50 MHz Current Feedback Amplifier Features General Description # # # # # # # # # The EL2020 is a fast settling, wide bandwidth amplifier optimized for gains between b 10 and a 10. Built using the Elantec monolithic Complementary Bipolar process, this amplifier uses current mode feedback to achieve more bandwidth at a given gain then a conventional voltage feedback operational amplifier. Slew rate 500 V/ms g 33 mA output current Drives g 2.4V into 75X Differential phase k 0.1§ Differential gain k 0.1% V supply g 5V to g 18V Output short circuit protected Uses current mode feedback 1% settling time of 50 ns for 10V step # Low cost # 9 mA supply current # 8-pin mini-dip Applications # # # # # Video gain block Residue amplifier Radar systems Current to voltage converter Coax cable driver with gain of 2 EL2020C EL2020C The EL2020 will drive two double terminated 75X coax cables to video levels with low distortion. Since it is a closed loop device, the EL2020 provides better gain accuracy and lower distortion than an open loop buffer. The device includes output short circuit protection, and input offset adjust capability. The bandwidth and slew rate of the EL2020 are relatively independent of the closed loop gain taken. The 50 MHz bandwidth at unity gain only reduces to 30 MHz at a gain of 10. The EL2020 may be used in most applications where a conventional op amp is used, with a big improvement in speed power product. Elantec products and facilities comply with Elantec document, QRA-1: Processing-Monolithic Products. Connection Diagrams SOL Ordering Information Part No. Temp. Range Pkg. OutlineÝ EL2020CN b 40§ C to a 85§ C P-DIP MDP0031 EL2020CM b 40§ C to a 85§ C 20-Lead MDP0027 SOL 2020 – 2 2020 – 1 Manufactured under U.S. Patent No. 4,893,091. Note: All information contained in this data sheet has been carefully checked and is believed to be accurate as of the date of publication; however, this data sheet cannot be a ‘‘controlled document’’. Current revisions, if any, to these specifications are maintained at the factory and are available upon your request. We recommend checking the revision level before finalization of your design documentation. © 1989 Elantec, Inc. December 1995 Rev G DIP EL2020C 50 MHz Current Feedback Amplifier Absolute Maximum Ratings (25§ C) VS VIN DVIN IIN IINS PD Supply Voltage Input Voltage Differential Input Voltage Input Current (Pins 2 or 3) Input Current (Pins 1, 5, or 8) Maximum Power Dissipation (See Curves) Peak Output Current IOP Output Short Circuit Duration (Note 2) TA TJ g 18V or 36V g 15V or VS g 10V TST g 10 mA b 40§ C to a 85§ C Operating Temperature Range Operating Junction Temperature Plastic Package, SOL Storage Temperature 150§ C b 65§ C to a 150§ C g 5 mA 1.25W Short Circuit Protected Continuous Important Note: All parameters having Min/Max specifications are guaranteed. The Test Level column indicates the specific device testing actually performed during production and Quality inspection. Elantec performs most electrical tests using modern high-speed automatic test equipment, specifically the LTX77 Series system. Unless otherwise noted, all tests are pulsed tests, therefore TJ e TC e TA. Test Level I II III IV V Test Procedure 100% production tested and QA sample tested per QA test plan QCX0002. 