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250 MHz, General Purpose Voltage Feedback Op Amps AD8047/AD8048
FEATURES Wide Bandwidth AD8047, G = +1 Small Signal 250 MHz Large Signal (2 V p-p) 130 MHz AD8048, G = +2 260 MHz 160 MHz FUNCTIONAL BLOCK DIAGRAM 8-Pin Plastic PDIP (N) and SOIC (R) Packages
NC -INPUT +INPUT -V S 1 2 3 4
(TOP VIEW) NC = NO CONNECT
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/ s (AD8047), 1000 V/ s (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
AD8047/ AD8048
8 7 6 5
NC +VS OUTPUT NC
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 (-40C to +85C) temperature ranges and are available in 8-lead PDIP and SOIC packages.
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, 250 MHz small signal, and 130 MHz large signal bandwidths.
1V
5ns
Figure 1. AD8047 Large Signal Transient Response, VO = 4 V p-p, G = +1
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 that may result from its use. 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 companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) 2003 Analog Devices, Inc. All rights reserved.
AD8047/AD8048-SPECIFICATIONS
ELECTRICAL CHARACTERISTICS
Parameter DYNAMIC PERFORMANCE Bandwidth (-3 dB) Small Signal Large Signal1 Bandwidth for 0.1 dB Flatness
( VS =
5 V, RLOAD = 100
, AV = 1 (AD8047), AV = 2 (AD8048), unless otherwise noted.)
Min AD8047A Typ Max AD8048A Min Typ Max Unit
Conditions
Slew Rate, Average +/- Rise/Fall Time Settling Time To 0.1% To 0.01% HARMONIC/NOISE PERFORMANCE Second Harmonic Distortion Third Harmonic Distortion Input Voltage Noise Input Current Noise Average Equivalent Integrated Input Noise Voltage Differential Gain Error (3.58 MHz) Differential Phase Error (3.58 MHz) DC PERFORMANCE2, RL = 150 Input Offset Voltage3
VOUT 0.4 V p-p VOUT = 2 V p-p VOUT = 300 mV p-p AD8047, RF = 0 ; AD8048, RF = 200 VOUT = 4 V Step VOUT = 0.5 V Step VOUT = 4 V Step VOUT = 2 V Step VOUT = 2 V Step 2 V p-p; 20 MHz RL = 1 k 2 V p-p; 20 MHz RL = 1 k f = 100 kHz f = 100 kHz 0.1 MHz to 10 MHz RL = 150 , G = +2 RL = 150 , G = +2
170 100
250 130
180 135
260 160
MHz MHz
475
35 750 1.1 4.3 13 30 -54 -64 -60 -61 5.2 1.0 16 0.02 0.03 1 3 4 3.5 6.5 2 3
740
50 1000 1.2 3.2 13 30 -48 -60 -56 -65 3.8 1.0 11 0.01 0.02 1 5 1 0.5 3 4 3.5 6.5 2 3
MHz V/s ns ns ns ns dBc dBc dBc dBc nV/Hz pA/Hz V rms % Degree mV mV V/C A A A A dB dB dB k pF V V mA mA V mA mA dB
TMIN to TMAX Offset Voltage Drift Input Bias Current TMIN to TMAX Input Offset Current Common-Mode Rejection Ratio Open-Loop Gain INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range OUTPUT CHARACTERISTICS Output Voltage Range, RL = 150 Output Current Output Resistance Short-Circuit Current POWER SUPPLY Operating Range Quiescent Current TMIN to TMAX Power Supply Rejection Ratio
NOTES 1 See Absolute Maximum Ratings and Theory of Operation sections. 2 Measured at AV = 50. 3 Measured with respect to the inverting input. Specifications subject to change without notice.
