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| EL4452C EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Features Complete variable-gain amplifier complete with output amplifier Compensated for Gain t 10 50 MHz signal bandwidth 50 MHz gain-control bandwidth Low 29 nV SHz input noise Operates on g5V to g15V supplies All inputs are differential l 70 dB attenuation 5 MHz General Description The EL4452 is a complete variable-gain circuit It offers wide bandwidth and excellent linearity while including a powerful output voltage amplifier drawing modest current The higher gain and lower input noise makes the EL4452 ideal for use in AGC systems The EL4452 operates on g5V to g15V and has an analog input range of g0 5V AC characteristics do not change appreciably over the supply range The circuit has an operational temperature of b 40 C to a 85 C and is packaged in 14-pin P-DIP and SO-14 The EL4452 is fabricated with Elantec's proprietary complementary bipolar process which gives excellent signal symmetry and is very rugged Applications AGC variable-gain amplifier IF amplifier Transducer amplifier Ordering Information Part No Temp Range Package Outline EL4452CN b 40 C to a 85 C 14-pin P-DIP MDP0031 MDP0027 EL4452CS b 40 C to a 85 C 14-lead SO Connection Diagram 4452 - 1 December 1994 Rev A 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 1994 Elantec Inc EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Absolute Maximum Ratings (TA e 25 C) Va VS VIN DVIN Positive Supply Voltage V a to Vb Supply Voltage Voltage at any Input or Feedback Difference between Pairs of Inputs or Feedback 16 5V 33V V a to Vb 6V IIN IOUT PD TA TS Current into any Input or Feedback Pin Output Current Maximum Power Dissipation Operating Temperature Range Storage Temperature Range 4 mA 30 mA See Curves b 40 C to a 85 C b 60 C to a 150 C 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 Open-Loop DC Electrical Characteristics Power supplies at g5V TA e 25 C RF e 910X RG e 100X RL e 500X Parameter VDIFF VCM VOS VOS FB VG 100% VG 0% VG 1V IB IOS FT RIN Signal RIN Gain RIN FB CMRR Description Signal Input Differential Input Voltage - Clipping 0 6% Nonlinearity Common-Mode Range (All Inputs VDIFF e 0) Input Offset Voltage Output Offset Voltage Extrapolated Voltage for 100% Gain Extrapolated Voltage for 0% Gain Gain at VGAIN e 1 (Rf e 910X Rg e 100X) Input Bias Current (All Inputs) Input Offset Current Between VIN a and VINb VGAIN a and VGAINb Signal Feedthrough VG e b1V Input Resistance Signal Input Input Resistance Gain Input Input Resistance Feedback Common-Mode Rejection Ratio VIN 25 50 25 70 18 b 0 16 Min 04 g2 0 g12 0 Typ 05 04 g2 8 g12 8 Max Test Level I V I V Units V V V V mV mV V V VV mA mA dB kX TD is 3 3in kX kX dB VS e g5V VS e g15V 10 10 21 b 0 06 I I I I I I I I I I V I 22 0 04 59 0 4 b 70 49 b 20 5 35 b9 05 b 100 60 120 60 90 2 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Open-Loop DC Electrical Characteristics Power supplies at g5V TA e 25 C RF e 910X RG e 100X RL e 500X Parameter PSRR EG NL VO ISC IS Description Power-Supply Rejection Ratio VOS FB Supplies from g5V to g15V Gain Error Excluding Feedback Resistors VGAIN e 2 5V Nonlinearity VIN from b0 25V to a 0 25 VGAIN e 1V Output Voltage Swing (VIN e 0 VREF Varied) Output Short-Circuit Current Supply Current VS e g15V VS e g5V VS e g15V g2 5 g12 5 Contd Min 65 b7 Typ 83 Max Test Level I Units dB % % V V mA mA a7 I I I I I 03 g2 8 g12 8 06 40 85 15 5 18 I Closed-Loop AC Electrical Characteristics Power supplies at g12V TA e 25 C RL e 500X CL e 15pF Parameter BW b3dB BW g0 1dB Peaking BW Gain SR VN Description b 3dB Small-Signal Bandwidth Signal Input Min Typ 50 10 01 50 Max Test Level V V V V Units MHz MHz dB TD is 1 5in MHz V ms nV rt-Hz 0 1dB Flatness Bandwidth Signal Input Frequency Response Peaking b 3dB Small-Signal Bandwidth Gain Input Slew Rate VOUT between b2V and a 2V Input-Referred Noise Voltage Density 350 400 29 550 I V Test Circuit 4452 - 2 Note For typical performance curves RF e 910X RG e 100X VGAIN e 1V RL e 500X and CL e 15 pF unless otherwise noted 3 TD is 1 5in EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Typical Performance Curves Frequency Response for Various Feedback Divider Ratios Frequency Response for Various Gains 4452 - 3 4452 - 4 Frequency Response for Various RL CL VS e g5V Frequency Response for Various RL CL VS e g15V 4452 - 5 4452 - 6 b 3 dB Bandwidth vs Supply Voltage b 3 dB Bandwidth vs Die Temperature 4452 - 7 4452 - 8 4 