EL4451C EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Features General Description # Complete variable-gain amplifier with output amplifier, requires no extra components # Excellent linearity of 0.2% # 70 MHz signal bandwidth # Operates on g 5V to g 15V supplies # All inputs are differential # 400V/ms slew rate # l 70dB attenuation @ 4 MHz The EL4451C is a complete variable gain circuit. It offers wide bandwidth and excellent linearity while including a powerful output voltage amplifier, drawing modest supply current. Applications The EL4451C is fabricated with Elantec’s proprietary complementary bipolar process which provides excellent signal symmetry and is free from latch up. # # # # Leveling of varying inputs Variable filters Fading Text insertion into video The EL4451C operates on g 5V to g 15V supplies and has an analog input range of g 2V, making it ideal for video signal processing. AC characteristics do not change appreciably over the g 5V to g 15V supply range. The circuit has an operational temperature range of b 40§ C to a 85§ C and is packaged in plastic 14-pin DIP and 14-lead SO. Connection Diagram Ordering Information Part No. Temp. Range Package Outline Ý EL4451CN b 40§ C to a 85§ C 14-Pin P-DIP MDP0031 EL4451CS b 40§ C to a 85§ C MDP0027 14-Lead SO 4451-1 October 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. EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Absolute Maximum Ratings (TA e 25§ C) Va VS VIN DVIN IIN Positive Supply Voltage V a to Vb Supply Voltage Voltage at any Input or Feedback Difference between Pairs of Inputs or Feedback Current into any Input, or Feedback Pin IOUT PD TA TS 16.5V 33V V a to Vb Continuous Output Current Maximum Power Dissipation Operating Temperature Range Storage Temperature Range 30mA See Curves b 40§ C to a 85§ C b 60§ C to a 150§ C 6V 4mA 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 Description VDIFF Signal input differential input voltage - Clipping 0.2% nonlinearity VCM Common-mode range of VIN; VDIFF e 0, Vs e g 5V Vs e g 15V Test Level Units 2.0 1.3 I V V V g 2.8 I V V V Min Typ 1.8 g 2.0 Max g 12.8 VOS Input offset voltage 7 25 I mV VOS, FB Output offset voltage 8 25 I mV VG, 100% Extrapolated voltage for 100% gain VG, 0% Extrapolated voltage for 0% gain VG, 1V 1.9 2.1 2.2 I V b 0.16 b 0.06 0.06 I V Gain at VGAIN e 1V 0.95 1.05 1.15 I V/V IB Input bias current (all inputs) b 20 b9 0 I mA IOS Input offset current between VIN a and VINb, Gain a and Gainb, FB and Ref 0.2 4 I mA NL Nonlinearity, VIN between b1V and a 1V, VG e 1V Ft Signal feedthrough, VG e b1V RIN, VIN Input resistance, VIN 100 RIN, FB Input resistance, FB 200 RIN, RGAIN Input resistance, gain input 50 2 0.2 0.5 I % b 100 b 70 I dB 230 I KX 460 V KX 100 I KX TD is 3.3in Open-Loop DC Electrical Characteristics Power Supplies at g 5V, TA e 25§ C, RL e 500X. TD is 1.8in EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Open-Loop DC Electrical Characteristics Ð Contd. Power Supplies at g 5V, TA e 25§ C, RL e 500X. Parameter Description CMRR Common-mode rejection ratio of VIN PSRR Power supply rejection ratio of VOS, FB, VS e g 5V to g 15V VO Output voltage swing VS e g 5V (VIN e 0, VREF varied) VS e g 15V ISC Output short-circuit current IS Supply current, VS e g 15V Test Level Units 90 I dB I dB I V Min Typ 70 50 60 g 2.5 g 2.8 g 12.5 g 12.8 40 Max 85 15.5 I mA I mA Test Level Units V MHz MHz 18 Closed-Loop AC Electrical Characteristics Parameter Description Min Typ 70 Max BW, b3dB b 3dB small-signal bandwidth, signal input BW, g 0.1dB 0.1dB flatness bandwidth, signal input 10 V Peaking Frequency response peaking 0.6 V dB BW, gain b 3dB small-signal bandwidth, gain input 70 V MHz SR Slew rate, VOUT between b2V and a 2V, RF e RG e 500X 400 V V/ms VN Input referred noise voltage density 110 V nV/ SHz dG Differential gain error, Voffset between b0.7V and a 0.7V 0.9 V % di Differential phase error, Voffset between b0.7V and a 0.7V 0. 2 V § Test Circuit 4451 – 3 Note: For typical performance curves, RF e 0, RG e % , VGAIN e 1V, RL e 500X, and CL e 15 pF unless otherwise noted. 