimensions ....................................................... 16
Changes to Ordering Guide .......................................................... 17
3/09—Rev. B to Rev. C
Added AD8508, 14-Ball WLCSP Package....................... Universal
Updated Outline Dimensions ....................................................... 17
Changes to Ordering Guide .......................................................... 18
10/08—Rev. A to Rev. B
Added WLCSP Package ..................................................... Universal
Added Figure 2; Renumbered Sequentially .................................. 1
Added Input Resistance Parameter ................................................ 3
Changes to Input Capacitance Differential Mode Parameter
Symbol and Input Capacitance Common Mode Parameter
Symbol ................................................................................................ 3
Added Input Resistance Parameter ................................................ 4
Changes to Input Capacitance Differential Mode Parameter
Symbol and Input Capacitance Common Mode Parameter
Symbol ................................................................................................ 4
Changes to Table 4.............................................................................5
Changes to Figure 46...................................................................... 16
Updated Outline Dimensions ....................................................... 17
Added Figure 49 ............................................................................. 17
Changes to Ordering Guide .......................................................... 18
7/08—Rev. 0 to Rev. A
Added AD8508 ................................................................... Universal
Added TSSOP Package ...................................................... Universal
Changes to Features Section and General Description Section ..1
Added Figure 2; Renumbered Sequentially ...................................1
Changed Electrical Characteristics Heading to Electrical
Characteristics—5 V Operation ......................................................3
Changes to Table 1.............................................................................3
Added Electrical Characteristics—1.8 V Operation Heading .....4
Changes to Table 2.............................................................................4
Changes to Table 3, Thermal Resistance Section, and Table 4 ....5
Added TA = 25°C Condition to Typical Performance
Characteristics Section .....................................................................6
Changes to Figure 3, Figure 4, Figure 6, and Figure 7 ..................6
Added Figure 11 and Figure 14 .......................................................7
Changes to Figure 17 Through Figure 20.......................................8
Changes to Figure 21 Through Figure 26.......................................9
Changes to Figure 27, Figure 28, Figure 30, and Figure 31....... 10
Changes to Figure 34, Figure 37, and Figure 38 ......................... 11
Added Figure 39 and Figure 40 .................................................... 12
Added Theory of Operation Section, Figure 41, and
Figure 42 .......................................................................................... 13
Added Figure 43 and Figure 44 .................................................... 14
Added Applications Information Section and Figure 45 .......... 15
Added Figure 46 ............................................................................. 16
Updated Outline Dimensions ....................................................... 17
Added Figure 48 ............................................................................. 17
Changes to Ordering Guide .......................................................... 17
11/07—Revision 0: Initial Version
Rev. E | Page 2 of 20
AD8505/AD8506/AD8508
SPECIFICATIONS
ELECTRICAL CHARACTERISTICS—1.8 V OPERATION
VSY = 1.8 V, VCM = VSY/2, TA = 25°C, RL = 100 kΩ to GND, unless otherwise noted.
Table 1.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Conditions
VOS
0 V ≤ VCM ≤ 1.8 V
−40°C ≤ TA ≤ +125°C
Min
IB
Typ
Max
Unit
0.5
2.5
3.5
10
100
600
5
50
100
1.8
115
mV
mV
pA
pA
pA
pA
pA
pA
V
dB
dB
dB
dB
2.5
220
3
4.2
dB
μV/°C
GΩ
pF
pF
1
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large-Signal Voltage Gain
AVO
Offset Voltage Drift
Input Resistance
Input Capacitance, Differential Mode
Input Capacitance, Common Mode
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
ΔVOS/ΔT
RIN
CINDM
CINCM
VOH
VOL
Short-Circuit Limit
POWER SUPPLY
Power Supply Rejection Ratio
ISC
Supply Current per Amplifier
AD8506/AD8508
ISY
PSRR
0
85
85
80
95
100
95
RL = 100 kΩ to GND
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to GND
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to VSY
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to VSY
−40°C ≤ TA ≤ +125°C
VOUT = VSY or GND
1.78
1.78
1.65
1.65
VSY = 1.8 V to 5 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
100
100
95
1.79
1.75
2
12
5
5
25
25
±4.5
110
V
V
V
V
mV
mV
mV
mV
mA
dB
dB
dB
VOUT = VSY/2
−40°C ≤ TA ≤ +125°C
VOUT = VSY/2
−40°C ≤ TA ≤ +125°C
16.5
SR
GBP
ΦM
RL = 100 kΩ, CL = 10 pF, G = 1
RL = 1 MΩ, CL = 20 pF, G = 1
RL = 1 MΩ, CL = 20 pF, G = 1
13
95
60
mV/μs
kHz
Degrees
en p-p
en
in
f = 0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz
2.8
45
15
μV p-p
nV/√Hz
fA/√Hz
AD8505
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
0.5
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
0 V ≤ VCM ≤ 1.8 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
0.05 V ≤ VOUT ≤ 1.75 V,
RL = 100 kΩ to VCM
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
Rev. E | Page 3 of 20
16.5
20
25
24
27.5
μA
μA
μA
μA
AD8505/AD8506/AD8508
ELECTRICAL CHARACTERISTICS—5 V OPERATION
VSY = 5 V, VCM = VSY/2, TA = 25°C, RL = 100 kΩ to GND, unless otherwise noted.