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Typical Performance Curves Gain and b 3 dB Bandwidth vs Load Resistance Contd Input Common-Mode Rejection Ratio vs Frequency 4452 - 9 4452 - 10 Slew Rate vs Supply Voltage Slew Rate vs Die Temperature 4452 - 11 4452 - 12 Input Voltage Noise vs Frequency Nonlinearity vs Input Signal 4452 - 13 4452 - 14 5 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Typical Performance Curves Bias Current vs Die Temperature Contd Gain vs VGAIN 4452 - 15 4452 - 16 Change in VG 100% and VG 0% vs Die Temperature VG 0% and VG 100% vs Supply Voltage 4452 - 18 4452 - 17 Common Mode Input Range vs Supply Voltage Supply Current vs Supply Voltage 4452 - 20 4452 - 19 6 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Typical Performance Curves Contd Supply Current vs Die Temperature Applications Information The EL4452 is a complete two-quadrant multiplier gain control with 50 MHz bandwidth It has three sets of inputs a differential signal input VIN a differential gain-controlling input VGAIN and another differential input which is used to complete a feedback loop with the output Here is a typical connection 4452 - 21 14-Pin Package Power Dissipation vs Ambient Temperature 4451-23 The gain of the feedback divider is H The transfer function of the part is VOUT e AO c (((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN b )) a (VREF b VFB)) VFB is connected to VOUT through a feedback network so VFB e H c VOUT AO is the openloop gain of the amplifier and is approximately 3300 The large value of AO drives ((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN b )) a (VREF b VFB) x0 4452 - 22 Rearranging and substituting for VFB VOUT e (((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN)) a VREF) H or VOUT e (VIN c VGAIN a VREF) H 7 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Contd Thus the output is equal to the difference of the VIN's times the difference of VGAIN'S and offset by VREF all gained up by the feedback divider ratio The EL4452 is stable for a divider ratio of and the divider may be set for higher output gain although with the traditional loss of bandwidth Input Connections The input transistors can be driven from resistive and capacitive sources but are capable of oscillation when presented with an inductive input It takes about 80nH of series inductance to make the inputs actually oscillate equivalent to four inches of unshielded wiring or 6 of unterminated input transmission line The oscillation has a characteristic frequency of 500 MHz Often placing one's finger (via a metal probe) or an oscilloscope probe on the input will kill the oscillation Normal high-frequency construction obviates any such problems where the input source is reasonably close to the input If this is not possible one can insert series resistors of around 51X to de-Q the inputs It is important to keep the feedback divider's impedance at the FB terminal low so that stray capacitance does not diminish the loop's phase margin The pole caused by the parallel impedance of the feedback resistors and stray capacitance should be at least 130 MHz typical strays of 3 pF thus require a feedback impedance of 400X or less Alternatively a small capacitor across RF can be used to create more of a frequency-compensated divider The value of the capacitor should scale with the parasitic capacitance at the FB input It is also practical to place small capacitors across both the feedback and the gain resistors (whose values maintain the desired gain) to swamp out parasitics For instance a 3 pF capacitor across RF and 27 pF to ground will dominate parasitic effects in a divider and allow a higher divider resistance The REF pin can be used as the output's ground reference for DC offsetting of the output or it can be used to sum in another signal Signal Amplitudes Signal input common-mode voltage must be between (V b ) a 2 5V and (V a ) b 2 5V to ensure linearity Additionally the differential voltage on any input stage must be limited to g6V to prevent damage The differential signal range is g0 5V in the EL4452 The input range is substantially constant with temperature The Ground Pin The ground pin draws only 6 mA maximum DC current and may be biased anywhere between (V b ) a 2 5V and (V a ) b 3 5V The ground pin is connected to the IC's substrate and frequency compensation components It serves as a shield within the IC and enhances input stage CMRR and feedthrough over frequency and if connected to a