5 1 0.5
TMIN to TMAX VCM = 2.5 V VOUT = 2.5 V TMIN to TMAX
74 58 54
80 62
74 65 56
80 68
500 1.5 3.4 2.8 3.0 50 0.2 130 5.0 6.0 5.8 6.6 7.5 78
500 1.5 3.4 2.8 3.0 50 0.2 130 3.0 5.0 6.0 5.9 6.6 7.5 72 78
3.0 72
-2-
REV. A
AD8047/AD8048
ABSOLUTE MAXIMUM RATINGS 1 MAXIMUM POWER DISSIPATION
Supply Voltage, (+VS) - (-VS) . . . . . . . . . . . . . . . . . . . . 12.6 V Voltage Swing x Bandwidth Product AD8047 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 V-MHz AD8048 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 V-MHz Internal Power Dissipation2 Plastic Package (N) . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 W Small Outline Package (R) . . . . . . . . . . . . . . . . . . . . . 0.9 W Input Voltage (Common Mode) . . . . . . . . . . . . . . . . . . . . VS Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . 1.2 V Output Short-Circuit Duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Observe Power Derating Curves Storage Temperature Range (N, R) . . . . . . . -65C to +125C Operating Temperature Range (A Grade) . . . -40C to +85C Lead Temperature Range (Soldering 10 sec) . . . . . . . . . 300C
NOTES 1 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. 2 Specification is for device in free air: 8-Lead PDIP Package, JA = 90C/W; 8-Lead SOIC Package, JA = 140C/W
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 150C. 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 175C 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 (150C) is not exceeded under all conditions. To ensure proper operation, it is necessary to observe the maximum power derating curves.
2.0 8-PIN PDIP PACKAGE TJ = +150 C
MAXIMUM POWER DISSIPATION (W)
1.5
METALLIZATION PHOTOS
Dimensions shown in inches and (mm) Connect Substrate to -V S.
1.0
AD8047
+VS
8-PIN SOIC PACKAGE 0.5
0.045 (1.14) VOUT
0 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 AMBIENT TEMPERATURE ( C)
70
80
90
Figure 2. Plot of Maximum Power Dissipation vs. Temperature
-IN
ORDERING GUIDE
+IN 0.044 (1.13) -VS
Model AD8047AN AD8047AR AD8047AR-REEL AD8047AR-REEL7 AD8048AN AD8048AR AD8048AR-REEL AD8048AR-REEL7
*N = PDIP, R= SOIC
Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description PDIP SOIC SOIC SOIC PDIP SOIC SOIC SOIC
Package Option* N-8 R-8 R-8 R-8 N-8 R-8 R-8 R-8
AD8048
+VS
0.045 (1.14) VOUT
-IN -VS 0.044 (1.13)
+IN
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 AD8047/AD8048 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.
REV. A
-3-
AD8047/AD8048-Typical Performance Characteristics
RF
+VS
10 F 0.1 F
PULSE GENERATOR TR/TF = 500ps RIN VIN 2 RT = 66.5 3 100
+VS
10 F 0.1 F
PULSE GENERATOR TR/TF = 500ps VIN RT = 49.9
2
7
7
AD8047
3 4
6 0.1 F
VOUT RL = 100
AD8047
4
6 0.1 F
VOUT RL = 100
10 F -VS
10 F -VS
TPC 1. AD8047 Noninverting Configuration, G = +1
