AD8336

General-Purpose, −55°C to +125°C, Wide Bandwidth, DC-Coupled VGA AD8336 FEATURES Low noise Voltage noise: 3 nV/√Hz Current noise: 3 pA/√Hz Small signal BW: 115 MHz Large signal BW: 2 V p-p = 80 MHz Slew rate: 550 V/µs, 2 V p-p Gain ranges (specified) −14 dB to +46 dB, 0 dB to 60 dB Gain scaling: 50 dB/V DC-coupled Single -ended input and output Supplies: ±3 V to ±12 V Temperature Range: −55°C to +125°C Power 150 mW @ ±3 V, −55°C < T < +125°C 84 mW @ ±3 V, PWRA = 3 V FUNCTIONAL BLOCK DIAGRAM PRAO VGAI 9 AD8336 INPP 4 INPN 5 + PrA – 8 ATTENUATOR –60dB TO 0dB 34dB 1 VOUT PW RA 2 BIAS GAIN CONTROL INTERFACE 10 13 3 11 12 VNEG VPOS VCOM GPOS GNEG Figure 1. APPLICATIONS Industrial process controls High performance AGC systems I/Q signal processing Video Industrial and medical ultrasound Radar receivers GENERAL DESCRIPTION The AD8336 is a low noise, single-ended, linear-in-dB, generalpurpose variable gain amplifier, usable over a large range of supply voltages. It features an uncommitted preamplifier (preamp) with a usable gain range of 6 dB to 26 dB established by external resistors in the classical manner. The VGA gain range is 0 dB to 60 dB, and its absolute gain limits are −26 dB to +34 dB. When the preamplifier gain is adjusted for 12 dB, the combined 3 dB bandwidth of the preamp and VGA is 100 MHz, and the amplifier is fully usable to 80 MHz. With ±5 V supplies, the maximum output swing is 2 V p-p. Thanks to its X-Amp® architecture, excellent bandwidth uniformity is maintained across the entire gain range of the VGA. Intended for a broad spectrum of applications, the differential gain control interface provides precise linear-in-dB gain scaling of 50 dB/V over the temperature span of −55°C to +125 °C. The differential gain control is easy to interface with a variety of external circuits within the common-mode voltage limits of the AD8336. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties 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. The large supply voltage range makes the AD8336 particularly suited for industrial medical applications and for video circuits. Dual-supply operation enables bipolar input signals, such as those generated by photodiodes or photomultiplier tubes. The fully independent voltage feedback preamp allows both inverting and noninverting gain topologies, making it a fully bipolar VGA. The AD8336 can be used within the specified gain range of −14 dB to +60 dB by selecting a preamp gain between 6 dB and 26 dB and choosing appropriate feedback resistors. For the nominal preamp gain of 4×, the overall gain range is −14 dB to +46 dB. In critical applications, the quiescent power can be reduced by about half by using the power adjust pin, PWRA. This is especially useful when operating with high supply voltages of up to ±12 V, or at high temperatures. The operating temperature range is −55°C to +125°C. The AD8336 is available in a 16-lead LFCSP (4 mm × 4 mm). 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 ©2006 Analog Devices, Inc. All rights reserved. 06228-001 AD8336 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 6 ESD Caution .................................................................................. 6 Pin Configuration and Functional Descriptions .......................... 7 Typical Performance Characteristics ............................................. 8 Test Circuits ..................................................................................... 17 Theory of Operation ...................................................................... 21 Overview...................................................................................... 21 Preamplifier ................................................................................. 21 VGA.............................................................................................. 21 Setting the Gain .......................................................................... 22 Noise ............................................................................................ 22 Offset Voltage .............................................................................. 22 Applications..................................................................................... 23 Amplifier Configuration ........................................................... 23 Preamplifier................................................................................. 23 Circuit Configuration for Noninverting Gain ................... 23 Circuit Configuration for Inverting Gain ........................... 24 Using the Power Adjust Feature ............................................... 24 Driving Capacitive Loads .......................................................... 24 Evaluation Board ............................................................................ 25 Optional Circuitry...................................................................... 25 Board Layout Considerations ................................................... 25 Outline Dimensions ....................................................................... 28 Ordering Guide .......................................................................... 