Table 2.
Parameter
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Symbol
Conditions
VOS
0 V ≤ VCM ≤ 5 V
−40°C ≤ TA ≤ +125°C
Min
IB
Typ
Max
Unit
0.5
2.5
3.5
10
100
600
5
50
130
5
120
mV
mV
pA
pA
pA
pA
pA
pA
V
dB
dB
dB
dB
2
220
3
4.2
dB
μV/°C
GΩ
pF
pF
1
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
Input Offset Current
IOS
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
Large-Signal Voltage Gain
AVO
Offset Voltage Drift
Input Resistance
Input Capacitance, Differential Mode
Input Capacitance, Common Mode
OUTPUT CHARACTERISTICS
Output Voltage High
Output Voltage Low
ΔVOS/ΔT
RIN
CINDM
CINCM
VOH
VOL
Short-Circuit Limit
POWER SUPPLY
Power Supply Rejection Ratio
ISC
Supply Current per Amplifier
AD8506/AD8508
ISY
AD8505
DYNAMIC PERFORMANCE
Slew Rate
Gain Bandwidth Product
Phase Margin
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
PSRR
0.5
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
0 V ≤ VCM ≤ 5 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
0.05 V ≤ VOUT ≤ 4.95 V,
RL = 100 kΩ to VCM
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
0
90
90
85
105
105
100
RL = 100 kΩ to GND
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to GND
−40°C ≤ TA ≤ +125°C
RL = 100 kΩ to VSY
−40°C ≤ TA ≤ +125°C
RL = 10 kΩ to VSY
−40°C ≤ TA ≤ +125°C
VOUT = VSY or GND
4.98
4.98
4.9
4.9
VSY = 1.8 V to 5 V
−40°C ≤ TA ≤ +85°C
−40°C ≤ TA ≤ +125°C
100
100
95
4.99
4.95
2
10
5
5
25
30
±45
110
V
V
V
V
mV
mV
mV
mV
mA
dB
dB
dB
VOUT = VSY/2
−40°C ≤ TA ≤ +125°C
−40°C ≤ TA ≤ +125°C
15
SR
GBP
ΦM
RL = 100 kΩ, CL = 10 pF, G = 1
RL = 1 MΩ, CL = 20 pF, G = 1
RL = 1 MΩ, CL = 20 pF, G = 1
13
95
60
mV/μs
kHz
Degrees
en p-p
en
in
f = 0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz
2.8
45
15
μV p-p
nV/√Hz
fA/√Hz
Rev. E | Page 4 of 20
20
25
25.5
μA
μA
μA
AD8505/AD8506/AD8508
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 3.
Parameter
Supply Voltage
Input Voltage
Input Current1
Differential Input Voltage2
Output Short-Circuit Duration to GND
Storage Temperature Range
Operating Temperature Range
Junction Temperature Range
Lead Temperature (Soldering, 60 sec)
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages with its
exposed paddle soldered to a pad, if applicable. Table 4 shows
simulated thermal values for a 4-layer (2S2P) JEDEC standard
thermal test board, unless otherwise specified.
Rating
5.5 V
±VSY ± 0.1 V
±10 mA
±VSY
Indefinite
−65°C to +150°C
−40°C to +125°C
−65°C to +150°C
300°C
Table 4.
1
Input pins have clamp diodes to the supply pins. The input current should
be limited to 10 mA or less whenever the input signal exceeds the power
supply rail by 0.5 V.
2
The 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.
