General-Purpose, Low Cost, DC-Coupled VGA AD8337 FEATURES APPLICATIONS Gain trim PET scanners High performance AGC systems I/Q signal processing Video Industrial and medical ultrasound Radar receivers FUNCTIONAL BLOCK DIAGRAM VPOS 8 AD8337 GAIN CONTROL INTERFACE GAIN 7 PREAMP (PrA) INPP 3 + INPN 4 – 18dB 1 VOUT EIGHT SECTIONS VCOM 2 5 6 PRAO VNEG 05575-001 Low noise Voltage noise = 2.2 nV/√Hz Current noise = 4.8 pA/√Hz (positive input) Wide bandwidth (−3 dB) = 280 MHz Nominal gain range: 0 dB to 24 dB (preamp gain = 6 dB) Gain scaling: 19.7 dB/V DC-coupled Single-ended input and output High speed uncommitted op amp input Supplies: +5 V, ±2.5 V, or ±5 V Low power: 78 mW with ±2.5 V supplies Figure 1. GENERAL DESCRIPTION The AD8337 is a low noise, single-ended, linear-in-dB, generalpurpose variable gain amplifier (VGA) usable at frequencies from dc to 100 MHz; the −3 dB bandwidth is 280 MHz. Excellent bandwidth uniformity across the entire gain range and low output-referred noise makes the AD8337 ideal for gain trim applications and for driving high speed analog-todigital converters (ADCs). Excellent dc characteristics combined with high speed make the AD8337 particularly suited for industrial ultrasound, PET scanners, and video applications. Dual-supply operation enables gain control of negative-going pulses, such as those generated by photodiodes or photomultiplier tubes. The AD8337 uses the popular and versatile X-AMP® architecture, exclusively from Analog Devices, Inc., with a gain range of 24 dB. The gain control interface provides precise linear-in-dB scaling of 19.7 dB/V, referenced to VCOM. The AD8337 includes an uncommitted operational currentfeedback preamplifier (PrA) that operates in inverting or noninverting configurations. Using external resistors, the device can be configured for gains of 6 dB or greater. The AD8337 is characterized by a noninverting PrA gain of 2× using two external 100 Ω resistors. The attenuator has a range of 24 dB, and the output amplifier has a fixed gain of 8× (18.06 dB). The lowest nominal gain range is 0 dB to 24 dB and can be shifted up or down by adjusting the preamp gain. Multiple AD8337 devices can be connected in series for larger gain ranges, interstage filtering to suppress noise and distortion, and nulling offset voltages. The operating temperature range of the AD8337 is −40°C to +85°C, and is available in an 8-lead, 3 mm × 3 mm LFCSP. Rev. C 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. Specifications subject to change without notice. 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 owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2005–2008 Analog Devices, Inc. All rights reserved. AD8337 TABLE OF CONTENTS Features .............................................................................................. 1 Single-Supply Operation and AC Coupling ........................... 19 Applications ....................................................................................... 1 Noise ............................................................................................ 19 Functional Block Diagram .............................................................. 1 Applications Information .............................................................. 20 General Description ......................................................................... 1 Preamplifier Connections ......................................................... 20 Revision History ............................................................................... 2 Driving Capacitive Loads .......................................................... 20 Specifications..................................................................................... 3 Gain Control Considerations ................................................... 21 Absolute Maximum Ratings............................................................ 5 Thermal Considerations............................................................ 22 ESD Caution .................................................................................. 5 PSI (Ψ) ......................................................................................... 22 Pin Configuration and Function Descriptions ............................. 6 Board Layout ............................................................................... 22 Typical Performance Characteristics ............................................. 7 Evaluation Boards........................................................................... 23 Test Circuits ..................................................................................... 14 Circuit Options ........................................................................... 24 Theory of Operation ...................................................................... 18 Output Protection ...................................................................... 24 Overview...................................................................................... 18 Measurement Setup.................................................................... 25 Preamplifier ................................................................................. 18 Board Layout Considerations ................................................... 25 VGA.............................................................................................. 18 Bill of Materials ........................................................................... 27 Gain Control ............................................................................... 18 Outline Dimensions ....................................................................... 29 Output Stage ................................................................................ 19 Ordering Guide .......................................................................... 29 Attenuator .................................................................................... 19 REVISION HISTORY 9/08—Rev. B to Rev. C Changes to Table 1 ............................................................................ 3 Added Exposed Pad Note to Figure 2 and Table 3 ....................... 6 Changes to Figure 49 ...................................................................... 14 Changes to Evaluation Boards Section ........................................ 23 Changes to Circuit Options Section............................................. 24 Changes to Output Protection Section ........................................ 24 Changes to Measurement Setup Section ..................................... 25 Changes to Board Layout Considerations Section ..................... 25 Changes to Bill of Materials Section ............................................ 27 Updated Outline Dimensions, Changes to Ordering Guide .... 29 6/06—Rev. 0 to Rev. A Updated Format .................................................................. Universal Changes to Table 3.............................................................................6 Changes to Figure 22, Figure 25, and Figure 26 ......................... 