Page 1
REV. 0
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.
a
250 MHz, General Purpose
Voltage Feedback Op Amps
AD8047/AD8048
The AD8047 and AD8048’s low distortion and cap load drive
make the AD8047/AD8048 ideal for buffering high speed
ADCs. They are suitable for 12 bit/10 MSPS or 8 bit/60 MSPS
ADCs. Additionally, the balanced high impedance inputs of the
voltage feedback architecture allow maximum flexibility when
designing active filters.
The AD8047 and AD8048 are offered in industrial (–40°C to
+85°C) temperature ranges and are available in 8-pin plastic
DIP and SOIC packages.
5ns
1V
Figure 1. AD8047 Large Signal Transient Response,
V
O
= 4 V p-p, G = +1
FEATURES
Wide Bandwidth AD8047, G = +1 AD8048, G = +2
Small Signal 250 MHz 260 MHz
Large Signal (2 V p-p) 130 MHz 160 MHz
5.8 mA Typical Supply Current
Low Distortion, (SFDR) Low Noise
–66 dBc typ @ 5 MHz
–54 dBc typ @ 20 MHz
5.2 nV/√
Hz (AD8047), 3.8 nV/√Hz (AD8048) Noise
Drives 50 pF Capacitive Load
High Speed
Slew Rate 750 V/µs (AD8047), 1000 V/µs (AD8048)
Settling 30 ns to 0.01%, 2 V Step
±3 V to ±6 V Supply Operation
APPLICATIONS
Low Power ADC Input Driver
Differential Amplifiers
IF/RF Amplifiers
Pulse Amplifiers
Professional Video
DAC Current to Voltage Conversion
Baseband and Video Communications
Pin Diode Receivers
Active Filters/Integrators
PRODUCT DESCRIPTION
The AD8047 and AD8048 are very high speed and wide bandwidth amplifiers. The AD8047 is unity gain stable. The
AD8048 is stable at gains of two or greater. The AD8047 and
AD8048, which utilize a voltage feedback architecture, meet the
requirements of many applications that previously depended on
current feedback amplifiers.
A proprietary circuit has produced an amplifier that combines
many of the best characteristics of both current feedback and
voltage feedback amplifiers. For the power (6.6 mA max) the
AD8047 and AD8048 exhibit fast and accurate pulse response
(30 ns to 0.01%) as well as extremely wide small signal and
large signal bandwidth and low distortion. The AD8047
achieves –54 dBc distortion at 20 MHz and 250 MHz small signal and 130 MHz large signal bandwidths.
FUNCTIONAL BLOCK DIAGRAM
8-Pin Plastic Mini-DIP (N), Cerdip (Q)
and SO (R) Packages
1
2
3
4
8
7
6
5
AD8047/48
NC
–INPUT
+INPUT
–V
S
NC
+V
S
OUTPUT
NC
(Top View)
NC = NO CONNECT
© Analog Devices, Inc., 1995
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
Page 2
AD8047A AD8048A
Parameter Conditions Min Typ Max Min Typ Max Units
DYNAMIC PERFORMANCE
Bandwidth (–3 dB)
Small Signal V
OUT
≤ 0.4 V p-p 170 250 180 260 MHz
Large Signal
1
V
OUT
= 2 V p-p 100 130 135 160 MHz
Bandwidth for 0.1 dB Flatness V
OUT
= 300 mV p-p
8047, R
F
=0 Ω; 8048, RF = 200 Ω 35 50 MHz
Slew Rate, Average +/– V
OUT
= 4 V Step 475 750 740 1000 V/µs
Rise/Fall Time V
OUT
= 0.5 V Step 1.1 1.2 ns
V
OUT
= 4 V Step 4.3 3.2 ns
Settling Time
To 0.1% V
OUT
= 2 V Step 13 13 ns
To 0.01% V
OUT
= 2 V Step 30 30 ns
HARMONIC/NOISE PERFORMANCE
2nd Harmonic Distortion 2 V p-p; 20 MHz –54 –48 dBc
R
L
= 1 kΩ –64 –60 dBc
3rd Harmonic Distortion 2 V p-p; 20 MHz –60 –56 dBc
R
L
= 1 kΩ –61 –65 dBc
Input Voltage Noise f = 100 kHz 5.2 3.8 nV/√
Hz
Input Current Noise f = 100 kHz 1.0 1.0 pA/√
Hz
Average Equivalent Integrated
Input Noise Voltage 0.1 MHz to 10 MHz 16 11 µV rms
Differential Gain Error (3.58 MHz) R
L
= 150 Ω, G = +2 0.02 0.01 %
Differential Phase Error (3.58 MHz) RL = 150 Ω, G = +2 0.03 0.02 Degree
DC PERFORMANCE
2,
RL = 150 Ω
Input Offset Voltage
3
13 13 mV
T
MIN–TMAX
44mV
Offset Voltage Drift ±5 ±5 µV/°C
Input Bias Current 1 3.5 1 3.5 µA
T
MIN–TMAX
6.5 6.5 µA
Input Offset Current 0.5 2 0.5 2 µA
T
MIN–TMAX
33µA
Common-Mode Rejection Ratio V
CM
= ±2.5 V 74 80 74 80 dB
Open-Loop Gain V
OUT
= ±2.5 V 58 62 65 68 dB
T
MIN–TMAX
54 56 dB
INPUT CHARACTERISTICS
Input Resistance 500 500 kΩ
Input Capacitance 1.5 1.5 pF
Input Common-Mode Voltage Range ±3.4 ±3.4 V
OUTPUT CHARACTERISTICS
Output Voltage Range, R
L
= 150 Ω±2.8 ±3.0 ±2.8 ±3.0 V
Output Current 50 50 mA
Output Resistance 0.2 0.2 Ω
Short Circuit Current 130 130 mA
POWER SUPPLY
Operating Range ±3.0 ± 5.0 ± 6.0 ±3.0 ±5.0 ±6.0 V
Quiescent Current 5.8 6.6 5.9 6.6 mA
T
MIN–TMAX
7.5 7.5 mA
Power Supply Rejection Ratio 72 78 72 78 dB
NOTES
1
See Max Ratings and Theory of Operation sections of data sheet.
