a
FEATURES
High Speed
41 MHz, –3 dB Bandwidth
125 V/ms Slew Rate
80 ns Settling Time
Input Bias Current of 20 pA and Noise Current of
10 fA/√Hz
Input Voltage Noise of 12 nV/√Hz
Fully Specified Power Supplies: 65 V to 615 V
Low Distortion: –76 dB at 1 MHz
High Output Drive Capability
Drives Unlimited Capacitance Load
50 mA Min Output Current
No Phase Reversal When Input Is at Rail
Available in 8-Lead SOIC
Low Cost, General Purpose
High Speed JFET Amplifier
AD825
CONNECTION DIAGRAM
8-Lead Plastic SOIC (R) Package
8 NC
NC 1
AD825
7 +VS
TOP VIEW
+IN 3 (Not to Scale) 6 OUTPUT
–IN 2
–VS 4
5 NC
NC = NO CONNECT
APPLICATIONS
CCD
Low Distortion Filters
Mixed Gain Stages
Audio Amplifier
Photo Detector Interface
ADC Input Buffer
DAC Output Buffer
PRODUCT DESCRIPTION
The AD825 is a superbly optimized operational amplifier for
high speed, low cost and dc parameters, making it ideally suited
for a broad range of signal conditioning and data acquisition
applications. The ac performance, gain, bandwidth, slew rate
and drive capability are all very stable over temperature. The
AD825 also maintains stable gain under varying load conditions.
The unique input stage has ultralow input bias current and
ultralow input current noise. Signals that go to either rail on this
high performance input do not cause phase reversals at the output.
These features make the AD825 a good choice as a buffer for
MUX outputs, creating minimal offset and gain errors.
The AD825 is fully specified for operation with dual ± 5 V and
± 15 V supplies. This power supply flexibility, and the low supply current of 6.5 mA with excellent ac characteristics under all
supply conditions, makes the AD825 well suited for many
demanding applications.
Figure 1. Performance with Rail-to-Rail Input Signals
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: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1998
AD825–SPECIFICATIONS (@ T = +258C, V = 615 V unless otherwise noted)
A
S
Parameter
Conditions
DYNAMIC PERFORMANCE
Unity Gain Bandwidth
Bandwidth for 0.1 dB Flatness
–3 dB Bandwidth
Slew Rate
Settling Time to 0.1%
Settling Time to 0.01%
Total Harmonic Distortion
Differential Gain Error
(RLOAD = 150 Ω)
Differential Phase Error
(RLOAD = 150 Ω)
Gain = +1
Gain = +1
RLOAD = 1 kΩ, G = 1
0 V–10 V Step, AV = –1
0 V–10 V Step, AV = –1
FC = 1 MHz, G = –1
NTSC
Gain = +2
NTSC
Gain = +2
INPUT OFFSET VOLTAGE
VS
Min
± 15 V
± 15 V
± 15 V
± 15 V
± 15 V
± 15 V
± 15 V
± 15 V
23
18
44
125
AD825A
Typ
Max
26
21
46
140
150
180
–77
1.3
± 15 V
2.1
± 15 V
1
180
220
± 15 V
15
40
pA
pA
pA
700
± 15 V
INPUT OFFSET CURRENT
20
30
5
TMIN
TMAX
440
VOUT = ±10 V
RLOAD = 1 kΩ
VOUT = ± 7.5 V
RLOAD = 1 kΩ
VOUT = ± 7.5 V
RLOAD = 150 Ω
(50 mA Output)
± 15 V
COMMON-MODE REJECTION
VCM = ± 10 V
± 15 V
INPUT VOLTAGE NOISE
f = 10 kHz
INPUT CURRENT NOISE
f = 10 kHz
pA
pA
pA
70
76
dB
70
76
dB
72
74
dB
71
80
dB
± 15 V
12
nV/√Hz
± 15 V
10
fA/√Hz
± 15 V
± 13.5
V
± 13.3
± 13.2
V
V
mA
mA
± 15 V
± 15 V
INPUT COMMON-MODE
VOLTAGE RANGE
OUTPUT VOLTAGE SWING
mV
mV
µV/°C
5
TMIN
TMAX
OPEN LOOP GAIN
2
5
10
INPUT BIAS CURRENT
MHz
MHz
MHz
V/µs
ns
ns
dB
%
Degrees
TMIN to TMAX
Offset Drift
Units
± 15 V
± 15 V
± 15 V
± 15 V
RLOAD = 1 kΩ
RLOAD = 500 Ω
Output Current
Short-Circuit Current
13
12.9
50
100
11
INPUT RESISTANCE
5 × 10
INPUT CAPACITANCE
6
pF
8
Ω
OUTPUT RESISTANCE
Open Loop
POWER SUPPLY
Quiescent Current
± 15 V
± 15 V
TMIN to TMAX
6.5
Ω
7.2
7.5
mA
mA
NOTES
All limits are determined to be at least four standard deviations away from mean value. .
