AD8047ARZ-REEL7

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 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 FUNCTIONAL BLOCK DIAGRAM 8-Pin Plastic PDIP (N) and SOIC (R) Packages AD8047/ AD8048 8 NC 2 7 +VS +INPUT 3 6 OUTPUT –V S 4 5 NC NC 1 –INPUT (TOP VIEW) NC = NO CONNECT 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-lead PDIP and SOIC packages. 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, 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 © 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 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) (VS = 5 V, RLOAD = 100 , AV = 1 (AD8047), AV = 2 (AD8048), unless otherwise noted.) Conditions Min VOUT ≤ 0.4 V p-p VOUT = 2 V p-p VOUT = 300 mV p-p AD8047, RF = 0 Ω; AD8048, RF = 200 Ω VOUT = 4 V Step VOUT = 0.5 V Step VOUT = 4 V Step 170 100 AD8047A Typ Max 475 250 130 35 750 1.1 4.3 Unit 180 135 260 160 MHz MHz 50 1000 1.2 3.2 MHz V/µs ns ns 740 VOUT = 2 V Step VOUT = 2 V Step 13 30 13 30 ns ns 2 V p-p; 20 MHz RL = 1 kΩ 2 V p-p; 20 MHz RL = 1 kΩ f = 100 kHz f = 100 kHz –54 –64 –60 –61 5.2 1.0 –48 –60 –56 –65 3.8 1.0 dBc dBc dBc dBc nV/√Hz pA/√Hz 0.1 MHz to 10 MHz RL = 150 Ω, G = +2 RL = 150 Ω, G = +2 16 0.02 0.03 11 0.01 0.02 µV rms % Degree DC PERFORMANCE2, RL = 150 Ω Input Offset Voltage3 1 TMIN to TMAX ±5 1 Offset Voltage Drift Input Bias Current TMIN to TMAX Input Offset Current Common-Mode Rejection Ratio Open-Loop Gain AD8048A Min Typ Max 0.5 TMIN to TMAX VCM = ± 2.5 V VOUT = ± 2.5 V TMIN to TMAX 74 58 54 INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Common-Mode Voltage Range OUTPUT CHARACTERISTICS Output Voltage Range, RL = 150 Ω Output Current Output Resistance Short-Circuit Current POWER SUPPLY Operating Range Quiescent Current 1 ±5 1 3.5 6.5 2 3 80 62 0.5 74 65 56 3 4 3.5 6.5 2 3 80 68 mV mV µV/°C µA µA µA µA dB dB dB 500 1.5 ± 3.4 500 1.5 ± 3.4 kΩ pF V ± 2.8 ± 3.0 50 0.2 130 ± 2.8 ± 3.0 50 0.2 130 V mA Ω mA ± 3.0 ± 5.0 ± 6.0 5.8 6.6 7.5 78 ± 3.0 ± 5.0 ± 6.0 5.9 6.6 7.5 72 78 V mA mA dB TMIN to TMAX Power Supply Rejection Ratio 3 4 72 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. –2– REV. A AD8047/AD8048 ABSOLUTE MAXIMUM RATINGS 1 MAXIMUM POWER DISSIPATION Supply Voltage, (+VS) – (–VS) . . . . . . . . . . . . . . . . . . . . 12.6 V Voltage Swing × 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) . . . . . . . –65°C to +125°C Operating Temperature Range (A Grade) . . . –40°C to +85°C Lead Temperature Range (Soldering 10 sec) . . . . . . . . . 300°C 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. 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 = 90°C/W; 8-Lead SOIC Package, ␪JA = 140°C/W 2.0 MAXIMUM POWER DISSIPATION (W) 8-PIN PDIP PACKAGE METALLIZATION PHOTOS Dimensions shown in inches and (mm) Connect Substrate to –V S. AD8047 +VS TJ = +150C 1.5 1.0 8-PIN SOIC PACKAGE 0.5 0 –50 –40 –30 –20 –10 0 10 20 30 40 50 60 AMBIENT TEMPERATURE (C) 0.045 (1.14) 70 80 90 Figure 2. Plot of Maximum Power Dissipation vs. Temperature VOUT –IN ORDERING GUIDE –VS +IN 0.044 (1.13) AD8048 +VS 0.045 (1.14) VOUT Model Temperature Range Package Description Package Option* AD8047AN AD8047AR AD8047AR-REEL AD8047AR-REEL7 AD8048AN AD8048AR AD8048AR-REEL AD8048AR-REEL7 –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C PDIP SOIC SOIC SOIC PDIP SOIC SOIC SOIC N-8 R-8 R-8 R-8 N-8 R-8 R-8 R-8 *N = PDIP, R= SOIC –IN –VS +IN 0.044 (1.13) 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 PULSE GENERATOR 10