2
Measured at AV = 50.
3
Measured with respect to the inverting input.
Specifications subject to change without notice.
(±VS = ±5 V; R
LOAD
= 100 Ω; AV = 1 (AD8047); AV = 2 (AD8048), unless otherwise noted)
AD8047/AD8048–SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
REV. 0
–2–
Page 3
AD8047/AD8048
REV. 0
–3–
MAXIMUM POWER DISSIPATION
The maximum power that can be safely dissipated by these devices is limited by the associated rise in junction temperature.
The maximum safe junction temperature for plastic encapsulated devices is determined by the glass transition temperature
of the plastic, approximately +150°C. Exceeding this limit temporarily may cause a shift in parametric performance due to a
change in the stresses exerted on the die by the package. Exceeding a junction temperature of +175°C for an extended period can
result in device failure.
While the AD8047 and AD8048 are internally short circuit protected, this may not be sufficient to guarantee that the maximum junction temperature (+150°C) is not exceeded under all
conditions. To ensure proper operation, it is necessary to observe the maximum power derating curves.
2.0
0
–50 80
1.5
0.5
–40
1.0
0 10 –10 –20 –30 20 30 40 50 60 70
90
AMBIENT TEMPERATURE –
°
C
MAXIMUM POWER DISSIPATION – Watts
TJ = +150°C
8-PIN MINI-DIP PACKAGE
8-PIN SOIC PACKAGE
Figure 2. Plot of Maximum Power Dissipation vs.
Temperature
ORDERING GUIDE
Temperature Package Package
Model Range Description Option*
AD8047AN –40°C to +85°C Plastic DIP N-8
AD8047AR –40°C to +85°C SOIC R-8
AD8047-EB Evaluation
Board
AD8048AN –40°C to +85°C Plastic DIP N-8
AD8048AR –40°C to +85°C SOIC R-8
AD8048-EB Evaluation
Board
*N = Plastic DIP; R= SOIC (Small Outline Integrated Circuit)
ABSOLUTE MAXIMUM RATINGS
1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 V
Voltage Swing × Bandwidth Product (AD8047) . . . 180 V – MHz
(AD8048) . . . 250 V – MHz
Internal Power Dissipation
2
Plastic Package (N) . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Watts
Small Outline Package (R) . . . . . . . . . . . . . . . . . . . 0.9 Watts
Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . ±V
S
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±1.2 V
Output Short Circuit Duration
. . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves
Storage Temperature Range (N, R) . . . . . . . .–65°C to +125°C
Operating Temperature Range (A Grade) . . . –40°C to +85°C
Lead Temperature Range (Soldering 10 sec) . . . . . . . . +300°C
NOTES
1
Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only, and 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.
2
Specification is for device in free air:
8-Pin Plastic DIP Package: θJA = 90°C/Watt
8-Pin SOIC Package: θJA = 140°C/Watt
WARNING!
ESD SENSITIVE DEVICE
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 these devices feature 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.
METALIZATION PHOTOS
Dimensions shown in inches and (mm).
Connect Substrate to –VS.