TPC 4. AD8047 Inverting Configuration, G = -1
1V
5ns
1V
5ns
TPC 2. AD8047 Large Signal Transient Response; VO = 4 V p-p, G = +1
TPC 5. AD8047 Large Signal Transient Response; VO = 4 V p-p, G = -1, RF = RIN = 200
100mV
5ns
100mV
5ns
TPC 3. AD8047 Small Signal Transient Response; VO = 400 mV p-p, G = +1
TPC 6. AD8047 Small Signal Transient Response; VO = 400 mV p-p, G = -1, RF = RIN = 200
-4-
REV. A
AD8047/AD8048
RF PULSE GENERATOR TR/TF = 500ps RIN 2 7 +VS 10 F 0.1 F
RF PULSE GENERATOR TR/TF = 500ps RIN VIN
6 0.1 F VOUT
+VS
10 F 0.1 F
2 RT = 66.5 3
7
AD8048
VIN RT = 49.9 -VS 3 4
AD8048
4
6 0.1 F 10 F
VOUT RL = 100
RL = 100 10 F
RS = 100 -VS
TPC 7. AD8048 Noninverting Configuration, G = +2
TPC 10. AD8048 Inverting Configuration, G= -1
1V
5ns
1V
5ns
TPC 8. AD8048 Large Signal Transient Response; VO = 4 V p-p, G = +2, RF = RIN = 200
TPC 11. AD8048 Large Signal Transient Response; VO = 4 V p-p, G = -1, RF = RIN = 200
100mV
5ns
100mV
5ns
TPC 9. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = +2, RF = RIN = 200
TPC 12. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = -1, RF = RIN = 200
REV. A
-5-
AD8047/AD8048
1 0 -1 -2 RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p
1 0 -1 -2 RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 2V p-p
OUTPUT (dBm)
-3 -4 -5 -6 -7 -8 -9 1M
OUTPUT (dBm)
100M 1G
-3 -4 -5 -6 -7 -8
10M
-9 1M
10M
100M
1G
FREQUENCY (Hz)
FREQUENCY (Hz)
TPC 13. AD8047 Small Signal Frequency Response, G = +1
TPC 16. AD8047 Large Signal Frequency Response, G = +1
0.1 0 -0.1 -0.2 OUTPUT (dBm) -0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 1M 10M 100M 1G RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p
1 0 -1 -2
OUTPUT (dBm)
RL = 100 RF = RF = 200 VOUT = 300mV p-p
-3 -4 -5 -6 -7 -8 -9 1M 10M 100M FREQUENCY (Hz) 1G
FREQUENCY (Hz)
TPC 14. AD8047 0.1 dB Flatness, G = +1
TPC 17. AD8047 Small Signal Frequency Response, G = -1
70 60 50 40
GAIN (dB)
100 80 PHASE MARGIN 60 40 20 GAIN 0 -20 -40 RL = 100 -60 -80 -100 1G
PHASE MARGIN (Degrees)
-20 -30 -40 -50
OUTPUT (dBm)
RL = 1k VOUT = 2V p-p
30 20 10 0 -10 -20 -30 1k 10k 100k 1M 10M 100M FREQUENCY (Hz)
-60 -70 -80 -90 -100 -110 -120 10k 100k 1M FREQUENCY (Hz) 10M 100M THIRD HARMONIC SECOND HARMONIC
TPC 15. AD8047 Open-Loop Gain and Phase Margin vs. Frequency
TPC 18. AD8047 Harmonic Distortion vs. Frequency, G = +1
-6-
REV. A
AD8047/AD8048
-20 -30
HARMONIC DISTORTION (dBc)
0.5
RL = 100 VOUT = 2V p-p
0.4 0.3 0.2
ERROR (%)
-40 -50 -60 -70 -80 -90 THIRD HARMONIC -100 -110 -120 10k 100k 1M FREQUENCY (Hz) 10M 100M SECOND HARMONIC
RL = 100 RF = 0 VOUT = 2V STEP
0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 0 5 10 15 25 30 20 SETTLING TIME (ns) 35 40 45
TPC 19. AD8047 Harmonic Distortion vs. Frequency, G = +1
TPC 22. AD8047 Short-Term Settling Time, G = +1
-25 -30
HARMONIC DISTORTION (dBc)