Specifications subject to change without notice.
–2–
REV. A
AD825
SPECIFICATIONS (@ T = +258C, V = 65 V unless otherwise noted)
A
S
Parameter
Conditions
DYNAMIC PERFORMANCE
Unity Gain Bandwidth
Bandwidth for 0.1 dB Flatness
–3 dB Bandwidth
Slew Rate
Settling Time to 0.1%
Settling Time to 0.01%
Total Harmonic Distortion
Differential Gain Error
(RLOAD = 150 Ω)
Differential Phase Error
(RLOAD = 150 Ω)
Gain = +1
Gain = +1
RLOAD = 1 kΩ, G = –1
–2.5 V to +2.5 V
–2.5 V to +2.5 V
FC = 1 MHz, G = –1
NTSC
Gain = +2
NTSC
Gain = +2
INPUT OFFSET VOLTAGE
VS
Min
±5 V
±5 V
±5 V
±5 V
±5 V
±5 V
±5 V
±5 V
18
8
34
115
AD825A
Typ
Max
21
10
37
130
75
90
–76
1.2
±5 V
1.4
±5 V
1
90
110
±5 V
TMIN
TMAX
±5 V
30
pA
pA
pA
15
25
5
TMIN
TMAX
280
±5 V
COMMON-MODE REJECTION
VCM = ± 2 V
±5 V
INPUT VOLTAGE NOISE
f = 10 kHz
INPUT CURRENT NOISE
f = 10 kHz
INPUT COMMON-MODE
VOLTAGE RANGE
OUTPUT VOLTAGE SWING
10
600
VOUT = ± 2.5 V
RLOAD = 500 Ω
RLOAD = 150 Ω
OPEN LOOP GAIN
mV
mV
µV/°C
5
INPUT OFFSET CURRENT
Offset Current Drift
2
5
10
INPUT BIAS CURRENT
RLOAD = 500 Ω
RLOAD = 150 Ω
pA
pA
pA
64
64
66
66
dB
dB
69
80
dB
±5 V
12
nV/√Hz
±5 V
10
fA/√Hz
±5 V
± 3.5
V
± 3.4
± 3.2
V
V
mA
mA
±5 V
±5 V
±5 V
Output Current
Short-Circuit Current
MHz
MHz
MHz
V/µs
ns
ns
dB
%
Degrees
TMIN to TMAX
Offset Drift
Units
3.2
3.1
50
80
11
INPUT RESISTANCE
5 × 10
INPUT CAPACITANCE
6
pF
8
Ω
OUTPUT RESISTANCE
Open Loop
POWER SUPPLY
Quiescent Current
±5 V
±5 V
TMIN to TMAX
POWER SUPPLY REJECTION
VS = ± 5 V to ± 15 V
NOTES
All limits are determined to be at least four standard deviations away from mean value.
Specifications subject to change without notice.