AD8047
+V
S
V
OUT
–V
S
–IN
+IN
0.045
(1.14)
0.044
(1.13)
AD8048
+V
S
–V
S
–OUT
–IN
+IN
0.045
(1.14)
0.044
(1.13)
Page 4
REV. 0
–4–
AD8047/AD8048
AD8047–Typical Characteristics
+V
S
PULSE
GENERATOR
RL = 100Ω
–V
S
V
IN
V
OUT
0.1µF
10µF
AD8047
3
2
7
6
0.1µF
10µF
4
TR/TF = 500ps
RT = 49.9Ω
Figure 3. Noninverting Configuration, G = +1
5ns
1V
Figure 4. Large Signal Transient Response;
V
O
= 4 V p-p, G = +1
5ns
100mV
Figure 5. Small Signal Transient Response;
V
O
= 400 mV p-p, G = +1
100Ω
+V
S
–V
S
0.1µF
10µF
AD8047
3
2
7
6
0.1µF
10µF
4
R
IN
R
F
RL = 100Ω
V
OUT
TR/TF = 500ps
PULSE
GENERATOR
V
IN
RT = 66.5Ω
Figure 6. Inverting Configuration, G = –1
5ns
1V
Figure 7. Large Signal Transient Response;
V
O
= 4 V p-p, G = –1, RF = RIN = 200
Ω
5ns
100mV
Figure 8. Small Signal Transient Response;
V
O
= 400 mV p-p, G = –1, RF = R
IN
= 200
Ω
Page 5
AD8047/AD8048
REV. 0
–5–
AD8048–Typical Characteristics
PULSE
GENERATOR
R
F
+V
S
RL = 100Ω
–V
S
V
IN
V
OUT
0.1µF
10µF
AD8048
3
2
7
6
0.1µF
10µF
4
TR/TF = 500ps
R
IN
RT = 49.9Ω
Figure 9. Noninverting Configuration, G = +2
5ns1V
Figure 10. Large Signal Transient Response;
V
O
= 4 V p-p, G = +2, RF = RIN = 200
Ω
5ns
100mV
Figure 11. Small Signal Transient Response;
V
O
= 400 mV p-p, G = +2, RF = RIN = 200
Ω
RS = 100Ω
R
F
+V
S
RL = 100Ω
–V
S
V
OUT
0.1µF
10µF
AD8048
3
2
7
6
0.1µF
10µF
4
TR/TF = 500ps
V
IN
PULSE
GENERATOR
RT = 66.5Ω
R
IN
Figure 12. Inverting Configuration, G= –1
5ns
1V
Figure 13. Large Signal Transient Response;
V
O
= 4 V p-p, G = –1, RF = RIN = 200
Ω
5ns
100mV
Figure 14. Small Signal Transient Response;
V
O
= 400 mV p-p, G = –1, RF = R
IN
= 200
Ω
Page 6
REV. 0
–6–
AD8047/AD8048
AD8047–Typical Characteristics
–6
–8
–4
–2
0
FREQUENCY – Hz
1G100M10M
RL = 100Ω
RF = 0Ω FOR DIP
R
F
= 66.5Ω FOR SOIC
V
OUT
= 300mV p-p
1M
–1
1
–3
–5
–7
OUTPUT – dBm
–9
Figure 15. AD8047 Small Signal Frequency Response
G = +1
–0.6
–0.8
–0.4
–0.2
0
FREQUENCY – Hz
1G100M10M
OUTPUT – dBm
RL = 100Ω
R
F
= 0Ω FOR DIP
R
F
= 66.5Ω FOR SOIC
V
OUT
= 300mV p-p
1M
0.1
–0.1
–0.3
–0.5
–0.7
–0.9
Figure 16. AD8047 0.1 dB Flatness, G = +1
0
–20
20
40
60
FREQUENCY – Hz
1G10M10k
GAIN – dB
1k
70
50
30
10
–10
–30
–40
–80
0
40
80
100
60
20
–20
–60
–100
PHASE MARGIN – Degrees
PHASE
MARGIN
GAIN
100k 1M 100M
RL = 100Ω
Figure 17. AD8047 Open-Loop Gain and Phase Margin vs.