Package Type
5-Lead SOT-23 (RJ-5)
6-Ball WLCSP (CB-6-7)
8-Lead MSOP (RM-8)
8-Ball WLCSP (CB-8-2)
14-Lead TSSOP (RU-14)
14-Ball WLCSP (CB-14-1)
ESD CAUTION
Rev. E | Page 5 of 20
θJA
190
105
142
82
112
64
θJC
92
N/A
45
N/A
35
N/A
Unit
°C/W
°C/W
°C/W
°C/W
°C/W
°C/W
AD8505/AD8506/AD8508
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
250
250
VSY = 1.8V
VCM = VSY/2
VSY = 5V
VCM = VSY/2
200
NUMBER OF AMPLIFIERS
150
100
150
100
–3
–2
–1
0
1
2
3
4
VOS (mV)
0
–4
06900-003
0
–4
–3
1
2
3
4
12
VSY = 5V
–40°C ≤ TA ≤ +125°C
VSY = 1.8V
–40°C ≤ TA ≤ +125°C
14
10
12
NUMBER OF AMPLIFIERS
10
8
6
4
8
6
4
2
2
1
2
3
4
5
6
7
8
9
10
11
12
13
TCVOS (µV/°C)
0
06900-004
0
0
1
1000
1000
500
500
VOS (µV)
1500
0
–1000
–1000
–1500
–1500
0.6
0.8
1.0
1.2
1.4
1.6
1.8
VCM (V)
06900-005
–500
0.4
6
7
8
9
10
11
12
13
Figure 9. Input Offset Voltage vs. Input Common-Mode Voltage
VSY = 5V
0
–500
0.2
5
2000
VSY = 1.8V
0
4
Figure 11. Input Offset Voltage Drift Distribution
1500
–2000
3
TCVOS (µV/°C)
Figure 8. Input Offset Voltage Drift Distribution
2000
2
06900-007
NUMBER OF AMPLIFIERS
0
Figure 10. Input Offset Voltage Distribution
16
VOS (µV)
–1
VOS (mV)
Figure 7. Input Offset Voltage Distribution
0
–2
06900-006
50
50
–2000
0
1
2
3
4
5
VCM (V)
Figure 12. Input Offset Voltage vs. Input Common-Mode Voltage
Rev. E | Page 6 of 20
06900-008
NUMBER OF AMPLIFIERS
200
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
–115
–120
VSY = 1.8V
VSY = 5V
–125
–120
VOS (µV)
VOS (µV)
–130
–125
–130
–135
–140
–135
0.6
0.8
1.0
VCM (V)
1.2
1.4
1.6
1.8
–150
500
450
450
IB (pA)
500
400
350
300
300
250
250
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
VCM (V)
200
5
VSY = 5V
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
VCM (V)
Figure 14. Input Bias Current vs. Input Common-Mode Voltage at 125°C
Figure 17. Input Bias Current vs. Input Common-Mode Voltage at 125°C
1000
1000
VSY = 1.8V
VCM = VSY/2
VSY = 5V
VCM = VSY/2
100
100
10
IB (pA)
IB (pA)
10
1
1
0.1
0.1
35
45
55
65
75
85
95
TEMPERATURE (°C)
105
115
125
06900-018
0.01
25
4
400
350
06900-009
IB (pA)
550
0.2
3
600
VSY = 1.8V
0
2
Figure 16. Input Offset Voltage vs. Input Common-Mode Voltage
550
200
1
VCM (V)
Figure 13. Input Offset Voltage vs. Input Common-Mode Voltage
600
0
06900-038
0.4
06900-012
0.2
0.01
25
Figure 15. Input Bias Current vs. Temperature
35
45
55
65
75
85
95
TEMPERATURE (°C)
105
Figure 18. Input Bias Current vs. Temperature
Rev. E | Page 7 of 20
115
125
06900-019
0
06900-037
–140
–145
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
10k
OUTPUT VOLTAGE TO SUPPLY RAIL (mV)
1k
100
VOL
VDD – VOH
10
1
0.1
0.001
0.01
0.1
LOAD CURRENT (mA)
1
10
1k
1
0.1
0.01
0.001
0.01
0.1
1
LOAD CURRENT (mA)
10
100
Figure 22. Output Voltage to Supply Rail vs. Load Current
14
12
VDD – VOH @ RL = 10kΩ
10
8
VOL @ RL = 10kΩ
6
4
VDD – VOH @ RL = 100kΩ
2
0
–40
VOL @ RL = 100kΩ
–25
–10
5
20
35
50
65
80
95
110
125
TEMPERATURE (°C)
VOL @ RL = 10kΩ
6
4
VDD – VOH @ RL = 100kΩ
2
VOL @ RL = 100kΩ
–25
–10
5
20
35
50
65
80
95
110
125
Figure 23. Output Voltage to Supply Rail vs. Temperature
90
VCM = VSY/2
80
TOTAL SUPPLY CURRENT (µA)
80
8
TEMPERATURE (°C)
AD8508
AD8506
AD8505
VCM = VSY/2
VDD – VOH @ RL = 10kΩ
10
0
–40
Figure 20. Output Voltage to Supply Rail vs. Temperature
90
VSY = 5V
12
06900-014
OUTPUT VOLTAGE TO SUPPLY RAIL (mV)
VSY = 1.8V
06900-011
70
60
50
40
30
20
10
70
60
50
40
AD8508,
AD8508,
AD8506,
AD8606,
AD8505,
AD8505,
1.8V
5V
1.8V
5V
1.8V
5V
30
20
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
06900-052
10
SUPPLY VOLTAGE (V)
0
–40
–25
–10
5
20
35
50
65
80
95
110 125
TEMPERATURE (°C)
Figure 21. Total Supply Current vs. Supply Voltage