potential other than ground it must be bypassed Gain-Control Characteristics The quantity VGAIN in the above equations is bounded as 0 s VGAIN s 2 even though the externally applied voltages exceed this range Actually the gain transfer function around 0 and 2V is ``soft'' that is the gain does not clip abruptly below the 0%-VGAIN voltage nor above the 100%-VGAIN level An overdrive of 0 3V must be applied to VGAIN to obtain truly 0% or 100% Because the 0%- or 100%- VGAIN levels cannot be precisely determined they are extrapolated from two points measured inside the slope of the gain transfer curve Generally an applied VGAIN range of b 0 5V to a 2 5V will assure the full numerical span of 0 s VGAIN s 2 The gain control has a small-signal bandwidth equal to the VIN channel bandwidth and overload recovery resolves in about 20 nsec 8 Power Supplies The EL4452 operates with power supplies from g3V to g15V The supplies may be of different voltages as long as the requirements of the ground pin are observed (see the Ground Pin section) The supplies should be bypassed close to the device with short leads 4 7 mF tantalum capacitors are very good and no smaller bypasses need be placed in parallel Capacitors as small as 0 01 mF can be used if small load currents flow Single-polarity supplies such as a 12V with a 5V can be used where the ground pin is connected to a 5V and V b to ground The inputs EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Contd and outputs will have to have their levels shifted above ground to accommodate the lack of negative supply The power dissipation of the EL4452 increases with power supply voltage and this must be compatible with the package chosen This is a close estimate for the dissipation of a circuit PD e 2 c VS c IS max a (VS b VO) c VO RPAR where IS max is the maximum supply current VS is the g supply voltage (assumed equal) VO is the output voltage RPAR is the parallel of all resistors loading the output For instance the EL4452 draws a maximum of % and the 18mA With light loading RPAR dissipation with g5V supplies is 180 mW The maximum supply voltage that the device can run on for a given PD and other parameters is Output Loading The output stage of the EL4452 is very powerful It can typically source 80 mA and sink 120 mA Of course this is too much current to sustain and the part will eventually be destroyed by excessive dissipation or by metal traces on the die opening The metal traces are completely reliable while delivering the 30 mA continuous output given in the Absolute Maximum Ratings table in this data sheet or higher purely transient currents Gain changes only 0 2% from no load to a 100X load Heavy resistive loading will degrade frequency response and distortion for loads k 100X Capacitive loads will cause peaking in the frequency response If capacitive loads must be driven a small-valued series resistor can be used to isolate it 12X to 51X should suffice A 22X series resistor will limit peaking to 1 dB with even a 220 pF load x AGC Circuits The basic AGC (automatic gain control) loop is this VS max e (PD a VO2 RPAR) (2IS a VO RPAR) The maximum dissipation a package can offer is PD max e (TJ max b TA max) Where iJA TJ max is the maximum die temperature 150 C for reliability less to retain optimum electrical performance TA max is the ambient temperature 70 C for commercial and 85 C for industrial range iJA is the thermal resistance of the mounted package obtained from data sheet dissipation curves 4452 - 24 Basic AGC Loop The more difficult case is the SO-14 package With a maximum die temperature of 150 C and a maximum ambient temperature of 85 C the 65 C temperature rise and package thermal resistance of 120 C W gives a dissipation of 542 mW at 85 C This allows the full maximum operating supply voltage unloaded but reduced if loaded A multiplier scales the input signal and provides necessary gain and buffers the signal presented to the output load a level detector (shown schematically here as a diode) converts some measure of the output signal amplitude to a DC level a low-pass filter attenuates any signal ripple present on that DC level and an amplifier compares that level to a reference and amplifies the error to create a gain-control voltage for the multiplier The circuitry is a servo that attempts to keep the output amplitude constant by continuously adjusting the multiplier's gain control input 9 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Contd Most AGC's deal with repetitive