F +VS TR/TF = 500ps 0.1
F PULSE GENERATOR 2 TR/TF = 500ps 3 VOUT 6 0.1
F 4 RT = 49.9 2 VIN AD8047 VIN 0.1
F RIN 7 3 RL = 100 4 RL = 100 10
F –VS TPC 1. AD8047 Noninverting Configuration, G = +1 TPC 4. AD8047 Inverting Configuration, G = –1 5ns 1V TPC 2. AD8047 Large Signal Transient Response; VO = 4 V p-p, G = +1 100mV VOUT 6 0.1
F 100 –VS 1V 7 AD8047 RT = 66.5 10
F 10
F +VS 5ns TPC 5. AD8047 Large Signal Transient Response; VO = 4 V p-p, G = –1, RF = RIN = 200 Ω 100mV 5ns TPC 3. AD8047 Small Signal Transient Response; VO = 400 mV p-p, G = +1 5ns TPC 6. AD8047 Small Signal Transient Response; VO = 400 mV p-p, G = –1, RF = RIN = 200 Ω –4– REV. A AD8047/AD8048 RF PULSE GENERATOR 10
F +VS TR/TF = 500ps PULSE GENERATOR 2 2 VIN VOUT 6 3 4 RL = 100 RL = 100 –VS TPC 7. AD8048 Noninverting Configuration, G = +2 TPC 10. AD8048 Inverting Configuration, G= –1 1V 5ns TPC 8. AD8048 Large Signal Transient Response; VO = 4 V p-p, G = +2, RF = RIN = 200 Ω 5ns TPC 11. AD8048 Large Signal Transient Response; VO = 4 V p-p, G = –1, RF = RIN = 200 Ω 100mV 5ns TPC 9. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = +2, RF = RIN = 200 Ω REV. A 4 10
F –VS 100mV VOUT 6 0.1
F RS = 100 10
F 1V 7 AD8048 RT = 66.5 0.1
F RT = 49.9 10
F 0.1
F RIN 7 AD8048 3 +VS TR/TF = 500ps 0.1
F RIN VIN RF 5ns TPC 12. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = –1, RF = RIN = 200 Ω –5– AD8047/AD8048 1 1 0 0 –1 –1 RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p –3 –2 OUTPUT (dBm) OUTPUT (dBm) –2 –4 –5 –3 –4 –5 –6 –6 –7 –7 –8 –8 –9 1M 10M 100M RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 2V p-p –9 1M 1G 10M FREQUENCY (Hz) TPC 13. AD8047 Small Signal Frequency Response, G = +1 1 0 0 RL = 100 RF = 0 FOR DIP RF = 66.5 FOR SOIC VOUT = 300mV p-p –1 –2 OUTPUT (dBm) OUTPUT (dBm) –0.2 –0.3 –0.4 –0.5 –4 –5 –6 –0.7 –7 –0.8 –8 10M 100M RL = 100 RF = RF = 200 VOUT = 300mV p-p –3 –0.6 –0.9 1M –9 1M 1G 10M FREQUENCY (Hz) 100 60 80 PHASE MARGIN 20 30 GAIN 0 –20 10 –40 0 RL = 100 –40 1k 10k 100k 1M 10M 100M –70 SECOND HARMONIC –80 THIRD HARMONIC –100 –80 –30 –60 –90 –60 –20 RL = 1k VOUT = 2V p-p –50 OUTPUT (dBm) 40 PHASE MARGIN (Degrees) GAIN (dB) –20 –30 60 40 –10 1G TPC 17. AD8047 Small Signal Frequency Response, G = –1 70 20 100M FREQUENCY (Hz) TPC 14. AD8047 0.1 dB Flatness, G = +1 50 1G TPC 16. AD8047 Large Signal Frequency Response, G = +1 0.1 –0.1 100M FREQUENCY (Hz) –110 –100 1G –120 10k FREQUENCY (Hz) 100k 1M 10M 100M FREQUENCY (Hz) 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 0.5 –20 RL = 100 VOUT = 2V p-p –40 0.3 –50 0.2 –60 –70 RL = 100 RF = 0 VOUT = 2V STEP 0.4 ERROR (%) HARMONIC DISTORTION (dBc) –30 SECOND HARMONIC –80 0.1 0.0 –0.1 –0.2 –90 THIRD HARMONIC –0.3 –100 –110 –0.4 –120 10k –0.5 100k 10M 1M 100M 0 5 10 FREQUENCY (Hz) –25 0.15 0.10 –40 ERROR (%) HARMONIC DISTORTION (dBc) 45 RL = 100 RF = 0 VOUT = 2V STEP 0.20 –35 –45 THIRD HARMONIC –50 0.05 0.00 –0.05 –0.10 –55 –0.15 SECOND HARMONIC –0.20 –65 1.5 2.5 3.5 4.5 5.5 –0.25 6.5 0 2 4 OUTPUT SWING (V p-p) TPC 20. AD8047 Harmonic Distortion vs. Output Swing, G = +1 6 10 12 8 SETTLING TIME (
