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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/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
250 MHz, General Purpose Voltage Feedback Op Amps AD8047/AD8048
FUNCTIONAL BLOCK DIAGRAM 8-Pin Plastic Mini-DIP (N), Cerdip (Q) and SO (R) Packages
NC -INPUT +INPUT -V S
1 2 3 4
8 7 6
NC +VS OUTPUT NC
AD8047/48
(Top View) NC = NO CONNECT
5
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-pin plastic DIP 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 and 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. 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. (c) 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
AD8047/AD8048-SPECIFICATIONS
ELECTRICAL CHARACTERISTICS (V = 5 V; R
S LOAD
= 100 ; AV = 1 (AD8047); AV = 2 (AD8048), unless otherwise noted)
AD8047A Min Typ Max AD8048A Min Typ Max Units
Parameter DYNAMIC PERFORMANCE Bandwidth (-3 dB) Small Signal Large Signal1 Bandwidth for 0.1 dB Flatness Slew Rate, Average +/- Rise/Fall Time Settling Time To 0.1% To 0.01% HARMONIC/NOISE PERFORMANCE 2nd Harmonic Distortion 3rd 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
Conditions
VOUT 0.4 V p-p VOUT = 2 V p-p VOUT = 300 mV p-p 8047, RF = 0 ; 8048, 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 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
180 135
260 160 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 MHz 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
475
740
TMIN -TMAX Offset Voltage Drift Input Bias Current TMIN -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 -TMAX Power Supply Rejection Ratio
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.
5 1 0.5
TMIN -TMAX VCM = 2.5 V VOUT = 2.5 V TMIN -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. 0
AD8047/AD8048
ABSOLUTE MAXIMUM RATINGS 1 MAXIMUM POWER DISSIPATION
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6 V Voltage Swing x Bandwidth Product (AD8047) . . . 180 V - MHz (AD8048) . . . 250 V - MHz Internal Power Dissipation2 Plastic Package (N) . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Watts Small Outline Package (R) . . . . . . . . . . . . . . . . . . . 0.9 Watts 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, 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: JA = 90C/Watt 8-Pin SOIC Package: JA = 140C/Watt
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 MINI-DIP PACKAGE TJ = +150C
MAXIMUM POWER DISSIPATION - Watts
1.5
1.0
METALIZATION PHOTOS
Dimensions shown in inches and (mm). Connect Substrate to -V S.
8-PIN SOIC PACKAGE 0.5
AD8047
+VS
0 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 AMBIENT TEMPERATURE - C
70
80
90
0.045 (1.14) VOUT
Figure 2. Plot of Maximum Power Dissipation vs. Temperature
ORDERING GUIDE
-IN -VS 0.044 (1.13) +IN
Model AD8047AN AD8047AR AD8047-EB AD8048AN AD8048AR AD8048-EB
Temperature Range -40C to +85C -40C to +85C
Package Package Description Option* Plastic DIP SOIC Evaluation Board Plastic DIP SOIC Evaluation Board N-8 R-8
AD8048
+VS
-40C to +85C -40C to +85C
N-8 R-8
0.045 -OUT (1.14)
*N = Plastic DIP; R= SOIC (Small Outline Integrated Circuit)
-IN
+IN 0.044 (1.13)
-VS
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.
WARNING!