3 TD is 1.8in Power supplies at g 12V, TA e 25§ C. RL e 500X, CL e 15pF, VG e 1V EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Typical Performance Curves Frequency Response for Various Feedback Divider Ratios Frequency Response for Various RL, CL VS e g 5V 4451 – 4 Gain, b 3 dB Bandwidth, and Peaking vs Load Resistance Frequency Response for Various RL, CL VS e g 15V 4451 – 5 b 3 dB Bandwidth and Peaking vs Supply Voltage b 3 dB Bandwidth and Peaking vs Die Temperature 4451 – 8 4451 – 7 Frequency Response for Various Gain Settings 4451 – 6 Slew Rate vs Supply Voltage Slew Rate vs Die Temperature 4451 – 11 4451 – 10 4 4451 – 9 4451 – 12 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Typical Performance Curves Ð Contd. Common-Mode Rejection Ratio vs Frequency Input Voltage Noise vs Frequency 4451 – 13 Nonlinearity vs Input Signal 4451 – 14 4451 – 15 Differential Gain Error vs Input Offset Voltage VS e g 5V or g 12V Differential Phase Error vs Input Offset Voltage VS e g 5V 4451 – 16 Differential Phase Error vs Input Offset Voltage VS e g 12V 4451 – 17 Differential Gain and Phase Errors vs Gain Setting 4451 – 18 Differential Gain and Phase Errors vs Load Resistance 4451 – 19 4451 – 20 5 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Typical Performance Curves Ð Contd. Change in VG, 100% and VG, 0% vs Die Temperature Gain vs VGAIN Common Mode Input Range vs Supply Voltage Bias Current vs Die Temperature 4451 – 24 Supply Current vs Die Temperature 4451 – 23 4451 – 22 4451 – 21 Offset Voltage vs Die Temperature VG, 0% and VG, 100% vs Supply Voltage 4451 – 25 Supply Current vs Supply Voltage 4451 – 27 4451 – 28 6 4451 – 26 14-Pin Package Power Dissipation vs Ambient Temperature 4451 – 29 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 360X 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, two 10pF capacitors across equal divider resistors for a maximum gain of 4 will dominate parasitic effects and allow a higher divider resistance. Applications Information The EL4451 is a complete two-quadrant multiplier/gain control with 70 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: 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. 4451-2 The gain of the feedback divider is He RG . RG a RF 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 600. The large value of AO drives ((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN b )) a (VREF b VFB) x 0. The gain control has a small-signal bandwidth equal to the VIN channel bandwidth, and overload recovery resolves in about 20 nsec. Rearranging and substituting for VFB VOUT e (((VIN a ) b (VIN b )) c ((VGAIN a ) b (VGAIN)) a VREF)/H, or Input Connections VOUT e (VIN c VGAIN a VREF)/H 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. 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 EL4451 is stable for a direct connection between VOUT and FB, and the divider may be used for higher output gain, although with the traditional loss of bandwidth. 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 150 MHz; typical strays of 3 pF thus require a feedback impedance of 7 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 For instance, the EL4451 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 Applications Information Ð Contd. x Signal Amplitudes Signal input common-mode voltage must be between (V b ) a 3V and (V a ) b 3V 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 2V in the EL4451. The input range is substantially constant with temperature. 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 The Ground Pin The ground pin draws only 6mA 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. 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 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. Power Supplies The EL4451 works with any 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. 4.7mF tantalum capacitors are very good, and no smaller bypasses need be placed in parallel. Capacitors as small as 0.01mF can be used if small load currents flow. Output Loading 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 and outputs will have to have their levels shifted above ground to accommodate the lack of negative supply. The output stage of the EL4451 is very powerful. It typically can source 80mA and sink 120mA. 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 30mA continuous output given in the Absolute Maximum Ratings table in this data sheet, or higher purely transient currents. The power dissipation of the EL4451 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: Gain changes only 0.2% from no load to 100X load. Heavy resistive loading will degrade frequency response and video distortion for loads k 100X. PD e 2 c VS c IS, max a (VS b VO) c VO/RPAR 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 2.5 dB with even a 220pF load. 