Frequency
–6
–8
–4
–2
0
FREQUENCY – Hz
1G100M10M1M
–1
1
–3
–5
–7
–9
OUTPUT – dBm
RL = 100Ω
R
F
= 0Ω FOR DIP
R
F
= 66.5Ω FOR SOIC
V
OUT
= 2V p-p
Figure 18. AD8047 Large Signal Frequency Response,
G = +1
–6
–8
–4
–2
0
FREQUENCY – Hz
1G100M10M1M
–1
1
–3
–5
–7
–9
OUTPUT – dBm
RL = 100Ω
R
F
= RIN = 200Ω
V
OUT
= 300mV p-p
Figure 19. AD8047 Small Signal Frequency Response,
G = –1
–90
–110
–70
–50
–30
FREQUENCY – Hz
100M1M100k10k
–40
–20
–60
–80
–100
–120
OUTPUT – dBm
10M
2ND HARMONIC
3RD HARMONIC
RL = 1kΩ
V
OUT
= 2V p-p
Figure 20. AD8047 Harmonic Distortion vs. Frequency,
G = +1
Page 7
AD8047/AD8048
REV. 0
–7–
–90
–110
–70
–50
–30
FREQUENCY – Hz
100M1M100k10k
–40
–20
–60
–80
–100
–120
10M
2ND HARMONIC
3RD HARMONIC
RL = 100Ω
V
OUT
= 2V p-p
HARMONIC DISTORTION – dBc
Figure 21. AD8047 Harmonic Distortion vs. Frequency,
G = +1
OUTPUT SWING – V p-p
–25
–30
HARMONIC DISTORTION – dBc
–65
1.6 6.52.5 3.5 4.5 5.5
–45
–50
–55
–60
–35
–40
2ND HARMONIC
3RD HARMONIC
f = 20MHz
R
L
= 1kΩ
RF = 0Ω
Figure 22. AD8047 Harmonic Distortion vs. Output Swing,
G = +1
0.04
DIFF GAIN – %
–0.04
0.00
–0.02
0.02
11th1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
11th1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
0.04
DIFF PHASE – Degrees
–0.04
0.00
–0.02
0.02
Figure 23. AD8047 Differential Gain and Phase Error,
G = +2, R
L
= 150 Ω, RF = 200 Ω, RIN = 200
Ω
SETTLING TIME – ns
0.5
0.4
–0.4
010
ERROR – %
20
0.0
–0.1
–0.2
–0.3
0.2
0.1
0.3
–0.5
51525354530 40
RL = 100Ω
R
F
= 0Ω
V
OUT
= 2V STEP
Figure 24. AD8047 Short-Term Settling Time, G = +1
SETTLING TIME – µs
0.25
0.20
–0.20
04
ERROR – %
8
0.00
–0.05
–0.10
–0.15
0.10
0.05
0.15
–0.25
2 6 10 14 1812 16
RL = 100Ω
R
F
= 0Ω
V
OUT
= 2V STEP
Figure 25. AD8047 Long-Term Settling Time, G = +1
17
13
3
100 100k10k1k10
15
9
11
5
7
FREQUENCY – Hz
INPUT NOISE VOLTAGE – nV/√Hz
Figure 26. AD8047 Noise vs. Frequency
Page 8
REV. 0
–8–
AD8047/AD8048
AD8048–Typical Characteristics
–3
10M 1G100M1M
5
1
3
–1
FREQUENCY – Hz
OUTPUT – dBm
6
4
0
2
–2
RL = 100Ω
R
F
= RIN = 200Ω
V
OUT
= 2V p-p
7
Figure 30. AD8048 Large Signal Frequency Response,
G = +2
–9
10M 1G100M1M
–1
–5
–3
–7
FREQUENCY – Hz
0
–2
–6
–4
–8
RL = 100Ω
R
F
= RIN = 200Ω
V
OUT
= 300mV p-p
OUTPUT – dBm
1
Figure 31. AD8048 Small Signal Frequency Response,
G = –1
HARMONIC DISTORTION – dBc
–90
–110
–70
–50
–30
FREQUENCY – Hz
100M1M100k10k
–40
–20
–60
–80
–100
–120
10M
2ND HARMONIC
3RD HARMONIC
RL = 1kΩ
V
OUT
= 2V p-p
Figure 32. AD8048 Harmonic Distortion vs. Frequency,
G = +2
Figure 27. AD8048 Small Signal Frequency Response,
G = +2
6.5
5.5
10M 1G100M1M
6.3
5.9
6.1
5.7
FREQUENCY – Hz
OUTPUT – dBm
6.4
6.2
5.8
6.0
5.6
RL = 100Ω
R
F
= RIN = 200Ω
V
OUT
= 300mV p-p
Figure 28. AD8048 0.1 dB Flatness, G = +2
70
–20
10k 100k 1G100M10M1M
FREQUENCY – Hz
60
20
30
40
50
–10
0
10
GAIN – dB
–40
–120
–20
0
20
–100
–80
–60
PHASE – Degrees
RL = 100Ω
PHASE
1k
40
60
80
100
80
90
Figure 29. AD8048 Open-Loop Gain and Phase Margin vs.
