AD AD824BN

Single Supply, Rail-to-Rail
Low Power, FET-Input Op Amp
AD824
a
FEATURES
Single Supply Operation: 3 V to 30 V
Very Low Input Bias Current: 2 pA
Wide Input Voltage Range
Rail-to-Rail Output Swing
Low Supply Current: 500 mA/Amp
Wide Bandwidth: 2 MHz
Slew Rate: 2 V/ms
No Phase Reversal
APPLICATIONS
Photo Diode Preamplifier
Battery Powered Instrumentation
Power Supply Control and Protection
Medical Instrumentation
Remote Sensors
Low Voltage Strain Gage Amplifiers
DAC Output Amplifier
PIN CONFIGURATIONS
14-Lead Epoxy DIP
(N Suffix)
14-Lead Epoxy SO
(R Suffix)
OUT A
1
14 OUT D
OUT A
1
14
OUT D
–IN A
2
13 –IN D
–IN A
2
13
–IN D
+IN A
3
12 +IN D
+IN A
3
12 +IN D
V+
4
V+
4
+IN B
5
10 +IN C
+INB
5
11
TOP VIEW
(Not to Scale) 10
–IN B
6
9
–IN C
–INB
6
9
–IN C
OUT B
7
8
OUT C
OUTB
7
8
OUT C
AD824
11 V–
AD824
V–
+IN C
TOP VIEW
16-Lead Epoxy SO
(R Suffix)
GENERAL DESCRIPTION
The AD824 is a quad, FET input, single supply amplifier, featuring rail-to-rail outputs. The combination of FET inputs and
rail-to-rail outputs makes the AD824 useful in a wide variety of
low voltage applications where low input current is a primary
consideration.
The AD824 is guaranteed to operate from a 3 V single supply
up to ± 15 volt dual supplies.
Fabricated on ADI’s complementary bipolar process, the AD824
has a unique input stage that allows the input voltage to safely
extend beyond the negative supply and to the positive supply
without any phase inversion or latchup. The output voltage
swings to within 15 millivolts of the supplies. Capacitive loads
to 350 pF can be handled without oscillation.
The FET input combined with laser trimming provides an input
that has extremely low bias currents with guaranteed offsets below 300 µV. This enables high accuracy designs even with high
source impedances. Precision is combined with low noise,
making the AD824 ideal for use in battery powered medical
equipment.
16 OUT D
OUT A 1
–IN A
15 –IN D
2
14 +IN D
+IN A 3
V+ 4
AD824
13 V–
+IN B 5
12 +IN C
–IN B
11 –IN C
6
OUT B 7
NC 8
10 OUT C
9
NC
NC = NO CONNECT
Applications for the AD824 include portable medical equipment,
photo diode preamplifiers and high impedance transducer
amplifiers.
The ability of the output to swing rail-to-rail enables designers
to build multistage filters in single supply systems and maintain
high signal-to-noise ratios.
The AD824 is specified over the extended industrial (–40°C to
+85°C) temperature range and is available in 14-pin DIP and
narrow 14-pin and 16-pin SO packages.
REV. A
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
World Wide Web Site: http://www.analog.com
Fax: 617/326-8703
© Analog Devices, Inc., 1997
AD824–SPECIFICATIONS
ELECTRICAL SPECIFICATIONS (@ V = +5.0 V, V
S
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage AD824A
VOS
CM
= 0 V, VOUT = 0.2 V, TA = +258C unless otherwise noted)
Conditions
Min
Typ
Max
Units
0.1
1.0
1.5
300
900
12
4000
10
1013i3.3
mV
mV
µV
µV
pA
pA
pA
pA
V
dB
dB
dB
ΩipF
TMIN to TMAX
Offset Voltage
AD824B
VOS
TMIN to TMAX
Input Bias Current
IB
2
300
2
300
TMIN to TMAX
Input Offset Current
IOS
TMIN to TMAX
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
VCM = 0 V to 2 V
VCM = 0 V to 3 V
TMIN to TMAX
–0.2
66
60
60
Input Impedance
Large Signal Voltage Gain
AVO
VO = 0.2 V to 4.0 V
RL = 2 kΩ
RL = 10 kΩ
RL = 100 kΩ
TMIN to TMAX, RL = 100 kΩ
20
50
250
180
40
100
1000
400
2
V/mV
V/mV
V/mV
V/mV
µV/°C
ISOURCE = 20 µA
TMIN to TMAX
ISOURCE = 2.5 mA
TMIN to TMAX
ISINK = 20 µA
TMIN to TMAX
ISINK = 2.5 mA
TMIN to TMAX
Sink/Source
TMIN to TMAX
f = 1 MHz, AV = 1
4.975
4.97
4.80
4.75
4.988
4.985
4.85
4.82
15
20
120
140
± 12
± 10
100
V
V
V
V
mV
mV
mV
mV
mA
mA
Ω