ESD SENSITIVE DEVICE
REV. 0
-3-
AD8047/AD8048 AD8047-Typical Characteristics
+VS 10F 0.1F PULSE GENERATOR TR /TF = 500ps VIN RT = 49.9 -VS
-V S PULSE GENERATOR TR/TF = 500ps RIN 2 RT = 66.5 3 100 +VS RF 10F 0.1F 7
2
7
AD8047
3 4
6 0.1F
VOUT RL = 100
VIN
AD8047
4
6 0.1F
VOUT RL = 100
10F
10F
Figure 3. Noninverting Configuration, G = +1
Figure 6. Inverting Configuration, G = -1
1V
5ns
1V
5ns
Figure 4. Large Signal Transient Response; VO = 4 V p-p, G = +1
Figure 7. Large Signal Transient Response; VO = 4 V p-p, G = -1, RF = RIN = 200
100mV
5ns
100mV
5ns
Figure 5. Small Signal Transient Response; VO = 400 mV p-p, G = +1
Figure 8. Small Signal Transient Response; VO = 400 mV p-p, G = -1, RF = RIN = 200
-4-
REV. 0
AD8047/AD8048 AD8048-Typical Characteristics
RF PULSE GENERATOR TR/T F = 500ps RIN 2 7 +V S 10F 0.1F
RF PULSE GENERATOR TR/TF = 500ps RIN VIN 2 RT = 66.5 3 RS = 100
6 0.1F VOUT RL = 100
+VS
10F 0.1F
7
AD8048
VIN RT = 49.9 -VS 3 4
AD8048
4
6 0.1F
VOUT RL = 100
10F
10F -VS
Figure 9. Noninverting Configuration, G = +2
Figure 12. Inverting Configuration, G= -1
1V
5ns
1V
5ns
Figure 10. Large Signal Transient Response; VO = 4 V p-p, G = +2, RF = RIN = 200
Figure 13. Large Signal Transient Response; VO = 4 V p-p, G = -1, RF = RIN = 200
100mV
5ns
100mV
5ns
Figure 11. Small Signal Transient Response; VO = 400 mV p-p, G = +2, RF = RIN = 200
Figure 14. Small Signal Transient Response; VO = 400 mV p-p, G = -1, RF = RIN = 200
REV. 0
-5-
AD8047/AD8048 AD8047-Typical Characteristics
1 0 -1 -2
OUTPUT - dBm
1 0 -1 RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 2V p-p
-3 -4 -5 -6 -7 -8 -9 1M
OUTPUT - dBm
RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p
-2 -3 -4 -5 -6 -7 -8
10M
100M
1G
-9 1M
10M
100M
1G
FREQUENCY - Hz
FREQUENCY - Hz
Figure 15. AD8047 Small Signal Frequency Response G = +1
Figure 18. AD8047 Large Signal Frequency Response, G = +1
0.1 0 -0.1 -0.2
OUTPUT - dBm
1 0 -1
RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p
-2
OUTPUT - dBm
-0.3 -0.4 -0.5 -0.6 -0.7 -0.8 -0.9 1M
-3 -4 -5 -6 -7 -8
RL = 100 RF = RIN = 200 VOUT = 300mV p-p
10M
100M
1G
-9 1M
10M
100M
1G
FREQUENCY - Hz
FREQUENCY - Hz
Figure 16. AD8047 0.1 dB Flatness, G = +1
Figure 19. AD8047 Small Signal Frequency Response, G = -1
70 60 50 40
GAIN - dB
100 80
-20 -30
PHASE MARGIN - Degrees
PHASE MARGIN
60
-40 -50
OUTPUT - dBm
RL = 1k VOUT = 2V p-p
40 20 GAIN 0 -20 -40 RL = 100 -60 -80 -100 1G
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 3RD HARMONIC 2ND HARMONIC
Figure 17. AD8047 Open-Loop Gain and Phase Margin vs. Frequency
Figure 20. AD8047 Harmonic Distortion vs. Frequency, G = +1
-6-
REV. 0
AD8047/AD8048
-20
0.5
-30
HARMONIC DISTORTION - dBc
RL = 100 VOUT = 2V p-p
0.4 0.3 0.2
-40 -50
ERROR - %
RL = 100 RF = 0 VOUT = 2V STEP
-60 -70 -80 -90 3RD HARMONIC -100 -110 -120 10k 100k 1M FREQUENCY - Hz 10M 100M 2ND HARMONIC
0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5 0 5 10 20 15 25 30 SETTLING TIME - ns 35 40 45
Figure 21. AD8047 Harmonic Distortion vs. Frequency, G = +1
Figure 24. AD8047 Short-Term Settling Time, G = +1
-25 -30 HARMONIC DISTORTION - dBc -35 -40 -45 3RD HARMONIC -50 -55 2ND HARMONIC -60 -65 1.6 f = 20MHz RL = 1k RF = 0