Figure 24. Total Supply Current vs. Temperature
Rev. E | Page 8 of 20
06900-053
OUTPUT VOLTAGE TO SUPPLY RAIL (mV)
VOL
10
14
TOTAL SUPPLY CURRENT (µA)
VDD – VOH
100
Figure 19. Output Voltage to Supply Rail vs. Load Current
0
VSY = 5V
06900-013
VSY = 1.8V
06900-010
OUTPUT VOLTAGE TO SUPPLY RAIL (mV)
10k
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
120
100
100
80
80
80
80
60
60
60
60
20
0
0
–20
–20
GAIN, CL = 0pF
PHASE, CL = 0pF
GAIN, CL = 50pF
PHASE, CL = 50pF
GAIN, CL = 100pF
PHASE, CL = 100pF
–40
–60
–80
–100
–120
100
1k
–40
–60
10k
FREQUENCY (Hz)
100k
40
20
0
0
–20
–60
–100
–80
–100
100
1k
40
CLOSED-LOOP GAIN (dB)
G = –1
–10
–20
20
10k
FREQUENCY (Hz)
0
VSY = 5V
G = –100
–40
10k
FREQUENCY (Hz)
100k
1M
G = –1
–20
–40
1k
G = –10
–10
–30
–50
100
–50
100
1k
10k
FREQUENCY (Hz)
100k
1M
Figure 29. Closed-Loop Gain vs. Frequency
Figure 26. Closed-Loop Gain vs. Frequency
10k
10k
VSY = 5V
VSY = 1.8V
1k
1k
G = 100
G = 100
G = 10
100
100
G = 10
G=1
G=1
ZOUT (Ω)
10
10
1
1
0.1
10
0.1
100
1k
10k
FREQUENCY (Hz)
100k
1M
0.01
10
100
1k
10k
FREQUENCY (Hz)
Figure 30. ZOUT vs. Frequency
Figure 27. ZOUT vs. Frequency
Rev. E | Page 9 of 20
100k
1M
06900-031
ZOUT (Ω)
–100
1M
100k
10
–30
06900-017
CLOSED-LOOP GAIN (dB)
–80
30
G = –10
10
0
–60
50
30
20
–40
Figure 28. Open-Loop Gain and Phase vs. Frequency
VSY = 1.8V
G = –100
–20
GAIN, CL = 0pF
PHASE, CL = 0pF
GAIN, CL = 50pF
PHASE, CL = 50pF
GAIN, CL = 100pF
PHASE, CL = 100pF
–40
06900-020
40
40
GAIN
Figure 25. Open-Loop Gain and Phase vs. Frequency
50
100
20
–80
–120
1M
PHASE
120
PHASE (Degrees)
20
VSY = 5V
06900-025
40
GAIN
06900-022
40
PHASE (Degrees)
VSY = 1.8V
PHASE
06900-028
OPEN-LOOP GAIN (dB)
100
OPEN-LOOP GAIN (dB)
120
120
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
100
90
80
80
CMRR (dB)
90
70
70
60
60
50
50
100
1k
10k
FREQUENCY (Hz)
100k
1M
40
10
Figure 31. CMRR vs. Frequency
1k
10k
FREQUENCY (Hz)
VSY = 1.8V
90
80
80
70
70
60
60
PSRR (dB)
90
50
40
PSRR+
20
VSY = 5V
50
40
PSRR+
20
10
10
1k
10k
100k
1M
FREQUENCY (Hz)
06900-023
100
0
10
100
100k
1M
80
80
VSY = 1.8V
RL = 100kΩ
VSY = 5V
RL = 100kΩ
70
60
OVERSHOOT (%)
60
50
40
30
–OVERSHOOT
50
40
30
–OVERSHOOT
20
20
+OVERSHOOT
+OVERSHOOT
10
10
100
LOAD CAPACITANCE (pF)
600
0
10
06900-027
OVERSHOOT (%)
10k
Figure 35. PSRR vs. Frequency
Figure 32. PSRR vs. Frequency
0
10
1k
FREQUENCY (Hz)
06900-026
PSRR–
PSRR–
70
1M
30
30
0
10
100k
Figure 34. CMRR vs. Frequency
100
100
PSRR (dB)
100
100
LOAD CAPACITANCE (pF)
Figure 36. Small-Signal Overshoot vs. Load Capacitance
Figure 33. Small-Signal Overshoot vs. Load Capacitance
Rev. E | Page 10 of 20
600
06900-030
40
10
VSY = 5V
06900-032
VSY = 1.8V
06900-029
CMRR (dB)
100
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
VSY = 1.8V
RL = 100kΩ
CL = 200pF
G=1
TIME (100µs/DIV)
06900-035
06900-033
VOLTAGE (1V/DIV)
VOLTAGE (500mV/DIV)
VSY = 5V
RL = 100kΩ
CL = 200pF
G=1
TIME (100µs/DIV)
Figure 37. Large-Signal Transient Response
Figure 40. Large-Signal Transient Response
VSY = 1.8V
RL = 100kΩ
CL = 200pF
G=1
TIME (100µs/DIV)
Figure 38. Small-Signal Transient Response
Figure 41. Small-Signal Transient Response
1k
TIME (4s/DIV)
06900-034
VOLTAGE NOISE DENSITY (nV/√Hz)
INPUT VOLTAGE NOISE (0.5µV/DIV)
VSY = 1.8V AND 5V
2.78µV p-p
VSY = 1.8V AND 5V
100
10
1
1
10
100
FREQUENCY (Hz)
1k
Figure 42. Voltage Noise Density vs. Frequency
Figure 39. Input Voltage Noise 0.1 Hz to 10 Hz
Rev. E | Page 11 of 20
10k
06900-047
TIME (100µs/DIV)
06900-046
06900-036
VOLTAGE (5mV/DIV)
VOLTAGE (5mV/DIV)
VSY = 5V
RL = 100kΩ
CL = 200pF
G=1
AD8505/AD8506/AD8508
TA = 25°C, unless otherwise noted.