28 REVISION HISTORY 10/06—Revision 0: Initial Version Rev. 0 | Page 2 of 28 AD8336 SPECIFICATIONS VS = ±5 V, T = 25°C, gain range = −14 dB to +46 dB, preamp gain = 4×, f = 1 MHz, CL = 5 pF, RL = 500 Ω, PWRA = GND, unless otherwise specified. Table 1. Parameter PREAMPLIFIER −3 dB Small Signal Bandwidth −3 dB Large Signal Bandwidth Bias Current, Either Input Differential Offset Voltage Input Resistance Input Capacitance PREAMPLIFIER + VGA –3 dB Small Signal Bandwidth Conditions VOUT = 10 mV p-p VOUT = 2 V p-p Min Typ 150 85 725 ±600 900 3 115 40 20 125 80 30 20 100 550 3.0 3.0 600 190 2500 200 700 250 Max Unit MHz MHz nA μV kΩ pF MHz MHz MHz MHz MHz MHz MHz MHz V/µs nV/√Hz pA/√Hz nV/√Hz nV/√Hz nV/√Hz nV/√Hz nV/√Hz nV/√Hz VOUT = 10 mV p-p VOUT = 10 mV p-p, PWRA = 5 V VOUT = 10 mV p-p, PrA gain = 20× VOUT = 10 mV p-p, PrA gain = –3× VOUT = 2 V p-p VOUT = 2 V p-p, PWRA = 5 V VOUT = 2 V p-p, PrA gain = 20× VOUT = 2 V p-p, PrA gain = –3× VOUT = 2 V p-p ±3 V ≤ VS ≤ ±12 V –3 dB Large Signal Bandwidth Slew Rate Short-Circuit Preamp Input Voltage Noise Spectral Density Input Current Noise Spectral Density Output Referred Noise VGAIN = 0.7 V, PrA gain = 4× VGAIN = –0.7 V, PrA gain = 4× VGAIN = 0.7 V, PrA gain = 20× VGAIN = –0.7 V, PrA gain = 20× VGAIN = 0.7 V, –55°C ≤ T ≤ +125°C VGAIN = –0.7 V, –55°C ≤ T ≤ +125°C VGAIN = 0 V, VOUT = 1 V p-p f = 1 MHz f = 1 MHz f = 10 MHz f = 10 MHz VGAIN = –0.7 V VGAIN = +0.7 V VGAIN = 0 V, VOUT = 1 V p-p, f1 = 0.95 MHz, f2 = 1.05 MHz VGAIN = 0 V, VOUT = 1 V p-p, f1 = 9.95 MHz, f2 = 10.05 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 0.95 MHz, f2 = 1.05 MHz VGAIN = 0 V, VOUT = 2 V p-p, f1 = 9.95 MHz, f2 = 10.05 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 1 MHz VGAIN = 0 V, VOUT = 1 V p-p, f = 10 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 1 MHz VGAIN = 0 V, VOUT = 2 V p-p, f = 10 MHz VGAIN = 0.7 V, VIN = 100 mV p-p to 5 mV p-p 1 MHz < f < 10 MHz, full gain range 1 MHz < f < 10 MHz, full gain range DYNAMIC PERFORMANCE Harmonic Distortion HD2 HD3 HD2 HD3 Input 1 dB Compression Point Two-Tone Intermodulation Distortion (IMD3) Output Third-Order Intercept Overdrive Recovery Group Delay Variation PrA Gain = 20 × –58 –68 –60 –60 11 –23 –71 –69 –60 –58 34 32 34 33 50 ±1 ±3 dBc dBc dBc dBc dBm1 dBm dBc dBc dBc dBc dBm dBm dBm dBm ns ns ns Rev. 0 | Page 3 of 28 AD8336 Parameter ABSOLUTE GAIN ERROR2 Conditions −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 < 0.5 V, ±3 V ≤ VS ≤ ±12 V −0.5 V < VGAIN < 0.5 V, −55 °C ≤ T ≤ +125 °C −0.5 V < VGAIN < 0.5 V, PrA gain = −3× 0.5 V < VGAIN < 0.6 V 0.6 V < VGAIN < 0.7 V Min 0 0 −1.25 Typ 1 to 5 0.5 to1.5 ±0.2 ±0.5 ±0.5 ±0.5 −1.5 to −3.0 −1 to −5 49.9 16.4 4.5 60 1 60 dB gain change ±3 V ≤ VS ≤ ±12 V RL ≥ 500 Ω (for |VSUPPLY| ≤ ±5V); RL ≥ 1 kΩ above that RL ≥ 1 kΩ (for |VSUPPLY| = ±12V) Linear operation − minimum discernable distortion VS = ±3 V VS = ±5 V VS = ±12 V VGAIN = 0.7 V, gain = 200× ±3 V ≤ VS ≤ ±12 V −55°C ≤ T ≤ +125°C VS = ±3 V VS = ±3 V VS = ±5 V VS = ±5 V VS = ±12 V VS = ±12 V 300 2.5 |VSUPPLY| − 1.5 |VSUPPLY| − 2.25 20 +123/−72 +123/−72 +72/−73 −125 −200 −200 Max 6 3 +1.25 1.25 Unit dB dB dB dB dB dB dB dB dB/V dB dB dB V μA pF ns Ω V V mA mA mA mA mV mV mV V V V V V V V −4.0 −9.0 48 0 0 52 GAIN CONTROL INTERFACE Gain Scaling Factor Intercept Gain Range Input Voltage (VGAIN) Range Input Current Input Capacitance Response Time OUTPUT PERFORMANCE Output Impedance, DC to 10 MHz Output Signal Swing Output Current Short-Circuit Current Preamp + VGA VGA Only No foldover 58 −VS 62 +VS Output Offset Voltage −250 150 PWRA Pin Normal Power (Logic Low) Low Power (Logic High) Normal Power (Logic Low) Low Power (Logic High) Normal Power (Logic Low) Low Power (Logic High) POWER SUPPLY Supply Voltage Operating Range Quiescent Current VS = ±3 V 0.7 1.5 1.2 2.0 3.2 4.0 ±3 22 25 23 to 31 14 26 23 to 31 14 28 24 to 33 16 ±12 30 −55°C ≤ T ≤ +125°C PWRA = 3 V VS = ±5 V −55°C ≤ T ≤ +125°C PWRA = 5 V VS = ±12 V −55°C ≤ T ≤ +125°C PWRA = 5 V mA 18 30 mA 18 31 mA 10 22 10 23 Rev. 0 | Page 4 of 28 AD8336 Parameter Power Dissipation Conditions VS = ±3 V VS = ±5 V VS = ±12 V VGAIN = 0.7 V, f = 1 MHz Min Typ 150 260 672 −40 Max Unit mW mW mW dB PSRR 1 2 All dBm values are calculated with 50 Ω reference, unless otherwise noted. Conformance to theoretical gain expression (see the Setting the Gain section). Rev. 0 | Page 5 of 28 AD8336 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage ( VPOS, VNEG) Input Voltage (INPP, INPN) Gain Voltage (GPOS, GNEG) PWRA Power Dissipation VS ≤ ±5 V ±5 V < VS ≤ ±12 V Operating Temperature Range ±3 V < VS ≤ ±10 V ±10 V < VS ≤ ±12 V Storage Temperature Range Lead Temperature (Soldering 60 sec) Thermal Data (4-layer JEDEC board, no air flow, exposed pad soldered to PC board) θJA θJB θJC ΨJT ΨJB Rating ±15 V VPOS, VNEG VPOS, VNEG 5 V, GND 0.43 W 1.12 W –55°C to +125°C –55°C to +85°C –65°C to +150°C 300°C Stresses above those listed under the 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. ESD CAUTION 58.2°C/W 35.9°C/W 9.2°C/W 1.1°C/W 34.5°C/W Rev. 0 | Page 6 of 28 AD8336 PIN CONFIGURATION AND FUNCTIONAL DESCRIPTIONS VOUT PWRA VCOM INPP 16 15 14 13 12 PIN 1 INDICATOR 2 11 VPOS GNEG GPOS VNEG VGAI 10 8 NC 1 3 5 NC 6 TOP VIEW 4 (Not to Scale) 9 7 AD8336 INPN NC NC NC PRAO NC = NO CONNECT Figure 2. 16-Lead LFCSP Pin Configuration Table 3. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic VOUT PWRA VCOM INPP INPN NC NC PRAO VGAI VNEG GPOS GNEG VPOS NC NC NC Function Output Voltage. Power Control. Normal power when grounded; power reduced by half if VPWRA is pulled high. Common-Mode Voltage. Normally GND when using a dual supply. Positive Input to Preamp. Negative Input to Preamp. No Connect. No Connect. Preamp Output. VGA Input. Negative Supply. Positive Gain Control Input. Negative Gain Control Input. Positive Supply. No Connect. No Connect. No Connect. Rev. 0 | Page 7 of 28 06228-002 AD8336 TYPICAL PERFORMANCE CHARACTERISTICS VS = ±5 V, T = 25°C, gain range = −14 dB to +46 dB, PrA gain = +4×, f = 1 MHz, CL = 5 pF, RL = 500 Ω, PWRA = GND, unless other wise specified. 