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 8 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 EL4451 Leveler Circuit Attenuation Ratio e 1.5 Applications Information Ð Contd. Leveling Circuits Often a variable-gain control is used to normalize an input signal to a standard amplitude from a modest range of possible input amplitude. A good example is in video systems, where an unterminated cable will yield a twice-sized standard video amplitude, and an erroneously twice-terminated cable gives a 2/3-sized input. Here is a g 6 dB range preamplifier: Linearized Leveling Amplifier 4451 – 31 EL4451 Leveler Circuit Attenuation Ratio e 2 4451 – 30 In this arrangement, the EL4451 outputs a mixture of the signal routed through the multiplier and the REF terminal. The multiplier port produces the most distortion and needs to handle a fraction of an oversized video input, whereas the REF port is just like an op-amp input summing into the output. Thus, for oversized inputs the gain will be decreased and the majority of the signal is routed through the linear REF terminal. For undersized inputs, the gain is increased and the multiplier’s contribution added to the output. 4451 – 32 With the higher attenuation ratio, the multiplier sees a smaller input amplitude and distorts less, however the higher output gain reduces circuit bandwidth. As seen in the next curves, the peak differential gain error is 0.47% for the attenuation ratio of 1.5, but only 0.27% with the gain of 2 constants. To maintain bandwidth, an external op amp can be used instead of the RF - RG divider to boost the EL4451’s output by the attenuation ratio. Here are some component values for two designs: Sinewave Oscillators Attenuation Ratio Generating a stable, low distortion sinewave has long been a difficult task. Because a linear oscillator’s output tends to grow or diminish continuously, either a clipping circuit or automatic gain control (AGC) is needed. Clipping circuits generate severe distortion which needs subsequent filtering, and AGC’s can be complicated. RF RG R1 R2 R3 b 3 dB Bandwidth 1.5 200X 400X 300X 100X 200X 47 MHz 2 400X 400X 500X 100X 200X 28 MHz 9 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 Applications Information Ð Contd. Here is the EL4451 used as an oscillator with simple AGC: Low-Distortion Sinewave Oscillator 4451 – 33 The oscillation frequency is set by the resonance of a series-tuned circuit, which may be an L-C combination or a crystal. At resonance, the series impedance of the tuned circuit drops and its phase lag is 0§ , so the EL4451 needs a gain just over unity to sustain oscillation. The VGAIN b terminal is initially at b 0.7V and the VGAIN a terminal at about a 2.1V, setting the maximum gain in the EL4451. At such high gain, the loop oscillates and output amplitude grows until D1 rectifies more positive voltage at VGAIN b , ultimately reducing gain until a stable 0.5Vrms output is produced. Filters The EL4451 can be connected to act as a voltagevariable integrator as shown: EL4451 Connected As Variable Integrator Using a 2 MHz crystal, output distortion was b 53 dBc, or 0.22%. Sideband modulation was only 14 Hz wide at b 90 dBc, limited by the filter of the spectrum analyzer used. 4451 – 34 The input RC cancels a zero produced by the output op-amp feedback connection at 0 e 1/RC. With the input RC connected VOUT/VIN e 1/sRC; without it VOUT/VIN e (1 a sRC)/sRC. This variable integrator may be used in networks such as the Bi-quad. In some applications the input RC may be omitted. If a negative gain is required, the VIN a and VIN b terminals can be exchanged. The circuit works up to 30 MHz. A parallel-tuned circuit can replace the 510X resistor and the 510X resistor moved in place of the series-tuned element to allow grounding of the tuned components. 10 EL4451C Wideband Variable-Gain Amplifier, Gain of 2 The main signal path is via the REF pin. This ensures maximum signal linearity, while the multiplier input is used to allow a variable amount of frequency-shaped input from R1, R2, and C. For optimum linearity, the multiplier input is attenuated by R1 and R2. This may not be necessary, depending on input signal amplitude, and R1 might be set to 0. R1and R2 should be set to provide sufficient peaking, depending on cable highfrequency losses, at maximum gain. RF and RG are chosen to provide the desired circuit gain, including backmatch resistor loss. Applications Information Ð Contd. A voltage-controlled equalizer and cable driver can be constructed so: Equalization and Line Driver Amplifier 4451 – 35 11 EL4451C EL4451C Wideband Variable-Gain Amplifier, Gain of 2 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. October 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.