0.25
f = 200MHz RL = 1k RF = 0 FOR SOIC
0.20 0.15 0.10
ERROR (%)
-35 -40 -45 THIRD HARMONIC -50 -55 SECOND HARMONIC -60 -65 1.5
-0.15 -0.20
RL = 100 RF = 0 VOUT = 2V STEP
0.05 0.00 -0.05 -0.10
2.5
3.5
4.5
5.5
6.5
-0.25
0
2
4
OUTPUT SWING (V p-p)
6 10 12 8 SETTLING TIME ( s)
14
16
18
TPC 20. AD8047 Harmonic Distortion vs. Output Swing, G = +1
TPC 23. AD8047 Long-Term Settling Time, G = +1
0.04
17
DIFF GAIN (%)
0.02
15
0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
INPUT NOISE VOLTAGE (nV/Hz)
13 11 9 7 5 3 10 100 1k FREQUENCY (Hz) 10k 100k
DIFF PHASE (Degrees)
0.04 0.02 0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
TPC 21. AD8047 Differential Gain and Phase Error, G = +2, RL = 150 , RF = 200 , RIN = 200
TPC 24. AD8047 Noise vs. Frequency
REV. A
-7-
AD8047/AD8048
7 6 5 4 RL = 100 RF = RIN = 200 VOUT = 300mV p-p
7 6 5
OUTPUT (dBm)
4 3 2 1 0 -1 -2 -3
RL = 100 RF = RIN = 200 VOUT = 2V p-p
OUTPUT (dBm)
3 2 1 0 -1 -2 -3 1M 10M 100M FREQUENCY (Hz) 1G
1M
10M
100M FREQUENCY (Hz)
1G
TPC 25. AD8048 Small Signal Frequency Response, G = +2
TPC 28. AD8048 Large Signal Frequency Response, G = +2
6.5 6.4 6.3 6.2 RL = 100 RF = RIN = 200 VOUT = 300mV p-p
1 0 -1 RL = 100 RF = RIN = 200 VOUT = 300mV p-p
OUTPUT (dBm)
6.1 6.0 5.9 5.8 5.7 5.6 5.5 1M 10M 100M 1G FREQUENCY (Hz)
OUTPUT (dBm)
-2 -3 -4 -5 -6 -7 -8 -9 1M
10M
100M FREQUENCY (Hz)
1G
TPC 26. AD8048 0.1 dB Flatness, G = +2
TPC 29. AD8048 Small Signal Frequency Response, G = -1
90 80 70 PHASE 60 50
100 80 60 40 20 0 -20 RL = 100 -40 -60 -80 -100 1k 10k 100k 1M 10M FREQUENCY (Hz) 100M -120 1G
-20 -30
HARMONIC DISTORTION (dBc)
-40 -50 -60 -70 -80 -90 -100 -110 -120 10k
RL = 1k VOUT = 2V p-p
40 30 20 10 0 -10 -20
PHASE (Degrees)
GAIN (dB)
SECOND HARMONIC
THIRD HARMONIC
100k
1M FREQUENCY (Hz)
10M
100M
TPC 27. AD8048 Open-Loop Gain and Phase Margin vs. Frequency
TPC 30. AD8048 Harmonic Distortion vs. Frequency, G = +2
-8-
REV. A
AD8047/AD8048
-20 -30 RL = 100 VOUT = 2V p-p
0.5 0.4 0.3 0.2
ERROR (%)
HARMONIC DISTORTION (dBc)
-40 -50 -60 -70 -80 -90 -100 -110 -120 10k 100k 1M FREQUENCY (Hz) 10M 100M THIRD HARMONIC SECOND HARMONIC
RL = 100 RF = 200 VOUT = 2V STEP
0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 0 5 10 15 20 25 30 35 40 45
SETTLING TIME (ns)
TPC 31. AD8048 Harmonic Distortion vs. Frequency, G = +2
TPC 34. AD8048 Short-Term Settling Time, G = +2
-15 -20
HARMONIC DISTORTION (dBc)
0.25
-25 -30 -35 -40 -45 -50
f = 20MHz RL = 1k RF = 200
0.20
THIRD HARMONIC
0.15 0.10
RL = 100 RF = 200 VOUT = 2V STEP
ERROR (%) SECOND HARMONIC 1.5 2.5 3.5 4.5 5.5 6.5
0.05 0.0 -0.05 -0.10 -0.15 -0.20 -0.25 0 2 4 6 10 12 8 SETTLING TIME ( s) 14 16 18
-55 -60 -65 -70
OUTPUT SWING (V p-p)
TPC 32. AD8048 Harmonic Distortion vs. Output Swing, G = +2
TPC 35. AD8048 Long-Term Settling Time 2 V Step, G = +2
0.04
17
DIFF GAIN (%)