50 40 30 GAIN ERROR (dB) GAIN (dB) T = +125°C T = +25°C T = –55°C 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 06228-003 T = +125°C T = +25°C T = –55°C 20 10 0 –10 –20 –800 –600 –400 –200 0 VGAIN (mV) 200 400 600 800 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 Figure 3. Gain vs. VGAIN for Three Values of Temperature (T) 50 40 30 VS = ±12V VS = ±5V VS = ±3V Figure 6. Gain Error vs. VGAIN for Three Values of Temperature (T) 2.0 1.5 1.0 VS = ±12V VS = ±5V VS = ±3V GAIN ERROR (dB) GAIN (dB) 0.5 0 –0.5 –1.0 –1.5 06228-007 06228-008 20 10 0 –10 –20 –800 06228-004 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 –2.0 –800 –600 –400 –200 200 0 VGAIN (mV) 400 600 800 Figure 4. Gain vs. VGAIN for Three Values of Supply Voltage (VS) 70 60 50 Figure 7. Gain Error vs. VGAIN for Three Values of Supply Voltage (VS) 2.0 1.5 1.0 GAIN ERROR (dB) 0.5 0 –0.5 –1.0 –1.5 06228-005 PREAM P GAIN = 20× PREAM P GAIN = 4× 40 GAIN (dB) 30 20 10 0 PREAMP GAIN = 20× PREAMP GAIN = 4× –10 –20 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 –2.0 –800 –600 –400 –200 200 0 VGAIN (mV) 400 600 800 Figure 5 Gain vs. VGAIN for Preamp Gains of 4× and 20× Figure 8. Gain Error vs. VGAIN for Preamp Gains of 4× and 20× Rev. 0 | Page 8 of 28 06228-006 –2.0 –800 AD8336 2.0 1.5 1.0 GAIN ERROR (dB) PREAMP GAIN = PREAM P GAIN = PREAM P GAIN = PREAM P GAIN = 4×, f = 1MHz 4×, f = 10M Hz 20×, f = 1M Hz 20×, f = 10M Hz 50 60 UNITS VGAIN = –0.3V VGAIN = +0.3V 40 % OF UNITS 06228-009 0.5 0 –0.5 –1.0 30 20 10 –1.5 –2.0 –800 0 0 0.04 0.08 0.12 –0.12 –0.08 GAIN ERROR (dB) Figure 9. Gain Error vs. VGAIN at 1 MHz and 10 MHz and for Preamp Gains of 4× and 20× 2.0 1.5 1.0 50 Figure 12. Gain Error Histogram PREAMP GAIN = –3×, f = 1MHz PREAMP GAIN = –3×, f = 10MHz PREAMP GAIN = –19×, f = 1MHz PREAMP GAIN = –19×, f = 10MHz 60 UNITS –0.3V ≤ VGAIN ≤ 0.3V 40 GAIN ERROR (dB) % OF UNITS 0.5 0 –0.5 –1.0 –1.5 06228-010 30 20 10 49.6 49.7 49.8 49.9 50.0 50.1 50.2 GAIN SCALING (dB/V) Figure 10. Gain Error vs. VGAIN at 1 MHz and 10 MHz and for Inverting Preamp Gains of −3× and −19× 50 45 40 20 0 Figure 13. Gain Scaling Factor Histogram OFFSET VOLTAGE (mV) VS = ±12V VS = ±5V VS = ±3V –20 –40 –60 –80 –100 –120 –140 –160 –180 06228-011 GAIN (dB) 35 0 –5 –10 –15 –15 –10 –5 0 5 10 15 –200 –220 –0.8 –0.2 0 0.2 VGAIN (V) 0.4 0.6 0.8 Figure 11. Common-Mode Voltage at Pin VGAIN vs. VGAIN Figure 14. Output Offset Voltage vs. VGAIN for Various Values of Temperature (T) Rev. 0 | Page 9 of 28 06228-014 COMMON-MODE VOLTAGE OF VGAIN T T T T T = +125°C = +85°C = +25°C = –40°C = –55°C –0.6 –0.4 06228-013 –2.0 –800 0 –600 –400 –200 200 0 VGAIN (mV) 400 600 800 06228-012 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 –0.04 0.16 AD8336 20 0 –20 50 40 30 20 VGAIN = +0.7V +0.5V OFFSET VOLTAGE (mV) –40 –60 –80 –100 –120 –140 –16 0 –180 –200 –0.8 VS = ±12V VS = ±5V VS = ±3V 06228-015 +0.2V 0V –0.2V GAIN (dB) 10 0 –0.5V –10 –20 –0.7V –0.6 –0.4 –0.2 0 0.2 VGAIN (V) 0.4 0.6 0.8 1M 10M FREQUENCY (Hz) 100M 200M Figure 15. Output Offset Voltage vs. VGAIN for Three Values of Supply Voltage (VS) 30 20 10 SAMPLE SIZE = 60 UNITS VGAIN = 0.7V Figure 18. Frequency Response for Various Values of VGAIN 50 40 30 20 VGAIN = +0.7V +0.5V +0.2V 0V –0.2V % OF UNITS –240 –200 –160 –120 –80 –40 OUTPUT OFFSET (mV) 0 40 80 GAIN (dB) 0 10 0 30 VGAIN = 0V 20 10 0 06228-016 –0.5V –10 –20 –0.7V LOW POWER MODE 1M 10M FREQUENCY (Hz) 100M 200M 06228-019 –24 –20 –16 –12 –8 –4 OUTPUT OFFSET (mV) 0 4 8 –30 100k Figure 16. Output Offset Histogram 50 60 UNITS Figure 19. Frequency Response for Various Values of VGAIN, Low Power Mode 70 60 VGAIN = +0.7V +0.5V 40 50 % OF UNITS GAIN (dB) 30 40 30 20 10 +0.2V 0V –0.2V 20 10 –0.5V –0.7V 0 0 16.25 16.30 16.35 16.40 16.45 INTERCEPT (dB) 16.50 16.55 06228-017 10M FREQUENCY (Hz) 100M 200M Figure 17. Intercept Histogram Figure 20. Frequency Response for Various Values of VGAIN when the Preamp Gain is 20× Rev. 0 | Page 10 of 28 06228-020 PREAMP GAIN = 20× –10 100k 1M 06228-018 –30 100k AD8336 50 VGAIN = +0.7V 30 +0.5V 40 30 25 20 GAIN = 20× +0.2V GAIN ( dB) GAIN (dB) 20 10 0 15 0V –0.2V GAIN = 4× 10 5 –10 –20 –0.5V –0.7V 0 –5 VS = ±12V VS = ±5V VS = ±3V 1M 10M FREQUENCY (Hz) 100M 500M PREAMP GAIN = –3× 1M 10M FREQUENCY (Hz) 100M 200M 06228-021 Figure 21. Frequency Response for Various Values of VGAIN for Preamp Gain of −3× 25 20 VGAIN = 0V Figure 24. Preamp Frequency Response for Three Values of Supply Voltage (VS) and Inverting Gain Values of −3× and −19× 20 PREAMP GAIN = 20× PREAMP GAIN = 4× 15 GROUP DELAY (ns) 15 GAIN (dB) 10 5 0 –5 CLOAD = CLOAD = CLOAD = CLOAD = 10 47pF 22pF 10pF 0pF 06228-022 5 1M 10M FREQUENCY ( Hz ) 100M 200M 10M FREQUENCY (Hz) 100M Figure 22. Frequency Response for Various Values of Load Capacitance (CLOAD) 30 Figure 25. Group Delay vs. Frequency for Preamp Gains of 4× and 20× 1k GAIN = 20× 25 100 20 15 GAIN (dB) GAIN = 4× IMPEDANCE (Ω) 10 10 5 0 –5 1 0.1 06228-023 1M 10M FREQUENCY (Hz) 100M 500M 1M 10M FREQUENCY (Hz) 100M 500M Figure 23. Preamp Frequency Response for Three Values of Supply Voltage (VS) and for Preamp Gains of 4× and 20× Figure 26. Output Resistance vs. Frequency of the Preamplifier Rev. 0 | Page 11 of 28 06228-026 –10 100k VS = ±12V VS = ±5V VS = ±3V 0.01 100k 06228-025 –10 100k 0 1M 06228-024 –30 100k –10 100k AD8336 1k 1k f = 5MHz 100 INPUT REFERRED NOISE (nV/√Hz) IMPEDANCE (Ω) 100 PREAM P GAIN = 4× 10 1 10 0.1 VS = ±12V VS = ±5V VS = ±3V 06228-027 PREAM P GAIN = 20× 06228-030 0.01 100k 1M 10M FREQUENCY (Hz) 100M 500M 1 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 Figure 27. Output Resistance vs. Frequency of the VGA for Three Values of Supply Voltage (VS) 1000 900 800 700 f = 5M Hz Figure 30. Input Referred Noise vs. VGAIN for Preamp Gains of 4× and 20× 6 VGAIN = 0.7V 5 NOISE (nV/√Hz) 600 500 400 300 200 100 0 –800 –600 –400 –200 200 0 VGAIN (mV) 400 T T T T T = +125°C = +85°C = +25°C = –40°C = –55°C 06228-028 NOISE (nV/√Hz) 4 3 2 1 600 800 1M 10M FREQUENCY (Hz) 100M Figure 28. Output Referred Noise vs. VGAIN at Various Temperatures (T) 3000 Figure 31. Short-Circuit Input Referred Noise vs. Frequency at Maximum Gain for Three Values of Power Supply Voltage (VS)n 6 f = 5MHz 2700 PREAMP GAIN = 20× 2400 2100 NOISE (nV/√Hz) VGAIN = 0.7V PREAMP GAIN = –3× 5 4 1800 1500 1200 900 600 300 0 –800 –600 –400 –200 0 VGAIN (mV) 200 400 T T T T T = +125°C = +85°C = +25°C = –40°C = –55°C 600 800 06228-029 NOISE (nV/√Hz) 3 2 1 1M 10M FREQUENCY (Hz) 100M Figure 29. Output Referred Noise vs. VGAIN at Various Temperatures (T) when the Preamp Gain is 20× Figure 32. Short-Circuit Input Referred Noise vs. Frequency at Maximum Inverting Gain Rev. 0 | Page 12 of 28 06228-032 0 100k 06228-031 0 100k VS = ±12V VS = ±5V VS = ±3V AD8336 100 VGAIN = 0.7V –40 –45 VOUT = 2V p-p VGAIN = 0V f = 5MHz INPUT NOISE (nV/√Hz) INPUT REFERRED NOISE DISTORTION (dBc) 10 –50 HD2 –55 HD3 1 RS THERM AL NOISE A LONE –60 –65 100 1k SOURCE RESISTANCE (Ω) 10k 06228-033 0 5 10 15 20 25 30 35 LOAD CAPACITANCE (pF) 40 45 50 Figure 33. Input Referred Noise vs. Source Resistance 70 60 50 SIMULATED DATA 40 30 20 10 0 –800 50Ω SOURCE –20 f = 10MHz –30 Figure 36. Harmonic Distortion vs. Load Capacitance VOUT = 1V p-p OUTPUT SWING OF PREAMP LIMITS VGAIN TO 400mV NOISE FIGURE (dB) DISTORTION (dBc) –40 –50 –60 HD2 @ 1MHz HD2 @ 10MHz HD3 @ 1MHz HD3 @ 10MHz –400 –200 0 200 VGAIN (mV) 400 600 800 06228-037 06228-038 UNTERMINATED –70 –600 –400 –200 0 VGAIN (mV) 200 400 600 800 06228-034 –80 –600 Figure 34. Noise Figure vs. VGAIN –40 Figure 37. 