10 Changes to Figure 39 and Figure 40............................................. 13 Changes to Figure 74 and Figure 75............................................. 23 Updated Outline Dimensions ....................................................... 25 Changes to Ordering Guide .......................................................... 25 9/05—Revision 0: Initial Version 2/07—Rev. A to Rev. B Changes to Figure 30, Figure 31, and Figure 32 ......................... 11 Changes to Single-Supply Operation and AC Coupling Section ..................................................................... 19 Moved Noise Section to Page ........................................................ 19 Changes to Ordering Guide .......................................................... 24 Rev. C | Page 2 of 32 AD8337 SPECIFICATIONS VS = ±2.5 V, TA = 25°C, PrA gain = +2, VCOM = GND, f = 10 MHz, CL = 5 pF, RL = 500 Ω, including a 20 Ω snubbing resistor, unless otherwise specified. Table 1. Parameter GENERAL PARAMETERS −3 dB Small Signal Bandwidth −3 dB Large Signal Bandwidth Slew Rate Input Voltage Noise Input Current Noise Noise Figure Output-Referred Noise Output Impedance Output Signal Range Output Offset Voltage DYNAMIC PERFORMANCE Harmonic Distortion HD2 HD3 HD2 HD3 HD2 HD3 Input 1 dB Compression Point Two-Tone Intermodulation Distortion (IMD3) Output Third-Order Intercept Overload Recovery Group Delay Variation Conditions VOUT = 10 mV p-p VOUT = 1 V p-p VOUT = 2 V p-p VOUT = 1 V p-p f = 10 MHz f = 10 MHz VGAIN = 0.7 V, RS = 50 Ω, unterminated VGAIN = 0.7 V, RS = 50 Ω, shunt terminated with 50 Ω VGAIN = 0.7 V (gain = 24 dB) VGAIN = −0.7 V (gain = 0 dB) DC to 10 MHz RL ≥ 500 Ω, VS = ±2.5 V, +5 V RL ≥ 500 Ω, VS = ±5 V VGAIN = 0.7 V (gain = 24 dB) VGAIN = 0 V, VOUT = 1 V p-p f = 1 MHz f = 10 MHz f = 45 MHz VGAIN = −0.7 V, f = 10 MHz (preamp limited) VGAIN = +0.7 V, f = 10 MHz (VGA limited) VGAIN = 0 V, VOUT = 1 V p-p, f1 = 10 MHz, f2 = 11 MHz VGAIN = 0 V, VOUT = 1 V p-p, f1 = 45 MHz, f2 = 46 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 10 MHz, f2 = 11 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 45 MHz, f2 = 46 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 10 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 45 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 10 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 45 MHz VGAIN = 0.75 V, VIN = 50 mV p-p to 500 mV p-p 1 MHz < f < 100 MHz, full gain range Rev. C | Page 3 of 32 Min Typ −25 280 100 625 490 2.15 4.8 8.5 14 34 21 1 VCOM ± 1.3 VCOM ± 2.4 ±5 −72 −66 −62 −63 −58 −56 8.2 −9.4 −71 −57 −58 −45 34 28 35 26 50 ±1 Max Unit +25 MHz MHz V/μs V/μs nV/√Hz pA/√Hz dB dB nV/√Hz nV/√Hz Ω V V mV dBc dBc dBc dBc dBc dBc dBm dBm dBc dBc dBc dBc dBm dBm dBm dBm ns ns AD8337 Parameter DYNAMIC PERFORMANCE Harmonic Distortion HD2 HD3 HD2 HD3 HD2 HD3 Input 1 dB Compression Point Two-Tone Intermodulation Distortion (IMD3) Output Third-Order Intercept Overload Recovery ACCURACY Absolute Gain Error GAIN CONTROL INTERFACE Gain Scaling Factor Gain Range Intercept Input Voltage (VGAIN) Range Input Impedance Bias Current Response Time POWER SUPPLY Supply Voltage VS = ±2.5 V Quiescent Current Power Dissipation PSRR VS = ±5 V Quiescent Current Power Dissipation PSRR Conditions VS = ±5 V VGAIN = 0 V, VOUT = 1 V p-p f = 1 MHz Min f = 35 MHz VGAIN = −0.7 V, f = 10 MHz VGAIN = +0.7 V, f = 10 MHz VGAIN = 0 V, VOUT = 1 V p-p, f1 = 10 MHz, f2 = 11 MHz VGAIN = 0 V, VOUT = 1 V p-p, f1 = 45 MHz, f2 = 46 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 10 MHz, f2 = 11 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 45 MHz, f2 = 46 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 10 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 45 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 10 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 45 MHz VGAIN = 0.7 V, VIN = 0.1 V p-p to 1 V p-p −1.25 −1.0 −1.25 −0.6 V < VGAIN < +0.6 V VGAIN = 0 V No foldover Max −85 −75 −90 −80 −75 −76 14.5 −1.7 −74 −60 −64 −49 35 28 36 28 50 f = 10 MHz −0.7 V < VGAIN < −0.6 V −0.6 V < VGAIN < −0.5 V −0.5 V < VGAIN < +0.5 V 0.5 V < VGAIN < 0.6 V 0.6 V < VGAIN < 0.7 V Typ 0.7 to 3.5 ±0.35 ±0.25 ±0.35 −0.7 to −3.5 dBc dBc dBc dBc dBc dBc dBm dBm dBc dBc dBc dBc dBm dBm dBm dBm ns +1.25 +1.0 +1.25 dB dB dB dB dB +VS dB/V dB dB V MΩ μA ns 19.7 24 12.65 −VS 70 0.3 200 −0.7 V < VGAIN < +0.7 V 24 dB gain change Unit VPOS to VNEG (dual- or single-supply operation) 4.5 5 10 V Each supply (VPOS and VNEG) No signal, VPOS to VNEG = 5 V VGAIN = 0.7 V, f = 1 MHz 10.5 15.5 78 −40 23.5 mA mW dB Each supply (VPOS and VNEG) No signal, VPOS to VNEG = 10 V VGAIN = 0.7 V, f = 1 MHz 13.5 18.5 185 −40 25.5 mA mW dB Rev. C | Page 4 of 32 AD8337 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Voltage Supply Voltage (VPOS, VNEG) Input Voltage (INPx) GAIN Voltage Power Dissipation (Exposed Pad Soldered to PCB) Temperature Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering, 60 sec) Thermal Data, 4-Layer JEDEC Board No Air Flow Exposed Pad Soldered to PCB θJA θJB θJC ΨJT ΨJB 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. Rating ±6 V VPOS, VNEG VPOS, VNEG 866 mW −40°C to +85°C −65°C to +150°C 300°C ESD CAUTION 75.4°C/W 47.5°C/W 17.9°C/W 2.2°C/W 46.2°C/W Rev. C | Page 5 of 32 AD8337 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 1 2 AD8337 INPP 3 INPN 4 TOP VIEW 6 (Not to Scale) 8 VPOS 7 GAIN 5 VNEG PRAO 05575-002 PIN 1 VOUT VCOM NOTES 1. FOR BEST THERMAL PERFORMANCE, EXPOSED PAD MUST BE SOLDERED TO PCB. Figure 2. Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 2 Mnemonic VOUT VCOM 3 4 5 6 7 8 EP INPP INPN PRAO VNEG GAIN VPOS Exposed Pad Description VGA Output. Common Ground When Using Plus and Minus Supply Voltages. For single-supply operation, provide half the positive supply voltage at the VPOS pin to VCOM pin. Positive Input to Preamplifier. Negative Input to Preamplifier. Preamplifier Output. Negative Supply (−VPOS for Dual-Supply; GND for Single-Supply). Gain Control Input Centered at VCOM. Positive Supply. For best thermal performance, exposed pad must be soldered to PCB. Rev. C | Page 6 of 32 AD8337 TYPICAL PERFORMANCE CHARACTERISTICS VS = ±2.5 V, TA = 25°C, RL = 500 Ω, including a 20 Ω snubbing resistor, f = 10 MHz, CL = 2 pF, VIN = 10 mV p-p, noninverting configuration, unless otherwise noted. 