100% production tested at TA e 25§ C and QA sample tested at TA e 25§ C , TMAX and TMIN per QA test plan QCX0002. QA sample tested per QA test plan QCX0002. Parameter is guaranteed (but not tested) by Design and Characterization Data. Parameter is typical value at TA e 25§ C for information purposes only. Parameter VOS (Note 1) Description Input Offset Voltage DVOS/DT Offset Voltage Drift CMRR (Note 3) Common Mode Rejection Ratio PSRR (Note 4) Power Supply Rejection Ratio Limits Temp Units a 10 I mV a 15 Typ Max 25§ C b 10 3 TMIN, TMAX b 15 III mV b 30 V mV/§ C II dB ALL 50 60 75 25§ C 65 TMIN, TMAX 60 25§ C, TMAX b 15 TMIN b 25 ALL 1 a IIN Non-inverting Input Current a RIN Non-Inverting Input Resistance a IPSR (Note 4) Non-Inverting Input Current Power Supply Rejection 25§ C, TMAX b Input Current 25§ C, TMAX b 40 TMIN b 50 b IIN (Note 1) Test Level Min 5 dB dB a 15 II mA a 25 III mA II MX 5 0.05 TMIN 2 I III 10 0.5 II mA/V 1.0 III mA/V a 40 II mA a 50 III mA TD is 2.8in Open Loop Characteristics VS e g 15V EL2020C 50 MHz Current Feedback Amplifier Open Loop Characteristics VS e g 15V Ð Contd. Description Limits Temp Min b Input Current Common Mode Rejection 25§ C, TMAX b Input Current Power Supply Rejection 25§ C, TMAX Rol Transimpedence (DVOUT/D(bIIN)) RL e 400X, VOUT e g 10V 25§ C, TMAX 300 TMIN 50 AVOL1 Open Loop DC Voltage Gain RL e 400X, VOUT e g 10V 25§ C, TMAX 70 TMIN 60 Open Loop DC Voltage Gain RL e 100X, VOUT e g 2.5V 25§ C, TMAX 60 TMIN 55 Output Voltage Swing RL e 400X 25§ C, TMAX g 12 TMIN g 11 IOUT Output Current RL e 400X 25§ C, TMAX g 30 TMIN g 27.5 Is Quiescent Supply Current b ICMR (Note 3) b IPSR (Note 4) AVOL2 VO Typ 0.5 TMIN 0.05 TMIN 25§ C Test Level 2.0 II mA/V 4.0 III mA/V 0.5 II mA/V 1.0 III mA/V II V/mA III V/mA 1000 80 70 g 13 g 32.5 9 TMIN, TMAX Units Max II dB III dB II dB III dB II V III V II mA III mA 12 I mA 15 III mA Is off Supply Current, Disabled, V8 e 0V ALL 5.5 7.5 II mA Ilogic Pin 8 Current, Pin 8 e 0V ALL 1.1 1.5 II mA ID Min Pin 8 Current to Disable ALL 120 250 II mA Ie Max Pin 8 Current to Enable ALL 30 II mA 3 TD is 4.1in Parameter EL2020C 50 MHz Current Feedback Amplifier Parameter Description SR1 FPBW1 tr1 tf1 tp1 Closed Loop Gain of 1 V/V (0 dB), RF e 1 kX Slew Rate, Rl e 400X, VO e g 10V, test at VO e g 5V Full Power Bandwidth (Note 5) Rise Time, Rl e 100X, VOUT e 1V, 10% to 90% Fall Time, Rl e 100X, VOUT e 1V, 10% to 90% Propagation Delay, Rl e 100X, VOUT e 1V, 50% Points BW ts ts Closed Loop Gain of 1 V/V (0 dB), RF e 820X b 3 dB Small Signal Bandwidth, Rl e 100X, VO e 100 mV 1% Settling Time, Rl e 400X, VO e 10V 0.1% Settling Time, Rl e 400X, VO e 10V SR10 FPBW10 tr10 tf10 tp10 Closed Loop Gain of 10 V/V (20 dB), RF e 1 kX, RG e 111X Slew Rate, Rl e 400X, VO e g 10V, Test at VO e g 5V Full Power Bandwidth (Note 5) Rise Time, Rl e 100X, VOUT e 1V, 10% to 90% Fall Time, Rl e 100X, VOUT e 1V, 10% to 90% Propagation Delay, Rl e 100X, VOUT e 1V, 50% points BW ts ts Closed Loop Gain of 10 V/V (20 dB), RF e 680X, RG e 76X b 3 dB Small Signal Bandwidth, Rl e 100X, VO e 100 mV 1% Settling Time, Rl e 400 X, VO e 10V 0.1% Settling Time, Rl e 400X, VO e 10V Test Level Units 500 7.95 6 6 8 I I V V V V/ms MHz ns ns ns 50 50 90 V V V MHz ns ns 500 7.95 25 25 12 I I V V V V/ms MHz ns ns ns 30 55 280 V V V MHz ns ns Min Typ 300 4.77 300 4.77 Max Note 1: The offset voltage and inverting input current can be adjusted with an external 10 kX pot between pins 1 and 5 with the wiper connected to VCC (Pin 7) to make the output offset voltage zero. Note 2: A heat sink is required to keep the junction temperature below the absolute maximum when the output is short circuited. Note 3: VCM e g 10V. Note 4: g 4.5V s VS s g 18V. Note 5: Full Power Bandwidth is guaranteed based on Slew Rate measurement. FPBW e SR/2qVpeak. 