–40
–60
–70
–80
–90
–100
10kΩ
–60
–70
–80
–90
–100
–110
1k
10k
FREQUENCY (Hz)
100k
Figure 43. Channel Separation vs. Frequency
–120
100
1k
10k
FREQUENCY (Hz)
Figure 44. Channel Separation vs. Frequency
Rev. E | Page 12 of 20
100k
06900-048
–110
–120
100
VSY = 5V
VIN = 4V p-p
100kΩ
–50
CHANNEL SEPARATION (dB)
10kΩ
06900-049
CHANNEL SEPARATION (dB)
–50
–40
VSY = 1.8V
VIN = 1.5V p-p
100kΩ
AD8505/AD8506/AD8508
THEORY OF OPERATION
VDD
The AD8505/AD8506/AD8508 are unity-gain, stable, CMOS, railto-rail input/output operational amplifiers designed to optimize
performance in current consumption, PSRR, CMRR, and zero
crossover distortion, all embedded in a small package. The
typical offset voltage is 500 μV, with a low peak-to-peak voltage
noise of 2.8 μV from 0.1 Hz to 10 Hz and a voltage noise density
of 45 nV/√Hz at 1 kHz.
VBIAS
VIN+
The AD8505/AD8506/AD8508 amplifiers are designed to solve
two key problems in low voltage battery-powered applications:
the battery voltage decrease over time and the rail-to-rail input
stage distortion.
The second problem with battery-powered applications is the
distortion caused by the standard rail-to-rail input stage. Using
a CMOS non-rail-to-rail input stage (that is, a single differential
pair) limits the input voltage to approximately one VGS (gatesource voltage) away from one of the supply lines. Because VGS
for normal operation is commonly over 1 V, a single differential
pair input stage op amp greatly restricts the allowable input
voltage range when using a low supply voltage. This limitation
restricts the number of applications where the non-rail-to-rail
input op amp was originally intended to be used. To solve this
problem, a dual differential pair input stage is usually implemented
(see Figure 45); however, this technique has its own drawbacks.
One differential pair amplifies the input signal when the commonmode voltage is on the high end, whereas the other pair amplifies
the input signal when the common-mode voltage is on the low
end. This method also requires control circuitry to operate the
two differential pairs appropriately. Unfortunately, this topology
leads to a very noticeable and undesirable problem: if the signal
level moves through the range where one input stage turns off
and the other one turns on, noticeable distortion occurs (see
Figure 46).
Q1
Q2
Q4
VIN–
IB
06900-039
IB
VSS
Figure 45. A Typical Dual Differential Pair Input Stage Op Amp
(Dual PMOS Q1 and Q2 Transistors Form the Lower End of the Input Voltage
Range, Whereas Dual NMOS Q3 and Q4 Compose the Upper End)
300
VSY = 5V
TA = 25°C
250
200
150
100
50
VOS (µV)
0
–50
–100
–150
–200
–250
–300
0
0.5
1.0
1.5
2.0
2.5
3.0
VCM (V)
3.5
4.0
4.5
5.0
06900-040
In battery-powered applications, the supply voltage available to
the IC is the voltage of the battery. Unfortunately, the voltage of
a battery decreases as it discharges itself through the load. This
voltage drop over the lifetime of the battery causes an error in
the output of the op amps. Some applications requiring precision
measurements during the entire lifetime of the battery use voltage
regulators to power up the op amps as a solution. If a design
uses standard battery cells, the op amps experience a supply
voltage change from roughly 3.2 V to 1.8 V during the lifetime
of the battery. This means that for a PSRR of 70 dB minimum in
a typical op amp, the input-referred offset error is approximately
440 μV. If the same application uses the AD8505/AD8506/
AD8508 amplifiers with a 100 dB minimum PSRR, the error is
only 14 μV. It is possible to calibrate out this error or to use an
external voltage regulator to power the op amp, but these solutions
can increase system cost and complexity. The AD8505/AD8506/
AD8508 amplifiers solve the impasse with no additional cost or
error-nullifying circuitry.