60 30 500 UNITS VGAIN = –0.4V +85°C +25°C –40°C 25 VGAIN = 0V 50 VGAIN = +0.4V 40 % OF UNITS GAIN (dB) 20 15 10 30 20 5 05575-003 0.5 0.4 0.3 0.2 0 800 0.1 600 0 400 –0.1 200 0 VGAIN (mV) –0.2 –200 –0.3 –400 –0.4 –600 –0.5 –5 –800 05575-006 10 0 GAIN ERROR (dB) Figure 6. Gain Error Histogram for Three Values of VGAIN Figure 3. Gain vs. VGAIN at Three Temperatures (See Figure 44) 50 2.0 +85°C +25°C –40°C 1.5 500 UNITS –0.4V ≤ VGAIN ≤ +0.4V 40 0.5 % OF UNITS 0 –0.5 –1.0 30 20 10 –2.0 –800 05575-004 –1.5 –600 –400 –200 0 200 400 600 05575-007 GAIN ERROR (dB) 1.0 0 19.3 800 19.4 19.5 VGAIN (mV) 1.5 1.0 20.1 12.9 13.0 500 UNITS 40 % OF UNITS 0.5 0 –0.5 30 20 –1.0 –2.0 –800 –600 –400 0 –200 200 VGAIN (mV) 400 600 05575-008 10 –1.5 05575-005 GAIN ERROR (dB) 50 f = 1MHz f = 10MHz f = 70MHz f = 100MHz f = 150MHz RELATIVE TO BEST FIT LINE FOR 10MHz 20.0 Figure 7. Gain Scaling Histogram Figure 4. Gain Error vs. VGAIN at Three Temperatures (See Figure 44) 2.0 19.6 19.7 19.8 19.9 GAIN SCALING (dB/V) 0 12.2 800 Figure 5. Gain Error vs. VGAIN at Five Frequencies (See Figure 44) 12.3 12.4 12.5 12.6 12.7 INTERCEPT (dB) 12.8 Figure 8. Intercept Histogram Rev. C | Page 7 of 32 AD8337 30 30 eIN = 10mV p-p 25 20 VGAIN = +0.7 25 VGAIN = +0.5 20 VGAIN = 0V GAIN (dB) VGAIN = 0 10 VGAIN = –0.2 5 VGAIN = –0.7 –5 100k 1M 10 5 VGAIN = –0.5 0 15 0 10M 100M –5 100k 500M CL CL CL CL = 47pF = 22pF = 10pF = 0pF 05575-012 15 05575-009 GAIN (dB) VGAIN = +0.2 1M 10 VGAIN = +0.7 15 VGAIN = +0.5 GAIN (dB) GAIN (dB) VGAIN = 0 5 500M VS = ±2.5V VS = ±5V 8 VGAIN = +0.2 10 100M Figure 12. Frequency Response for Three Values of CL with a 20 Ω Snubbing Resistor (See Figure 45) Figure 9. Frequency Response for Various Values of VGAIN (See Figure 45) 20 10M FREQUENCY (Hz) FREQUENCY (Hz) VGAIN = –0.2 0 VGAIN = –0.5 6 4 –5 VGAIN = –0.7 1M 05575-010 –15 100k 10M 100M 0 100k 500M FREQUENCY (Hz) 20 15 GROUP DELAY (ns) 20 15 10 5 CL = 47pF CL = 22pF CL = 10pF CL = 0pF 500M 1M 10M 100M 10 5 0 –5 05575-011 GAIN (dB) 100M 25 25 –5 100k 10M Figure 13. Frequency Response—Preamp (See Figure 46) VGAIN = 0V eIN = 10mV p-p 0 1M FREQUENCY (Hz) Figure 10. Frequency Response for Various Values of VGAIN—Inverting Input (See Figure 58) 30 05575-013 2 eIN = 10mV p-p –10 1M 500M FREQUENCY (Hz) 05575-014 –10 10M FREQUENCY (Hz) Figure 11. Frequency Response for Three Values of CL (See Figure 45) Figure 14. Group Delay vs. Frequency (See Figure 47) Rev. C | Page 8 of 32 100M AD8337 10 40 +85°C +25°C –40°C VS = ±5V 8 35 4 NOISE (nV/√Hz) 2 0 –2 VS = ±2.5V 30 25 –4 20 –6 –8 –10 –800 –600 05575-015 +85°C +25°C –40°C –400 –200 0 200 400 15 –800 800 600 05575-018 OFFSET VOLTAGE (mV) 6 –600 –400 –200 VGAIN (mV) Figure 15. Offset Voltage vs. VGAIN at Three Temperatures (See Figure 48) 200 400 600 800 Figure 18. Output-Referred Noise vs. VGAIN at Three Temperatures (See Figure 50) 25 80 70 500 UNITS VGAIN = –0.4V 60 VGAIN = +0.4V +85°C +25°C –40°C VGAIN = 0V 20 NOISE (nV/√Hz) % OF UNITS 0 VGAIN (mV) 50 40 30 15 10 20 05575-016 0 –15 –10 –5 0 5 10 15 20 0 –800 25 05575-019 5 10 –600 –400 –200 OUTPUT OFFSET VOLTAGE (mV) Figure 16. Output Offset Voltage Histogram for Three Values of VGAIN 7 VS = ±2.5V VS = ±5V 600 800 VGAIN = 0.7V RFB1 = RFB2 = 100Ω 6 NOISE (nV/√Hz) 5 10 PREAMP GAIN = –1 4 3 PREAMP GAIN = +2 2 1 1 05575-017 IMPEDANCE (Ω) 400 Figure 19. Short-Circuit, Input-Referred Noise at Three Temperatures (See Figure 50) 100 0.1 1M 200 10M 100M 0 100k 500M 1M 10M 100M FREQUENCY (Hz) FREQUENCY (Hz) Figure 17. VGA Output Impedance vs. Frequency (See Figure 49) 05575-020 1k 0 VGAIN (mV) Figure 20. Short-Circuit, Input-Referred Noise vs. Frequency at Maximum Gain—Inverting and Noninverting Preamp Gain = −1 and +2 (See Figure 50) Rev. C | Page 9 of 32 AD8337 –40 INPUT-REFERRED NOISE 1 RS THERMAL NOISE ALONE 10 1 100 –50 –60 –70 –80 1k 0 5 10 15 50Ω SOURCE NOISE FIGURE (dB) 30 25 WITH 50Ω SHUNT TERMINATION AT INPUT UNTERMINATED 15 05575-022 10 –600 –400 –200 0 200 400 600 SECOND-ORDER HARMONIC DISTORTION (dBc) 35 5 –800 35 40 800 –60 –70 –80 –800 1MHz 10MHz 35MHz 100MHz –600 –400 –200 200 0 VGAIN (mV) 400 05575-023 –70 200 400 600 800 1.0k 1.2k 1.4k LOAD RESISTANCE (Ω) 800 1.6k 1.8k –40 –50 –60 –70 –80 –800 2.0k 1MHz 10MHz 35MHz 100MHz 05575-026 –60 THIRD-ORDER HARMONICDISTORTION (dBc) –50 0 600 Figure 25. HD2 vs. VGAIN at Four Frequencies (See Figure 52) HD3 VS = ±2.5V HD3 VS = ±5V HD2 VS = ±2.5V HD2 VS = ±5V VOUT = 1V p-p VGAIN = 0V 50 –50 –30 –40 45 –40 Figure 22. Noise Figure vs. VGAIN (See Figure 51) HARMONIC DISTORTION (dBc) 30 –30 VGAIN (mV) –80 25 Figure 24. Harmonic Distortion vs. Load Capacitance (See Figure 52) Figure 21. Input-Referred Noise vs. RS (See Figure 61) 20 20 LOAD CAPACITANCE (pF) SOURCE RESISTANCE (Ω) 05575-025 0.1 HD3 HD2 05575-024 HARMONIC DISTORTION (dBc) f = 10MHz, VGAIN = 0.7V 05575-021 INPUT-REFERRED NOISE (nV/√Hz) 10 –600 –400 –200 200 0 VGAIN (mV) 400 Figure 26. HD3 vs. VGAIN at Four Frequencies (See Figure 52) Figure 23. Harmonic Distortion vs. RL and Supply Voltage (See Figure 52) Rev. C | Page 10 of 32 600 800 50 OUTPUT-REFERRED IP3 (dBm) LIMITED BY MAXIMUM PREAMP OUTPUT SWING –50 –60 –70 –80 –90 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 40 30 20 10 VOUT = 1V p-p TONES SEPARATED BY 100kHz 0 –800 –600 –400 –200 0 200 VGAIN (mV) 800 Figure 27. HD2 vs. VGAIN for Three Levels of Output Voltage (See Figure 52) –40 LIMITED BY MAXIMUM PREAMP OUTPUT SWING –50 –60 –70 –80 –90 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 15 –60 –70 –600 –400 –200 0 200 VGAIN (mV) 400 600 VS = ±2.5V VS = ±5V 800 PREAMP LIMITED 10 5 0 –5 –10 05575-029 IMD3 (dBc) –50 VS = ±2.5V VS = ±5V 1MHz 10MHz 45MHz 70MHz 100MHz 10 20 –40 10M 20 Figure 31. Output-Referred IP3 (OIP3) vs. VGAIN, VS = ±5 V at Five Frequencies (See Figure 64) VOUT = 1V p-p VGAIN = 0V TONES SEPARATED BY 100kHz –80 1M 30 0 –800 800 INPUT-REFERRED P1dB (dBm) –30 800 40 VS = ±5V VOUT = 1V p-p TONES SEPARATED BY 100kHz Figure 28. HD3 vs. VGAIN for Three Levels of Output Voltage (See Figure 52) –20 600 50 OUTPUT-REFERRED IP3 (dBm) VOUT = 2V p-p VOUT = 1V p-p VOUT = 0.5V p-p 400 Figure 30. Output-Referred IP3 (OIP3) vs. VGAIN at Five Frequencies (See Figure 64) 05575-028 THIRD-ORDER HARMONIC DISTORTION (dBc) –30 1MHz 10MHz 45MHz 70MHz 100MHz 05575-031 –40 05575-030 VOUT = 2V p-p VOUT = 1V p-p VOUT = 0.5V p-p –15 –800 100M FREQUENCY (Hz) Figure 29. IMD3 vs. Frequency (See Figure 64) 05575-032 –30 05575-027 SECOND-ORDER HARMONIC DISTORTION (dBc) AD8337 –600 –400 –200 0 200 VGAIN (mV) 400 600 Figure 32. Input-Referred P1dB (IP1dB) vs. VGAIN (See Figure 63) Rev. C | Page 11 of 32 800 AD8337 800 60 6 600 40 4 400 40 20 2 200 20 0 0 –60 –80 –20 –10 0 10 20 30 TIME (ns) 40 50 60 –200 –4 –400 –6 –600 –8 70 0 –60 VS = ±2.5V VGAIN = 0.7V –10 0 10 20 30 TIME (ns) 40 50 60 –80 70 8 800 6 600 40 4 400 40 20 2 200 20 0 0 VGAIN = 0.7V 60 VIN (mV) VOUT (mV) INPUT –2 –20 –40 –200 –4 –400 –6 –600 –10 0 10 20 30 TIME (ns) 40 50 60 –8 70 Figure 34. Small Signal Pulse Response—Inverting Feedback (See Figure 59) 800 0 40 0.4 200 20 0.2 OUTPUT –600 –800 –20 –10 0 10 20 30 TIME (ns) 40 50 60 0 10 20 30 TIME (ns) 40 50 60 –80 70 –0.2 –40 –0.4 –60 –0.6 –80 70 Figure 35. Large Signal Pulse Response (See Figure 53) VOUT 0 –20 05575-035 –400 INPUT (V) 0.6 400 VIN (mV) 60 –200 –10 Figure 37. Large Signal Pulse Response for Three Capacitive Loads, VS = ±5 V (See Figure 53) 600 0 –60 VS = ±5V VGAIN = 0.7V 0.8 0 –40 OUTPUT 80 VGAIN = 0.7V –20 INPUT –800 –20 05575-034 –80 –20 60 0 OUTPUT –60 80 CL = 0pF CL = 10pF CL = 22pF CL = 47pF –0.8 –0.5 05575-038 80 VOUT (mV) –40 OUTPUT Figure 36. Large Signal Pulse Response for Three Capacitive Loads (See Figure 53) Figure 33. Small Signal Pulse Response (See Figure 53) VOUT (mV) –20 INPUT –800 –20 VIN (mV) 0 05575-036 OUTPUT 60 VIN (mV) –40 VIN (mV) –2 INPUT 80 CL = 0pF CL = 10pF CL = 22pF CL = 47pF 05575-037 –20 05575-033 VOUT (mV) VGAIN = 0.7V VOUT (mV) 8 80 VGAIN 0 0.5 1.0 TIME (µs) Figure 38. Gain Response (See Figure 54) Rev. C | Page 12 of 32 1.5 2.0 AD8337 1.5 10 VIN (V) VOUT (V) VGAIN = 0.7V VGAIN = +0.7V, VS = ±2.5V VGAIN = +0.7V, VS = ±5V VGAIN = 0V, VS = ±2.5V VGAIN = 0V, VS = ±5V VGAIN = –0.7V, VS = ±2.5V VGAIN = –0.7V, VS = ±5V 0 1.0 –10 –20 PSRR (dB) (V) 0.5 0 –0.5 –30 –40 –50 –60 –1.0 –0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 05575-042 05575-039 –1.5 –0.3 –70 –80 100k 1.7 1M TIME (µs) Figure 39. Preamp Overdrive Recovery (See Figure 55) 24 1.0 (V) 0.5 0 –0.5 –1.5 –0.3 05575-040 –1.0 –0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 TIME (µs) 0 –10 VGAIN = +0.7V, VS = ±2.5V VGAIN = +0.7V, VS = ±5V VGAIN = 0V, VS = ±2.5V VGAIN = 0V, VS = ±5V VGAIN = –0.7V, VS = ±2.5V VGAIN = –0.7V, VS = ±5V PSRR (dB) –20 –30 –40 –50 05575-041 –60 –70 –80 100k 1M 10M FREQUENCY (Hz) 22 20 18 16 14 12 –50 –30 –10 10 30 50 TEMPERATURE (°C) 70 Figure 43. Quiescent Supply Current vs. Temperature (See Figure 57) Figure 40. VGA Overdrive Recovery (See Figure 56) 10 VS = ±5V VS = ±2.5V 05575-043 VIN (V) VOUT (V) VGAIN = 0.7V 100M Figure 42. PSRR vs. Frequency of Negative Supply (See Figure 60) QUIESCENT SUPPLY CURRENT (mA) 1.5 10M FREQUENCY (Hz) 100M Figure 41. PSRR vs. Frequency of Positive Supply (See Figure 60) Rev. C | Page 13 of 32 90 AD8337 TEST CIRCUITS NETWORK ANALYZER NETWORK ANALYZER OUT OUT IN 50Ω 50Ω IN 50Ω AD8337 49.9Ω AD8337 + PrA – 3 4 50Ω 453Ω 20Ω 453Ω 1 49.9Ω 56.2Ω 5 + PrA – 3 4 20Ω 1 56.2Ω 7 100Ω 05575-044 5 100Ω 05575-047 VGAIN 100Ω 7 100Ω Figure 47. Group Delay Figure 44. Gain and Gain Error vs. VGAIN NETWORK ANALYZER OSCILLOSCOPE FUNCTION GENERATOR OUT IN 50Ω OUT 50Ω 3 4 50Ω VGAIN DIFFERENTIAL FET PROBE AD8337 20Ω + PrA – CH2 50Ω 7 453Ω AD8337 49.9Ω CH1 50Ω 453Ω + PrA – 3 1 4 1 50Ω OPTIONAL POSITIONS FOR CL 100Ω VGAIN 100Ω 5 100Ω 100Ω Figure 45. Frequency Response Figure 48. Offset Voltage NETWORK ANALYZER OUT 05575-048 7 05575-045 5 NETWORK ANALYZER IN IN 50Ω 50Ω CONFIGURE TO MEASURE Z CONVERTED S11 50Ω 0Ω 4 + PrA – 1 5 100Ω 100Ω 20Ω 453Ω 49.9Ω 3 + 4 – 0Ω PrA 1 5 7 NC 453Ω 7 100Ω 05575-046 3 49.9Ω AD8337 NC NC 100Ω NC Figure 49. Output Impedance vs. Frequency Figure 46. Frequency Response—Preamp Rev. C | Page 14 of 32 05575-049 AD8337 AD8337 OSCILLOSCOPE PULSE GENERATOR SPECTRUM ANALYZER POWER SPLITTER OUT CH2 CH1 IN 50Ω 50Ω 50Ω AD8337 0Ω AD8337 + PrA – 3 49.9Ω 4 + PrA – 3 0Ω 4 1 56.2Ω 49.9Ω 5 5 7 100Ω 7 0.7V 100Ω 05575-053 100Ω 05575-050 VGAIN 100Ω Figure 53. Pulse Response Figure 50. Input-Referred and Output-Referred Noise DUAL FUNCTION GENERATOR OSCILLOSCOPE POWER SPLITTER NOISE FIGURE METER NOISE SOURCE DRIVE SINE WAVE INPUT SQUARE WAVE CH2 CH1 50Ω NOISE SOURCE 0Ω AD8337 + PrA – 4 1 5 49.9Ω 20Ω 453Ω + PrA – 3 0Ω 4 NC 1 5 7 100Ω 100Ω 100Ω 05575-051 VGAIN 100Ω Figure 54. Gain Response Figure 51. Noise Figure vs. VGAIN SPECTRUM ANALYZER SIGNAL GENERATOR FUNCTION GENERATOR RL INPUT 05575-054 3 50Ω VGAIN DIFFERENTIAL FET PROBE 7 AD8337 49.9Ω (OR ∞) 20Ω 453Ω 1 OSCILLOSCOPE 50Ω CH2 CH1 OUTPUT LOWPASS FILTER 50Ω NC AD8337 7 49.9Ω 4 AD8337 20Ω + PrA – 3 1 CL 3 49.9Ω 5 4 + PrA – 1 NC 7 100Ω 5 100Ω 100Ω 100Ω Figure 55. Preamp Overdrive Recovery Figure 52. Harmonic Distortion Rev. C | Page 15 of 32 05575-055 VGAIN 05575-052 100Ω AD8337 FUNCTION GENERATOR OSCILLOSCOPE POWER SPLITTER OSCILLOSCOPE PULSE GENERATOR OUTPUT POWER SPLITTER CH2 CH1 50Ω OUT 50Ω CH2 CH1 50Ω 50Ω AD8337 4 1 AD8337 NC 100Ω 5 4 100Ω 20Ω 453Ω + PrA – 3 1 56.2Ω 100Ω 5 7 100Ω 05575-056 100Ω Figure 56. VGA Overdrive Recovery 05575-059 49.9Ω 20Ω 453Ω + PrA – 3 0.7V Figure 59. Pulse Response—Inverting Feedback +SUPPLY TO NETWORK ANALYZER BIAS PORT NETWORK ANALYZER BENCH POWER SUPPLY DMM (+I) OUT 8 BYPASS CAPACITORS REMOVED FOR MEASUREMENT AD8337 3 4 + PrA – DMM (V) 1 7 50Ω VPOS AD8337 + PrA – 3 49.9Ω 5 IN 50Ω 4 1 DIFFERENTIAL FET PROBE 6 100Ω 5 DMM (–I) Figure 60. PSRR SPECTRUM ANALYZER NETWORK ANALYZER IN IN 50Ω 50Ω 50Ω 453Ω AD8337 3 100Ω 4 + PrA – 05575-060 VGAIN 100Ω Figure 57. Supply Current OUT 7 100Ω 05575-057 100Ω AD8337 3 20Ω 1 4 + PrA – 1 100Ω 5 7 7 VGAIN 100Ω Figure 58. Frequency Response—Inverting Feedback VGAIN Figure 61. Input-Referred Noise vs. RS Rev. C | Page 16 of 32 05575-061 100Ω 05575-058 5 100Ω AD8337 NETWORK ANALYZER POWER SWEEP SPECTRUM ANALYZER 22dB OUT IN IN 50Ω 50Ω 50Ω 453Ω AD8337 AD8337 + PrA – 3 + PrA – 1 5 49.9Ω 4 5 7 7 100Ω 0.7V 05575-062 100Ω 100Ω 20Ω 1 VGAIN 100Ω Figure 63. IP1dB vs. VGAIN Figure 62. Short-Circuit Input Noise vs. Frequency SPECTRUM ANALYZER INPUT 50Ω +22dB –6dB SIGNAL GENERATOR –6dB COMBINER –6dB AD8337 453Ω 3 +22dB –6dB 49.9Ω 4 20Ω + PrA – 1 SIGNAL GENERATOR 5 7 100Ω 100Ω Figure 64. IMD and OIP3 Rev. C | Page 17 of 32 VGAIN 05575-063 4 05575-064 3 AD8337 THEORY OF OPERATION VPOS 8 RFB1 = RFB2 = 100Ω INPP 3 RG INPN 4 + 18dB (8x) – 749Ω + ATTENUATOR –24dB TO 0dB – + PrA 6dB – 1 VOUT PRAO RFB2 RFB1 5 GAIN INTERFACE INTERPOLATOR BIAS VCOM 2 6 7 VNEG GAIN 05575-065 107Ω Figure 65. Circuit Block Diagram OVERVIEW VGA The AD8337 is a low noise, single-ended, linear-in-dB, generalpurpose variable gain amplifier (VGA) usable at frequencies up to 100 MHz. It is fabricated using a proprietary Analog Devices dielectrically isolated, complementary bipolar process. The bandwidth is dc to 280 MHz and features low dc offset voltage and an ideal nominal gain range of 0 dB to 24 dB. Requiring about 15.5 mA, the power consumption is only 78 mW from either a single +5 V or a dual ±2.5 V supply. Figure 65 is the circuit block diagram of the AD8337. This X-AMP, with its linear-in-dB gain characteristic architecture, yields the optimum dynamic range for receiver applications. Referring to Figure 65, the signal path consists of a −24 dB variable attenuator followed by a fixed gain amplifier of 18 dB, for a total VGA gain range of −6 dB to +18 dB. With the preamplifier configured for a gain of 6 dB, the composite gain range is 0 dB to 24 dB. The VGA plus preamp, with 6 dB of gain, implements the following exact gain law: PREAMPLIFIER An uncommitted current-feedback op amp included in the AD8337 can be used as a preamplifier to buffer the ladder network attenuator of the X-AMP. As with any op amp, the gain is established using external resistors, and the preamplifier is specified with a noninverting gain of 6 dB (2×) and gain resistor values of 100 Ω. The preamplifier gain can be increased using larger values of RFB2, trading off bandwidth and offset voltage. The value of RFB2 is to be ≥100 Ω because the value and an internal compensation capacitor