0.02 0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
15
INPUT NOISE VOLTAGE (nV/Hz)
13 11 9 7 5 3
DIFF PHASE (Degrees)
0.04 0.02 0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
10
100
1k FREQUENCY (Hz)
10k
100k
TPC 33. AD8048 Differential Gain and Phase Error, G = +2, RL = 150 , RF = 200 , RIN = 200
TPC 36. AD8048 Noise vs. Frequency
REV. A
-9-
AD8047/AD8048
100 90 80
CMRR (dB)
100
VCM = 1V RL = 100
90 80 70 60 50 40 30 20 100k
VCM = 1V RL = 100
CMRR (dB)
70 60 50 40 30 20 100k
1M
10M FREQUENCY (Hz)
100M
1G
1M
10M FREQUENCY (Hz)
100M
1G
TPC 37. AD8047 CMRR vs. Frequency
TPC 40. AD8048 CMRR vs. Frequency
100
100
10
10
ROUT ( )
1
ROUT ( )
1
0.1
0.1
0.01 10k
100k
1M
10M
100M
1G
0.01 10k
100k
1M
10M
100M
1G
FREQUENCY (Hz)
FREQUENCY (Hz)
TPC 38. AD8047 Output Resistance vs. Frequency, G = +1
TPC 41. AD8048 Output Resistance vs. Frequency, G = +2
90 80 70 60 -PSRR
PSRR (dB)
90 80 -PSRR
+PSRR
70 +PSRR 60 50 40 30 20 10
PSRR (dB)
50 40 30 20 10 0 10k
100k
1M
10M
100M
1G
0 3k 10k 100k 1M 100M 500M FREQUENCY (Hz)
FREQUENCY (Hz)
TPC 39. AD8047 PSRR vs. Frequency
TPC 42. AD8048 PSRR vs. Frequency, G = +2
-10-
REV. A
AD8047/AD8048
4.1 3.9 +VOUT 3.7 -VOUT RL = 1k
82.0 AD8047 81.0 83.0
OUTPUT SWING (V)
3.5 3.3 +VOUT 3.1 -VOUT 2.9 RL = 150 CMRR (-dB)
80.0 AD8048 79.0 78.0
2.7 +VOUT 2.5 2.3 -60 -VOUT -40 -20 RL = 50
77.0 76.0 -60
0 20 40 60 80 100 JUNCTION TEMPERATURE ( C)
120
140
-40
-20
0
20
40
60
80
100
120
140
JUNCTION TEMPERATURE ( C)
TPC 43. AD8047/AD8048 Output Swing vs. Temperature
TPC 46. AD8047/AD8048 CMRR vs. Temperature
2600 2400 AD8048
SUPPLY CURRENT (mA)
8.0 AD8048 7.5 6V 7.0 6V AD8048 6.0 5V 5.5 5V 5.0 4.5 -60 AD8047 AD8047
OPEN-LOOP GAIN (V/V)
2200 2000 1800 1600 1400 1200 1000 -60
6.5
AD8047
-40
-20
0
20
40
60
80
100
120
140
-40
-20
0
20
40
60
80
100
120
140
JUNCTION TEMPERATURE ( C)
JUNCTION TEMPERATURE ( C)
TPC 44. AD8047/AD8048 Open-Loop Gain vs. Temperature
TPC 47. AD8047/AD8048 Supply Current vs. Temperature
94 92 90 88 +PSRR AD8048
900 800
INPUT OFFSET VOLTAGE ( V)
700 600
AD8048
PSRR (-dB)
86 84 82 +PSRR 80 78 -PSRR 76 -60 -40 -20 0 20 40 60 80 100 120 140 AD8047 AD8047 -PSRR AD8048
AD8047 500 400 300 200 100 -60
-40
-20
JUNCTION TEMPERATURE ( C)
0 20 40 60 80 100 JUNCTION TEMPERATURE ( C)
120
140
TPC 45. AD8047/AD8048 PSRR vs. Temperature
TPC 48. AD8047/AD8048 Input Offset Voltage vs. Temperature
REV. A
-11-
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
For general voltage gain applications, the amplifier bandwidth can be closely estimated as O f 3 dB R 2 1+ F RG 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, TPCs 13 and 25). As a general rule, capacitor CF will not be required if NG (RF RG ) x CI 4 O where NG is the Noise Gain (1 + RF/RG) of the circuit. For most voltage gain applications, this should be the case.