REV. A
–3–
6.2
76
88
Ω
6.8
7.5
mA
mA
dB
AD825
ABSOLUTE MAXIMUM RATINGS 1
PIN CONFIGURATION
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 18 V
Internal Power Dissipation2
Small Outline (R) . . . . . . . . . . . . . . . . . See Derating Curves
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ± VS
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . ± VS
Output Short Circuit Duration . . . . . . . . See Derating Curves
Storage Temperature Range R . . . . . . . . . . . –65°C to +125°C
Operating Temperature Range . . . . . . . . . . . –40°C to +85°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . +300°C
8 NC
NC 1
AD825
7 +VS
TOP VIEW
+IN 3 (Not to Scale) 6 OUTPUT
–IN 2
5 NC
–VS 4
NC = NO CONNECT
NOTES
1Stresses 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.
2Specification is for device in free air: 8-lead SOIC package: θ = 160°C/watt.
JA
MAXIMUM POWER DISSIPATION – Watts
2.0
TJ = +1508C
1.5
1.0
8-LEAD SOIC PACKAGE
0.5
0
–50 –40 –30 –20 –10 0 10 20 30 40 50 60 70
AMBIENT TEMPERATURE – °C
80 90
Figure 2. Maximum Power Dissipation vs. Temperature
ORDERING GUIDE
Model
Temperature
Range
Package
Description
Package
Option
AD825AR
AD825AR-REEL
AD825AR-REEL7
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
8-Lead Plastic SOIC
SOIC On REEL
SOIC On 7" REEL
R-8
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD825 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
–4–
WARNING!
ESD SENSITIVE DEVICE
REV. A
Typical Characteristics– AD825
20
100
15
OUTPUT IMPEDANCE – V
OUTPUT SWING – Volts
10
5
RL = 150V
0
RL = 1kV
–5
–10
10
1
0.1
–15
0
2
4
6
8
10
12
SUPPLY VOLTAGE – Volts
14
16
0.01
100
18
Figure 3. Output Voltage Swing vs. Supply
10M
1M
35
80
BANDWIDTH
30
UNITY GAIN BANDWIDTH – MHz
10
VS = 615V
OUTPUT SWING – Volts
10k
100k
FREQUENCY – Hz
Figure 6. Closed-Loop Output Impedance vs. Frequency
15
5
VS = 65V
0
–5
VS = 615V
–10
–15
1k
25
60
20
PHASE MARGIN
15
40
10
PHASE MARGIN – 8C
–20
5
0
100
200
300 400 500 600 700
LOAD RESISTANCE – Ohms
800
900
0
–60
1000
Figure 4. Output Voltage Swing vs. Load Resistance
20
–40
–20
0
60
20
40
80
TEMPERATURE – 8C
100
120
140
Figure 7. Unity Gain Bandwidth and Phase Margin vs.
Temperature
7.0
180
80
VS = 615V
135
70
OPEN-LOOP GAIN – dB
SUPPLY CURRENT – mA
6.5
+858
6.0
5.5
60
VS = 65V
90
50
45
40
0
30
20
10
5.0
0
2
4
6
8
10
12
14
SUPPLY VOLTAGE – ±V
16
18
0
1k
20
Figure 5. Quiescent Supply Current vs. Supply Voltage for
Various Temperatures
REV. A
10k
100k
1M
FREQUENCY – Hz
10M
100M
Figure 8. Open-Loop Gain and Phase Margin vs.