VS = 2.7 V to 12 V
TMIN to TMAX
TMIN to TMAX
70
66
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
∆VOS/∆T
VOH
Output Voltage Low
VOL
Short Circuit Limit
ISC
Open-Loop Impedance
ZOUT
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
PSRR
ISY
DYNAMIC PERFORMANCE
Slew Rate
Full-Power Bandwidth
Settling Time
Gain Bandwidth Product
Phase Margin
Channel Separation
SR
BWP
tS
GBP
φo
CS
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
Total Harmonic Distortion
en p-p
en
in
THD
RL = 10 kΩ, AV = 1
1% Distortion, VO = 4 V p-p
VOUT = 0.2 V to 4.5 V, to 0.01%
3.0
80
74
25
30
150
200
80
500
600
dB
dB
µA
No Load
f = 1 kHz, RL = 2 kΩ
2
150
2.5
2
50
–123
V/µs
kHz
µs
MHz
Degrees
dB
0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz
f = 10 kHz, RL = 0, AV = +1
2
16
0.8
0.005
µV p-p
nV/√Hz
fA/√Hz
%
–2–
REV. A
AD824
ELECTRICAL SPECIFICATIONS (@ V = 615.0 V, V
S
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage AD824A
VOS
OUT =
0 V, TA = +258C unless otherwise noted)
Conditions
Min
TMIN to TMAX
Offset Voltage
AD824B
VOS
Input Bias Current
IB
Input Bias Current
Input Offset Current
IB
IOS
TMIN to TMAX
VCM = 0 V
TMIN to TMAX
VCM = –10 V
TMIN to TMAX
Typ
Max
Units
0.5
0.6
0.5
0.6
4
500
25
3
500
2.5
4.0
1.5
2.5
35
4000
1013i3.3
mV
mV
mV
mV
pA
pA
pA
pA
pA
V
dB
dB
ΩipF
20
Input Voltage Range
Common-Mode Rejection Ratio
CMRR
VCM = –15 V to 13 V
TMIN to TMAX
–15
70
66
Input Impedance
Large Signal Voltage Gain
AVO
Vo = –10 V to +10 V;
RL = 2 kΩ
RL = 10 kΩ
RL = 100 kΩ
TMIN to TMAX, RL = 100 kΩ
12
50
300
200
50
200
2000
1000
2
V/mV
V/mV
V/mV
V/mV
µV/°C
ISOURCE = 20 µA
TMIN to TMAX
ISOURCE = 2.5 mA
TMIN to TMAX
ISINK = 20 µA
TMIN to TMAX
ISINK = 2.5 mA
TMIN to TMAX
Sink/Source, TMIN to TMAX
f = 1 MHz, AV = 1
14.975
14.970
14.80
14.75
14.988
14.985
14.85
14.82
–14.985
–14.98
–14.88
–14.86
± 20
100
V
V
V
V
V
V
V
V
mA
Ω
VS = 2.7 V to 15 V
TMIN to TMAX
VO = 0 V
TMIN to TMAX
70
68
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
∆VOS/∆T
VOH
Output Voltage Low
VOL
Short Circuit Limit
Open-Loop Impedance
ISC
ZOUT
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
PSRR
ISY
DYNAMIC PERFORMANCE
Slew Rate
Full-Power Bandwidth
Settling Time
Gain Bandwidth Product
Phase Margin
Channel Separation
SR
BWP
tS
GBP
φo
CS
RL = 10 kΩ, AV = 1
1% Distortion, VO = 20 V p-p
VOUT = 0 V to 10 V, to 0.01%
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
Total Harmonic Distortion
en p-p
en
in
THD
0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz
f =10 kHz, VO = 3 V rms,
RL = 10 kΩ
REV. A
f = 1 kHz, RL =2 kΩ
–3–
±8
13
80
–14.975
–14.97
–14.85
–14.8
80
560
625
675
dB
dB
µA
µA
2
33
6
2
50
–123
V/µs
kHz
µs
MHz
Degrees
dB
2
16
1.1
µV p-p
nV/√Hz
fA/√Hz
0.005
%
AD824–SPECIFICATIONS
ELECTRICAL SPECIFICATIONS
(@ VS = +3.0 V, VCM = 0 V, VOUT = 0.2 V, TA = +258C unless otherwise noted)
Parameter
Symbol
INPUT CHARACTERISTICS
Offset Voltage AD824A -3 V
VOS
Conditions
Min
Typ
Max
Units
0.2
1.0
1.5
12
4000
10
1013i3.3
mV
mV
pA
pA
pA
pA
V
dB
dB
ΩipF
TMIN to TMAX
Input Bias Current
IB
2
250
2
250
TMIN to TMAX
Input Offset Current
IOS
TMIN to TMAX
Input Voltage Range
Common-Mode Rejection Ratio
Input Impedance
Large Signal Voltage Gain
Offset Voltage Drift
OUTPUT CHARACTERISTICS
Output Voltage High
CMRR
AVO
∆VOS/∆T
VOH
Output Voltage Low
VOL
Short Circuit Limit
Short Circuit Limit
Open-Loop Impedance
ISC
ISC
ZOUT
POWER SUPPLY
Power Supply Rejection Ratio
Supply Current/Amplifier
PSRR
ISY
VCM = 0 V to 1 V
TMIN to TMAX
0
58
56
VO = 0.2 V to 2.0 V
RL = 2 kΩ
RL = 10 kΩ
RL = 100 kΩ
TMIN to TMAX, RL = 100 kΩ
10
30
180
90
20
65
500
250
2
V/mV
V/mV
V/mV
V/mV
µV/°C
ISOURCE = 20 µA
TMIN to TMAX
ISOURCE = 2.5 mA
TMIN to TMAX
ISINK = 20 µA