determine the 3 dB bandwidth, and smaller values can compromise preamplifier stability. Because the AD8337 is dc-coupled, larger preamp gains increase the offset voltage. The offset voltage can be compensated by connecting a resistor between the INPN input and the supply voltage. If the offset is negative, the resistor value connects to the negative supply. For ease of adjustment, a trimmer network can be used. For larger gains, the overall noise is reduced if a low value of RFB1 is selected. For values of RFB1 = 20 Ω and RFB2 = 301 Ω, the preamp gain is 16× (24.1 dB), and the input-referred noise is approximately 1.5 nV/√Hz. For this value of gain, the overall gain range increases by 18 dB; therefore, the gain range is 18 dB to 42 dB. dB ⎡ ⎤ ×V Gain(dB) = ⎢19.7 + ICPT (dB) GAIN ⎥⎦ V ⎣ where the nominal intercept (ICPT) = 12.65 dB. The ICPT increases as the gain of the preamp is increased. For example, if the gain of the preamp is increased by 6 dB, ICPT increases to 18.65 dB. Although the previous equation shows the exact gain law as based on statistical data, a quick estimation of signal levels can be made using the default slope of 20 dB/V for a particular gain setting. For example, the change in gain for a VGAIN change of 0.3 V is 6 dB using a slope of 20 dB/V and 5.91 dB using the exact slope of 19.6 dB/V. This is a difference of only 0.09 dB. GAIN CONTROL The gain control interface provides a high impedance input and is referenced to the VCOM pin (in a single-supply application to midsupply at [VPOS + VNEG]/2 for optimum swing). When dual supplies are used, VCOM is connected to ground. The voltage on the VCOM pin determines the midpoint of the gain range. For a ground referenced design, the VGAIN range is from −0.7 V to +0.7 V with the most linear-in-dB section of the gain control between −0.6 V and +0.6 V. In the center 80% of the VGAIN range, the gain error is typically less than ±0.2 dB. The gain control voltage can be increased or decreased to the positive or negative rails without gain foldover. Rev. C | Page 18 of 32 AD8337 The gain scaling factor (gain slope) is designed for 20 dB/V. This relatively low slope ensures that noise on the GAIN input is not unduly amplified. Because a VGA functions as a multiplier, it is important that the GAIN input does not inadvertently modulate the output signal with unwanted noise. Because of its high input impedance, a simple low-pass filter can be added to the GAIN input to filter unwanted noise. OUTPUT STAGE The output stage is a Class AB, voltage-feedback, complementary emitter-follower with a fixed gain of 18 dB, similar to the preamplifier in speed and bandwidth. Because of the ac-beta roll-off of the output devices and the inherent reduction in feedback beyond the −3 dB bandwidth, the impedance looking into the output pin of the preamp and output stages appears to be inductive (increasing impedance with increasing frequency). The high speed output amplifier used in the AD8337 can drive large currents, but its stability is susceptible to capacitive loading. A small series resistor mitigates the effects of capacitive loading (see the Applications Information section). ATTENUATOR The input resistance of the VGA attenuator is nominally 265 Ω. For example, if the default preamplifier feedback network RFB1 + RFB2 is 200 Ω, the effective preamplifier load is approximately 114 Ω. The attenuator is composed of eight 3.01 dB sections for a total attenuation range of −24.08 dB. Following the attenuator is a fixed gain amplifier with 8× (18.06 dB) gain. Because of this relatively low gain, the output offset is kept well below 20 mV over temperature; the offset is largest at maximum gain when the preamplifier offset is amplified. The VCOM pin defines the common-mode reference for the output, as shown in Figure 65. SINGLE-SUPPLY OPERATION AND AC COUPLING If the AD8337 is to be operated from a single 5 V supply, the bias supply for VCOM must be a very low impedance 2.5 V reference, especially if dc coupling is used. If the device is dccoupled, the VCOM source must be able to handle the preamplifier and VGA dynamic load currents in addition to the bias currents. When ac coupling the preamplifier input, a bias network and bypass capacitor must be connected to the opposite polarity input pin. The bias generator for the VCOM pin must provide the dynamic current to the preamplifier feedback network and the VGA attenuator. For many single 5 V applications, a reference, such as the ADR391, and a good op amp provide an adequate VCOM source if a 2.5 V supply is unavailable. NOISE The total input-referred voltage and current noise of the positive input of the preamplifier are about 2.2 nV/√Hz and 4.8 pA/√Hz. The VGA output-referred noise is about 21 nV/√Hz at low gains. This result is divided by the VGA fixed gain amplifier gain of 8× and results in a voltage noise density of 2.6 nV/√Hz referred to the VGA input. This value includes the noise of the VGA gain setting resistors as well. If this voltage is again divided by the preamp gain of 2, the VGA noise referred all the way to the preamp input is about 1.3 nV/√Hz. From this, it is determined that the preamplifier, including the 100 Ω gain setting resistors, contributes about 1.8 nV/√Hz. The two 100 Ω resistors contribute 1.29 nV/√Hz each at the output of the preamp. With the gain resistor noise subtracted, the preamplifier noise is approximately 1.55 nV/√Hz. Equation 2 shows the calculation that determines the outputreferred noise at maximum gain (24 dB or 16×). where: At is the total gain from preamp input to VGA output. RS is the source resistance. en − PrA is the input-referred voltage noise of the preamp. in − PrA is the current noise of the preamp at the INPP pin. en − RFB1 is the voltage noise of RFB1. en − RFB 2 is the voltage noise of RFB2. en − VGA is the input-referred voltage noise of the VGA (low gain, output-referred noise divided by a fixed gain of 8×). Assuming RS = 0 Ω, RFB1 = RFB2 = 100 Ω, At = 16×, and AVGA = 8×, the noise simplifies to en − out = (1.75 × 16)2 + 2(1.29 × 8)2 + (1.9 × 8)2 = 35 nV Hz (1) Dividing the result by 16 gives the total input-referred noise with a short-circuited input as 2.2 nV/√Hz. When the preamplifier is used in the inverting configuration with the same RFB1 and RFB2 = 100 Ω as previously noted, en − out does not change. However, because the gain dropped by 6 dB, the input-referred noise increases by a factor of 2 to about 4.4 nV/√Hz. The reason for this increase is that the noise gain to the output of the noise generators stays the same, yet the preamp in the inverting configuration has a gain of −1 compared to the +2 in the noninverting configuration; this increases the input-referred noise by 2. R en − out = (enR × At )2 + (en − PrA × At ) 2 + (in − PrA × R ) 2 + (en − R FB1 × FB2 × A ) 2 + (en − R FB2 × A ) 2 + (en − VGA × A )2 S S VGA VGA VGA R FB1 Rev. C | Page 19 of 32 (2) AD8337 APPLICATIONS INFORMATION PREAMPLIFIER