4 TD is 3.2in AC Closed Loop Characteristics EL2020C VS e g 15V, TA e 25§ C EL2020C 50 MHz Current Feedback Amplifier Typical Performance Curves Non-Inverting Gain of One AVCL e a 1 Settling Time vs Output Swing Gain vs Frequency Phase Shift vs Frequency b 3 dB Bandwidth vs Supply Voltage Rise Time and Prop Delay vs Temperature Slew Rate vs Supply Voltage Slew Rate vs Temperature 2020 – 4 5 EL2020C 50 MHz Current Feedback Amplifier Typical Performance Curves Ð Contd. Inverting Gain of One AVCL e b 1 Settling Time vs Output Swing Gain vs Frequency Phase Shift vs Frequency b 3 dB Bandwidth vs Supply Voltage Rise Time and Prop Delay vs Temperature Slew Rate vs Supply Voltage Slew Rate vs Temperature 2020 – 5 6 EL2020C 50 MHz Current Feedback Amplifier Typical Performance Curves Ð Contd. Non-Inverting Gain of Two AVCL e a 2 Gain vs Frequency Settling Time vs Output Swing b 3 dB Bandwidth vs Supply Voltage Slew Rate vs Supply Voltage Phase Shift vs Frequency Rise Time and Prop Delay vs Temperature Slew Rate vs Temperature 2020 – 6 7 EL2020C 50 MHz Current Feedback Amplifier Typical Performance Curves Ð Contd. Non-Inverting Gain of Ten AVCL e a 10 Gain vs Frequency b 3 dB Bandwidth vs Supply Voltage Settling Time vs Output Swing Slew Rate vs Supply Voltage Phase Shift vs Frequency Rise Time and Prop Delay vs Temperature Slew Rate vs Temperature 2020 – 7 8 EL2020C 50 MHz Current Feedback Amplifier Typical Performance Curves Ð Contd. Maximum Undistorted Output Voltage vs Frequency Input Resistance vs Temperature PSRR vs Frequency Voltage Noise vs Frequency Current Noise vs Frequency Output Impedance vs Frequency Supply Current vs Supply Voltage 8-Lead Plastic DIP Maximum Power Dissipation vs Ambient Temperature 20-Lead SOL Maximum Power Dissipation vs Ambient Temperature 2020 – 8 9 EL2020C 50 MHz Current Feedback Amplifier in a lower b 3 dB frequency. Attenuation at high frequency is limited by a zero in the closed loop transfer function which results from stray capacitance between the inverting input and ground. Application Information Theory of Operation The EL2020 has a unity gain buffer similar to the EL2003 from the non-inverting input to the inverting input. The error signal of the EL2020 is a current flowing into (or out of) the inverting input. A very small change in current flowing through the inverting input will cause a large change in the output voltage. This current amplification is the transresistance (ROL) of the EL2020 [VOUT e ROL * IINV] . Since ROL is very large ( & 106), the current flowing into the inverting input in the steady state (non-slewing) condition is very small. Power Supplies The EL2020 may be operated with single or split power supplies as low as g 3V (6V total) to as high as g 18V (36V total). The slew rate degrades significantly for supply voltages less than g 5V (10V total), but the bandwidth only changes 25% for supplies from g 3V to g 18V. It is not necessary to use equal value split power supplies, i.e., b 5V and a 12V would be excellent for 0V to 1V video signals. Bypass capacitors from each supply pin to a ground plane are recommended. The EL2020 will not oscillate even with minimal bypassing, however, the supply will ring excessively with inadequate capacitance. To eliminate supply ringing and the errors it might cause, a 4.7 mF tantalum capacitor with short leads is recommended for both supplies. Inadequate supply bypassing can also result in lower slew rate and longer settling times. Therefore we can still use op-amp assumptions as a first order approximation for circuit analysis, namely that. . . 1. The voltage across the inputs & 0 and 2. The current into the inputs is & 0 Simplified Block Diagram of EL2020 Non-Inverting Amplifier 2020 – 10 Resistor Value Selection and Optimization 2020 – 11 The value of the feedback resistor (and an internal capacitor) sets the AC dynamics of the EL2020. A nominal value for the feedback resistor is 1 kX, which is the value used for production testing. This value guarantees stability. For a given gain, the bandwidth may be increased by decreasing the feedback resistor and, conversely, the bandwidth will be decreased by increasing the feedback resistor. EL2020 Typical Non-Inverting Amplifier Characteristics Reducing