TMIN to TMAX
ISINK = 2.5 mA
TMIN to TMAX
Sink/Source
Sink/Source, TMIN to TMAX
f = 1 MHz, AV = 1
2.975
2.97
2.8
2.75
2.988
2.985
2.85
2.82
15
20
120
140
±8
±6
100
V
V
V
V
mV
mV
mV
mV
mA
mA
Ω
VS = 2.7 V to 12 V,
TMIN to TMAX
VO = 0.2 V, TMIN to TMAX
70
66
DYNAMIC PERFORMANCE
Slew Rate
Full-Power Bandwidth
Settling Time
Gain Bandwidth Product
Phase Margin
Channel Separation
SR
BWP
tS
GBP
φo
CS
RL =10 kΩ, AV = 1
1% Distortion, VO = 2 V p-p
VOUT = 0.2 V to 2.5 V, to 0.01%
NOISE PERFORMANCE
Voltage Noise
Voltage Noise Density
Current Noise Density
Total Harmonic Distortion
en p-p
en
in
THD
0.1 Hz to 10 Hz
f = 1 kHz
f = 1 kHz, RL = 2 kΩ
f = 10 kHz, RL = 0, AV = +1
–4–
1
74
500
25
30
150
200
600
dB
dB
µA
2
300
2
2
50
–123
V/µs
kHz
µs
MHz
Degrees
dB
2
16
0.8
0.01
µV p-p
nV/√Hz
fA/√Hz
%
REV. A
AD824
WAFER TEST LIMITS (@ V = +5.0 V, V
S
CM
= 0 V, TA = +258C unless otherwise noted)
Parameter
Symbol
Offset Voltage
Input Bias Current
Input Offset Current
Input Voltage Range
Common-Mode Rejection Ratio
Power Supply Rejection Ratio
Large Signal Voltage Gain
Output Voltage High
Output Voltage Low
Supply Current/Amplifier
VOS
IB
IOS
VCM
CMRR
PSRR
AVO
VOH
VOL
ISY
Conditions
Limit
Units
VCM = 0 V to 2 V
V = + 2.7 V to +12 V
RL = 2 kΩ
ISOURCE = 20 µA
ISINK = 20 µA
VO = 0 V, RL = ∞
1.0
12
20
–0.2 to 3.0
66
70
15
4.975
25
600
mV max
pA max
pA
V min
dB min
µV/V
V/mV min
V min
mV max
µA max
NOTE
Electrical tests and wafer probe to the limits shown. Due to variations in assembly
methods and normal yield loss, yield after packaging is not guaranteed for
standard product dice. Consult factory to negotiate specifications based on dice
lot qualifications through sample lot assembly and testing.
DICE CHARACTERISTICS
ABSOLUTE MAXIMUM RATINGS 1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . –VS – 0.2 V to +VS
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ± 30 V
Output Short Circuit Duration to GND . . . . . . . . . Indefinite
Storage Temperature Range
N, R Package . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Operating Temperature Range
AD824A, B . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C
Junction Temperature Range
N, R Package . . . . . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature Range (Soldering, 60 sec) . . . . . . . +300°C
Package Type
θJA2
θJC
Units
14-Pin Plastic DIP (N)
14-Pin SOIC (R)
16-Pin SOIC (R)
76
120
92
33
36
27
°C/W
°C/W
°C/W
AD824 Die Size 0.70 X 0.130 inch, 9,100 sq. mils.
Substrate (Die Backside) Is Connected to V+. Transistor
Count, 143.
VCC
I5
R1
NOTES
1
Absolute maximum ratings apply to both DICE and packaged parts unless
otherwise noted.
2
θJA is specified for the worst case conditions, i.e., θJA is specified for device in socket
for P-DIP packages; θJA is specified for device soldered in circuit board for SOIC
package.
I6
Q18
R2
Q21 Q27
Q6
Q4
+IN
C3
Q5
J2
J1
ORDERING GUIDE
R7
R13
Model
Package Option
AD824AN
AD824BN
AD824AR
AD824AR-3V
AD824AN-3V
AD824AR-14
AD824AR-14-3V
AD824AR-16
AD824AChips
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
+25°C
14-Pin Plastic DIP
14-Pin Plastic DIP
14-Pin SOIC
14-Pin SOIC
14-Pin Plastic DIP
14-Pin SOIC
14-Pin SOIC
16-Pin SOIC
DICE
C4
Q23
Q22
C2
R15
–IN
Q20
Q19
Q7
Temperature
Range
Q29
R9
VOUT
Q24 Q25
Q8
C1
Q2
Q3
Q31
R12
I1
R14
Q28
I2
I3
I4
Q26
R17
VEE
Figure 1. Simplified Schematic of 1/4 AD824
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
WARNING!
accumulate on the human body and test equipment and can discharge without detection.
Although the AD824 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
ESD SENSITIVE DEVICE
precautions are recommended to avoid performance degradation or loss of functionality.