CONNECTIONS DRIVING CAPACITIVE LOADS Noninverting Gain Configuration Because of the large bandwidth of the AD8337, stray capacitance at the output pin can induce peaking in the frequency response as the gain of the amplifier begins to roll off. Figure 68 shows peaking with two values of load capacitance using ±2.5 V supplies and VGAIN = 0 V. The AD8337 preamplifier is an uncommitted current-feedback op amp that is stable for values of RFB2 ≥ 100 Ω. See Figure 66 for the noninverting feedback connections. INPP RG INPN PREAMPLIFIER 3 + 4 – 25 VGAIN = 0V CL = 0pF CL = 10pF CL = 22pF 20 NO SNUBBING RESISTOR PRAO 5 15 05575-066 5 Figure 66. AD8337 Preamplifier Configured for Noninverting Gain Two surface-mount resistors establish the preamplifier gain. Equal values of 100 Ω configure the preamplifier for a 6 dB gain and the device for a default gain range of 0 dB to 24 dB. For preamplifier gains ≥2, select a value of RFB2 ≥ 100 Ω and RFB1 ≤ 100 Ω. Higher values of RFB2 reduce the bandwidth and increase the offset voltage, but smaller values compromise stability. If RFB1 ≤ 100 Ω, the gain increases and the inputreferred noise decreases. –5 100k RFB1 INPN PREAMPLIFIER 3 + 4 – RFB2 5 05575-067 PRAO 1M 10M 100M 500M FREQUENCY (Hz) Figure 68. Peaking in the Frequency Response for Two Values of Output Capacitance with ±2.5 V Supplies and No Snubbing Resistor 25 VGAIN = 0V CL = 0pF CL = 10pF 20 CL = 22pF WITH 20Ω SNUBBING RESISTOR For applications requiring polarity inversion of negative pulses, or for waveforms that require current sinking, the preamplifier can be configured as an inverting gain amplifier. When configured with bipolar supplies, the preamplifier amplifies positive or negative input voltages with no level shifting of the commonmode input voltage required. Figure 67 shows the AD8337 configured for inverting gain operation. Because the AD8337 is a very high frequency device, stability issues can occur unless the circuit board on which it is used is carefully laid out. The stability of the preamp is affected by parasitic capacitance around the INPN pin. To minimize stray capacitance position the preamp gain resistors, RFB1 and RFB2, as close as possible to the INPN pin. 05575-068 0 Inverting Gain Configuration INPP 10 GAIN (dB) 15 10 5 0 –5 100k 05575-069 RFB1 GAIN (dB) RFB2 1M 10M FREQUENCY (Hz) 100M 500M Figure 69. Frequency Response for Two Values of Output Capacitance with a 20 Ω Snubbing Resistor In the time domain, stray capacitance at the output pin can induce overshoot on the edges of transient signals, as shown in Figure 70 and Figure 72. The amplitude of the overshoot is also a function of the slewing of the transient (not shown in Figure 70 and Figure 72). The transition time of the input pulses used for Figure 70 and Figure 72 is deliberately set high at 300 ps to demonstrate the fast response time of the amplifier. Signals with longer transition times generate less overshoot. Figure 67. The AD8337 Preamplifier Configured for Inverting Gain Rev. C | Page 20 of 32 AD8337 80 800 800 80 400 200 –200 400 40 20 200 20 0 –20 INPUT –400 40 VOUT (mV) 0 60 VIN (mV) CL = 0pF CL = 10pF CL = 22pF NO SNUBBING RESISTOR 600 –40 OUTPUT –600 –60 –800 –20 0 –10 10 20 30 40 TIME (ns) 50 60 70 –200 INPUT –400 OUTPUT 800 80 600 60 400 40 –800 –20 –20 INPUT OUTPUT –40 –600 –800 –20 –10 VIN (mV) 0 0 0 10 20 30 40 TIME (ns) 50 –60 60 70 –80 80 Figure 71. Pulse Response for Two Values of Output Capacitance with ±2.5 V Supplies and a 20 Ω Snubbing Resistor VS = ±5V 600 60 400 40 20 –200 –400 –40 OUTPUT CL = 0pF CL= 10pF CL = 22pF WITH NO SNUBBING RESISTOR –600 –800 –20 –10 0 10 20 30 40 TIME (ns) 50 –60 –80 60 70 20 30 40 TIME (ns) 50 –80 60 70 80 The best way to avoid the effects of stray capacitance is to exercise care in the PCB layout. Locate the passive components or devices connected to the AD8337 output pins as close as possible to the package. In typical applications, voltages applied to the GAIN input are dc or relatively low frequency signals. The high input impedance of the AD8337 enables several devices to be connected in parallel. This is useful for arrays of VGAs, such as those used for calibration adjustments. –20 INPUT 10 GAIN CONTROL CONSIDERATIONS VIN (mV) 0 0 80 Figure 72. Large Signal Pulse Response for Two Values of Output Capacitance with ±5 V Supplies and No Snubbing Resistor 05575-072 VOUT (mV) 200 0 Although a nonissue, the preamplifier output is also sensitive to load capacitance. However, the series connection of RFB1 and RFB2 is typically the only load connected to the preamplifier. If overshoot appears, it can be mitigated by inserting a snubbing resistor, the same way as the VGA output. 80 800 –10 –60 The effects of stray output capacitance are mitigated with a small value snubbing resistor, RSNUB, placed in series with, and as near as possible to, the VOUT pin. Figure 69, Figure 71, and Figure 73 show the improvement in dynamic performance with a 20 Ω snubbing resistor. RSNUB reduces the gain slightly by the ratio of RL/(RSNUB + RL), a very small loss when used with high impedance loads, such as ADCs. For other loads, alternate values of RSNUB can be determined empirically. The data for the curves in the Typical Performance Characteristics section are derived using a 20 Ω snubbing resistor. 20 CL = 0pF CL = 10pF CL = 22pF WITH 20Ω SNUBBING RESISTOR –40 CL = 0pF CL = 10pF CL = 22pF WITH 20Ω SNUBBING RESISTOR Figure 73. Pulse Response for Two Values of Output Capacitance with ±5 V Supplies and a 20 Ω Snubbing Resistor 05575-071 VOUT (mV) 200 –400 –20 –600 –80 80 Figure 70. Pulse Response for Two Values of Output Capacitance with ±2.5 V Supplies and No Snubbing Resistor –200 0 0 VIN (mV) 60 05575-073 600 05575-070 VOUT (mV) VS = ±5V Under dc or slowly changing ramp conditions, the gain tracks the gain control voltage, as shown in Figure 3. However, it is often necessary to consider other effects influenced by the VGAIN input. Rev. C | Page 21 of 32 AD8337 The offset voltage effect of the AD8337, as with all VGAs, can appear as a complex waveform when observed across the range of VGAIN voltage. Generated by multiple sources, each device has a unique offset voltage (VOS) profile while the GAIN input is swept through its voltage range. The offset voltage profile seen in Figure 15 is a typical example. If the VGAIN input voltage is modulated, the output is the product of the VGAIN and the dc profile of the offset voltage. This is observed on a scope as a small ac signal, as shown in Figure 74. In Figure 74, the signal applied to the VGAIN input is a 1 kHz ramp, and the output voltage signal is slightly less than 4 mV p-p. 10 8 VS = ±2.5V INPUT VSOUTPUT = 2.5 OFFSET VOLTAGE (mV) 6 4 2 –2 –4 05575-075 –6 –10 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 Figure 74. Offset Voltage vs. VGAIN for a 1 kHz Ramp The profile of the waveform shown in Figure 74 is consistent over a wide range of signals from dc to about 20 kHz. Above 20 kHz, secondary artifacts can be generated due to the effects of minor internal circuit tolerances, as shown in Figure 75. These artifacts are caused by settling and time constants of the interpolator circuit and appear at the output as the voltage spikes, as shown in Figure 75. 