2nd and 3rd Harmonic Distortion vs. VGAIN at 1 MHz and 10 MHz –20 –45 VOUT = 2V p-p VGAIN = 0V f = 5MHz HD2 f = 5MHz OUTPUT SWING OF PREAMP LIMITS VGAIN LEVELS –30 DISTORTION (dBc) HD2 –55 HD3 –60 DISTORTION (dBc) –50 –40 –50 –60 –65 –70 0 200 400 600 800 1.0k 1.2k 1.4k 1.6k 1.8k 2.0k 2.2k LOAD RESISTANCE (Ω) 06228-035 –70 –80 –600 VOUT = 0.5V p-p VOUT = 1V p-p VOUT = 2V p-p VOUT = 4V p-p –400 –200 0 200 VGAIN (mV) 400 600 800 Figure 35. Harmonic Distortion vs. Load Resistance Figure 38. 2nd Harmonic Distortion vs. VGAIN for Four Values of Output Voltage (VOUT) Rev. 0 | Page 13 of 28 06228-036 0.1 10 –70 AD8336 –20 HD3 f = 5MHz OUTPUT SWING OF PREAMP LIMITS MINIMUM USABLE VGAIN LEVELS 40 35 30 –30 1MHz 500mV 1MHz 1V 10MHz 500mV 10MHz 1V DISTORTION (dBc) –40 OUTPUT IP3 (dBm) VOUT = 0.5V p-p VOUT = 1V p-p VOUT = 2V p-p VOUT = 4V p-p 06228-039 25 20 15 10 –50 –60 –70 5 –400 –200 0 200 VGAIN (mV) 400 600 800 –600 –400 200 –200 0 VGAIN (mV) 400 600 800 Figure 39. 3rd Harmonic Distortion vs. VGAIN for Four Values of Output Voltage (VOUT) –20 VOUT = 2V p-p VGAIN = 0V Figure 42. Output Referred IP3 (OIP3) vs. VGAIN at Two Frequencies and Two Input Levels 30 VS = ±12V VS = ±5V 10 INPUT LEVEL LIMITED BY GAIN OF PREAMP –30 20 HD (dBc) –40 HD2 –50 IP1dB (dBm) VS = ±3V 0 –10 –60 HD3 06228-040 06228-043 –20 –70 1M 10M FREQUENCY (Hz) 50M –30 –800 –600 –400 –200 0 200 VGAIN (mV) 400 600 800 Figure 40. Harmonic Distortion vs. Frequency 0 –10 –20 –30 –40 –50 –60 –70 Figure 43. Input P1dB (IP1dB) vs. VGAIN at Three Power Supply Values (VS) 3 VOUT = 1V p-p VGAIN = 0V TONES SEPARATED BY 100kHz 2 1 VO LTAGE ( V) IMD3 (dBc) 0 VIN (V) VOUT (V) –1 –2 –80 06228-041 06228-044 –90 1M 10M FREQUENCY (Hz) 100M –3 –100 0 100 TIME (ns) 200 300 Figure 41. IMD3 vs. Frequency Figure 44. Large Signal Pulse Response of the Preamp Rev. 0 | Page 14 of 28 06228-042 –80 –600 0 –800 VOUT = 1V p-p VGAIN = 0V COMPOSITE INPUTS SEPARATED BY 100kHz AD8336 0.6 VGAIN = 0.7V 0.4 60 25 20 OUTPUT 2.5 2.0 1.5 1.0 40 15 10 VGAIN = 0.7V PREAMP GAIN = –3 0.2 20 VOUT (mV) 0 0 0 –5 INPUT 0 –0.5 –1.0 –1.5 –2.0 –50 0 50 100 150 TIME (ns) 200 250 300 –0.2 –20 –10 –15 –20 –0.4 –50 0 50 100 150 TIME (ns) 200 250 300 Figure 45. Noninverting Small Signal Pulse Response for Both Power Levels 0.6 OUTPUT 0.4 40 60 06228-045 Figure 48. Inverting Gain Large Signal Pulse Response 20 15 10 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 06228-049 VGAIN = 0.7V VS= ±3V VGAIN = 0.7V PREAMP GAIN = –3 0.2 20 VOUT (mV) 5 0 0 VIN (mV) 0 –5 –0.2 INPUT –0.4 –20 –10 –40 –15 06228-046 INPUT CL = 0pF CL = 10pF CL = 22pF CL = 47pF –0.6 –100 –50 0 50 100 150 TIME (ns) 200 250 300 –60 350 –20 –100 –50 0 50 100 150 200 TIME (ns) 250 300 350 –2.0 400 Figure 46. Inverting Gain Small Signal Pulse Response 25 20 15 10 VGAIN = 0.7V 2.5 2.0 1.5 1.0 Figure 49. Large Signal Pulse Response for Various Values of Load Capacitance Using ±3V Power Supplies 30 VGAIN = 0.7V VS = ±5V 3 20 2 10 1 VOUT (mV) 0 –5 0 –0.5 –1.0 INPUT OUTPUT WHEN PWRA = 0 OUTPUT WHEN PWRA = 1 –50 0 50 100 150 TIME (ns) 200 250 300 –1.5 –2.0 0 0 –10 –15 –20 –25 –100 –10 –20 INPUT CL = 0pF CL = 10pF CL = 22pF CL = 47pF* –1 –2 06228-047 300 Figure 47. Large Signal Pulse Response for Both Power Levels Figure 50. Large Signal Pulse Response for Various Values of Load Capacitance Using ±5V Power Supplies Rev. 0 | Page 15 of 28 06228-050 –2.5 350 *WITH 20Ω RESISTOR IN SERIES WITH OUTPUT. –30 –100 –50 0 50 100 150 200 250 TIME (ns) –3 350 VOUT (mV) VIN (mV) VIN (mV) 5 0.5 VOUT (V) VIN (mV) 06228-048 –0.6 –100 INPUT OUTPUT WHEN PWRA = 0 OUTPUT WHEN PWRA = 1 –40 –60 350 –25 –100 –2.5 350 VOUT (mV) VIN (mV) VIN (mV) 5 0.5 AD8336 30 VGAIN = 0.7V VS = ±12V 3 10 0 –10 PSRR VPOS VNEG 20 2 VGAIN = 0.7V VGAIN = 0V VGAIN = –0.7V 10 1 VOUT (mV) PSRR (dB) 06228-051 VIN (mV) –20 –30 –40 0 0 –10 INPUT CL = 0pF CL = 10pF* CL = 22pF* CL = 47pF* –1 –20 –2 –50 –60 100k –50 0 50 100 150 TIME (ns) 200 250 300 1M FREQUENCY (Hz) 5M Figure 51. Large Signal Pulse Response for Various Values of Load Capacitance Using ±12V Power Supplies 2.5 40 Figure 54 PSRR vs. Frequency for Three Values of VGAIN QUIESCENT SUPPLY CURRENT (mA) 1.5 HIGH POWER 30 0.5 (V) VOUT VGAIN 20 LOW POWER –0.5 10 VS = ±12V VS = ±5V VS = ±3V –45 –25 –5 15 25 45 55 75 95 125 06228-055 –1.5 0 1.0 0.5 TIME (µs) 1.5 2.0 06228-052 –2.5 –0.5 0 –65 TEMPERATURE (°C) Figure 52. Gain Response 0.5 0.4 0.3 5 4 3 2 1 0 –1 –2 –3 VIN (V) VOUT (V) –6 –3 TIME (µs) 0 3 6 –4 06228-053 Figure 55. IQ vs. Temperature for Three Values of Supply Voltage and High and Low Power VGAIN = 0.7V INPUT VOLTAGE (V) 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 –0.5 –9 –5 Figure 53. VGA Overdrive Recovery OUTPUT VOLTAGE (V) Rev. 0 | Page 16 of 28 06228-054 –30 –100 *WITH 20Ω RESISTOR IN SERIES WITH OUTPUT –3 350 AD8336 TEST CIRCUITS NETWORK ANALYZER NETWORK ANALYZER OUT 50Ω 50Ω IN OUT 50Ω 50Ω IN AD8336 4 AD8336 453Ω 1 49.9Ω 5 + PrA – 453Ω 1 4 + – 49.9Ω PrA 5 8 9 12 11 301Ω 100Ω 06228-056 8 9 12 11 VGAIN 301Ω 100Ω 06228-059 Figure 56. Gain vs. VGAIN and Gain Error vs. VGAIN NETWORK ANALYZER Figure 59. Group Delay OUT 50Ω 50Ω IN AD8336 4 AD8336 4 453Ω 5 + PrA – 1 453Ω 50Ω DMM + – 49.9Ω PrA 8 9 12 11 1 + 06228-060 5 301Ω 100Ω ¯ 5 8 12 11 301Ω 100Ω VGAIN