s) 14 16 18 TPC 23. AD8047 Long-Term Settling Time, G = +1 0.04 17 0.02 15 INPUT NOISE VOLTAGE (nV/√Hz) DIFF GAIN (%) 40 0.25 f = 200MHz RL = 1k RF = 0 FOR SOIC –60 0.00 –0.02 –0.04 1st DIFF PHASE (Degrees) 35 TPC 22. AD8047 Short-Term Settling Time, G = +1 TPC 19. AD8047 Harmonic Distortion vs. Frequency, G = +1 –30 15 25 30 20 SETTLING TIME (ns) 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 0.04 0.02 0.00 13 11 9 7 5 –0.02 –0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 3 10th 11th 10 100 1k 10k FREQUENCY (Hz) TPC 21. AD8047 Differential Gain and Phase Error, G = +2, RL = 150 Ω, RF = 200 Ω, RIN = 200 Ω REV. A TPC 24. AD8047 Noise vs. Frequency –7– 100k AD8047/AD8048 7 7 6 6 RL = 100 RF = RIN = 200 VOUT = 300mV p-p OUTPUT (dBm) 4 5 OUTPUT (dBm) 5 3 2 1 4 3 2 1 0 0 –1 –1 –2 –2 –3 –3 1M 10M 100M FREQUENCY (Hz) 1M 1G 10M 1G TPC 28. AD8048 Large Signal Frequency Response, G = +2 6.5 1 6.4 0 RL = 100 RF = RIN = 200 VOUT = 300mV p-p 6.3 –1 OUTPUT (dBm) 6.2 6.1 6.0 5.9 –2 –4 –5 –6 5.7 –7 5.6 –8 1M 10M 100M RL = 100 RF = RIN = 200 VOUT = 300mV p-p –3 5.8 5.5 –9 1M 1G 10M FREQUENCY (Hz) TPC 26. AD8048 0.1 dB Flatness, G = +2 100 –20 80 80 –30 70 60 HARMONIC DISTORTION (dBc) 90 40 50 20 40 0 –20 RL = 100 20 –40 PHASE (Degrees) 60 30 –60 10 –80 0 –10 –100 –20 –120 1G 1k 10k 100k 1M 10M FREQUENCY (Hz) 100M 100M FREQUENCY (Hz) 1G TPC 29. AD8048 Small Signal Frequency Response, G = –1 PHASE GAIN (dB) 100M FREQUENCY (Hz) TPC 25. AD8048 Small Signal Frequency Response, G = +2 OUTPUT (dBm) RL = 100 RF = RIN = 200 VOUT = 2V p-p –40 RL = 1k VOUT = 2V p-p –50 –60 –70 SECOND HARMONIC –80 –90 THIRD HARMONIC –100 –110 –120 10k 100k 1M FREQUENCY (Hz) 10M 100M TPC 30. AD8048 Harmonic Distortion vs. Frequency, G = +2 TPC 27. AD8048 Open-Loop Gain and Phase Margin vs. Frequency –8– REV. A AD8047/AD8048 0.5 –20 RL = 100 VOUT = 2V p-p 0.4 –40 0.3 –50 0.2 –60 0.1 –70 ERROR (%) HARMONIC DISTORTION (dBc) –30 SECOND HARMONIC –80 0.0 –0.1 THIRD HARMONIC –90 –0.2 –100 –0.3 –110 –0.4 –0.5 –120 10k 100k 10M 1M FREQUENCY (Hz) 100M 0 5 10 25 30 35 40 0.20 f = 20MHz RL = 1k RF = 200 –25 –30 RL = 100 RF = 200 VOUT = 2V STEP 0.15 THIRD HARMONIC 0.10 ERROR (%) –35 –40 –45 0.05 0.0 –0.05 –50 SECOND HARMONIC –0.10 –55 –0.15 –60 –0.20 –65 –70 1.5 2.5 3.5 4.5 5.5 –0.25 6.5 0 2 4 OUTPUT SWING (V p-p) TPC 32. AD8048 Harmonic Distortion vs. Output Swing, G = +2 6 10 12 8 SETTLING TIME (
s) 14 16 18 TPC 35. AD8048 Long-Term Settling Time 2 V Step, G = +2 17 0.04 0.02 INPUT NOISE VOLTAGE (nV/√Hz) 15 0.00 –0.02 –0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 0.04 0.02 0.00 13 11 9 7 5 –0.02 3 –0.04 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 10 100 1k 10k FREQUENCY (Hz) TPC 33. AD8048 Differential Gain and Phase Error, G = +2, RL = 150 Ω, RF = 200 Ω, RIN = 200 Ω REV. A 45 0.25 –20 DIFF GAIN (%) 20 TPC 34. AD8048 Short-Term Settling Time, G = +2 –15 DIFF PHASE (Degrees) 15 SETTLING