EL4452C EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Features General Description # 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 g 5V to g 15V supplies # All inputs are differential # l 70 dB attenuation @ 5 MHz 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. Applications # AGC variable-gain amplifier # IF amplifier # Transducer amplifier Ordering Information Part No. Temp. Range Package The EL4452 operates on g 5V to g 15V and has an analog input range of g 0.5V. 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. Connection Diagram Outline Ý 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 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) Positive Supply Voltage V a to Vb Supply Voltage Voltage at any Input or Feedback Difference between Pairs of Inputs or Feedback Va VS VIN DVIN IIN 16.5V 33V V a to Vb IOUT PD TA TS 6V 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 Parameter Description VDIFF Signal Input Differential Input Voltage - Clipping 0.6% Nonlinearity VCM Common-Mode Range (All Inputs; VDIFF e 0) VS e g 5V VS e g 15V Test Level Units 0.5 0.4 I V V V g 2.0 g 2.8 g 12.0 g 12.8 I V V V Min Typ 0.4 Max VOS Input Offset Voltage 10 I mV VOS, FB Output Offset Voltage 10 I mV VG, 100% Extrapolated Voltage for 100% Gain I V 1.8 2.1 2.2 b 0.16 b 0.06 0.04 I V 4.9 5.35 5.9 I V/V b 20 b9 0 I mA 0.5 4 I mA b 100 b 70 VG, 0% Extrapolated Voltage for 0% Gain VG, 1V Gain at VGAIN e 1 (Rf e 910X, Rg e 100X) IB Input Bias Current (All Inputs) IOS Input Offset Current Between VIN a and VINb, VGAIN a and VGAINb FT Signal Feedthrough, VG e b1V I dB RIN, Signal Input Resistance, Signal Input 25 60 I kX RIN, Gain Input Resistance, Gain Input 50 120 I kX RIN, FB Input Resistance, Feedback 25 60 V kX CMRR Common-Mode Rejection Ratio, VIN 70 90 I dB 2 TD is 3.3in Power supplies at g 5V, TA e 25§ C, RF e 910X, RG e 100X, RL e 500X TD is 1.5in EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Open-Loop DC Electrical Characteristics Ð Contd. Power supplies at g 5V, TA e 25§ C, RF e 910X, RG e 100X, RL e 500X Parameter Description Min Typ 83 PSRR Power-Supply Rejection Ratio, VOS, FB; Supplies from g 5V to g 15V 65 EG Gain Error, Excluding Feedback Resistors, VGAIN e 2.5V b7 NL Nonlinearity, VIN from b0.25V to a 0.25, VGAIN e 1V VO Output Voltage Swing (VIN e 0, VREF Varied) ISC Output Short-Circuit Current IS Supply Current, VS e g 15V 0.3 VS e g 5V VS e g 15V g 2.5 g 2.8 g 12.5 g 12.8 40 Max Test Level Units I dB a7 I % 0.6 I % I I V V 85 15.5 18 I mA I mA Closed-Loop AC Electrical Characteristics Parameter Description Min Typ Max Test Level Units BW, b3dB b 3dB Small-Signal Bandwidth, Signal Input 50 V MHz BW, g 0.1dB 0.1dB Flatness Bandwidth, Signal Input 10 V MHz Peaking Frequency Response Peaking 0.1 V dB BW, Gain b 3dB Small-Signal Bandwidth, Gain Input SR Slew Rate, VOUT between b2V and a 2V VN Input-Referred Noise Voltage Density 50 350 400 29 550 V MHz I V/ms V nV/rt-Hz 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 Power supplies at g 12V, TA e 25§ C, RL e 500X, CL e 15pF 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 g 5V Frequency Response for Various RL, CL, VS e g 15V 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 Ð Contd. Input Common-Mode Rejection Ratio vs Frequency Gain and b 3 dB Bandwidth vs Load Resistance 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 Ð Contd. Bias Current vs Die Temperature Gain vs VGAIN 4452 – 16 4452 – 15 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 Ð Applications Information Contd. 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: Supply Current vs Die Temperature 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 (/2 ((VGAIN a ) b (VGAIN b )) a (VREF b VFB) x 0. Rearranging and substituting for VFB 4452 – 22 VOUT e (((VIN a ) b (VIN b )) c (/2 ((VGAIN a ) b (VGAIN)) a VREF)/H, or VOUT e (VIN c (/2 VGAIN a VREF)/H 7 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Ð Contd. Input Connections 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 (/10, and the divider may be set for higher output gain, although with the traditional loss of bandwidth. 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 (/10 divider and allow a higher divider resistance. 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 g 6V to prevent damage. The differential signal range is g 0.5V 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. 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. 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. Power Supplies The EL4452 operates with power supplies from g 3V to g 15V. 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 The gain control has a small-signal bandwidth equal to the VIN channel bandwidth, and overload recovery resolves in about 20 nsec. 8 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 Applications Information Ð Contd. Output Loading and outputs will have to have their levels shifted above ground to accommodate the lack of negative supply. 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. 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 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. 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 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. For instance, the EL4452 draws a maximum of % and the 18mA. With light loading, RPAR dissipation with g 5V supplies is 180 mW. The maximum supply voltage that the device can run on for a given PD and other parameters is 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) / iJA Where 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 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. 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. 9 EL4452C Wideband Variable-Gain Amplifier with Gain of 10 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. Applications Information Ð 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 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 ther, although it contributes to loop overshoot when input amplitude changes suddenly. The opamp can be any inexpensive low-frequency type. Applications Information Ð 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 fur- 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 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. Applications Information Ð 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. 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 1994 Rev A 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 12 Printed in U.S.A.