0.25 0.20 0.15 0.10 RL = 100 RF = 0 VOUT = 2V STEP
ERROR - %
0.05 0.00 -0.05 -0.10 -0.15 -0.20 -0.25
2.5
3.5 4.5 OUTPUT SWING - V p-p
5.5
6.5
0
2
4
8 6 10 12 SETTLING TIME - s
14
16
18
Figure 22. AD8047 Harmonic Distortion vs. Output Swing, G = +1
Figure 25. AD8047 Long-Term Settling Time, G = +1
0.04
DIFF GAIN - %
17
0.02 0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
INPUT NOISE VOLTAGE - nV/Hz
15 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
Figure 23. AD8047 Differential Gain and Phase Error, G = +2, RL = 150 , RF = 200 , RIN = 200
Figure 26. AD8047 Noise vs. Frequency
REV. 0
-7-
AD8047/AD8048 AD8048-Typical Characteristics
7 6 5 4
OUTPUT - dBm
7 6
3 2 1 0 -1 -2 -3 1M
OUTPUT - dBm
RL = 100 RF = RIN = 200 VOUT = 300mV p-p
5 4 3 2 1 0 -1 -2 -3
RL = 100 RF = RIN = 200 VOUT = 2V p-p
10M 100M FREQUENCY - Hz
1G
1M
10M
100M
1G
FREQUENCY - Hz
Figure 27. AD8048 Small Signal Frequency Response, G = +2
Figure 30. AD8048 Large Signal Frequency Response, G = +2
6.5 6.4 6.3 6.2
OUTPUT - dBm
1
RL = 100 RF = RIN = 200 VOUT = 300mV p-p
0 -1 -2 RL = 100 RF = RIN = 200 VOUT = 300mV p-p
6.1 6.0 5.9 5.8 5.7 5.6 5.5 1M 10M 100M 1G FREQUENCY - Hz
OUTPUT - dBm
-3 -4 -5 -6 -7 -8 -9 1M
10M
100M FREQUENCY - Hz
1G
Figure 28. AD8048 0.1 dB Flatness, G = +2
Figure 31. AD8048 Small Signal Frequency Response, G = -1
90 80 70 PHASE 60 50 GAIN - dB 40 30 20 10 0 -10 -20 1k 10k 100k 1M 10M FREQUENCY - Hz 100M RL = 100
100 80 60 40 20 0 -20 -40 -60 -80 -100 -120 1G PHASE - Degrees
HARMONIC DISTORTION - dBc
-20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 10k 100k 1M FREQUENCY - Hz 10M 100M 3RD HARMONIC 2ND HARMONIC RL = 1k VOUT = 2V p-p
Figure 29. AD8048 Open-Loop Gain and Phase Margin vs. Frequency
Figure 32. AD8048 Harmonic Distortion vs. Frequency, G = +2
-8-
REV. 0
AD8047/AD8048
-20 -30
HARMONIC DISTORTION - dBc
0.5 RL = 100 VOUT = 2V p-p 0.4 0.3 0.2 RL = 100 RF = 200 VOUT = 2V STEP
-40 -50 -60 -70 -80 -90 -100 -110 -120 10k 100k 1M FREQUENCY - Hz 10M 100M 3RD HARMONIC 2ND HARMONIC
ERROR - %
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
Figure 33. AD8048 Harmonic Distortion vs. Frequency, G = +2
-15 -20
HARMONIC DISTORTION - dBc
Figure 36. AD8048 Short-Term Settling Time, G = +2
0.25
f = 20MHz RL = 1k RF = 200
0.20
3RD HARMONIC
-25 -30 -35 -40 -45 -50 -55 -60 -65 -70 1.5
0.15 0.10
ERROR - %
RL = 100 RF = 200 VOUT = 2V STEP
0.05 0.0 -0.05 -0.10 -0.15 -0.20
2ND HARMONIC
2.5
3.5 4.5 OUTPUT SWING - Volts p-p
5.5
6.5
-0.25
0
2
4
8 6 10 12 SETTLING TIME - s
14
16
18
Figure 34. AD8048 Harmonic Distortion vs. Output Swing, G = +2
Figure 37. AD8048 Long-Term Settling Time 2 V Step, G = +2
0.04
DIFF GAIN - %
17
0.02 0.00 -0.02 -0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th
INPUT NOISE VOLTAGE - nV/Hz 15 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
Figure 35. AD8048 Differential Gain and Phase Error, G = +2, RL = 150 , RF = 200 , RIN = 200
Figure 38. AD8048 Noise vs. Frequency
REV. 0
-9-
AD8047/AD8048-Typical Characteristics
100 90 80 70 60 50 40 30 20 100k VCM = 1V RL = 100
100 90 80 70 60 50 40 30
1M 10M FREQUENCY - Hz 100M 1G
VCM = 1V RL = 100
CMRR - dB
CMRR - dB
20 100k
1M
10M FREQUENCY - Hz
100M
1G
Figure 39. AD8047 CMRR vs. Frequency