Q3
Figure 46. Typical Input Offset Voltage vs. Common-Mode Voltage
Response in a Dual Differential Pair Input Stage Op Amp (Powered by 5 V
Supply; Results of Approximately 100 Units per Graph Are Displayed)
This distortion forces the designer to devise impractical ways
to avoid the crossover distortion areas, therefore narrowing the
common-mode dynamic range of the operational amplifier. The
AD8505/AD8506/AD8508 amplifiers solve this crossover distortion problem by using an on-chip charge pump to power the
input differential pair. The charge pump creates a supply voltage
higher than the voltage of the battery, allowing the input stage to
handle a wide range of input signal voltages without using a second
differential pair. With this solution, the input voltage can vary from
one supply extreme to the other with no distortion, thereby
restoring the full common-mode dynamic range of the op amp.
Rev. E | Page 13 of 20
AD8505/AD8506/AD8508
The charge pump has been carefully designed so that switching
noise components at any frequency, both within and beyond the
amplifier bandwidth, are much lower than the thermal noise floor.
Therefore, the spurious-free dynamic range (SFDR) is limited only
by the input signal and the thermal or flicker noise. There is no
intermodulation between the input signal and the switching noise.
Figure 48, the input offset voltage vs. input common-mode voltage
response, shows the typical response of 12 devices. Figure 48 is
expanded to make it easier to compare with Figure 46, the typical
input offset voltage vs. common-mode voltage response in a
dual differential pair input stage op amp.
300
250
Figure 47 displays a typical front-end section of an operational
amplifier with an on-chip charge pump.
150
VPP = POSITIVE PUMPED VOLTAGE = VDD + 1.8V
VPP
100
VDD
VOS (µV)
50
VBIAS
Q1
Q2
–IN
CASCODE
STAGE
AND
RAIL-TO-RAIL
OUTPUT
STAGE
0
–50
–100
–150
OUT
–200
VSS
Figure 47. Typical Front-End Section of an Op Amp
with Embedded Charge Pump
0
0.5
1.0
1.5
2.0
2.5
3.0
VCM (V)
3.5
4.0
4.5
5.0
06900-042
–250
–300
06900-041
+IN
VSY = 5V, TA = 25°C
200
Figure 48. Input Offset Voltage vs. Input Common-Mode Voltage Response
(Powered by a 5 V Supply; Results of 12 Units Are Displayed)
This solution improves the CMRR performance tremendously.
For instance, if the input varies from rail to rail on a 2.5 V
supply rail, using a part with a CMRR of 70 dB minimum, an
input-referred error of 790 μV is introduced. Another part with
a CMRR of 52 dB minimum generates a 6.3 mV error. The
AD8505/AD8506/AD8508 CMRR of 90 dB minimum causes only
a 79 μV error. As with the PSRR error, there are complex ways to
minimize this error, but the AD8505/AD8506/AD8508 amplifiers
solve this problem without incurring unnecessary circuitry
complexity or increased cost.
Rev. E | Page 14 of 20
AD8505/AD8506/AD8508
APPLICATIONS INFORMATION
A pulse oximeter is a noninvasive medical device used for continuously measuring the percentage of hemoglobin (Hb) saturated
with oxygen and the pulse rate of a patient. Hemoglobin that is
carrying oxygen (oxyhemoglobin) absorbs light in the infrared
(IR) region of the spectrum; hemoglobin that is not carrying
oxygen (deoxyhemoglobin) absorbs visible red (R) light. In
pulse oximetry, a clip containing two LEDs (sometimes more,
depending on the complexity of the measurement algorithm) and
the light sensor (photodiode) is placed on the finger or earlobe
of the patient. One LED emits red light (600 nm to 700 nm) and
the other emits light in the near IR (800 nm to 900 nm) region.
The clip is connected by a cable to a processor unit. The LEDs
are rapidly and sequentially excited by two current sources (one
for each LED), whose dc levels depend on the LED being driven,
based on manufacturer requirements, and the detector is synchronized to capture the light from each LED as it is transmitted
through the tissue.
drift of the total design need to be improved, then a more accurate
and low temperature coefficient drift voltage reference and current
source resistor should be utilized. C3 and C4 are used to improve
stabilization of U1; R3 and R7 are used to provide some current
limit into the U1 inverting pin; and R2 and R6 are used to slow
down the rise time of the N-MOSFET when it turns on. These
elements may not be needed, or some bench adjustments may
be required.
+5V
+5V
C1
0.1µF
U1
1/2
8
R2 V
22Ω OUT1
V+
7
Q1
IRLMS2002
V–
4
U2
ADG733
+5V
S1A 12
14 D1
5
S1B 13
6
S2A 2
15 D2
S2B 1
C3
22pF
R3
1kΩ
R1
20Ω
0.1%
1/4W MIN
16
VDD
AD8506
62.5mA
An example design of a dc current source driving the red and
infrared LEDs is shown in Figure 49. These dc current sources
allow 62.5 mA and 101 mA to flow through the red and infrared
LEDs, respectively. First, to prolong battery life, the LEDs are
driven only when needed. One-third of the ADG733 SPDT
analog switch is used to disconnect or connect the 1.25 V voltage
reference from or to each current circuit. When driving the LEDs,
the ADR1581 1.25 V voltage reference is buffered by half of the
AD8506; the presence of this voltage on the noninverting input
forces the output of the op amp (due to the negative feedback)
to maintain a level that causes its inverting input to track the
noninverting pin. Therefore, the 1.25 V appears in parallel with
the 20 Ω R1 or 12.4 Ω R5 current source resistor, creating the flow
of 62.5 mA or 101 mA current through the red or infrared LED
as the output of the op amp turns on the Q1 or Q2 N-MOSFET
IRLMS2002.