the feedback resistor too much will result in overshoot and ringing, and eventually oscillations. Increasing the feedback resistor results 10 AV RF RG Bandwidth a1 a2 a5 a 10 820X 750X 680X 680X None 750X 170X 76X 50 MHz 50 MHz 50 MHz 30 MHz 10V Settling Time 1% 0.1% 50 ns 50 ns 50 ns 55 ns 90 ns 100 ns 200 ns 280 ns EL2020C 50 MHz Current Feedback Amplifier pling. Inductive sources may cause oscillations; a 1 kX resistor in series with the input lead will usually eliminate problems without sacrificing too much speed. Application Information Ð Contd. Summing Amplifier Current Limit The EL2020 has internal current limits that protect the output transistors. The current limit goes down with junction temperature rise. At a junction temperature of a 175§ C the current limits are at about 50 mA. If the EL2020 output is shorted to ground when operating on g 15V supplies, the power dissipation could be as great as 1.1W. A heat sink is required in order for the EL2020 to survive an indefinite short. Recovery time to come out of current limit is about 50 ns. 2020 – 12 EL2020 Typical Inverting Amplifier Characteristics AV RF R1, R2 Bandwidth b1 b2 b5 b 10 750X 750X 680X 680X 750X 375X 130X 68X 40 MHz 40 MHz 40 MHz 30 MHz 10V Settling Time 1% 0.1% 50 ns 55 ns 55 ns 70 ns 130 ns 160 ns 160 ns 170 ns Using the 2020 with Output Buffers When more output current is required, a wideband buffer amplifier can be included in the feedback loop of the EL2020. With the EL2003 the subsystem overshoots about 10% due to the phase lag of the EL2003. With the EL2004 in the loop, the overshoot is less than 2%. For even more output current, several buffers can be paralleled. Input Range The non-inverting input to the EL2020 looks like a high resistance in parallel with a few picofarads in addition to a DC bias current. The input characteristics change very little with output loading, even when the amplifier is in current limit. EL2020 Buffered with an EL2004 The input charactersitics also change when the input voltage exceeds either supply by 0.5V. This happens because the input transistor’s base-collector junctions forward bias. If the input exceeds the supply by LESS than 0.5V and then returns to the normal input range, the output will recover in less than 10 ns. However if the input exceeds the supply by MORE than 0.5V, the recovery time can be 100’s of nanoseconds. For this reason it is recommended that Schottky diode clamps from input to supply be used if a fast recovery from large input overloads is required. 2020 – 13 Capacitive Loads The EL2020 is like most high speed feedback amplifiers in that it does not like capacitive loads between 50 pF and 1000 pF. The output resistance works with the capacitive load to form a second non-dominate pole in the loop. This results in excessive peaking and overshoot and can lead to oscillations. Standard resistive isolation techniques used with other op amps work well to isolate capacitive loads from the EL2020. Source Impedance The EL2020 is fairly tolerant of variations in source impedances. Capacitive sources cause no problems at all, resistive sources up to 100 kX present no problems as long as care is used in board layout to minimize output to input cou- 11 EL2020C 50 MHz Current Feedback Amplifier Driving Cables Application Information Ð Contd. The EL2020 was designed with driving coaxial cables in mind. With 30 mA of output drive and low output impedance, driving one to three 75X double terminated coax cables with one EL2020 is practical. Since it is easy to set up a gain of a 2, the double matched method is the best way to drive coax cables, because the impedance match on both ends of the cable will suppress reflections. For a discussion on some of the other ways to drive cables, see the section