OPTIONAL CLOAD 06228-057 Figure 57. Frequency Response NETWORK ANALYZER Figure 60. Offset Voltage NETWORK ANALYZER CONFIGURE TO MEASURE Z-CONVERTED S22 OUT 50Ω 50Ω IN 50Ω IN 0Ω AD8336 4 NC AD8336 4 49.9Ω 5 + – PrA 453Ω NC 1 49.9Ω 5 + PrA – 1 0Ω 8 9 12 11 8 9 12 11 301Ω 100Ω NC 453Ω 100Ω 06228-058 301Ω NC 06228-061 NC = NO CONNECT NC = NO CONNECT Figure 58. Frequency Response of the Preamp Figure 61. Output Resistance vs. Frequency Rev. 0 | Page 17 of 28 AD8336 OSCILLOSCOPE SPECTRUM ANALYZER PULSE GENERATOR OUT POWER SPLITTER CH1 50Ω 50Ω CH2 IN 50Ω AD8336 4 5 AD8336 4 1 + PrA – 5 + PrA – OPTIONAL 20Ω 453Ω 1 49.9Ω 8 9 12 11 8 9 12 11 301Ω 06228-062 301Ω VGAIN 0.7V 06228-065 100Ω 100Ω Figure 62. Input Referred Noise and Output Referred Noise Figure 65. Pulse Response OSCILLOSCOPE NOISE FIGURE METER NOISE SOURCE DRIVE NOISE SOURCE INPUT PULSE FUNCTION GENERATOR GENERATOR SINE WAVE SQUARE WAVE POWER SPLITTER CH 1 50Ω 50Ω CH 2 0Ω AD8336 49.9Ω (OR ∞) 4 5 11 AD8336 1 0Ω 49.9Ω 4 5 DIFFERENTIAL FET PROBE 453Ω 1 + PrA – + PrA – NC 8 9 12 11 301Ω 100Ω 06228-063 8 9 12 VGAIN 301Ω 100Ω NC = NO CONNECT 06228-066 Figure 63. Noise Figure vs. VGAIN SPECTRUM ANALYZER SIGNAL GENERATOR INPUT 50Ω RLOAD Figure 66. Gain Response OSCILLOSCOPE ARBITRARY WAVEFORM GENERATOR –20dB POWER SPLITTER CH 1 50Ω 50Ω CH 2 LOW-PASS FILTER AD8336 4 AD8336 4 1 49.9Ω 5 + PrA – 49.9Ω CLOAD 5 + PrA – 453Ω 1 NC 8 9 12 11 8 9 12 11 301Ω 06228-064 301Ω VGAIN 0.7V 06228-067 100Ω 100Ω NC = NO CONNECT Figure 64. Harmonic Distortion Figure 67. VGA Overdrive Recovery Rev. 0 | Page 18 of 28 AD8336 POWER SUPPLIES CONNECTED TO NETWORK ANALYZER BIAS PORT NETWORK ANALYZER DMM (+I) 13 BENCH POWER SUPPLY OUT 50Ω 50Ω IN AD8336 4 5 + – PrA 1 BYPASS CAPACITORS REMOVED FOR MEASUREMENT 4 VPOS OR VNEG AD8336 + PrA – 1 8 9 12 11 10 301Ω 100Ω DMM (–I) 06228-068 49.9Ω 5 DIFFERENTIAL FET PROBE 8 9 12 11 301Ω 100Ω 06228-071 VGAIN Figure 68. Supply Current NETWORK ANALYZER Figure 71. Power Supply Rejection Ratio SPECTRUM ANALYZER OUT 50Ω 50Ω IN 50Ω IN 453Ω AD8336 4 + 4 AD8336 1 100Ω 100Ω 49.9Ω 5 PrA – 5 + PrA – 1 8 9 12 11 06228-072 8 9 12 11 301Ω 301Ω VGAIN 06228-069 100Ω 0.7V Figure 69. Frequency Response, Inverting Gain Figure 72. Input Referred Noise vs. Source Resistance SPECTRUM ANALYZER PULSE GENERATOR OSCILLOSCOPE POWER SPLITTER OUT CH1 50Ω CH2 50Ω IN 50Ω AD8336 4 AD8336 1 100Ω 100Ω 49.9Ω + – PrA 453Ω 4 5 5 + PrA – 1 8 9 12 11 06228-070 8 9 12 11 06228-073 301Ω 301Ω 100Ω 0.7V 0.7V Figure 70. Pulse Response, Inverting Gain Figure 73. Short-Circuit Input Noise vs. Frequency Rev. 0 | Page 19 of 28 AD8336 SPECTRUM ANALYZER SIGNAL GENERATOR OUT 50Ω 22dB 50Ω OPTIONAL 20dB ATTENUATOR IN AD8336 453Ω 4 + 49.9Ω PrA 5 – 1 8 9 12 11 301Ω 100Ω 06228-074 VGAIN Figure 74. IP1dB vs. VGAIN SPECTRUM ANALYZER SIGNAL GENERATOR OUT 50Ω 50Ω –20dB IN AD8336 AMPLIFIER 4 AD8336 DUT 0Ω 1 5 4 49.9Ω 5 + PrA – + – 453Ω PrA 1 8 9 12 11 8 9 12 11 301Ω 100Ω 0.7V 100Ω 301Ω 06228-075 VGAIN Figure 75. IP1dB vs. VGAIN, High Signal Level Inputs SPECTRUM ANALYZER INPUT 50Ω +22dB SIGNAL GENERATOR –6dB COMBINER –6dB 4 AD8336 DUT + – 453Ω +22dB SIGNAL GENERATOR –6dB 49.9Ω PrA 1 5 8 9 12 11 301Ω 100Ω 06228-076 VGAIN Figure 76. IMD and OIP3 Rev. 0 | Page 20 of 28 AD8336 THEORY OF OPERATION OVERVIEW The AD8336 is the first VGA designed for operation over exceptionally broad ranges of temperature and supply voltage. Its performance has been characterized from temperatures extending from −55°C to 125°C, and supply voltages from ±3 V to ±12 V. It is ideal for applications requiring dc coupling, large output voltage swings, ver y large gain ranges, extreme temperature variations, or a combination thereof. The simplified block diagram is shown in Figure 77. The AD8336 includes a voltage feedback preamplifier, an amplifier with a fixed gain of 34 dB, a 60 dB attenuator, and various bias and interface circuitr y. The independent voltage feedback op amp can be used in noninverting and inverting configurations, and functions as a preamplifier to the variable gain amplifier (VGA). If desired, the op amp output (PRAO) and VGA input (VGAI) pins provide for connection of an interstage filter to eliminate noise and offset. The bandwidth of the AD8336 is dc to 100 MHz with a gain range of 60 dB (−14 dB to +46 dB.) For applications that require large supply voltages, a reduction in power is advantageous. The power reduction pin (PWRA) permits the power and bandwidth to be reduced by about half in such applications. RFB2 301Ω * PRAO VGAI INPP + PREAMPLIFIER The gain of the uncommitted voltage feedback preamplifier is set with external resistors. The combined preamplifier and VGA gain is specified in two ranges, between −14 dB to +46 dB and 0 dB to 60 dB. Since the VGA gain is fixed at 34 dB (50×), the preamp gain is adjusted for gains of 12 dB (4×) and 26 dB (200×). With low preamplifier gains between 2× and 4×, it may be desirable to reduce the high frequency gain with a shunt capacitor across RFB2, to ameliorate peaking in the frequency domain (see Figure 77). To maintain stability, the gain of the preamplifier must be 6 dB (2×) or greater. Typical of voltage feedback amplifier configurations, the gainbandwidth product of the AD8336 is fixed (at 400); thus, the bandwidth decreases as the gain is increased beyond the nominal gain value of 4×. For example, if the preamp gain is increased to 20×, the bandwidth reduces by a factor-of-five to about 20 MHz. The −3 dB bandwidth of the preamplifier with a gain of 4× is about 150 MHz, and for the 20× gain is about 30 MHz. The preamp gain diminishes for an amplifier configured for inverting gain, using the same value of feedback resistors as for a noninverting amplifier, but the bandwidth remains unchanged. For example, if the noninverting gain is 4×, the inverting gain is −3×, but the bandwidth stays the same as in the noninverting gain of 4×. However, because the output referred noise of the preamplifier is the same in both cases, the input referred noise increases as the ratio of the two gain values. For the previous example, the input referred noise will increase by a factor of 4/3. 