RF
The value of the feedback resistor is critical for optimum performance on the AD8047 and AD8048. For maximum flatness at a gain of 2, RF and RG should be set to 200 for the AD8048. When the AD8047 is configured as a unity gain follower, RF should be set to 0 (no feedback resistor should be used) for the plastic DIP and 66.5 for the SOIC.
G = 1+ VIN RTERM 2 RF RG 3 7 0.1 F 6 0.1 F VOUT +VS 10 F
CF
AD8047/ AD8048
4
II
RG -VS 10 F RF
CI
AD8047
VOUT
Figure 3. Noninverting Operation
+VS RF RG 3 7 10 F
Figure 5. Transimpedance Configuration
Pulse Response
G= -
0.1 F 6 0.1 F VOUT
AD8047/ AD8048
2 4
VIN RTERM
RG
-VS
10 F RF
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/s) comparable 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
Figure 4. Inverting Operation
When the AD8047 is used in the transimpedance (I to V) mode, such as in photodiode detection, the values of RF and diode capacitance (CI) are usually known. Generally, the value of RF selected will be in the k range, and a shunt capacitor (CF) across RF will be required to maintain good amplifier stability. The value of CF required to maintain optimal flatness (<1 dB peaking) and settling time can be estimated as
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, VO 1.8 V p-p) on the AD8047 and the 250 V-MHz product must be observed on the AD8048.
Power Supply Bypassing
CF (2 O CI RF - 1)/O RF
[
2
2
]
1/2
where O is equal to the unity gain bandwidth product of the amplifier in rad/sec, and CI is the equivalent total input capacitance at the inverting input. Typically, O = 800 x 106 rad/sec (see Open-Loop Frequency Response curve, TPC 15). As an example, choosing RF = 10 k and CI = 5 pF requires CF to be 1.1 pF (Note: CI includes both source and parasitic circuit capacitance). The bandwidth of the amplifier can be estimated using the CF calculated as f 3 dB 1.6 2R F CF
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 F) will be required to provide the best settling time and lowest distortion. A parallel combination of at least 4.7 F, and between 0.1 F and 0.01 F, is recommended. Some brands of electrolytic capacitors will require a small series damping resistor 4.7 for optimum results.
Driving Capacitive Loads
The AD8047/AD8048 have excellent cap load drive capability for high speed op amps, as shown in Figures 7 and 9. However, when driving cap loads greater than 25 pF, the best frequency response is obtained by the addition of a small series resistance. -12- REV. A
AD8047/AD8048
It is worth noting that the frequency response of the circuit when driving large capacitive loads will be dominated by the passive roll-off of RSERIES and CL.
RF
margin (65), low noise current (1.0 pA/Hz), and slew rate (1000 V/s) give higher performance capabilities to these applications 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
AD8047
RSERIES RL 1k CL
Figure 6. Driving Capacitive Loads
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.
200 +VS 200 10 F 0.1 F 2 75 CABLE VIN 3 75 -VS 7 75 CABLE VOUT 75
AD8047/ AD8048
4
75 6 0.1 F 10 F
500mV
5ns
Figure 7. AD8047 Large Signal Transient Response; VO = 2 V p-p, G = +1, RF = 0 , RSERIES = 0 , CL = 27 pF
Active Filters
RF
Figure 10. Video Line Driver
RIN
AD8048
RSERIES RL 1k CL
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 10 times the bandwidth of the filter if problems due to phase shift of the amplifier are to be avoided. Figure 11 is an example of a 20 MHz low-pass multiple feedback active filter using an AD8048.