Frequency
–5–
OPEN-LOOP PHASE – Degrees
–408
+258
AD825
30
80
OUTPUT VOLTAGE – Volts p-p
OPEN-LOOP GAIN – dB
RL = 1kV
75
VS = 615V
70
VS = 65V
65
60
100
1k
LOAD RESISTANCE – V
20
RL = 150V
10
0
10k
Figure 9. Open-Loop Gain vs. Load Resistance
10k
100k
1M
FREQUENCY – Hz
10M
Figure 12. Large Signal Frequency Response; G = +2
10
200
0
180
–10
160
–PSRR
SETTLING TIME – ns
PSR – dB
–20
–30
+PSRR
–40
–50
–60
140
0.01%
100
40
20
100k
1M
FREQUENCY – Hz
0.1%
60
–80
10k
0.1%
80
–70
–90
0.01%
120
0
10M
10
Figure 10. Power Supply Rejection vs. Frequency
8
6
4
2
0
–2
–4
OUTPUT SWING – 0 to 6V
–6
–8
–10
Figure 13. Output Swing and Error vs. Settling Time
130
–50
120
–55
110
CMR – dB
DISTORTION – dB
–60
100
VS = 615
90
VS = 65
80
70
60
2nd
–65
3rd
–70
–75
50
–80
40
30
10
100
1k
100k
10k
FREQUENCY – Hz
1M
–85
10M
Figure 11. Common-Mode Rejection vs. Frequency
100k
1M
FREQUENCY – Hz
10M
Figure 14. Harmonic Distortion vs. Frequency
–6–
REV. A
AD825
160
+VS
615V
10mF
140
SLEW RATE – V/ms
0.01mF
65V
120
100
HP
PULSE (LS)
OR FUNCTION
(SS)
GENERATOR
80
60
VOUT
AD825
VIN
TEKTRONIX
P6204 FET
PROBE
TEKTRONIX
7A24
PREAMP
0.01mF
RL
50V
10mF
40
–VS
20
0
–60
–40
–20
0
20
40
80
60
TEMPERATURE – 8C
100
120 140
Figure 15. Slew Rate vs. Temperature
Figure 18. Noninverting Amplifier Connection
2
1
0
–1
GAIN – dB
–2
–3
–4
VOUT
VIN
VS
0.1dB FLATNESS
65V
10MHz
615V
21MHz
–5
–6
–7
–8
1k
10k
100k
1M
FREQUENCY – Hz
10M
Figure 16. Closed-Loop Gain vs. Frequency, Gain = +1
Figure 19. Noninverting Large Signal Pulse
Response, RL = 1 k Ω
2
1
0
GAIN – dB
–1
–2
–3
VIN
1kV
–4
1kV
VOUT
–5
VS
0.1dB FLATNESS
65V
7.7MHz
615V
9.8MHz
–6
–7
–8
1k
10k
100k
1M
FREQUENCY – Hz
10M
Figure 17. Closed-Loop Gain vs. Frequency, Gain = –1
REV. A
Figure 20. Noninverting Small Signal Pulse
Response, RL = 1 k Ω
–7–
AD825
Figure 21. Noninverting Large Signal Pulse
Response, RL = 150 Ω
Figure 24. Inverting Large Signal Pulse
Response, RL = 1 kΩ
Figure 25. Inverting Small Signal Pulse
Response, RL = 1 kΩ
Figure 22. Noninverting Small Signal Pulse
Response, RL = 150 Ω
1kV
+VS
10mF
0.01mF
RIN
HP
VIN 1kV
PULSE
GENERATOR
50V
VOUT
AD825
TEKTRONIX
P6204 FET
PROBE
TEKTRONIX
7A24
PREAMP
0.01mF
10mF
CL
1000pF
–VS
Figure 23. Inverting Amplifier Connection
–8–
REV. A
AD825
DRIVING CAPACITIVE LOADS
1kV
+VS
The internal compensation of the AD825, together with its high
output current drive, permits excellent large signal performance
while driving extremely high capacitive loads.
10mF
0.01mF
HP
PULSE
GENERATOR
THEORY OF OPERATION
RIN
VIN 1kV
50V
VOUT
TEKTRONIX
P6204 FET
PROBE
AD825
TEKTRONIX
7A24
PREAMP
0.01mF
CL
10mF
–VS
The AD825 (Figure 27) consists of common-drain commonbase FET input stage driving a cascoded, common base matched
NPN gain stage. The output buffer stage uses emitter followers
in a class AB amplifier that can deliver large current to the load
while maintaining low levels of distortion.