input signals that are capacitively coupled It is generally desirable to keep DC offsets from mixing with AC signals and fooling the level detector into maintaining the DC output offset level constant rather than a smaller AC component To that end either the level detector is AC-coupled or the reference voltage must be made greater than the maximum multiplier gain times the input offset For instance if the level detector output equaled the reference voltage at 1V of EL4452 output the 8 mV of input offset would require a maximum gain of 125 through the EL4452 Bias current-induced offsets could increase this further Depending on the nature of the signal different level detector strategies will be employed If the system goal is to prevent overload of subsequent stages peak detectors are preferred Other strategies use an RMS detector to maintain constant output power Here is a simple AGC using peak detection 4452 - 25 10 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Contd The output of the EL4452 drives a diode detector which is compared to VREF by an offset integrator Its output feeds the gain-control input of the EL4452 The integrator's output is attenuated by the 2 kX and 2 7 kX resistors to prevent the opamp from overloading the gain-control pin during zero input conditions The 510 kX resistor provides a pull-down current to the peak level storage capacitor C1 to allow it to drift negative when output amplitude reduces Thus the detector is of fast attack and slow decay design able to reduce AGC gain rapidly when signal amplitude suddenly increases and increases gain slowly when the input drops out momentarily The value of C1 determines drop-out reaction rates and the value of CF affects overall loop time constant as well as the amount of ripple on the gain-control line C2 can be used to reduce this ripple further although it contributes to loop overshoot when input amplitude changes suddenly The opamp can be any inexpensive low-frequency type The major problem with diode detectors is their large and variable forward voltage They require at least a 2 VP-P peak output signal to function reliably and the forward voltage should be compensated by including a negative VD added to VREF Even this is only moderately successful At the expense of bandwidth op-amp circuits can greatly improve diode rectifiers (see ``An Improved Peak Detector'' an Elantec application note) Fortunately the detector will see a constant amplitude of signal if the AGC is operating correctly A better-calibrated method is to use a four-quadrant multiplier as a square-law detector Here is a circuit employing the EL4450 4452 - 26 11 EL4452C EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Contd In this circuit the EL4450 not only calculates the square of the input but also provides the offset integrator function The product of the two multiplier inputs adds to the b Reference input and are passed to the output amplifier which through CF behaves as a pseudo-integrator The ``integrator'' gain does not pass through zero at high frequencies but has a zero at 1 (2qCF c 1 kX) This zero is cancelled by the pole caused by the second capacitor of value CF connected at the EL4452 b VGAIN input The b Reference can be exchanged for a positive reference by connecting it to the ground return of the 1 kX resistor at the FB terminal and grounding REF As a general consideration the input signal applied to an EL4452 should be kept below about 250 mV peak for good linearity If the AGC were designed to produce a 1V peak output the input range would be 100 mV-250 mV peak when the EL4452 has a feedback network that establishes a maximum gain of 10 This is an input range of only 2 5 1 for precise output regulation Raising the maximum gain to 25 allows a 40 mV-250 mV input range with the output still regulated better than 6 1 Unfortunately the bandwidth will be reduced Bandwidth can be maintained by adding a high frequency op-amp cascaded with the output to make up gain beyond the 10 of the EL4452 current feedback devices being the most flexible The op-amp's input should be capacitor coupled to prevent gained-up offsets from confusing the level detector during AGC control line variations 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 WARNING Life Support Policy December 1994 Rev A 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 12 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 Printed in U S A |
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