Figure 42. AD8048 CMRR vs. Frequency
100
100
10
10
ROUT -
ROUT -
1
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
Figure 40. AD8047 Output Resistance vs. Frequency, G = +1
Figure 43. AD8048 Output Resistance vs. Frequency, G = +2
90 80 70 60 -PSRR PSRR - dB +PSRR
90 80 70 +PSRR 60 50 40 30 20 10 0 -PSRR
PSRR - dB
50 40 30 20 10 0 10k
100k
1M
10M
100M
1G
3k
10k
100k
1M
100M
500M
FREQUENCY - Hz
FREQUENCY - Hz
Figure 41. AD8047 PSRR vs. Frequency
Figure 44. AD8048 PSRR vs. Frequency, G = +2
-10-
REV. 0
AD8047/AD8048
4.1 3.9 +VOUT 3.7 RL = 1k
83.0
82.0 AD8047 81.0
CMRR - -dB
OUTPUT SWING - Volts
-VOUT 3.5 3.3 +VOUT 3.1 2.9 -VOUT RL = 150
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
Figure 45. AD8047/AD8048 Output Swing vs. Temperature
Figure 48. AD8047/AD8048 CMRR vs. Temperature
2600 2400 AD8048 SUPPLY CURRENT - mA 2200
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
2000 1800 1600 1400 1200 1000 -60
6.5
AD8047
-40
-20
0 20 40 60 80 100 JUNCTION TEMPERATURE - C
120
140
-40
-20
0 20 40 60 80 100 JUNCTION TEMPERATURE - C
120
140
Figure 46. AD8047/AD8048 Open-Loop Gain vs. Temperature
Figure 49. AD8047/AD8048 Supply Current vs. Temperature
94 92 90 88
PSRR - -dB
900 800
+PSRR AD8048
INPUT OFFSET VOLTAGE - V
700 600
AD8048
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
Figure 47. AD8047/AD8048 PSRR vs. Temperature
Figure 50. AD8047/AD8048 Input Offset Voltage vs. Temperature
REV. 0
-11-
AD8047/AD8048
THEORY OF OPERATION General
For general voltage gain applications, the amplifier bandwidth can be closely estimated as:
f 3 dB O R 2 1+ F RG
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, 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 0.1F VOUT +VS 10F
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 CF will not be required if: (RF RG ) x CI NG 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 CF
AD8047/48 6
4 0.1F
RG
II
-VS 10F RF
CI
AD8047
VOUT
Figure 51. Noninverting Operation
+VS G= - RF RG 3 7 0.1F VOUT 10F
Figure 53. Transimpedance Configuration
Pulse Response
AD8047/48 6
VIN RTERM -VS RF RG 2 4 0.1F
10F
Figure 52. Inverting Operation
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
When the AD8047 is used in the transimpedance (I to V) mode, such as in photodiode detection, the value 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 250 V-MHz product 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, Figure 17). 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 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 -12- REV. 0
AD8047/AD8048
circuit when driving large capacitive loads will be dominated by the passive roll-off of RSERIES and CL.
RF
(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
RSERIES
AD8047
RL 1k CL
Figure 54. 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.
200 200
+VS
10F
0.1F 2 75 CABLE
500mV 5ns
7
AD8047/ AD8048
3 4
75 6 0.1F
75 CABLE VOUT 75
VIN 75
10F
Figure 55. AD8047 Large Signal Transient Response; VO = 2 V p-p, G = +1, RF = 0 , RSERIES = 0 , CL = 27 pF
RF
-VS
Figure 58. Video Line Driver
Active Filters
RIN
RSERIES
AD8048
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 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.