C1 50pF R3 78.7 C2 100pF 1 2 7
Figure 8. Driving Capacitive Loads
R4 154 R1 154
+5V
10 F 0.1 F
500mV
5ns
VIN
AD8048
3 5 4
6 0.1 F
VOUT
Figure 9. AD8048 Large Signal Transient Response; VO = 2 V p-p, G = +2, RF = RIN = 200 , RSERIES = 0 , CL = 27 pF
APPLICATIONS
100 -5V
10 F
Figure 11. Active Filter Circuit
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 REV. A -13-
AD8047/AD8048
Choose FO = Cutoff Frequency = 20 MHz = Damping Ratio = 1/Q = 2 H = Absolute Value of Circuit Gain = -R4 = 1 R1 Then,
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. 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 12). 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 F to 10 F) tantalum electrolytic capacitor should be connected in parallel, though not necessarily so close, to the 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 or 75 and be properly terminated at each end.
k = 2 FO C1 C2 = 4 C1(H +1) 2 R1 = 2 HK R3 = 2 K (H +1)
R4 = 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 12 is an example of an AD8047 used as an input driver for an AD872A, a 12-bit, 10 MSPS A/D converter.
+5V DIGITAL +5V ANALOG DVDD DGND AVDD DRVDD AGND DRGND 10 F CLK 0.1 F 2 ANALOG IN 3 7 22 23 21 20 19 18 17 16 15 14 13 12 11 10 9 8 24 49.9 0.1 F CLOCK INPUT 7 6 0.1 F +5V DIGITAL 10
4 +5V ANALOG 0.1 F
5
AD872A
OTR MSB BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 BIT8 BIT9 BIT10 BIT11 BIT12 AGND AVSS 25 0.1 F
AD8047
4
6 0.1 F
1
VINA
10 F -5V ANALOG 0.1 F
2 VINB 27 REF GND
DIGITAL OUTPUT
28 REF IN 26 1F REF OUT AVSS 3 0.1 F
-5V ANALOG
Figure 12. AD8047 Used as Driver for an AD872A, a 12-Bit, 10 MSPS A/D Converter
-14-
REV. A
AD8047/AD8048
OUTLINE DIMENSIONS 8-Lead Plastic Dual In-Line Package [PDIP] (N-8)
Dimensions shown in inches and (millimeters)
0.375 (9.53) 0.365 (9.27) 0.355 (9.02)
8 5
1
4
0.295 (7.49) 0.285 (7.24) 0.275 (6.98) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.015 (0.38) MIN SEATING PLANE 0.060 (1.52) 0.050 (1.27) 0.045 (1.14)
0.100 (2.54) BSC 0.180 (4.57) MAX 0.150 (3.81) 0.130 (3.30) 0.110 (2.79) 0.022 (0.56) 0.018 (0.46) 0.014 (0.36)
0.150 (3.81) 0.135 (3.43) 0.120 (3.05)
0.015 (0.38) 0.010 (0.25) 0.008 (0.20)
COMPLIANT TO JEDEC STANDARDS MO-095AA CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
8-Lead Standard Small Outline Package [SOIC] (R-8)
Dimensions shown in millimeters and (inches)
5.00 (0.1968) 4.80 (0.1890)
8 5 4
4.00 (0.1574) 3.80 (0.1497)
1
6.20 (0.2440) 5.80 (0.2284)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY SEATING 0.10 PLANE
1.75 (0.0688) 1.35 (0.0532) 8 0.25 (0.0098) 0 0.17 (0.0067)
0.50 (0.0196) 0.25 (0.0099)
45
0.51 (0.0201) 0.31 (0.0122)
1.27 (0.0500) 0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-012AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN
REV. A
-15-
AD8047/AD8048 Revision History
Location 7/03--Data Sheet changed from REV. 0 to REV. A. Page
Renumbered Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal Updated ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
C01061-0-7/03(A)
Deleted Evaluation Board Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal
-16-
REV. A

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