12dB PrA – INPN RFB1 100Ω –60dB TO 0dB ATTENUATOR AND GAIN CONTROL INTERFACE 34dB + _ 4.48kΩ 91.43Ω VOUT VGA The architecture of the variable gain amplifier (VGA) section of the AD8336 is based on the Analog Devices, Inc., X-AMP (exponential amplifier), found in a wide variety of Analog Devices variable gain amplifiers. This type of VGA combines a ladder attenuator and interpolator, followed by a fixed-gain amplifier. The gain control interface is fully differential, permitting positive or negative gain slopes. Note that the common-mode voltage of the gain control inputs increases with increasing supply. The gain slope is 50 dB/V and the intercept is 16.4 dB when the nominal preamp gain is 4× (12 dB). The intercept changes with the preamp gain; for example, when the preamp gain is set to 20× (26 dB) the intercept becomes 30.4 dB. Pin VGAI is connected to the input of the ladder attenuator. The ladder ratio is R/2R and the nominal resistance is 320 Ω. To reduce preamp loading and large-signal dissipation, the input resistance at Pin VGAI is 1.28 kΩ. Safe current density and power dissipation levels are maintained even when large dc signals are applied to the ladder. The tap resistance of the resistors within the R/2R ladder is 640 Ω/3 or 213.3 Ω, the Johnson noise source of the attenuator. BIAS PWRA VPOS VNEG GPOS GNEG VCOM *OPTIONAL DEPEAKING CAPACITOR. SEE TEXT. Figure 77. Simplified Block Diagram To maintain low noise, the output stages of both the preamplifier and the VGA are capable of driving relatively small load resistances. However, at the largest supply voltages, the signal current may exceed safe operating limits for the amplifiers and the load current must not exceed 50 mA. With a ±12 V supply and ±10 V output voltage at the preamplifier or VGA output, load resistances as low as 200 Ω are acceptable. For power supply voltages ≥ ±10 V, the maximum operating temperature range is derated to +85°C, as the power may exceed safe limits (see the Absolute Maximum Ratings section). Since harmonic distortion products may increase for various combinations of low impedance loads and high output voltage swings, it is recommended that the user determine load and drive conditions empirically. Rev. 0 | Page 21 of 28 06228-077 AD8336 SETTING THE GAIN The overall gain of the AD8336 is the sum (in dB) or the product (magnitude) of the preamp gain and the VGA gain. The preamp gain is calculated as with any op amp, as seen in the Applications section. It is most convenient to think of the device gain in exponential terms (that is, in dB) since the VGA responds linearly-in-dB with changes in control voltage VGAIN at the gain pins. The gain equation for the VGA is NOISE The noise of the AD8336 is dependent on the value of the VGA gain. At maximum VGAIN, the dominant noise source is the preamp but shifts to the VGA as VGAIN diminishes. The input referred noise at the highest VGA gain and a preamp gain of 4×, with RFB1 =100 Ω and RFB2 = 301 Ω, is 3 nV/√Hz, and determined by the preamp and its gain setting resistors. See Table 4 for the noise components for the preamp. Table 4. AD8336 Noise Components for Preamp Gain = 4× Noise Component Op Amp (Gain = 4×) RFB1 = 100 Ω RFB2 = 301 Ω VGA Noise Voltage (nV/√Hz) 2.6 0.96 0.55 0.77 ⎡ 50 dB ⎤ VGA Gain (dB) = ⎢VG AIN (V) × + 4. 4 dB V⎥ ⎦ ⎣ where VG = VGPOS − VGNEG The gain and gain range of the VGA are both fixed at 34 dB and 60 dB, respectively ; thus, the composite device gain is changed by adjusting the preamp gain. For a preamp gain of 12 dB (4×), the composite gain is −14 dB to +46 dB. Thus, the calculation for the composite gain (in dB) is Composite Gain = G PRA + [VG (V) × 49.9 dB/V] + 4.4 dB For example, the midpoint gain when the preamp gain is 12 dB is 12 dB + [0 V × 49.9 dB /V] + 4.4 dB = 16.4 dB Figure 3 is a plot of gain in dB vs. VGAIN in mV, when the preamp gain is 12 dB (4×). Note that the computed result closely matches the plot of actual gain. In Figure 3, the gain slope flattens at the limits of the VG input. The gain response is linear-in-dB over the center 80% of the control range of the device. Figure 78 shows the ideal gain characteristics for the VGA stage and composite VGA + preamp. 70 60 50 40 GAIN (dB) Using the listed values, the total noise of the AD8336 is slightly less than 3 nV/√Hz, referred to the input. Although the output noise VGA is 3.1 nV/√Hz, the input referred noise is 0.77 nV/√Hz when divided by the preamplifier gain of 4× At other than maximum gain, the noise of the VGA is determined from the output noise. The noise in the center of the gain range is about 150 nV/√Hz. Since the gain of the fixed gain amplifier that is part of the VGA is 50×, the VGA input referred noise is approximately 3 nV/√Hz, the same value as the preamp and VGA combined. This is expected since the input referred noise is the same at the input of the attenuator at maximum gain. However, the noise referred to the VGAI pin (the preamp output) increases by the amount of attenuation through the ladder network. The noise at any point along the ladder network is primarily comprised of the ladder resistance noise, the noise of the input devices, and the feedback resistor network noise. The ladder network and the input devices are the largest noise sources. At minimum gain, the output noise increases slightly to about 180 nV/√Hz because of the finite structure of the X-AMP. GAIN CHARACTERISTICS COMPOSITE GAIN VGA STAGE GAIN FOR PREAMP GAIN = 26dB USABLE GAIN RANGE OF AD8336 30 20 10 0 OFFSET VOLTAGE Extensive cancellation circuitr y included in the variable gain amplifier section minimizes locally generated offset voltages. However when operated at ver y large values of gain, dc voltage errors at the output can still result from small dc input voltages. When configured for the nominal gain range of −14 dB to 46 dB, the maximum gain is 200× and an offset of only 100 