C1 50pF R3 78.7 2 C2 100pF 100 3 4 1 7 +5V 10F
Figure 56. Driving Capacitive Loads
R4 154 VIN
500mV 5ns
R1 154
0.1F
AD8048
5
6 0.1F
VOUT
Figure 57. AD8048 Large Signal Transient Response; VO = 2 V p-p, G = +2, RF = RIN = 200 , RSERIES = 0 , CL = 27 pF
APPLICATIONS
10F -5V
Figure 59. 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 margin (65), low noise current (1.0 pA/Hz), and slew rate REV. 0
Choose: FO = Cutoff Frequency = 20 MHz = Damping Ratio = 1/Q = 2 -13-
AD8047/AD8048
H = Absolute Value of Circuit Gain = Then:
k = 2 FO C1 C2 = 4 C1(H +1) 2 R1 = 2 HK R3 = 2 K (H +1) R4 = H(R1)
-R4 R1 = 1
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 F-10 F) 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 or 75 and be properly terminated at each end.
Evaluation Board
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
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.
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
+5V ANALOG
+5V DIGITAL
10 DV DD 4 +5V ANALOG 0.1F 5 AGND DRGND 10F CLK DGND AV DD DRV DD 7 6 0.1F +5V DIGITAL
22 23 21 20 19 18 17 16 15 14 13 12 11 10 9 8 24 49.9 0.1F CLOCK INPUT
AD872
1 2 ANALOG IN 3 4 7 0.1F 1
OTR MSB BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 BIT8 BIT9 BIT10 BIT11 BIT12 AGND AV SS 25
AD8047
5
6 0.1F
VINA
2 VINB 27 REF GND
DIGITAL OUTPUT
-5V ANALOG
10F
0.1F 28 REF IN 26 1F REF OUT AV SS 3 0.1F
0.1F
-5V ANALOG
Figure 60. AD8047 Used as Driver for an AD872, a 12-Bit, 10 MSPS A/D Converter
-14-
REV. 0
AD8047/AD8048
RF +V S RO OUT IN RT -VS
-V S +VS OPTIONAL C1 1000pF C2 1000pF C3 0.1F C4 0.1F C5 10F C6 10F
RG
Noninverting Configuration
Supply Bypassing
Figure 61. Noninverting Configurations for Evaluation Boards
Table I.
Component RF RG RO RS RT Small Signal BW (-3 dB)
-1 200 200 49.9 - 66.5 90 MHz
+1 66.5 - 49.9 0 49.9
AD8047 +2 1 k 1 k 49.9 0 49.9
+10 1 k 110 49.9 0 49.9 10 MHz
+101 1 k 10 49.9 0 49.9 1 MHz
-1 200 200 49.9 - 66.5
+2
AD8048 +10 1 k 110 49.9 0 49.9
+101 1 k 10 49.9 0 49.9 2 MHz
200 200 49.9 0 49.9
260 MHz 95 MHz
250 MHz 250 MHz 22 MHz
SOIC (R) INVERTER
SOIC (R) NONINVERTER
Figure 62. Evaluation Board Silkscreen (Top)
SOIC (R) INVERTER
SOIC (R) NONINVERTER
Figure 63. Board Layout (Solder Side)
REV. 0
-15-
AD8047/AD8048
SOIC (R) INVERTER
SOIC (R) NONINVERTER
Figure 64. Board Layout (Component Side)
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Plastic DIP (N Package)
8 PIN 1 1 4 5 0.280 (7.11) 0.240 (6.10)
0.430 (10.92) 0.348 (8.84) 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93) 0.060 (1.52) 0.015 (0.38)
0.325 (8.25) 0.300 (7.62) 0.195 (4.95) 0.115 (2.93)
0.130 (3.30) MIN SEATING PLANE
0.015 (0.381) 0.008 (0.204)
0.022 (0.558) 0.014 (0.356)
0.100 (2.54) BSC
0.070 (1.77) 0.045 (1.15)
8-Pin Plastic SOIC (R Package)
0.150 (3.81)
8 0.244 (6.20) 0.228 (5.79) PIN 1 1
5 0.157 (3.99) 0.150 (3.81) 4 0.020 (0.051) x 45 CHAMF 0.190 (4.82) 0.170 (4.32) 8 0 10 0 0.098 (0.2482) 0.075 (0.1905) 0.030 (0.76) 0.018 (0.46)
0.197 (5.01) 0.189 (4.80) 0.010 (0.25) 0.004 (0.10) 0.050 (1.27) BSC 0.102 (2.59) 0.094 (2.39)
0.090 (2.29)
0.019 (0.48) 0.014 (0.36)
-16-
REV. 0
PRINTED IN U.S.A.
C1995-10-1/95

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