on driving cables in the EL2003 data sheet. Offset Adjust To calculate the amplifier system offset voltage from input to output we use the equation: Output Offset Voltage e VOS (RF/RG a 1) g IBIAS (RF) The EL2020 output offset can be nulled by using a 10 kX potentiometer from pins 1 to 5 with the slider tied to pin 7 ( a VCC). This adjusts both the offset voltage and the inverting input bias current. The typical adjustment range is g 80 mV at the output. Video Performance Characteristics The EL2020 makes an excellent gain block for video systems, both RS-170 (NTSC) and faster. It is capable of driving 3 double terminated 75X cables with distortion levels acceptable to broadcasters. A common video application is to drive a 75X double terminated coax with a gain of 2. Compensation The EL2020 is internally compensated to work with external feedback resistors for optimum bandwidth over a wide range of closed loop gain. The part is designed for a nominal 1 kX of feedback resistance, although it is possible to get more bandwidth by decreasing the feedback resistance. To measure the video performance of the EL2020 in the non-inverting gain of 2 configuration, 5 identical gain-of-two circuits were cascaded (with a divide by two 75X attenuator between each stage) to increase the errors. The EL2020 becomes less stable by adding capacitance in parallel with the feedback resistor, so feedback capacitance is not recommended. The results, shown in the photos, indicate the entire system of 5 gain-of-two stages has a differential gain of 0.5% and a differential phase of 0.5§ . This implies each device has a differential gain/phase of 0.1% and 0.1§ , but these are too small to measure on single devices. The EL2020 is also sensitive to stray capacitance from the inverting input to ground, so the board should be laid out to keep the physical size of this node small, with ground plane kept away from this node. Differential Phase of 5 Cascaded Gain-Of-Two Stages Active Filters The EL2020’s low phase lag at high frequencies makes it an excellent choice for high performance active filters. The filter response more closely approaches the theoritical response than with conventional op amps due to the EL2020’s smaller propagation delay. Because the internal compensation of the EL2020 depends on resistive feedback, the EL2020 should be set up as a gain block. Differential Gain of 5 Cascaded Gain-Of-Two Stages 2020 – 14 12 EL2020C 50 MHz Current Feedback Amplifier Using the EL2020 as a Multiplexer Application Information Ð Contd. An interesting use of the enable feature is to combine several amplifiers in parallel with their outputs common. This combination then acts similar to a MUX in front of an amplifier. A typical circuit is shown. Video Distribution Amplifier The distribution amplifier shown below features a difference input to reject common mode signals on the 75X coax cable input. Common mode rejection is often necessary to help to eliminate 60 Hz noise found in production environments. When the EL2020 is disabled, the DC output impedance is very high, over 10 kX. However there is also an output capacitance that is non-linear. For signals of less than 5V peak to peak, the output capacitance looks like a simple 15 pF capacitor. However, for larger signals the output capacitance becomes much larger and non-linear. Video Distribution Amplifier with Difference Input The example multiplexer will switch between amplifiers in 5 ms for signals of less than g 2V on the outputs. For full output signals of 20V peak to peak, the selection time becomes 25 ms. The disabled outputs also present a capacitive load and therefore only three amplifiers can have their outputs shorted together. However an unlimited number can sum together if a small resistor (25X) is inserted in series with each output to isolate it from the ‘‘bus’’. There will be a small gain loss due to the resistors of course. 