AD8048

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 (–40°C to +85°C) 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 R EV. 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 ( 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 Ω Input Offset Voltage3 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 VOUT = 2 V Step VOUT = 2 V Step 2 V p-p; 20 MHz R L = 1 kΩ 2 V p-p; 20 MHz R L = 1 kΩ f = 100 kHz f = 100 kHz 0.1 MHz to 10 MHz RL = 150 Ω, G = +2 RL = 150 Ω, 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/µs ns ns ns ns dBc dBc dBc dBc nV/√Hz pA/√Hz µV rms % Degree mV mV µV/°C µA µA µA µA dB dB dB kΩ pF V V mA Ω 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 Ω 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– R EV. 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 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 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 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 –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 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. R EV. 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 Ω 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 Ω –4– R EV. 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 Ω TPC 11. AD8048 Large Signal Transient Response; VO = 4 V p-p, G = –1, RF = RIN = 200 Ω 100mV 5ns 100mV 5ns TPC 9. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = +2, RF = RIN = 200 Ω TPC 12. AD8048 Small Signal Transient Response; VO = 400 mV p-p, G = –1, RF = RIN = 200 Ω R EV. 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– R EV. 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 Ω, RF = 200 Ω, RIN = 200 Ω TPC 24. AD8047 Noise vs. Frequency R EV. 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– R EV. 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 Ω, RF = 200 Ω, RIN = 200 Ω TPC 36. AD8048 Noise vs. Frequency R EV. 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– R EV. 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 R EV. 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 ωO f 3 dB ≅   R  2π 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 ) × CI ≤ 4 ωO 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 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+ 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/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. 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 (