Frequency
7
–3
10M 1G100M1M
5
1
3
–1
FREQUENCY – Hz
OUTPUT – dBm
6
4
0
2
–2
RL = 100Ω
R
F
= RIN = 200Ω
V
OUT
= 300mV p-p
Page 9
AD8047/AD8048
REV. 0
–9–
SETTLING TIME – ns
0.5
0.4
–0.4
010
ERROR – %
20
0.0
–0.1
–0.2
–0.3
0.2
0.1
0.3
–0.5
51525354530 40
RL = 100Ω
RF = 200Ω
V
OUT
= 2V STEP
Figure 36. AD8048 Short-Term Settling Time, G = +2
SETTLING TIME – µs
0.25
0.20
–0.20
04
ERROR – %
8
0.0
–0.05
–0.10
–0.15
0.10
0.05
0.15
–0.25
2 6 10 14 1812 16
RL = 100Ω
R
F
= 200Ω
V
OUT
= 2V STEP
Figure 37. AD8048 Long-Term Settling Time 2 V Step,
G = +2
17
13
3
100 100k10k1k10
15
9
11
5
7
FREQUENCY – Hz
INPUT NOISE VOLTAGE – nV/√Hz
Figure 38. AD8048 Noise vs. Frequency
OUTPUT SWING – Volts p-p
–15
–70
1.5 5.52.5 3.5 4.5 6.5
HARMONIC DISTORTION – dBc
–55
–65
–25
–35
–45
f = 20MHz
R
L
= 1kΩ
RF = 200
2ND HARMONIC
3RD HARMONIC
–20
–60
–30
–40
–50
Figure 34. AD8048 Harmonic Distortion vs. Output Swing,
G = +2
0.04
DIFF GAIN – %
–0.04
0.00
–0.02
0.02
11th1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
11th1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th
0.04
DIFF PHASE – Degrees
–0.04
0.00
–0.02
0.02
Figure 35. AD8048 Differential Gain and Phase Error,
G = +2, R
L
= 150 Ω, RF = 200 Ω, RIN = 200
Ω
Figure 33. AD8048 Harmonic Distortion vs. Frequency,
G = +2
HARMONIC DISTORTION – dBc
–90
–110
–70
–50
–30
FREQUENCY – Hz
100M1M100k10k
–40
–20
–60
–80
–100
–120
10M
2ND HARMONIC
3RD HARMONIC
RL = 100Ω
V
OUT
= 2V p-p
Page 10
REV. 0–10–
30
60
80
90
FREQUENCY – Hz
1G10M1M100k
100
70
50
40
20
100M
CMRR – dB
∆VCM = 1V
R
L
= 100Ω
Figure 39. AD8047 CMRR vs. Frequency
100
0.01
1G
1
0.1
100k10k
10
100M10M1M
FREQUENCY – Hz
R
OUT
– Ω
Figure 40. AD8047 Output Resistance vs. Frequency,
G = +1
90
80
70
50
40
30
20
10
0
PSRR – dB
10k 100k 1G100M10M1M
FREQUENCY – Hz
60
+PSRR
–PSRR
Figure 41. AD8047 PSRR vs. Frequency
AD8047/AD8048–Typical Characteristics
30
60
80
90
FREQUENCY – Hz
1G10M1M100k
100
70
50
40
20
100M
CMRR – dB
∆VCM = 1V
R
L
= 100Ω
Figure 42. AD8048 CMRR vs. Frequency
100
0.01
1G
1
0.1
100k10k
10
100M10M1M
FREQUENCY – Hz
R
OUT
– Ω
Figure 43. AD8048 Output Resistance vs. Frequency,
G = +2
90
70
60
50
40
30
20
10
0
3k 10k 100M1M100k
FREQUENCY – Hz
PSRR – dB
80
–PSRR
+PSRR
500M
Figure 44. AD8048 PSRR vs. Frequency,
G = +2
Page 11
AD8047/AD8048
REV. 0
–11–
JUNCTION TEMPERATURE – °C
3.9
2.9
2.3
–60 140–40
OUTPUT SWING – Volts
–20 0 20 40 60 80 100 120
3.7
3.1
2.7
2.5
3.5
3.3
4.1
+V
OUT
–V
OUT
+V
OUT
–V
OUT
+V
OUT
–V
OUT
RL = 1kΩ
RL = 50Ω
RL = 150Ω
Figure 45. AD8047/AD8048 Output Swing vs. Temperature
JUNCTION TEMPERATURE – °C
OPEN-LOOP GAIN – V/V
2400
1600
1000
–60 140–40 –20 0 20 40 60 80 100 120
2200
1400
1200
2000
1800
2600
AD8048
AD8047
Figure 46. AD8047/AD8048 Open-Loop Gain vs.
Temperature
JUNCTION TEMPERATURE – °C
94
–60
92
90
88
86
84
82
80
78
76
–40 –20 0 20 40 60 80 100 120 140
+PSRR
AD8048
–PSRR
–PSRR
AD8047
+PSRR
AD8047
PSRR – –dB
AD8048
Figure 47. AD8047/AD8048 PSRR vs. Temperature
83.0
140–40–60 120806040 100200–20
JUNCTION TEMPERATURE – °C
CMRR – –dB
82.0
81.0
80.0
79.0
78.0
77.0
76.0
AD8047
AD8048
Figure 48. AD8047/AD8048 CMRR vs. Temperature
JUNCTION TEMPERATURE – °C
7.5
5.5
–60 140–40 –20 0 20 40 60 80 100 120
7.0
6.0
5.0
4.5
6.5
8.0
SUPPLY CURRENT – mA
±6V
±6V
±5V
±5V
AD8048
AD8047
AD8048
AD8047
Figure 49. AD8047/AD8048 Supply Current vs.
