LMH6715

LMH6715 Dual Wideband Video Op Amp January 2003 LMH6715 Dual Wideband Video Op Amp General Description The LMH6715 combines National’s VIP10™ high speed complementary bipolar process with National’s current feedback topology to produce a very high speed dual op amp. The LMH6715 provides 400MHz small signal bandwidth at a gain of +2V/V and 1300V/µs slew rate while consuming only 5.8mA per amplifier from ± 5V supplies. The LMH6715 offers exceptional video performance with its 0.02% and 0.02˚ differential gain and phase errors for NTSC and PAL video signals while driving up to four back terminated 75Ω loads. The LMH6715 also offers a flat gain response of 0.1dB to 100MHz and very low channel-tochannel crosstalk of −70dB at 10MHz. Additionally, each amplifier can deliver 70mA of output current. This level of performance makes the LMH6715 an ideal dual op amp for high density, broadcast quality video systems. The LMH6715’s two very well matched amplifiers support a number of applications such as differential line drivers and receivers. In addition, the LMH6715 is well suited for Sallen Key active filters in applications such as anti-aliasing filters for high speed A/D converters. Its small 8-pin SOIC package, low power requirement, low noise and distortion allow the LMH6715 to serve portable RF applications such as IQ channels. Features TA = 25˚C, RL = 100Ω, typical values unless specified. n Very low diff. gain, phase: 0.02%, 0.02˚ n Wide bandwidth: 480MHz (AV = +1V/V); 400MHz (AV = +2V/V) n 0.1dB gain flatness to 100MHz n Low power: 5.8mA/channel n −70dB channel-to-channel crosstalk (10MHz) n Fast slew rate: 1300V/µs n Unity gain stable n Improved replacement for CLC412 Applications n n n n n n HDTV, NTSC & PAL video systems Video switching and distribution IQ amplifiers Wideband active filters Cable drivers DC coupled single-to-differential conversions Differential Gain & Phase with Multiple Video Loads Frequency Response vs. VOUT 20042916 20042908 © 2003 National Semiconductor Corporation DS200429 www.national.com LMH6715 Absolute Maximum Ratings (Note 1) Storage Temperature Range Lead Temperature (Soldering 10 sec) −65˚C to +150˚C +300˚C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance (Note 4) Human Body Model Machine Model VCC IOUT Common-Mode Input Voltage Differential Input Voltage Maximum Junction Temperature 2000V 150V Operating Ratings Thermal Resistance Package SOIC (θJC) 65˚C/W (θJA) 145˚C/W −40˚C to +85˚C ± 6.75V (Note 3) ± VCC 2.2V +150˚C Operating Temperature Range Nominal Operating Voltage ± 5V to ± 6V Electrical Characteristics AV = +2, RF = 500Ω, VCC = ± 5 V, RL = 100Ω; unless otherwise specified. Boldface limits apply at the temperature extremes. Symbol SSBW LSBW GFP GFR LPD DG DP Tr Ts OS SR HD2 HD3 VN IN INN SNF XTLKA VIO DVIO IBN DIBN IBI DIBI PSRR Parameter -3dB Bandwidth -3dB Bandwidth Gain Flatness Peaking Rolloff Linear Phase Deviation Differential Gain Differential Phase Rise and Fall Time Settling Time to 0.05% Overshoot Slew Rate 2nd Harmonic Distortion 3rd Harmonic Distortion Equivalent Input Noise Non-Inverting Voltage Inverting Current Non-Inverting Current Noise Floor Crosstalk Input Offset Voltage Average Drift Input Bias Current Average Drift Input Bias Current Average Drift Power Supply Rejection Ratio DC 46 44 Inverting Non-Inverting Conditions VOUT < 0.5VPP, RF = 300Ω VOUT < 4.0VPP, RF = 300Ω VOUT < 0.5VPP DC to 100MHz, RF = 300Ω DC to 100MHz, RF = 300Ω DC to 100MHz, RF = 300Ω RL = 150Ω, 4.43MHz RL = 150Ω, 4.43MHz 0.5V Step 4V Step 2V Step 0.5V Step 2V Step 2VPP, 20MHz 2VPP, 20MHz 0.1 0.1 0.25 0.02 0.02 1.4 3 12 1 1300 −60 −75 3.4 10.0 1.4 −153 −70 dB dB deg % deg ns ns ns % V/µs dBc dBc nV/ pA/ pA/ dB1Hz dB Min 280 Typ 400 170 Max Units MHz MHz Frequency Domain Response Time Domain Response Distortion And Noise Response > 1MHz > 1MHz > 1MHz > 1MHz Input Referred 10MHz Static, DC Performance ±2 ± 30 ±5 ± 30 ±6 ± 20 60 ±6 ±8 ± 12 ± 20 ± 21 ± 35 mV µV/˚C µA nA/˚C µA nA/˚C dB www.national.com 2 LMH6715 Electrical Characteristics Symbol CMRR ICC Parameter Common Mode Rejection Ratio Supply Current per Amplifier (Continued) AV = +2, RF = 500Ω, VCC = ± 5 V, RL = 100Ω; unless otherwise specified. Boldface limits apply at the temperature extremes. Conditions DC RL = ∞ Min 50 47 4.7 4.1 Typ 56 5.8 7.6 8.1 Max Units dB mA Miscellaneous Performance RIN CIN ROUT VO VOL CMIR IO Input Voltage Range Output Current Input Resistance Input Capacitance Output Resistance Output Voltage Range Non-Inverting Non-Inverting Closed Loop RL = ∞ RL = 100Ω Common Mode 1000 1.0 .06 kΩ pF Ω V V V mA ± 3.5 ± 3.4 ± 4.0 ± 3.9 ± 2.2 70 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications, see the Electrical Characteristics tables. Note 2: Electrical Table values apply only for factory testing conditions at the temperature indicated. Factory testing conditions result in very limited self-heating of the device such that TJ = TA. No guarantee of parametric performance is indicated in the electrical tables under conditions of internal self heating where TJ > TA. See Applications Section for information on temperature de-rating of this device." Min/Max ratings are based on product characterization and simulation. Individual