The maximum total quiescent currents for the AD8506 (that is,
half of the AD8506), ADR1581, and ADG733 are 25 μA, 70 μA,
and 1 μA, respectively, resulting in a total of 96 μA current consumption (480 μW power consumption) per circuit, which is good
for a system powered by a battery. If the accuracy and temperature
C2
0.1µF
CONNECT TO RED LED
R4
53.6kΩ
VREF = 1.25V
U3
ADR1581
S3A 5
4 D3
S3B 3
RED CURRENT
SOURCE
8
9
A2
10
A1
11
A0
6
EN
GND
VSS
CONNECT TO INFRARED LED
101mA
U1
1/2
7
+5V
AD8506
R6
22Ω VOUT2
Q2
IRLMS2002
8
1
V+
V–
4
3
2
I_BIT2
I_BIT1
I_BIT0
I_ENA
C4
22pF
R7
1kΩ
R5
INFRARED CURRENT
12.4Ω
SOURCE
0.1%
1/2W MIN
06900-043
PULSE OXIMETER CURRENT SOURCE
Figure 49. Pulse Oximeter Red and Infrared Current Sources Using the
AD8506 as a Buffer to the Voltage Reference Device
Rev. E | Page 15 of 20
AD8505/AD8506/AD8508
the I-to-V converter requires low input bias current. The
AD8505/AD8506/AD8508 are excellent choices because these
amplifiers provide 1 pA typical and 10 pA maximum of input
bias current at ambient temperature.
FOUR-POLE, LOW-PASS BUTTERWORTH FILTER
FOR GLUCOSE MONITOR
There are several methods of glucose monitoring: spectroscopic
absorption of infrared light in the 2 μm to 2.5 μm range, reflectance spectrophotometry, and the amperometric type using
electrochemical strips with glucose oxidase enzymes. The
amperometric type generally uses three electrodes: a reference
electrode, a control electrode, and a working electrode. Although
this is a well established and widely used technique, signal-to-noise
ratio and repeatability can be improved using the AD8505/
AD8506/AD8508 amplifiers with their low peak-to-peak voltage
noise of 2.8 μV from 0.1 Hz to 10 Hz and voltage noise density
of 45 nV/√Hz at 1 kHz.
A low-pass filter with a cutoff frequency of 80 Hz to 100 Hz is
desirable in a glucose meter device to remove extraneous noise;
this can be a simple two-pole or four-pole Butterworth filter. Low
power op amps with bandwidths of 50 kHz to 500 kHz should
be adequate. The AD8505/AD8506/AD8508 amplifiers with their
95 kHz GBP and 15 μA typical current consumption meet these
requirements. A circuit design of a four-pole Butterworth filter
(preceded by a one-pole, low-pass filter) is shown in Figure 50.
With a 3.3 V battery, the total power consumption of this design
is 297 μW typical at ambient temperature.
Another consideration is operation from a 3.3 V battery. Glucose
signal currents are usually less than 3 μA full scale; therefore,
C1
1000pF
R1
5MΩ
+3.3V
WORKING
CONTROL
+3.3V
3
8
V+
1
V–
2
4
U1
1/2
R3
22.6kΩ
5
C3
0.047µF
8
V+
7
V–
AD8506
U1
1/2
AD8506
6
4
+3.3V
R4
22.6kΩ
R5
22.6kΩ
AD8506
3
C5
0.047µF
8
V+
1
V–
C2
0.1µF
U2
1/2
2
VOUT
4
C4
0.1µF
DUPLICATE OF CIRCUIT ABOVE
06900-044
REFERENCE
R2
22.6kΩ
Figure 50. A Four-Pole Butterworth Filter That Can Be Used in a Glucose Meter
Rev. E | Page 16 of 20
AD8505/AD8506/AD8508
OUTLINE DIMENSIONS
3.00
2.90
2.80
5
1.70
1.60
1.50
1
4
2
3.00
2.80
2.60
3
0.95 BSC
1.90
BSC
1.45 MAX
0.95 MIN
0.15 MAX
0.05 MIN
0.20 MAX
0.08 MIN
10°
5°
0°
SEATING
PLANE
0.50 MAX
0.35 MIN
0.55
0.45
0.35
0.20
BSC
121608-A
1.30
1.15
0.90
COMPLIANT TO JEDEC STANDARDS MO-178-AA