REV. A
–5–
AD824–Typical Characteristics
VS = ±15V
80
VS = +5V
80
NO LOAD
NO LOAD
60
45
90
20
135
180
0
100
1k
10k
100k
1M
40
45
90
20
135
180
0
10M
100
1k
10k
100k
10M
100
90
100
90
10
10
0%
0%
50mV
50mV
1µs
VS = ±15V
80
1µs
Figure 4. Open-Loop Gain/Phase and Small Signal
Response, VS = +5 V, No Load
Figure 2. Open-Loop Gain/Phase and Small Signal
Response, VS = ± 15 V, No Load
VS = +5V
60
CL = 220pF
CL = 100pF
GAIN – dB
45
90
20
135
180
0
100
1k
10k
100k
1M
PHASE – Degrees
40
45
90
20
135
180
0
PHASE – Degrees
40
60
GAIN – dB
1M
PHASE – Degrees
GAIN – dB
40
PHASE – Degrees
GAIN – dB
60
–20
1k
10M
10k
100k
1M
10M
100
100
90
90
10
10
0%
0%
50mV
50mV
1µs
1µs
Figure 5. Open-Loop Gain/Phase and Small Signal
Response, VS = +5 V, CL = 220 pF
Figure 3. Open-Loop Gain/Phase and Small Signal
Response, VS = ± 15 V, CL = 100 pF
–6–
REV. A
AD824
t
VS = +3V
60
NO LOAD
9.950 µs
100
90
45
90
20
135
180
0
PHASE – Degrees
GAIN – dB
40
10
0%
5V
2µs
–20
t
1k
10k
100k
1M
10M
10.810 µs
100
90
100
90
10
0%
5V
2µs
Figure 8. Slew Rate, RL = 10k
10
0%
50mV
1µs
Figure 6. Open-Loop Gain/Phase and Small Signal
Response, VS = +3 V, No Load
100
90
VOUT
60
VS = +3V
10
CL = 220pF
0%
100µs
5V
45
90
20
135
180
0
PHASE – Degrees
GAIN – dB
40
Figure 9. Phase Reversal with Inputs Exceeding Supply by
1 Volt
0.8
–20
0.7
10k
100k
1M
10M
OUTPUT TO RAIL – Volts
1k
100
90
0.6
0.5
SOURCE
0.4
0.3
0.2
SINK
0.1
0
1µ
10
0%
50mV
1µs
10µ
50µ 100µ 500µ
LOAD CURRENT – A
1m
5m
10m
Figure 10. Output Voltage to Supply Rail vs. Sink and
Source Load Currents
Figure 7. Open-Loop Gain/Phase and Small Signal
Response, VS = +3 V, CL = 220 pF
REV. A
5µ
–7–
AD824–Typical Characteristics
14
COUNT = 60
12
NOISE DENSITY – nV/√Hz
+3V ≤ VS ≤ ±15V
10
NUMBER OF UNITS
60
40
20
8
6
4
2
5
10
15
FREQUENCY – kHz
20
0
–2.5
–2.0
–1.5
–1.0 –0.5
0
0.5
1.0
OFFSET VOLTAGE DRIFT
1.5
2.0
2.5
Figure 14. TC VOS Distribution, –55°C to +125°C, VS = 5, 0
Figure 11. Voltage Noise Density
150
VS = 5, 0
0.1
125
INPUT OFFSET CURRENT – pA
RL = 0
AV = +1
VS = +3
THD+N – %
0.010
VS = +5
0.001
VS = ±15
0.0001
20
100
1k
FREQUENCY – Hz
10k
20k
100
75
50
25
0
–25
–60
–40
–20
0
20
40
60
80
100
120
140
TEMPERATURE – °C
Figure 12. Total Harmonic Distortion
Figure 15. Input Offset Current vs. Temperature
100k
280
VS = 5, 0
COUNT = 860
240
INPUT BIAS CURRENT – pA
10k
NUMBER OF UNITS
200
160
120
80
100
10
1
40
0
–0.5
1k
–0.4
–0.3
–0.2 –0.1
0
0.1
0.2
OFFSET VOLTAGE – mV
0.3
0.4
20
0.5
40
60
80
100
120
140
TEMPERATURE – °C
Figure 16. Input Bias Current vs. Temperature
Figure 13. Input Offset Distribution, VS = 5, 0
–8–
REV. A
AD824
120
.. .
100
INPUT VOLTAGE NOISE – nV/√Hz
COMMON-MODE REJECTION – dB
1k
80
60
40
20
0
10
100
1k
10k
100k
FREQUENCY – Hz
1M
100
10M
1
POWER SUPPLY REJECTION – dB
THD – dB
–60
–80
–100
–120
100
1k
10k
FREQUENCY – Hz
100
1k
FREQUENCY – Hz
10k
100k
60
25
40
+3, 0V
20
20
0
0
1k
10k
100k
FREQUENCY – Hz
1M
20
80
60
100
40
30
±15V
40
60
100
OUTPUT VOLTAGE – Volts
80
80
100
1k
10k
100k
FREQUENCY – Hz
1M
10M
Figure 21. Power Supply Rejection vs. Frequency
PHASE MARGIN – Degrees
100
100
0
10
100k
Figure 18. THD vs. Frequency, 3 V rms
OPEN-LOOP GAIN – dB
10
120
–40
20
15
10
5
0
1k
–20
10M
3k
10k
30k
100k
INPUT FREQUENCY – Hz
300k
1M
Figure 22. Large Signal Frequency Response
Figure 19. Open-Loop Gain and Phase vs. Frequency
REV. A
1
Figure 20. Input Voltage Noise Spectral Density vs.