10 8 VS = ±2.5V INPUT VOUTPUT S = 2.5 OFFSET VOLTAGE (mV) 6 4 SPIKE 2 0 –2 SPIKE –4 –6 The thermal performance of LFCSPs, such as the AD8337, departs significantly from that of leaded devices such as the larger TSSOP or QFSP. In larger packages, heat is conducted away from the die by the path provided by the bond wires and the device leads. In LFCSPs, the heat transfer mechanisms are surface-to-air radiation from the top and side surfaces of the package and conduction through the metal solder pad on the mounting surface of the device. The θJC value of the AD8837 listed in Table 2 assumes that the tab is soldered to the board and that there are three additional ground layers beneath the device connected by at least four vias. For a device with an unsoldered pad, the θJC nearly doubles, becoming 138°C/W. PSI (Ψ) Table 2 lists a subset of the classic theta specification, ΨJT (Psi junction to top). θJC is the metric of heat transfer from the die to the case, involving the six outside surfaces of the package. Ψ(XY) is a subset of the theta value and the thermal gradient from the junction (die) to each of the six surfaces. Ψ can be different for each of the surfaces, but since the top of the package is a fraction of a millimeter from the die, the surface temperature of the package is very close to the die temperature. The die temperature is calculated as the product of the power dissipation and ΨJT. Since the top surface temperature and power dissipation are easily measured, it follows that the die temperature is easily calculated. For example, for a dissipation of 180 mW and a ΨJT of 5.3°C/W, the die temperature is slightly less than 1°C higher than the surface temperature. 05575-074 BOARD LAYOUT –8 –10 –800 THERMAL CONSIDERATIONS θJC is the traditional thermal metric used for integrated circuits. Heat transfer away from the die is a three-dimensional dynamic, and the path is through the bond wires, leads, and the six surfaces of the package. Because of the small size of LFCSPs, the θJC is not measured conventionally. Instead, it is calculated using thermodynamic rules. 0 –8 Under certain circumstances, the product of VGAIN and the offset profile plus spikes is a coherent spurious signal within the signal band of interest and indistinguishable from desired signals. In general, the slower the ramp applied to the GAIN Pin, the smaller the spikes are. In most applications, these effects are benign and not an issue. –600 –400 –200 0 200 VGAIN (mV) 400 Figure 75. VOS Profile for a 50 kHz Ramp 600 800 Because the AD8337 is a high frequency device, board layout is critical. It is very important to have a good ground plane connection to the VCOM pin. Coupling through the ground plane, from the output to the input, can cause peaking at higher frequencies. Rev. C | Page 22 of 32 AD8337 EVALUATION BOARDS The AD8337evaluation boards provide a family of platforms for testing and evaluating the AD8337 VGA. Three circuit configurations are available: • AD8337-EVALZ, dc-coupled, with noninverting gain and dual power supplies • AD8337-EVALZ-INV, dc-coupled, with inverting gain and dual power supplies • AD8337-EVALZ-SS, ac-coupled, with noninverting gain configuration and a single supply 05575-178 These fully assembled and tested boards are ready to use. Only the appropriate power supply and signal source connections need to be made. SMA connectors are provided for the preamplifier (PrA) and VGA outputs. Photos of fully assembled boards are shown in Figure 76 and Figure 77. The board component side layouts are shown in Figure 78 and Figure 79. 05575-176 Figure 78. Assembly, Dual-Supply Evaluation Board 05575-179 Figure 76. AD8337 Evaluation Board for dual Supplies Figure 79. Assembly, Single-Supply Evaluation Board 05575-177 Schematic diagrams of the dual-supply board for noninverting and inverting configurations are shown in Figure 80 and Figure 81. The dual-supply boards require ±2.5 V to ±5 V supplies capable of supplying 20 mA or greater. A schematic diagram of the single-supply board is shown in Figure 82. The single supply version accepts a +5 V to +10 V supply with 20 mA or greater capability. Figure 77. AD8337 Evaluation Board for Single Supply Rev. C | Page 23 of 32 AD8337 GND1 GND2 GND GND3 J1 2 3 R4 0Ω IN CIRCUIT OPTIONS 4 VOUT U1 VPOS AD8337 VCOM GAIN INPP VNEG INPN PRAO R2 49.9Ω Table 4. AD8337 Evaluation Board Variations L1 120nH Part Number AD8337-EVALZ AD8337-EVALZ-INV AD8337-EVALZ-SS C3 0.1µF 8 GAIN 7 CG 1nF 6 R1 49.9Ω C4 0.1µF RPO2 453Ω PRAO OUTPUT PROTECTION 05575-180 RFB1 100Ω DO NOT INSTALL PARTS IN GRAY The AD8337 VGA output stage is specified for driving loads of 500 Ω or greater. To protect the stage from an accidental overload, a 453 Ω resistor is provided, which when connected to 50 Ω test equipment inputs, enables safe operation. In certain high load impedance situations, the value of this resistor can be reduced. However, if load capacitance values greater than approximately 20 pF are anticipated, such as a BNC cable, the minimum series resistor value is not to be less than 20 Ω. Figure 80. Schematic—AD8337-EVALZ - Noninverting Configuration GND1 GND2 GND GND3 RVO3 0Ω 100Ω R4 0Ω + C2 10µF L2 120nH 1 2 3 4 VOUT U1 VPOS AD8337 VCOM GAIN INPP VNEG INPN PRAO R2 49.9Ω 8 C3 0.1µF 6 An alternate test pin is also provided for direct access to the output of the AD8337 VGA. The pin is typically used for a probe, and a 0 Ω resistor is provided between the test loop and the output pin. If the test loop is connected to loads ≤500 Ω, then the 0 Ω resistor is to be changed to an appropriate value. GAIN 7 CG 1nF R1 49.9Ω 5 C4 0.1µF RFB2 100Ω R5 100Ω L1 120nH RPO2 453Ω PRAO RFB1 100Ω 05575-181 DO NOT INSTALL PARTS IN GRAY Figure 81. Schematic—AD8337-EVALZ-INV Inverting Configuration L1 120nH FB +VS + GND1 GND2 GND3 GND4 IN C1 10µF 10V C6 0.1µF C3 0.1µF 8 3 C4 0.1µF VPOS INPP VOUT 3 GND 5 ADR391AUJZ-R2 INPN 4 R1 49.9Ω AD8541AR 3 7 2 4 C9 0.1µF VOUT U1 C10 0.1µF VOUT U2 RVO1 453Ω AD8337 GAIN 2 1 VIN SHDN 1 U3 C7 0.1µF R6 100Ω 6 C2 + 1µF 16V 4 C8 0.22µF RFB1 100Ω PRAO 5 VCOM VNEG 2 6 CG 1nF RFB2 100Ω C5 0.1µF R4 10kΩ Figure 82. Evaluation Board Schematic—Single-Supply Version Rev. C | Page 24 of 32 GAIN 7 05575-182 IN J1 –VS C1 + 10µF VOUT RVO1 453Ω TP1 +VS GND4 Configuration Dual-supply noninverting Dual-supply inverting Single-supply noninverting Figure 80, Figure 81, and Figure 82 are schematics for the various circuit configurations. Within limits, the AD8337 preamplifier gain is controlled by Resistor RFB1 and Resistor RFB2. For simple guidelines applying to the current-feedback preamplifier, see the Theory of Operation section. 