Temperature
JUNCTION TEMPERATURE – °C
800
400
100
–60 140–40 –20 0 20 40 60 80 100 120
700
300
200
600
500
900
INPUT OFFSET VOLTAGE – µV
AD8048
AD8047
Figure 50. AD8047/AD8048 Input Offset Voltage vs.
Temperature
Page 12
REV. 0
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AD8047/AD8048
THEORY OF OPERATION
General
The AD8047 and AD8048 are wide bandwidth, voltage feedback amplifiers. Since their open-loop frequency response follows the conventional 6 dB/octave roll-off, their gain bandwidth
product is basically constant. Increasing their closed-loop gain
results in a corresponding decrease in small signal bandwidth.
This can be observed by noting the bandwidth specification
between the AD8047 (gain of 1) and AD8048 (gain of 2).
Feedback Resistor Choice
The value of the feedback resistor is critical for optimum performance on the AD8047 and AD8048. For maximum flatness at a
gain of 2, R
F
and RG should be set to 200 Ω for the AD8048.
When the AD8047 is configured as a unity gain follower, R
F
should be set to 0 Ω (no feedback resistor should be used) for
the plastic DIP and 66.5 Ω for the SOIC.
V
IN
+V
S
6
7
2
4
3
V
OUT
G = 1 +
R
F
R
G
AD8047/48
R
TERM
0.1µF
10µF
–V
S
0.1µF
10µF
R
G
R
F
Figure 51. Noninverting Operation
V
IN
6
2
3
R
G
R
TERM
V
OUT
G = –
R
F
R
G
AD8047/48
+V
S
7
0.1µF
10µF
4
–V
S
0.1µF
10µF
R
F
Figure 52. Inverting Operation
When the AD8047 is used in the transimpedance (I to V) mode,
such as in photodiode detection, the value of R
F
and diode
capacitance (C
I
) are usually known. Generally, the value of R
F
selected will be in the kΩ range, and a shunt capacitor (CF)
across R
F
will be required to maintain good amplifier stability.
The value of C
F
required to maintain optimal flatness (<1 dB
Peaking) and settling time can be estimated as:
C
F
≅ (2 ω
OCIRF
–1)/ω
O
2
R
F
2
[]
1/2
where ωO is equal to the unity gain bandwidth product of the
amplifier in rad/sec, and C
I
is the equivalent total input
capacitance at the inverting input. Typically ω
O
= 800 × 10
6
rad/sec (see Open-Loop Frequency Response curve, Figure 17).
As an example, choosing R
F
= 10 kΩ and CI = 5 pF, requires
C
F
to be 1.1 pF (Note: CI includes both source and parasitic
circuit capacitance). The bandwidth of the amplifier can be
estimated using the C
F
calculated as:
f
3 dB
≅
1. 6
2 πR
FCF
For general voltage gain applications, the amplifier bandwidth
can be closely estimated as:
f
3 dB
≅
ω
O
2π 1+
R
F
R
G
This estimation loses accuracy for gains of +2/–1 or lower due
to the amplifier’s damping factor. For these “low gain” cases,
the bandwidth will actually extend beyond the calculated value
(see Closed-Loop BW plots, Figures 15 and 26).
As a rule of thumb, capacitor C
F
will not be required if:
(R
FiRG
)× CI≤
NG
4 ω
O
where NG is the Noise Gain (1 + RF/RG) of the circuit. For
most voltage gain applications, this should be the case.
R
F
V
OUT
AD8047
C
F
C
I
I
I
Figure 53. Transimpedance Configuration
Pulse Response
Unlike a traditional voltage feedback amplifier, where the slew
speed is dictated by its front end dc quiescent current and gain
bandwidth product, the AD8047 and AD8048 provide “on demand” current that increases proportionally to the input “step”
signal amplitude. This results in slew rates (1000 V/µs) compa-
rable to wideband current feedback designs. This, combined
with relatively low input noise current (1.0 pA/√
Hz), gives the
AD8047 and AD8048 the best attributes of both voltage and
current feedback amplifiers.
Large Signal Performance
The outstanding large signal operation of the AD8047 and
AD8048 is due to a unique, proprietary design architecture.
In order to maintain this level of performance, the maximum
180 V-MHz product must be observed, (e.g., @ 100 MHz,
V
O
≤ 1.8 V p-p) on the AD8047 and 250 V-MHz product on
the AD8048.
Power Supply Bypassing
Adequate power supply bypassing can be critical when optimizing the performance of a high frequency circuit. Inductance in
the power supply leads can form resonant circuits that produce
peaking in the amplifier’s response. In addition, if large current
transients must be delivered to the load, then bypass capacitors
(typically greater than 1 µF) will be required to provide the best
settling time and lowest distortion. A parallel combination of at
least 4.7 µF, and between 0.1 µF and 0.01 µF, is recommended.
Some brands of electrolytic capacitors will require a small series
damping resistor ≈4.7 Ω for optimum results.