Frequency
Figure 17. Common-Mode Rejection vs. Frequency
–20
10
10
–9–
AD824
–80
5V
5µs
–90
100
CROSSTALK – dB
90
–100
–110
1 TO 4
–120
10
1 TO 3
1 TO 2
0%
–130
–140
10
1k
FREQUENCY – Hz
100
10k
100k
Figure 23. Crosstalk vs. Frequency
Figure 26. Large Signal Response
10k
2750
2500
VS = ±15V
SUPPLY CURRENT – µA
OUTPUT IMPEDANCE – Ω
1k
100
10
1
2250
2000
VS = 3, 0
1750
1500
.1
1250
.01
10
100
1k
10k
100k
FREQUENCY – Hz
1M
1000
–60
10M
Figure 24. Output Impedance vs. Frequency, Gain = +1
–40
–20
0
20
40
60
80
TEMPERATURE – °C
100
120
140
Figure 27. Supply Current vs. Temperature
1000
VS = ±15V
500ns
OUTPUT SATURATION VOLTAGE – mV
20mV
100
90
10
0%
VS = 3, 0
100
VOL – VS
10
0
0.01
Figure 25. Small Signal Response, Unity Gain Follower,
10ki100 pF Load
VS – VOH
0.10
1.0
LOAD CURRENT – mA
10.0
Figure 28. Output Saturation Voltage
–10–
REV. A
AD824
APPLICATION NOTES
INPUT CHARACTERISTICS
In the AD824, n-channel JFETs are used to provide a low
offset, low noise, high impedance input stage. Minimum input
common-mode voltage extends from 0.2 V below –VS to 1 V less
than +VS. Driving the input voltage closer to the positive rail will
cause a loss of amplifier bandwidth.
The AD824 does not exhibit phase reversal for input voltages up
to and including +VS. Figure 29a shows the response of an
AD824 voltage follower to a 0 V to +5 V (+VS) square wave input. The input and output are superimposed. The output tracks
the input up to +VS without phase reversal. The reduced bandwidth above a 4 V input causes the rounding of the output wave
form. For input voltages greater than +VS, a resistor in series
with the AD824’s noninverting input will prevent phase reversal
at the expense of greater input voltage noise. This is illustrated
in Figure 29b.
1V
2µs
100
90
OUTPUT CHARACTERISTICS
The AD824’s unique bipolar rail-to-rail output stage swings
within 15 mV of the positive and negative supply voltages. The
AD824’s approximate output saturation resistance is 100 Ω for
both sourcing and sinking. This can be used to estimate output
saturation voltage when driving heavier current loads. For
instance, the saturation voltage will be 0.5 volts from either
supply with a 5 mA current load.
0%
If the AD824’s output is overdriven so as to saturate either of
the output devices, the amplifier will recover within 2 µs of its
input returning to the amplifier’s linear operating region.
1V
(a)
1V
+VS
Input voltages less than –VS are a completely different story.
The amplifier can safely withstand input voltages 20 volts below
the minus supply voltage as long as the total voltage from the
positive supply to the input terminal is less than 36 volts. In addition, the input stage typically maintains picoamp level input
currents across that input voltage range.
For load resistances over 20 kΩ, the AD824’s input error
voltage is virtually unchanged until the output voltage is driven
to 180 mV of either supply.
10
GND
A current-limiting resistor should be used in series with the input of the AD824 if there is a possibility of the input voltage exceeding the positive supply by more than 300 mV or if an input
voltage will be applied to the AD824 when ± VS = 0. The amplifier will be damaged if left in that condition for more than 10
seconds. A 1 kΩ resistor allows the amplifier to withstand up to
10 volts of continuous overvoltage and increases the input voltage noise by a negligible amount.
Direct capacitive loads will interact with the amplifier’s effective
output impedance to form an additional pole in the amplifier’s
feedback loop, which can cause excessive peaking on the pulse
response or loss of stability. Worst case is when the amplifier is
used as a unity gain follower. Figures 5 and 7 show the AD824’s
pulse response as a unity gain follower driving 220 pF. Configurations with less loop gain, and as a result less loop bandwidth,
will be much less sensitive to capacitance load effects. Noise
gain is the inverse of the feedback attenuation factor provided
by the feedback network in use.
10µs
1V
100
90
10
GND
0%
1V
Figure 30 shows a method for extending capacitance load drive
capability for a unity gain follower. With these component values, the circuit will drive 5,000 pF with a 10% overshoot.