μV at the input generates 20 mV at the output. The primar y source for dc offset errors is the preamplifier; ac coupling between the PRAO and VGAI pins is the simplest solution. In applications where dc coupling is essential, a compensating current can be injected at the INPN input (Pin 5) to cancel preamp offset. The direction of the compensating current depends on the polarity of the offset voltage. FOR PREAMP GAIN = 12dB FOR PREAMP GAIN = 6dB –10 –20 –0.5 –0.3 –0.1 0.1 VG (V) 0.3 0.5 0.7 Figure 78. Ideal Gain Characteristics of the AD8336 06228-078 –30 –0.7 Rev. 0 | Page 22 of 28 AD8336 APPLICATIONS AMPLIFIER CONFIGURATION The AD8336 amplifiers can be configured in various options. In addition to the 60 dB gain range variable gain stage, an uncommitted voltage gain amplifier is available to the user as a preamplifier. The preamplifier connections are separate to enable noninverting or inverting gain configurations or the use of interstage filtering. The AD8336 can be used as a cascade connected VGA with preamp input, as a standalone VGA, or as a standalone preamplifier. This section describes some of the possible applications. PRAO 8 Circuit Configuration for Noninverting Gain The noninverting configuration is shown in Figure 80. The preamp gain is described by the classical op amp gain equation Gain = R FB 2 R FB1 +1 VGAI 9 The practical gain limits for this amplifier are 6 dB to 26 dB. The gain bandwidth product is about 600 MHz, so that at 150 MHz, the maximum achievable gain is 12 dB (4×). The minimum gain is established internally by fixed loop compensation, and is 6 dB (2×). This amplifier is not designed for unity gain operation. Table 5 shows the gain bandwidth for the noninverting gain configuration. CIRCUIT CONFIGURATION FOR NONINVERTING GAIN INPP INPN INPP 4 INPN 5 + PrA – ATTENUATOR –60dB TO 0dB 34dB 1 VOUT AD8336 RFB1 100Ω AD8336 4 5 PREAMPLIFIER –60dB TO 0dB PRAO 9 2 10 3 13 06228-080 PWRA 2 BIAS GAIN CONTROL INTERFACE 06228-079 RFB2 301Ω 8 34dB 1 VOUT GAIN = 12dB VGAI PWRA VNEG VCOM VPOS –5V +5V 10 13 3 11 12 VNEG VPOS VCOM GPOS GNEG Figure 80. Circuit Configuration for Noninverting Gain Figure 79. Application Block Diagram PREAMPLIFIER While obser ving just a few constraints, the uncommitted voltage feedback preamplifier of the AD8336 can be connected in a variety of standard high frequency op amp configurations. The amplifier is optimized for a gain of 4×, (12 dB) and has a gain bandwidth product of 600 MHz. At a gain of 4×, the bandwidth is 150 MHz. The preamplifier gain can be adjusted to a minimum gain of 2×; however, there will be a small peak in the response at high frequencies. At higher preamplifier gains, the bandwidth diminishes proportionally in conformance to the classical voltage gain amplifier GBW relationship. While setting the overall gain of the AD8336, the user needs to consider the input referred offset voltage of the preamplifier. Although the offset of the attenuator and postamplifier are almost negligible, the preamplifier offset voltage, if uncorrected, is increased by the combined gain of the preamplifier and postamplifier. Thus for a maximum gain of 60 dB, an input offset voltage of only 200 μV results in an error of 200 mV at the output. The preamplifier output reliably sources and sinks currents up to 50 mA. When using ±5 V power supplies, the suggested sum of the output resistor values is 400 Ω total for the optimal tradeoff between distortion and noise. Much of the low gain value device characterization was performed with resistor values of 301 Ω and 100 Ω, resulting in a preamplifier gain of 12 dB (4×). With supply voltages between ±5 V and ±12 V, the sum of the output resistance should be increased accordingly and a total resistance of 1 kΩ is recommended. Larger resistance values, subject to a trade-off in higher noise performance, can be used if circuit power and load driving is an issue. When considering the total power dissipation, remember that the input ladder resistance of the VGA is part of the preamp load. Table 5. Gain vs. Bandwidth for Noninverting Preamplifier Configuration. Preamp Gain Numerical dB 4× 12 8× 18 16× 24 20× 26 Preamp BW (MHz) 150 60 30 25 Composite Gain (dB) −14 to +46 −8 to +52 −2 to +58 0 to 60 Rev. 0 | Page 23 of 28 AD8336 Circuit Configuration for Inverting Gain The preamplifier can also be used in an inverting configuration, as shown in Figure 81. CIRCUIT CONFIGURATION FOR INVERTING GAIN INPP GAIN = 9.6dB INPN RFB1 100Ω RFB2 301Ω PREAMPLIFIER 4 5 USING THE POWER ADJUST FEATURE The AD8336 has the provision to operate at lower power with a trade-off in bandwidth. The power reduction applies to the preamp and the VGA sections, and the bandwidth is reduced equally between them. Reducing the power is particularly useful when operating with higher supply voltages and lower values of output loading that would other wise stress the output amplifiers. When Pin PWRA is grounded, the amplifiers operate in their default mode, and the combined 3 dB bandwidth is 80 MHz with the preamp gain adjusted to 4×. When the voltage on Pin PWRA is between 1.2 V and 5 V, the power is reduced by approximately half and the 3 dB bandwidth reduces to approximately 35 MHz. The voltage at pin PWRA must not exceed 5 V. AD8336 + –60dB TO 0dB – PRAO 34dB 1 VOUT 8 9 2 10 3 13 –5V +5V Figure 81. Circuit Configuration for Inverting Gain The same considerations regarding total resistance vs. distortion, noise, and power as noted in the noninverting case apply, except that the amplifier can be operated at unity inverting gain. The signal gain is reduced while the noise gain is the same as for the noninverting configuration: Signal Gain = R FB 2 R FB1 R FB 2 R FB1 06228-081 PWRA VNEG VCOM VPOS DRIVING CAPACITIVE LOADS The output stages of the AD8336 are stable with capacitive loads up to 47 pF for a supply voltage of ±3 V, and capacitive loads up to 10 pF for supply voltages up to ±8 V. For larger combined values of load capacitance and/or supply voltage, a 20 