Driving Capacitive Loads
The AD8047/AD8048 have excellent cap load drive capability
for high speed op amps as shown in Figures 55 and 57. However, when driving cap loads greater than 25 pF, the best frequency response is obtained by the addition of a small series
resistance. It is worth noting that the frequency response of the
Page 13
AD8047/AD8048
REV. 0
–13–
circuit when driving large capacitive loads will be dominated by
the passive roll-off of R
SERIES
and CL.
R
F
R
SERIES
R
L
1kΩ
C
L
AD8047
Figure 54. Driving Capacitive Loads
5ns
500mV
Figure 55. AD8047 Large Signal Transient Response;
V
O
= 2 V p-p, G = +1, RF = 0 Ω, R
SERIES
= 0 Ω, CL = 27 pF
R
F
R
SERIES
R
L
1kΩ
C
L
AD8048
R
IN
Figure 56. Driving Capacitive Loads
5ns
500mV
Figure 57. AD8048 Large Signal Transient Response;
V
O
= 2 V p-p, G = +2, RF = RIN = 200 Ω, R
SERIES
= 0 Ω,
C
L
= 27 pF
APPLICATIONS
The AD8047 and AD8048 are voltage feedback amplifiers well
suited for such applications as photodetectors, active filters, and
log amplifiers. The devices’ wide bandwidth (260 MHz), phase
margin (65°), low noise current (1.0 pA/√
Hz), and slew rate
(1000 V/µs) give higher performance capabilities to these appli-
cations over previous voltage feedback designs.
With a settling time of 30 ns to 0.01% and 13 ns to 0.1%, the
devices are an excellent choice for DAC I/V conversion. The
same characteristics along with low harmonic distortion make
them a good choice for ADC buffering/amplification. With superb linearity at relatively high signal frequencies, the AD8047
and AD8048 are ideal drivers for ADCs up to 12 bits.
Operation as a Video Line Driver
The AD8047 and AD8048 have been designed to offer outstanding performance as video line drivers. The important
specifications of differential gain (0.01%) and differential phase
(0.02°) meet the most exacting HDTV demands for driving
video loads.
75Ω
CABLE
200Ω
200Ω
75Ω
CABLE
75Ω
75Ω
V
OUT
+V
S
–V
S
75Ω
V
IN
0.1µF
10µF
AD8047/
AD8048
3
2
7
0.1µF
10µF
4
6
Figure 58. Video Line Driver
Active Filters
The wide bandwidth and low distortion of the AD8047 and
AD8048 are ideal for the realization of higher bandwidth active
filters. These characteristics, while being more common in many
current feedback op amps, are offered in the AD8047 and AD8048
in a voltage feedback configuration. Many active filter configurations are not realizable with current feedback amplifiers.
A multiple feedback active filter requires a voltage feedback
amplifier and is more demanding of op amp performance than
other active filter configurations such as the Sallen-Key. In
general, the amplifier should have a bandwidth that is at least
ten times the bandwidth of the filter if problems due to phase
shift of the amplifier are to be avoided.
Figure 59 is an example of a 20 MHz low pass multiple feedback active filter using an AD8048.
1
V
IN
R4
154Ω
C1
50pF
C2
100pF
R1
154Ω
AD8048
R3
78.7Ω
+5V
0.1µF
3
2
100Ω
6
V
OUT
10µF
5
0.1µF
–5V
10µF
4
7
Figure 59. Active Filter Circuit
Choose:
F
O
= Cutoff Frequency = 20 MHz
α = Damping Ratio = 1/Q = 2
Page 14
REV. 0
–14–
AD8047/AD8048
H = Absolute Value of Circuit Gain =
–R4
R1
= 1
Then:
k =2 π FOC1
C2 =
4 C1(H + 1)
α
2
R1 =
α
2 HK
R3 =
α
2 K (H +1)
R 4 = H (R1)
A/D Converter Driver
As A/D converters move toward higher speeds with higher resolutions, there becomes a need for high performance drivers that
will not degrade the analog signal to the converter. It is desirable from a system’s standpoint that the A/D be the element in
the signal chain that ultimately limits overall distortion. This
places new demands on the amplifiers used to drive fast, high
resolution A/Ds.
With high bandwidth, low distortion and fast settling time the
AD8047 and AD8048 make high performance A/D drivers for
advanced converters. Figure 60 is an example of an AD8047
used as an input driver for an AD872, a 12-bit, 10 MSPS A/D
converter.