2020 – 15 EL2020 Disable/Enable Operation The EL2020 has an enable/disable control input at pin 8. The device is enabled and operates normally when pin 8 is left open or returned to pin 7, VCC. When more than 250 mA is pulled from pin 8, the EL2020 is disabled. The output becomes a high impedance, the inverting input is no longer driven to the positive input voltage, and the supply current is halved. To make it easy to use this feature, there is an internal resistor to limit the current to a safe level ( E 1.1 mA) if pin 8 is grounded. Using the EL2020 as a Multiplexer To draw current out of pin 8 an ‘‘open collector output’’ logic gate or a discrete NPN transistor can be used. This logic interface method has the advantage of level shifting the logic signal from 5V supplies to whatever supply the EL2020 is operating on without any additional components. 2020 – 16 13 EL2020C 50 MHz Current Feedback Amplifier Burn-In Circuit 2020 – 17 Pin numbers are for DIP Packages. All Packages Use the Same Schematic. Equivalent Circuit 2020 – 18 14 EL2020C TAB WIDE 50 MHz Current Feedback Amplifier EL2020 Macromodel * Revision A. March 1992 * Enhancements include PSRR, CMRR, and Slew Rate Limiting a input * Connections: b input * l a Vsupply * l l b Vsupply * l l l output * l l l l * l l l l l 7 4 6 TD is 6.4in .subckt M2020 3 2 * * Input Stage * e1 10 0 3 0 1.0 vis 10 9 0V h2 9 12 vxx 1.0 r1 2 11 50 l1 11 12 29nH iinp 3 0 10mA iinm 2 0 5mA * * Slew Rate Limiting * h1 13 0 vis 600 r2 13 14 1K d1 14 0 dclamp d2 0 14 dclamp * * High Frequency Pole * *e2 30 0 14 0 0.00166666666 15 30 17 1.5mH c5 17 0 1pF r5 17 0 500 * * Transimpedance Stage * g1 0 18 17 0 1.0 rol 18 0 1Meg cdp 18 0 5pF * * Output Stage * q1 4 18 19 qp q2 7 18 20 qn q3 7 19 21 qn q4 4 20 22 qp r7 21 6 4 r8 22 6 4 15 EL2020C 50 MHz Current Feedback Amplifier EL2020 Macromodel Ð Contd. TD is 3.1in ios1 7 19 2.5mA ios2 20 4 2.5mA * * Supply * ips 7 4 3mA * * Error Terms * ivos 0 23 5mA vxx 23 0 0V e4 24 0 6 0 1.0 e5 25 0 7 0 1.0 e6 26 0 4 0 1.0 r9 24 23 1K r10 25 23 1K r11 26 23 1K * * Models * .model qn npn (is e 5eb15 bf e 100 tf e 0.2nS) .model qp pnp (is e 5eb15 bf e 100 tf e 0.2nS) .model dclamp d(is e 1eb30 ibv e 0.266 bv e 1.67 n e 4) .ends 16 EL2020C 50 MHz Current Feedback Amplifier EL2020 Macromodel 2020 – 22 17 18 BLANK 19 BLANK EL2020C EL2020C 50 MHz Current Feedback Amplifier General Disclaimer Specifications contained in this data sheet are in effect as of the publication date shown. Elantec, Inc. reserves the right to make changes in the circuitry or specifications contained herein at any time without notice. Elantec, Inc. assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. December 1995 Rev G WARNING Ð Life Support Policy Elantec, Inc. products are not authorized for and should not be used within Life Support Systems without the specific written consent of Elantec, Inc. Life Support systems are equipment intended to support or sustain life and whose failure to perform when properly used in accordance with instructions provided can be reasonably expected to result in significant personal injury or death. Users contemplating application of Elantec, Inc. products in Life Support Systems are requested to contact Elantec, Inc. factory headquarters to establish suitable terms & conditions for these applications. Elantec, Inc.’s warranty is limited to replacement of defective components and does not cover injury to persons or property or other consequential damages. Elantec, Inc. 1996 Tarob Court Milpitas, CA 95035 Telephone: (408) 945-1323 (800) 333-6314 Fax: (408) 945-9305 European Office: 44-71-482-4596 20 Printed in U.S.A.