(b)
+5V
RP
+V S
VIN
VOUT
0.01µF
8
VIN
100Ω
1/4
AD824
VOUT
0.01µF
4
Figure 29. (a) Response with RP = 0; VIN from 0 to +VS
(b) VIN = 0 to + VS + 200 m V
VOUT = 0 to + VS
RP = 49.9 kΩ
20pF
20kΩ
Since the input stage uses n-channel JFETs, input current during normal operation is positive; the current flows out from the
input terminals. If the input voltage is driven more positive than
+VS – 0.4 V, the input current will reverse direction as internal
device junctions become forward biased. This is illustrated in
Figure 9.
REV. A
CL
–VS
Figure 30. Extending Unity Gain Follower Capacitive Load
Capability Beyond 350 pF
–11–
AD824
APPLICATIONS
Single Supply Voltage-to-Frequency Converter
Table I. AD824 In Amp Performance
The circuit shown in Figure 31 uses the AD824 to drive a low
power timer, which produces a stable pulse of width t1. The
positive going output pulse is integrated by R1-C1 and used as
one input to the AD824, which is connected as a differential
integrator. The other input (nonloading) is the unknown voltage, VIN. The AD824 output drives the timer trigger input, closing the overall feedback loop.
+10V
U4
REF02
2
V
6 REF = 5V
C5
0.1µF
3
5
CMOS
74HCO4
RSCALE **
10k
4
R1
U1
3
C1
U3A
2
CMRR
Common-Mode
Voltage Range
3 dB BW, G = 10
G = 100
tSETTLING
2 V Step (VS = 0 V, 3 V)
5 V (VS = ± 5 V)
Noise @ f = 1 kHz, G = 10
G = 100
74 dB
80 dB
–0.2 V to +2 V –5.2 V to +4 V
180 kHz
180 kHz
18 kHz
18 kHz
2 µs
5 µs
270 nV/√Hz
2.2 µV/√Hz
270 nV/√Hz
2.2 µV/√Hz
5µs
1
OUT1
100
U2
CMOS 555
R3*
116k
1/4
AD824B
4
6
2
7
VI N
C6
390pF
5%
(NPO)
499k, 1%
0V TO 2.5V
FULL SCALE
C2
0.01µF, 2%
VS = 65 V
C3
0.1µF
0.01µF, 2%
R2
499k, 1%
VS = 3 V, 0 V
OUT2
U3B
4
Parameters
R
THR
90
8
V+
OUT
TR
DIS
GND
CV
3
5
10
0%
1V
1
C4
0.01µF
Figure 32a. Pulse Response of In Amp to a 500 mV p-p
Input Signal; VS = +5 V, 0 V; Gain = 10
NOTES:
fOUT = VIN /(VREF*t1), t1 = 1.1*R3*C6
= 25kHz fS AS SHOWN.
* = 1% METAL FILM, <50ppm/°C TC
** = 10%, 20T FILM, <100ppm/°C TC
VREF
t1 = 33µs FOR f OUT = 20kHz @ VIN = 2.0V
Figure 31. Single Supply Voltage-to-Frequency Converter
The AD824 can be configured as a single supply instrumentation amplifier that is able to operate from single supplies down
to 3 V or dual supplies up to ± 15 V. AD824 FET inputs’ 2 pA
bias currents minimize offset errors caused by high unbalanced
source impedances.
R2
R3
R4
R5
R6
90k
9k
1k
1k
9k
90k
G =10
Typical AD824 bias currents of 2 pA allow megaohm-range
source impedances with negligible dc errors. Linearity errors on
the order of 0.01% full scale can be achieved with this circuit.
This performance is obtained with a 5 volt single supply, which
delivers less than 3 mA to the entire circuit.
Single Supply Programmable Gain Instrumentation Amplifier
R1
G =100
G =100
OHMTEK
PART # 1043
G =10
+VS
0.1µF
6
2
VIN1
1/4 8
3 AD824
RP
1kΩ
1
1/4
7
5 AD824
11
RP
VOUT
VIN2
1kΩ
(G =10)
VOUT = (VIN1 – VIN2 ) (1+
(G =100)
R6
) +VREF
R4 + R5
VOUT = (VIN1 – VIN2 ) (1+
R5 + R6
) +VREF
R4
FOR R1 = R6, R2 = R5 AND R3 = R4
An array of precision thin-film resistors sets the in amp gain to
be either 10 or 100. These resistors are laser-trimmed to ratio
match to 0.01% and have a maximum differential TC of
5 ppm/°C.
Figure 32b. A Single Supply Programmable
Instrumentation Amplifier
–12–
REV. A
AD824
of +4.5 V can be used to drive an A/D converter front end. The
other half of the AD824 is configured as a unity-gain inverter
and generates the other bridge input of –4.5 V. Resistors R1 and
R2 provide a constant current for bridge excitation. The AD620
low power instrumentation amplifier is used to condition the
differential output voltage of the bridge. The gain of the AD620
is programmed using an external resistor RG and determined by:
3 Volt, Single Supply Stereo Headphone Driver
The AD824 exhibits good current drive and THD+N performance, even at 3 V single supplies. At 1 kHz, total harmonic
distortion plus noise (THD+N) equals –62 dB (0.079%) for a
300 mV p-p output signal. This is comparable to other single
supply op amps that consume more power and cannot run on 3
V power supplies.