TIME (ns) TPC 31. AD8048 Harmonic Distortion vs. Frequency, G = +2 HARMONIC DISTORTION (dBc) RL = 100 RF = 200 VOUT = 2V STEP TPC 36. AD8048 Noise vs. Frequency –9– 100k AD8047/AD8048 100 100 VCM = 1V RL = 100 80 80 70 70 60 60 50 50 40 40 30 30 20 100k 1M 10M 100M VCM = 1V RL = 100 90 CMRR (dB) CMRR (dB) 90 20 100k 1G 1M FREQUENCY (Hz) 100M 1G TPC 40. AD8048 CMRR vs. Frequency 100 100 10 10 ROUT () ROUT () TPC 37. AD8047 CMRR vs. Frequency 10M FREQUENCY (Hz) 1 0.1 1 0.1 0.01 10k 100k 1M 10M 100M 0.01 10k 1G 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 90 80 80 –PSRR +PSRR 70 +PSRR –PSRR 60 PSRR (dB) PSRR (dB) 60 70 50 40 50 40 30 30 20 20 10 10 0 10k 100k 1M 10M 100M 0 1G 3k FREQUENCY (Hz) 10k 100k 1M 100M 500M FREQUENCY (Hz) TPC 39. AD8047 PSRR vs. Frequency TPC 42. AD8048 PSRR vs. Frequency, G = +2 –10– REV. A AD8047/AD8048 4.1 83.0 3.9 RL = 1k +VOUT 82.0 AD8047 3.7 OUTPUT SWING (V) –VOUT  81.0 CMRR (–dB) 3.5 3.3 +VOUT RL = 150 3.1 –VOUT  80.0 AD8048 79.0 2.9 78.0 2.7 +VOUT 2.5 2.3 –60 –40 –20 77.0 RL = 50 –VOUT  0 20 40 60 80 100 JUNCTION TEMPERATURE (C) 120 76.0 –60 140 –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 8.0 2400 7.5 AD8048 SUPPLY CURRENT (mA) OPEN-LOOP GAIN (V/V) AD8048 2200 2000 1800 1600 1400 6V 6.5 AD8048 6.0 5V 5.0 –40 –20 0 20 40 60 80 100 120 4.5 –60 140 –40 –20 JUNCTION TEMPERATURE (C) 92 800 PSRR (–dB) INPUT OFFSET VOLTAGE (
V) 900 +PSRR 88 AD8048 86 84 –PSRR AD8048 +PSRR AD8047 82 80 78 –PSRR –20 0 20 40 60 80 100 120 700 60 80 100 120 140 AD8048 600 AD8047 500 400 300 100 –60 140 JUNCTION TEMPERATURE (C) TPC 45. AD8047/AD8048 PSRR vs. Temperature REV. A 40 200 AD8047 –40 20 TPC 47. AD8047/AD8048 Supply Current vs. Temperature 94 90 0 JUNCTION TEMPERATURE (C) TPC 44. AD8047/AD8048 Open-Loop Gain vs. Temperature 76 –60 AD8047 5V 5.5 AD8047 1200 1000 –60 AD8047 6V 7.0 –40 –20 0 20 40 60 80 100 JUNCTION TEMPERATURE (C) 120 140 TPC 48. AD8047/AD8048 Input Offset Voltage vs. Temperature –11– AD8047/AD8048 For general voltage gain applications, the amplifier bandwidth can be closely estimated as ωO f 3 dB ≅   R  2π 1+  F     RG   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). 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). 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 Ω for the AD8048. When the AD8047 is configured as a unity gain follower, RF should be set to 0 Ω (no feedback resistor should be used) for the plastic DIP and 66.5 Ω for the SOIC. G = 1+ where NG is the Noise Gain (1 + RF/RG) of the circuit. For most voltage gain applications, this should be the case. RF 10
F +VS RF As a general rule, capacitor CF will not be required if NG (RF
RG ) × CI ≤ 4 ωO RG VIN 7 3 RTERM 2 CF 0.1
F AD8047/ AD8048 VOUT 6 0.1
F 4 II RG –VS CI AD8047 VOUT 10
F RF Figure 5. Transimpedance Configuration Figure 3. Noninverting Operation Pulse Response G= – RF 7 3 RG RG VIN 0.1
F AD8047/ AD8048 2 RTERM 4 –VS 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) 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. 10
F +VS VOUT 6 0.1
F 10
F RF 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 kΩ 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 (