Layout Considerations
The specified high speed performance of the AD8047 and
AD8048 requires careful attention to board layout and component selection. Proper RF design techniques and low pass parasitic component selection are mandatory
Figure 60. AD8047 Used as Driver for an AD872, a 12-Bit, 10 MSPS A/D Converter
MSB
BIT2
BIT3
BIT4
BIT5
BIT6
BIT7
BIT8
BIT9
BIT10
BIT11
BIT12
AV
DD
AGND
V
INA
REF GND
REF IN
REF OUT
AV
SS
AV
SS
AGND
OTR
CLK
DRGND
DRV
DD
DGND
DV
DD
19
18
17
16
15
14
13
12
11
10
9
8
24
25
3
26
28
27
1
20
21
23
22
6
7
4
5
V
INB
0.1µF
–5V ANALOG
AD872
1
6
3
2
5
1µF
+5V ANALOG
AD8047
ANALOG IN
0.1µF
0.1µF
0.1µF
DIGITAL OUTPUT
0.1µF
0.1µF
10Ω
49.9Ω
CLOCK INPUT
0.1µF
0.1µF
+5V ANALOG
+5V DIGITAL
+5V DIGITAL
–5V
ANALOG
2
10µF
10µF
4
7
The PCB should have a ground plane covering all unused portions of the component side of the board to provide a low impedance path. The ground plane should be removed from the
area near the input pins to reduce stray capacitance.
Chip capacitors should be used for the supply bypassing (see
Figure 60). One end should be connected to the ground plane
and the other within 1/8 inch of each power pin. An additional
large (0.47 µF–10 µF) tantalum electrolytic capacitor should be
connected in parallel, though not necessarily so close, to supply
current for fast, large signal changes at the output.
The feedback resistor should be located close to the inverting
input pin in order to keep the stray capacitance at this node to a
minimum. Capacitance variations of less than 1 pF at the inverting input will significantly affect high speed performance.
Stripline design techniques should be used for long signal traces
(greater than about 1 inch). These should be designed with a
characteristic impedance of 50 Ω or 75 Ω and be properly terminated at each end.
Evaluation Board
An evaluation board for both the AD8047 and AD8048 is available that has been carefully laid out and tested to demonstrate
that the specified high speed performance of the device can be
realized. For ordering information, please refer to the Ordering
Guide.
The layout of the evaluation board can be used as shown or
serve as a guide for a board layout.
Page 15
AD8047/AD8048
REV. 0
–15–
Table I.
AD8047 AD8048
Component –1 +1 +2 +10 +101 –1 +2 +10 +101
R
F
200 Ω 66.5 Ω 1 kΩ 1 kΩ 1 kΩ 200 Ω 200 Ω 1 kΩ 1 kΩ
R
G
200 Ω –1 kΩ110 Ω 10 Ω 200 Ω 200 Ω 110 Ω 10 Ω
R
O
49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω
R
S
–0 Ω0 Ω 0 Ω 0 Ω –0 Ω0 Ω 0 Ω
R
T
66.5 Ω 49.9 Ω 49.9 Ω 49.9 Ω 49.9 Ω 66.5 Ω 49.9 Ω 49.9 Ω 49.9 Ω
Small Signal
BW (–3 dB) 90 MHz 260 MHz 95 MHz 10 MHz 1 MHz 250 MHz 250 MHz 22 MHz 2 MHz
Figure 61. Noninverting Configurations for Evaluation Boards
Figure 62. Evaluation Board Silkscreen (Top)
Figure 63. Board Layout (Solder Side)
SOIC (R)
INVERTER
SOIC (R)
NONINVERTER
SOIC (R)
INVERTER
SOIC (R)
NONINVERTER
C1
1000pFC30.1µF
C5
10µF
C2
1000pFC40.1µF
C6
10µF
+V
S
–V
S
OPTIONAL
Noninverting Configuration
Supply Bypassing
R
F
R
O
+V
S
–V
S
R
T
R
G
OUT
NI
Page 16
REV. 0
–16–
AD8047/AD8048
SOIC (R)
NONINVERTER
SOIC (R)
INVERTER
Figure 64. Board Layout (Component Side)
PRINTED IN U.S.A.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic DIP
(N Package)
PIN 1
0.280 (7.11)
0.240 (6.10)
4
58
1
0.060 (1.52)
0.015 (0.38)
0.130
(3.30)
MIN
0.210
(5.33)
MAX
0.160 (4.06)
0.115 (2.93)
0.430 (10.92)
0.348 (8.84)
SEATING
PLANE
0.022 (0.558)
0.014 (0.356)
0.070 (1.77)
0.045 (1.15)
0.100
(2.54)
BSC
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.195 (4.95)
0.115 (2.93)
8-Pin Plastic SOIC
(R Package)
0.019 (0.48)
0.014 (0.36)
0.050
(1.27)
BSC
0.102 (2.59)
0.094 (2.39)
0.197 (5.01)
0.189 (4.80)
0.010 (0.25)
0.004 (0.10)
0.098 (0.2482)
0.075 (0.1905)
0.190 (4.82)
0.170 (4.32)
0.030 (0.76)
0.018 (0.46)
10
°
0
°
0.090
(2.29)
8
°
0
°
0.020 (0.051) x 45
°
CHAMF
1
8
5
4
PIN 1
0.157 (3.99)
0.150 (3.81)
0.244 (6.20)
0.228 (5.79)
0.150 (3.81)
C1995–10–1/95
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