In Figure 33, each channel’s input signal is coupled via a 1 µF
Mylar capacitor. Resistor dividers set the dc voltage at the
noninverting inputs so that the output voltage is midway between the power supplies (+1.5 V). The gain is 1.5. Each half of
the AD824 can then be used to drive a headphone channel. A
5 Hz high-pass filter is realized by the 500 µF capacitors and the
headphones, which can be modeled as 32 ohm load resistors to
ground. This ensures that all signals in the audio frequency
range (20 Hz–20 kHz) are delivered to the headphones.
+3V
0.1µF
95.3k
1µF
0.1µF
CHANNEL 1
MYLAR
1/4
AD824
47.5k
500µF
95.3k
L
4.99k
10k
HEADPHONES
32Ω IMPEDANCE
G=
A 3.3 Volt/5 Volt Precision Sample-and-Hold Amplifier
In battery-powered applications, low supply voltage operational
amplifiers are required for low power consumption. Also, low
supply voltage applications limit the signal range in precision
analog circuitry. Circuits like the sample-and-hold circuit
shown in Figure 35, illustrate techniques for designing precision
analog circuitry in low supply voltage applications. To maintain
high signal-to-noise ratios (SNRs) in a low supply voltage application requires the use of rail-to-rail, input/output operational
amplifiers. This design highlights the ability of the AD824 to operate rail-to-rail from a single +3 V/+5 V supply, with the advantages
of high input impedance. The AD824, a quad JFET-input op
amp, is well suited to S/H circuits due to its low input bias currents (3 pA, typical) and high input impedances (3 × 1013 Ω,
typical). The AD824 also exhibits very low supply currents so
the total supply current in this circuit is less than 2.5 mA.
10k
3.3/5V
3.3/5V
R
R1
50k
4.99k
1/4
AD824
47.5k
1µF
500µF
CHANNEL 2
49.4 kΩ
+1
RG
R2
50k
AD824A
3
2
0.1µF
4
1
A1
FALSE GROUND (FG)
11
R4
2kΩ
MYLAR
3.3/5V
13
Figure 33. 3 Volt Single Supply Stereo Headphone Driver
14 ADG513
15
Low Dropout Bipolar Bridge Driver
R5
2kΩ
The AD824 can be used for driving a 350 ohm Wheatstone
bridge. Figure 34 shows one half of the AD824 being used to
buffer the AD589—a 1.235 V low power reference. The output
16
10
11
9
AD824B
6
A2
2
7
3
1
+VS
10
49.9k
AD589
10k
1%
9
R1
20Ω
+1.235V
12
26.4k, 1%
+VS
3
350Ω
–VS
C
500pF
14
FG
+VS
+5V
0.1µF
GND
1µF
0.1µF
–VS
1µF
–5V
In many single supply applications, the use of a false ground
generator is required. In this circuit, R1 and R2 divide the supply voltage symmetrically, creating the false ground voltage at
one-half the supply. Amplifier A1 then buffers this voltage creating a low impedance output drive. The S/H circuit is configured in an inverting topology centered around this false ground
level.
Figure 34. Low Dropout Bipolar Bridge Driver
REV. A
VOUT
Figure 35. 3.3 V/5.5 V Precision Sample and Hold
4
–VS
R2
20Ω
5
–
6
VREF
–4.5V
A4
4
+
5
1%
1/4
AD824
13
FG
8
7
AD620
RG
2
1%
SAMPLE/
HOLD
350Ω
10k
10k
AD824D
A3
AD824C
8
TO A/D CONVERTER
REFERENCE INPUT
350Ω
6
7
1/4
AD824
350Ω
CH
500pF
FG
5
–13–
AD824
A design consideration in sample-and-hold circuits is voltage
droop at the output caused by op amp bias and switch leakage
currents. By choosing a JFET op amp and a low leakage CMOS
switch, this design minimizes droop rate error to better than
0.1 µV/µs in this circuit. Higher values of CH will yield a lower
droop rate. For best performance, CH and C2 should be polystyrene, polypropylene or Teflon capacitors. These types of
capacitors exhibit low leakage and low dielectric absorption. Additionally, 1% metal film resistors were used throughout the design.
In the sample mode, SW1 and SW4 are closed, and the output
is VOUT = –VIN. The purpose of SW4, which operates in parallel with SW1, is to reduce the pedestal, or hold step, error by
injecting the same amount of charge into the noninverting input
of A3 that SW1 injects into the inverting input of A3. This creates a common-mode voltage across the inputs of A3 and is then
rejected by the CMR of A3; otherwise, the charge injection from
SW1 would create a differential voltage step error that would
appear at VOUT. The pedestal error for this circuit is less than 2
mV over the entire 0 V to 3.3 V/5 V signal range. Another
method of reducing pedestal error is to reduce the pulse amplitude applied to the control pins. In order to control the
ADG513, only 2.4 V are required for the “ON” state and 0.8 V
for the “OFF” state. If possible, use an input control signal
whose amplitude ranges from 0.8 V to 2.4 V instead of a full
range 0 V to 3.3 V/5 V for minimum pedestal error.
Other circuit features include an acquisition time of less than
3 µs to 1%; reducing CH and C2 will speed up the acquisition
time further, but an increased pedestal error will result. Settling
time is less than 300 ns to 1%, and the sample-mode signal BW
is 80 kHz.