Ω series resistor is recommended for stability. The influence of capacitance and supply voltage are shown in, Figure 50 and Figure 51, where representative combinations of load capacitance and supply voltage requiring a 20 Ω resistor are marked with an asterisk. No resistor is required for the ±3 V plots in Figure 49, while a resistor is required for most of the ±12 V plots in Figure 51. and Noise Gain = +1 Rev. 0 | Page 24 of 28 AD8336 EVALUATION BOARD An evaluation board, AD8336-EVALZ, is available online for the AD8336. Figure 82 is a photo of the board. The board is shipped from the factor y, configured for a preamp gain of 4×. To change the value of the gain of the preamp or the gain polarity to inverting is a matter of changing component values, or installing components in alternate locations provided. All components are standard 0603 size, and the board is designed for RoHS compliancy. Figure 83 shows the locations of components provided for changing the amplifier configuration to inverting gain. Simply install the components shown in red and remove those in gray. OPTIONAL CIRCUITRY The AD8336 features differential inputs for the gain control, permitting nonzero or floating gain control inputs. In order to avoid any delay in making the board operational, the gain input circuit is shipped with Pin GNEG connected to ground via a 0 Ω resistor in location R17. The user can simply adjust the gain of the device by driving the GPOS test loop with a power supply or voltage reference. Resistor networks are provided for fixed gain bias voltages at Pin GNEG and Pin GPOS for commonmode voltages other than 0 V. If it is desired to drive the gain control with an active input such as a ramp, SMA connectors can be installed in the locations GAIN− and GAIN+. Provision is made for an optional SMA connector at PRVG for monitoring the preamp output or driving the VGA from an external source. Remove the 0 Ω resistor at R9 to isolate the preamp from an external generator. 06228-083 Figure 82. AD8336 Evaluation Board BOARD LAYOUT CONSIDERATIONS The evaluation board uses four layers, with power and ground planes located between two conductor layers. This arrangement is highly recommended for customers and several views of the board are provided as reference for board layout details. When laying out a printed circuit board for the AD8336, remember to provide a pad beneath the device to solder the exposed pad of the matching device. The pad in the board should have at least five vias in order to provide a thermal path for the chip scale package. Unlike leaded devices, the thermal pad is the primar y means to remove heat dissipated within the device. Table 6 is a bill of materials for the evaluation board. Figure 83. Components for Inverting Gain Operation Rev. 0 | Page 25 of 28 06228-084 AD8336 Figure 84. Component Side Copper 06228-085 Figure 87. Internal Ground Plane Figure 85. Secondary Side Copper 06228-086 Figure 88. Internal Power Plane Figure 86. Component Side Silk Screen Rev. 0 | Page 26 of 28 06228-087 06228-089 06228-088 AD8336 VPOS GND1 GND2 GND3 GND4 C4 10µF 25V + L2 120nH (BLK LOOPS IN 4 CORNERS) VOUT VOUTL VP R16 4.99kΩ CR1 5.1V VIN R2 49.9Ω VIN1 R5 C8 0.1µF R3 0Ω W1 R1 0Ω VOUTD 1 2 3 R4 0Ω R6 4 C3 0.1µF 16 15 14 13 NC NC NC VPOS VOUT U1 PWRA VCOM INPP GNEG GPOS VNEG VGAI 12 11 10 GNEG C6 1nF GPOS C7 1nF L1 120nH C2 10µF 25V R15 R17 0Ω R14 GAIN+ R13 GAIN– AD8336 C5 9 0.1µF VNEG INPN NC NC PRAO 5 6 7 8 R8 301 Ω R7 100Ω R9 0Ω R11 0Ω + R12 0Ω PRVG NC = NO CONNECT C1 Figure 89. AD8336-EVALZ Schematic Shown as Shipped, Configured for a Noninverting Gain of 4× Table 6. AD8336 Evaluation Board Bill of Materials Q ty 2 3 1 1 2 4 2 2 6 1 1 1 1 1 1 1 1 4 Name Capacitor Capacitor Capacitor Diode Connector Test Loop Test Loop Inductor Resistor Resistor Resistor Resistor Resistor Test Loop Test Loop Header Integrated Circuit Rubber Bumper Description Tantalum 10 μF, 25 V 0.1 μF, 16 V, 0603, X7R 1 nF, 50 V, 0603, X7R Zener, 5.1 V, 1 W SMA Fem, RA, PC Mt Black Violet Ferrite Bead 0 Ω, 5%, 0603 49.9 Ω 1% 1/16 W 0603 100 Ω 1% 1/16 W 0603 301 Ω 1/16 W 1% 0603 4.99 kΩ 1/16 W 1% 0603 Green Red 0.1” Center VGA Foot Reference Designator C2, C4 C3, C5, C8 C7 CR1 VIN, VOUT GND, GND1, GND2, GND3 GNEG, GPOS L1, L2 R1, R3, R4, R9, R11, R17 R2 R7 R8 R16 VNEG VPOS W1 Z1 NA Manufacturer Nichicon KEMET Panasonic Diodes, Inc. Amphenol Components Corporation Components Corporation Murata Panasonic Panasonic Panasonic Panasonic Panasonic Components Corporation Components Corporation Molex Analog Devices 3M Mfg. Part Number F931E106MCCC C0603C104K4RSCTU ECJ-1VB2A102K DFLZ5V1-7 901-143-6RFX TP-104-01-00 TP-104-01-07 BLM18BA750SN1D ERJ-2GE0R00X ERJ-3EKF49R9V ERJ-3EKF1000V ERJ-3EKF3010V ERJ-3EKF4991V TP-104-01-05 TP-104-01-02 22-10-2031 AD8336ACPZ SJ67A11 Rev. 0 | Page 27 of 28 06228-082 R10 49.9Ω AD8336 OUTLINE DIMENSIONS 4.00 BSC SQ 0.60 MAX 0.60 MAX 0.65 BSC 3.75 BSC SQ 0.75 0.60 0.50 (BOTTOM VIEW) PIN 1 INDICATOR 13 12 16 PIN 1 INDICATOR 1 TOP VIEW EXPOSED PAD 9 8 5 4 2.25 2.10 SQ 1.95 0.25 MIN 12° MAX 1.00 0.85 0.80 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 1.95 BSC THE EXPOSED PAD IS NOT CONNECTED INTERNAL LY. FOR INCREASED RELIABILIT Y OF THE SOLDER JOINTS AND MAXIMUM THERMA L CAPABILITY, IT IS RECOMMENDED THAT THE PADDLE BE SOLDERED TO THE GROUND PLANE. 100506-A SEATING PLANE 0.35 0.30 0.25 0.20 REF COPLANARIT Y 0.08 COMPLIANT TO JEDEC STANDARDS MO-220-VGGC Figure 90. 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 4 mm × 4 mm Body, Very Thin Quad (CP-16-4) Dimensions shown in millimeters ORDERING GUIDE Model AD8336ACPZ1 AD8336ACPZ-R71 AD8336ACPZ-RL1 AD8336ACPZ-WP1 AD8336-EVALZ1 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 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] 16-Lead Lead Frame Chip Scale Package [LFCSP_VQ] Evaluation Board Package Option CP-16-4 CP-16-4 CP-16-4 CP-16-4 Z = Pb-free part. ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 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