Figure 26a. Inverting Amplifier Driving a Capacitive Load
INPUT
The capacitor, CF, in the output stage, enables the AD825 to
drive heavy capacitive load. For light load, the gain of the output buffer is close to unity, CF is bootstrapped and not much
happens. As the capacitive load is increased, the gain of the
output buffer is decreased and the bandwidth of the amplifier is
reduced through a portion of CF adding to the dominant pole.
As the capacitive load is further increased, the amplifier’s bandwidth continues to drop, maintaining the stability of the AD825.
OUTPUT
Input Consideration
The AD825 with its unique input stage assures no phase reversal for signals as large or even larger than the supply voltages.
Also, layout considerations of the input transistors assure functionality even with a large differential signal.
Figure 26b. Inverting Amplifier Pulse Response
While Driving a 400 pF Capacitive Loads
The need for a low noise input stage calls for a larger FET transistor. One should consider the additional capacitance that is added
to assure stability. When filters are designed with the AD825,
one needs to consider the input capacitance (5 pF–6 pF) of the
AD825 as part of the passive network.
VPOS
NEG
Grounding and Bypassing
POS
CF
VOUT
VNEG
Figure 27. Simplified Schematic
REV. A
The AD825 is a low cost, wide band, high performance FET
input operational amplifier. With its unique input stage design,
the AD825 assures no phase reversal even for inputs that exceed
the power supply voltages, and its output stage is designed to
drive heavy capacitive or resistive load with small changes relative to no load condition.
–9–
The AD825 is a low input bias current FET amplifier. Its high
frequency response makes it useful in applications such as photo
diode interfaces, filters and audio circuits. When designing high
frequency circuits, some special precautions are in order. Circuits must be built with short interconnects, and resistances
should have low inductive paths to ground. Power supply leads
should be bypassed to common as close as possible to the amplifier pins. Ceramic capacitors of 0.1 µF are recommended.
AD825
Second Order Low-Pass Filter
A second order Butterworth low-pass filter can be implemented
using the AD825 as shown in Figure 28. The extremely low bias
currents of the AD825 allow the use of large resistor values, and
consequently small capacitor values, without concern for developing large offset errors. Low current noise is another factor in
permitting the use of large resistors without having to worry
about the resultant voltage noise.
With the values shown, the corner frequency will be 1 MHz.
The equations for component selection are shown below. Note
that the noninverting input (and the inverting input) has an
input capacitance of 6 pF. As a result, the calculated value of
C1 (12 pF) is reduced to 6 pF.
C3
0.1mF
R2
9.31kV
VIN
C2
6pF
VOUT
AD825
–5V
Figure 28. Second Order Butterworth Low-Pass Filter
0
0.707
C2 ( farads) =
2π f CUTOFF R1
(
+5V
C4
0.1mF
1.414
2π f CUTOFF R1
R1= R2 = user selected typically10kΩ to 100 kΩ
R1
9.31kV
HIGH FREQUENCY REJECTION – dB
C1=
C1
24pF
)
A plot of the filter frequency response is shown in Figure 29;
better than 40 dB of high frequency rejection is provided.
–10
–20
–30
–40
–50
–60
–70
–80
10k
100k
1M
FREQUENCY – Hz
10M
100M
Figure 29. Frequency Response of Second Order
Butterworth Filter
–10–
REV. A
AD825
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead Plastic SOIC
(R-8)
0.1968 (5.00)
0.1890 (4.80)
0.2440 (6.20)
0.2284 (5.80)
8
5
1
4
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.102 (2.59)
0.094 (2.39)
0.0098 (0.25)
0.0040 (0.10)
0.0500 0.0192 (0.49)
SEATING (1.27) 0.0138 (0.35) 0.0098 (0.25)
PLANE BSC
0.0075 (0.19)
REV. A
–11–
0.0196 (0.50)
x 45°
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
–12–
PRINTED IN U.S.A.
C3206a–0–2/98