The ADG513 was chosen for its ability to work with 3 V/5 V
supplies and for having normally-open and normally-closed precision CMOS switches on a dielectrically isolated process. SW2
is not required in this circuit; however, it was used in parallel
with SW3 to provide a lower RON analog switch.
–14–
REV. A
AD824
* AD824 SPICE Macro-model
9/94, Rev. A *
ARG/ADI
*
* Copyright 1994 by Analog Devices, Inc.
*
* Refer to “README.DOC” file for License Statement.
Use of this model indicates your acceptance with
the terms and provisions in the License Statement. *
* Node assignments
*
noninverting input
*
| inverting input
*
| | positive supply
*
| | | negative supply
*
| | | | output
*
| | | | |
.SUBCKT AD824
1 2 99 50 25
*
* INPUT STAGE & POLE AT 3.1 MHz
*
R3
5
99
1.193E3
R4
6
99
1.193E3
CIN
1
2
4E-12
C2
5
6
19.229E-12
I1
4
50
108E-6
IOS
1
2
1E-12
EOS
7
1
POLY(1) (12,98) 100E-6 1
J1
4
2
5
JX
J2
4
7
6
JX
*
* GAIN STAGE & DOMINANT POLE
*
EREF
98
0
(30,0) 1
R5
9
98
2.205E6
C3
9
25
54E-12
G1
98
9
(6,5) 0.838E-3
V1
8
98
-1
V2
98
10
-1
D1
9
10
DX
D2
8
9
DX
*
* COMMON-MODE GAIN NETWORK WITH ZERO AT 1 kHz *
R21
11
12
1E6
R22
12
98
100
C14
11
12
159E-12
E13
11
98
POLY(2) (2,98) (1,98) 0 0.5 0.5
*
* POLE AT 10 MHz
*
R23
18
98
1E6
C15
18
98
15.9E-15
G15
98
18
(9,98) 1E-6
*
* OUTPUT STAGE
*
ES
26
98
(18,98) 1
RS
26
22
500
IB1
98
21
2.404E-3
IB2
23
98
2.404E-3
D10
21
98
DY
D11
98
23
DY
C16
20
25
2E-12
C17
24
25
2E-12
DQ1
97
20
DQ
Q2
20
21
22 NPN
Q3
24
23
22 PNP
DQ2
24
51
DQ
Q5
25
20
97 PNP 20
Q6
25
24
51 NPN 20
VP
96
97
0
VN
51
52
0
EP
96
0
(99,0) 1
EN
52
0
(50,0) 1
R25
30
99
5E6
R26
30
50
5E6
REV. A
FSY1
99
0
VP 1
FSY2
0
50
VN 1
DC1
25
99
DX
DC2
50
25
DX
*
* MODELS USED
*
.MODEL JX NJF(BETA=3.2526E-3 VTO=-2.000 IS=2E-12) .MODEL
NPN NPN(BF=120 VAF=150 VAR=15 RB=2E3
+ RE=4 RC=550 IS=1E-16)
.MODEL PNP PNP(BF=120 VAF=150 VAR=15 RB=2E3 + RE=4
RC=750 IS=1E-16)
.MODEL DX D(IS=1E-15)
.MODEL DY D()
.MODEL DQ D(IS=1E-16)
.ENDS AD824
–15–
AD824
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
14
C1988a–2–1/97
14-Pin Plastic (N) Package
(N-14)
8
0.280 (7.11)
0.240 (6.10)
PIN 1
1
7
0.325 (8.25)
0.300 (7.62)
0.795 (20.19)
0.725 (18.42)
0.060 (1.52)
0.015 (0.38)
0.210
(5.33)
MAX
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
0.022 (0.558)
0.014 (0.356)
0.100
(2.54)
BSC
0.195 (4.95)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
SEATING
PLANE
0.070 (1.77)
0.045 (1.15)
14-Pin SOIC (R) Package
(R-14)
14
8
0.1574 (4.00)
0.1497 (3.80)
PIN 1
0.2440 (6.20)
0.2284 (5.80)
7
1
0.3444 (8.75)
0.3367 (8.55)
0.0196 (0.50)
x 45 °
0.0099 (0.25)
0.0688 (1.75)
0.0532 (1.35)
0.0098 (0.25)
0.0040 (0.10)
0.0500
(1.27)
BSC
0.0192 (0.49)
0.0138 (0.35)
0.0098 (0.25)
0.0075 (0.19)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
16-Pin SOIC Package
(R-16)
0.4133 (10.50)
8
PIN 1
0.0118 (0.30)
0.1043 (2.65)
0.0291 (0.74)
0.0926 (2.35)
0.0098 (0.25) x 45°
PRINTED IN U.S.A.
1
0.3937 (10.00)
9
0.2914 (7.40)
0.4193 (10.65)
16
0.2992 (7.60)
0.3977 (10.00)
0.0040 (0.10)
0.0500
(1.27)
BSC
0.0192 (0.49)
SEATING 0.0125 (0.32)
0.0138 (0.35)
PLANE
0.0091 (0.23)
–16–
8°
0°
0.0500 (1.27)
0.0157 (0.40)
REV. A