5 RFB2 100Ω R5 100Ω Part numbers for fully assembled boards are listed in Table 4. C2 + 10µF L2 120nH 1 RVO3 0Ω –VS C1 + 10µF VOUT RVO1 453Ω TP1 +VS GND4 AD8337 TOP: SIGNAL GENERATOR 10.05MHz, 500mV p-p BOTTOM: SIGNAL GENERATOR 9.95MHz, 500mV p-p POWER AMPLIFIERS SPECTRUM ANALYZER POWER SPLITTER SIGNAL INPUT PREAMP OUTPUT VGAIN +5V POWER SUPPLY 05575-183 –5V Figure 83. Typical Board Test Connections MEASUREMENT SETUP Figure 83 shows board connections for two generators. In this example, the experiment illustrates IMD measurements using standard off-the-shelf test equipment used by Analog Devices. However, any equivalent equipment can be used. BOARD LAYOUT CONSIDERATIONS The AD8337 evaluation board is designed using four layers. Interconnecting circuitry is located on the component and wiring sides, with the inner layers dedicated to power and ground planes. Figure 84 through Figure 88 show the copper layouts. For ease of assembly, all board components are located on the primary side and are 0603 size surface mounts. Higher density applications may require components on both sides of the board and present no problem to the AD8337, as demonstrated in unreleased versions of the board that featured secondary-side components and vias. Not evident in the figures are thermal vias within the pad that solder to the mating pad of the AD8337 chip-scale package. These vias serve as a thermal path and are the primary means of removing heat from the device. The thermal specifications for the AD8337 are predicated on the use of multilayer board construction with these thermal vias to enable heat conductivity from the die. Rev. C | Page 25 of 32 05575-109 05575-113 AD8337 Figure 84. Dual-Supply Component Side Copper 05575-114 05575-110 Figure 88. Dual-Supply Power Plane Figure 89. Single-Supply Component Side Copper 05575-111 05575-115 Figure 85. Dual-Supply Wiring Side Copper Figure 90. Single-Supply Wiring Side Copper 05575-116 05575-112 Figure 86. Dual-Supply Component Side Silk-Screen Figure 91. Single-Supply Component Side Silkscreen Figure 87. Dual-Supply Ground Plane Rev. C | Page 26 of 32 05575-117 05575-118 AD8337 Figure 93. Single-Supply Power Plane Figure 92. Single-Supply Ground Plane BILL OF MATERIALS Table 5. Dual-Supply Noninverting Bill of Materials Qty. 1 4 1 1 2 1 2 1 4 2 1 2 2 2 Reference Designator +VS GND1 to GND4 −VS TP1 C3, C4 CG C1, C2 U1 GAIN, IN, PRAO, VOUT L1, L2 R2 R4, RVO3 RFB1, RFB2 RPO2, RVO1 Description Red test loop, 0.125” diameter Black test loop, 0.125” diameter Blue test loop, 0.125” diameter Purple test loop, 0.125” diameter SM 0.1 μF, 16 V, 0603, X7R capacitors SM 1 nF, 50 V, X7R, 10%, 0603 capacitor SM tantalum, 10 μF, 10 V, A size capacitors Integrated circuit VGA SMA fem PC mount RA connectors 120 nH, 0603 ferrite beads 49.9 Ω, 1%, 1/16 W, 0603 resistor 0 Ω, 5%, 1/10 W, 0603 resistors 100 Ω, 1%, 1/16 W, 0603 resistors 453 Ω, 1/16 W, 1%, 0603 resistors Manufacturer Bisco Industries Bisco Industries Bisco Industries Bisco Industries KEMET Panasonic Nichicon Analog Devices, Inc. Amphenol Murata Panasonic Panasonic Panasonic Panasonic Mfg. Part Number TP-104-01-02 TP-104-01-00 TP-104-01-06 TP-104-01-07 C0603C104K4RACTU ECJ-1VB2A102K T491A106M010AS AD8337BCPZ-WP 901-143-6RFX BLM18BA750SN1D ERJ-3EKF49R9V ERJ-2GE0R00X ERJ-3EKF1000V ERJ-3EKF4530V Manufacturer Bisco Industries Bisco Industries Bisco Industries Bisco Industries KEMET Panasonic Nichicon Analog Devices, Inc. Amphenol Murata Panasonic Panasonic Panasonic Panasonic Mfg. Part Number TP-104-01-02 TP-104-01-00 TP-104-01-06 TP-104-01-07 C0603C104K4RACTU ECJ-1VB2A102K T491A106M010AS AD8337BCPZ-WP 901-143-6RFX BLM18BA750SN1D ERJ-3EKF49R9V ERJ-2GE0R00X ERJ-3EKF1000V ERJ-3EKF4530V Table 6. Dual-Supply Inverting Gain Bill of Materials Qty. 1 4 1 1 2 1 2 1 4 2 1 1 3 2 Reference Designator +VS GND1 to GND4 −VS TP1 C3, C4 CG C1, C2 U1 GAIN, IN, PRAO, VOUT L1, L2 R2 RVO3 RFB2, R5, J1 (J1 POSITION) RPO2, RVO1 Description Red test loop, 0.125” diameter Black test loop, 0.125” diameter Blue test loop, 0.125” diameter Purple test loop, 0.125” diameter SM 0.1 μF, 16 V, 0603, X7R capacitors SM 1 nF, 50 V, X7R, 10%, 0603 capacitor SM tantalum, 10 μF, 10 V, A size capacitors Integrated circuit VGA SMA fem PC mount RA connectors 120 nH, 0603 ferrite beads 49.9 Ω, 1%, 1/16 W, 0603 resistor 0 Ω, 5%, 1/10 W, 0603 resistor 100 Ω, 1%, 1/16 W, 0603 resistors 453 Ω, 1/16 W, 1%, 0603 resistors Rev. C | Page 27 of 32 AD8337 Table 7. Single-Supply Bill of Materials Qty. 1 1 1 7 1 1 3 4 1 1 1 3 1 1 1 1 Reference Designator +VS C1 C2 C3, C4, C5, C6, C7, C9, C10 C8 CG GAIN, IN, VOUT GND1 to GND4 L1 R1 R4 RFB1, RFB2, R6 RVO1 U1 U2 U3 Description Red test point, 0.125” diameter Tantalum, 10 μF, 10 V, A size capacitor Tantalum, 1 μF, P size capacitor 0.1 μF, 16 V, 0603, X7R capacitors 0.22 μF, 10%, 0603, X7R capacitor 1 nF, 50 V, X7R, 10%, 0603 capacitor SMA fem PC mount RA connectors Loop, 0.125” diameter, black test points 120 nH, 0603 ferrite bead 49.9 Ω, 1%, 1/16 W, 0603 resistor 10 kΩ, 1%, 1/16 W, 0603 resistor 100 Ω, 1%, 1/16 W, 0603 resistors 453 Ω, 1%, 1/16 W, 0603 resistor VGA integrated circuit 2.5 V regulator integrated circuit SS rail-to-rail op amp integrated circuit Rev. C | Page 28 of 32 Manufacturer Bisco Industries Nichicon Nichicon KEMET Panasonic Panasonic Amphenol Bisco Industries Murata Panasonic Panasonic Panasonic Panasonic Analog Devices, Inc. Analog Devices, Inc. Analog Devices, Inc. Mfg. Part Number TP-104-01-02 T491A106M010AS F921C105MPA C0603C104K4RACTU ECJ-1VB1H223K ECJ-1VB2A102K 901-143-6RFX TP-104-01-00 BLM18BA750SN1D ERJ-3EKF49R9V ERJ-3EKF1002V ERJ-3EKF1000V ERJ-3EKF4530V AD8337BCPZ-WP ADR391AUJZ-R2 AD8541AR AD8337 OUTLINE DIMENSIONS 0.60 MAX 5 TOP VIEW PIN 1 INDICATOR 2.95 2.75 SQ 2.55 8 12° MAX 0.50 0.40 0.30 0.70 MAX 0.65 TYP 0.05 MAX 0.01 NOM 0.30 0.23 0.18 SEATING PLANE 0.20 REF 1.60 1.45 1.30 EXPOSED PAD (BOTTOM VIEW) 4 0.90 MAX 0.85 NOM 0.50 BSC 0.60 MAX 1 1.89 1.74 1.59 PIN 1 INDICATOR FOR PROPER CONNECTION OF THE EXPOSED PAD, REFER TO THE PIN CONFIGURATION AND FUNCTION DESCRIPTIONS SECTION OF THIS DATA SHEET. 072408-B 3.25 3.00 SQ 2.75 Figure 94. 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] 3 mm × 3 mm Body, Very Thin, Dual Lead (CP-8-2) Dimensions shown in millimeters ORDERING GUIDE Model AD8337BCPZ-R2 1 AD8337BCPZ-REEL1 AD8337BCPZ-REEL71 AD8337BCPZ-WP1 AD8337-EVALZ1 AD8337-EVALZ-INV1 AD8337-EVALZ-SS1 1 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Package Description 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] 8-Lead Lead Frame Chip Scale Package [LFCSP_VD] Evaluation Board with Noninverting Gain Configuration Evaluation Board with Inverting Gain Configuration Evaluation Board with Single-Supply Operation Z = RoHS Compliant Part. Rev. C | Page 29 of 32 Package Option CP-8-2 CP-8-2 CP-8-2 CP-8-2 Branding HVB HVB HVB HVB AD8337 NOTES Rev. C | Page 30 of 32 AD8337 NOTES Rev. C | Page 31 of 32 AD8337 NOTES ©2005–2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05575-0-9/08(C) Rev. C | Page 32 of 32