Figure 51. 5-Lead Small Outline Transistor Package [SOT-23]
(RJ-5)
Dimensions shown in millimeters
0.945
0.905
0.865
0.645
0.600
0.555
0.415
0.400
0.385
BALL A1
IDENTIFIER
SEATING
PLANE
0.287
0.267
0.247
1.425
1.385
1.345
2
1
A
0.80
BSC
B
0.40
BSC
C
0.230
0.200
0.170
0.05 NOM
COPLANARITY
0.40 BSC
Figure 52. 6-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-6-7)
Dimensions shown in millimeters
Rev. E | Page 17 of 20
BOTTOM VIEW
(BALL SIDE UP)
081709-A
TOP VIEW
(BALL SIDE DOWN)
AD8505/AD8506/AD8508
3.20
3.00
2.80
8
3.20
3.00
2.80
1
5.15
4.90
4.65
5
4
PIN 1
IDENTIFIER
0.65 BSC
0.95
0.85
0.75
15° MAX
1.10 MAX
0.40
0.25
0.80
0.55
0.40
0.23
0.09
6°
0°
100709-B
0.15
0.05
COPLANARITY
0.10
COMPLIANT TO JEDEC STANDARDS MO-187-AA
Figure 53. 8-Lead Mini Small Outline Package [MSOP]
(RM-8)
Dimensions shown in millimeters
0.650
0.595
0.540
1.460
1.420 SQ
1.380
SEATING
PLANE
3
2
1
0.340
0.320
0.300
BALL 1
IDENTIFIER
A
B
0.50
BALL PITCH
0.380
0.355
0.330
COPLANARITY
0.075
C
BOTTOM VIEW
0.270
0.240
0.210
Figure 54. 8-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-8-2)
Dimensions shown in millimeters
Rev. E | Page 18 of 20
(BALL SIDE UP)
011008-B
TOP VIEW
AD8505/AD8506/AD8508
5.10
5.00
4.90
14
8
4.50
4.40
4.30
6.40
BSC
1
7
PIN 1
0.65 BSC
0.15
0.05
COPLANARITY
0.10
1.20
MAX
0.20
0.09
SEATING
PLANE
0.30
0.19
0.75
0.60
0.45
8°
0°
061908-A
1.05
1.00
0.80
COMPLIANT TO JEDEC STANDARDS MO-153-AB-1
Figure 55. 14-Lead Thin Shrink Small Outline Package [TSSOP]
(RU-14)
Dimensions shown in millimeters
0.650
0.595
0.540
1.50
1.46
1.42
0.25
BSC
0.25
BSC
3
SEATING
PLANE
2
0.25
BSC
0.25
BSC
1
A
BALL 1
IDENTIFIER
0.50 BSC
B
3.00
2.96
2.92
0.340
0.320
0.300
2.00
BSC
0.50 BSC
C
0.50 BSC
D
E
0.380
0.355
0.330
0.10 MAX
COPLANARITY
0.270
0.240
0.210
Figure 56. 14-Ball Wafer Level Chip Scale Package [WLCSP]
(CB-14-1)
Dimensions shown in millimeters
Rev. E | Page 19 of 20
BOTTOM VIEW
(BALL SIDE UP)
1.00
BSC
061208-A
TOP VIEW
(BALL SIDE DOWN)
0.50
BSC
AD8505/AD8506/AD8508
ORDERING GUIDE
Model1
AD8505ARJZ-R2
AD8505ARJZ-R7
AD8505ARJZ-RL
AD8505ACBZ-R7
AD8505ACBZ-RL
AD8506ACBZ-REEL
AD8506ACBZ-REEL7
AD8506ARMZ
AD8506ARMZ-R7
AD8506ARMZ-REEL
AD8508ARUZ
AD8508ARUZ-REEL
AD8508ACBZ-REEL
AD8508ACBZ-REEL7
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
5-Lead Small Outline Transistor Package [SOT-23]
5-Lead Small Outline Transistor Package [SOT-23]
5-Lead Small Outline Transistor Package [SOT-23]
6-Ball Wafer Level Chip Scale Package [WLCSP]
6-Ball Wafer Level Chip Scale Package [WLCSP]
8-Ball Wafer Level Chip Scale Package [WLCSP]
8-Ball Wafer Level Chip Scale Package [WLCSP]
8-Lead Mini Small Outline Package [MSOP]
8-Lead Mini Small Outline Package [MSOP]
8-Lead Mini Small Outline Package [MSOP]
14-Lead Thin Shrink Small Outline Package [TSSOP]
14-Lead Thin Shrink Small Outline Package [TSSOP]
14-Ball Wafer Level Chip Scale Package [WLCSP]
14-Ball Wafer Level Chip Scale Package [WLCSP]
Z = RoHS Compliant Part.
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D06900-0-5/10(E)
Rev. E | Page 20 of 20
Package Option
RJ-5
RJ-5
RJ-5
CB-6-7
CB-6-7
CB-8-2
CB-8-2
RM-8
RM-8
RM-8
RU-14
RU-14
CB-14-1
CB-14-1
Branding
A2E
A2E
A2E
A2H
A2H
A1X
A1X
A1X
A1X
A1X
A27
A27