parameters are tested as noted. Note 3: The maximum output current (IOUT) is determined by device power dissipation limitations. See the Power Dissipation section of the Application Division for more details. Note 4: Human body model, 1.5kΩ in series with 100pF. Machine model, 0Ω In series with 200pF. Connection Diagram 8-Pin SOIC 20042904 Top View Ordering Information Package 8-pin SOIC Part Number LMH6715MA LMH6715MAX Package Marking LMH6715MA Transport Media Rails 2.5k Units Tape and Reel NSC Drawing M08A 3 www.national.com LMH6715 Typical Performance Characteristics 100Ω, unless otherwise specified). Non-Inverting Frequency Response (TA = 25˚C, VCC = ± 5V, AV = ± 2V/V, RF = 500Ω, RL = Inverting Frequency Response 20042913 20042912 Non-Inverting Frequency Response vs. VOUT Small Signal Channel Matching 20042916 20042901 Frequency Response vs. Load Resistance Non-Inverting Frequency Response vs. RF 20042915 20042914 www.national.com 4 LMH6715 Typical Performance Characteristics (TA = 25˚C, VCC = ±5V, AV = ±2V/V, RF = 500Ω, RL = 100Ω, unless otherwise specified). (Continued) Small Signal Pulse Response Large Signal Pulse Response 20042918 20042919 Input-Referred Crosstalk Settling Time vs. Accuracy 20042907 20042924 −3dB Bandwidth vs. VOUT DC Errors vs. Temperature 20042925 20042926 5 www.national.com LMH6715 Typical Performance Characteristics (TA = 25˚C, VCC = ±5V, AV = ±2V/V, RF = 500Ω, RL = 100Ω, unless otherwise specified). (Continued) Open Loop Transimpedance, Z(s) Equivalent Input Noise vs. Frequency 20042920 20042923 Differential Gain & Phase vs. Load Differential Gain vs. Frequency 20042908 20042909 Differential Phase vs. Frequency Gain Flatness & Linear Phase Deviation 20042910 20042911 www.national.com 6 LMH6715 Typical Performance Characteristics (TA = 25˚C, VCC = ±5V, AV = ±2V/V, RF = 500Ω, RL = 100Ω, unless otherwise specified). (Continued) 2nd Harmonic Distortion vs. Output Voltage 3rd Harmonic Distortion vs. Output Voltage 20042902 20042905 Closed Loop Output Resistance PSRR & CMRR 20042906 20042917 Suggested RS vs. CL 20042927 7 www.national.com LMH6715 Application Section FEEDBACK RESISTOR SELECTION One of the key benefits of a current feedback operational amplifier is the ability to maintain optimum frequency response independent of gain by using appropriate values for the feedback resistor (RF). The Electrical Characteristics and Typical Performance plots specify an RF of 500Ω, a gain of +2V/V and ± 5V power supplies (unless otherwise specified). Generally, lowering RF from it’s recommended value will peak the frequency response and extend the bandwidth while increasing the value of RF will cause the frequency response to roll off faster. Reducing the value of RF too far below it’s recommended value will cause overshoot, ringing and, eventually, oscillation. Frequency Response vs. RF 20042935 FIGURE 1. Non-Inverting Configuration with Power Supply Bypassing 20042914 20042937 FIGURE 2. Inverting Configuration with Power Supply Bypassing The plot labeled “Frequency Response vs. RF” shows the LMH6715’s frequency response as RF is varied (RL = 100Ω, AV = +2). This plot shows that an RF of 200Ω results in peaking and marginal stability. An RF of 300Ω gives near maximal bandwidth and gain flatness with good stability, but with very light loads (RL > 300Ω) the device may show some peaking. An RF of 500Ω gives excellent stability with good bandwidth and is the recommended value for most applications. Since all applications are slightly different it is worth some experimentation to find the optimal RF for a given circuit. For more information see Application Note OA-13 which describes the relationship between RF and closedloop frequency response for current feedback operational amplifiers. When configuring the LMH6715 for gains other than +2V/V, it is usually necessary to adjust the value of the feedback resistor. The two plots labeled “RF vs. Non-inverting Gain” and “RF vs. Inverting Gain” provide recommended feedback resistor values for a number of gain selections. Application Introduction Offered in an 8-pin package for reduced space and cost, the wideband LMH6715 dual current-feedback op amp provides closely matched DC and AC electrical performance characteristics making the part an ideal choice for wideband signal processing. Applications such as broadcast quality video systems, IQ amplifiers, filter blocks, high speed peak detectors, integrators and transimedance amplifiers will all find superior performance in the LMH6715 dual op amp. www.national.com 8 LMH6715 Application Introduction (Continued) RF vs. Non-Inverting Gain tances (to AC ground) arising from traces or pads placed too closely ( < 0.1”) to power or ground planes. In some cases, due to the frequency response peaking caused by these parasitics, a small adjustment of the feedback resistor value will serve to compensate the frequency response. Also, it is very important to keep the parasitic capacitance across the feedback resistor to an absolute minimum. The performance plots in the data sheet can be reproduced using the evaluation boards available from National. The CLC730036 board uses all SMT parts for the evaluation of the LMH6715. The board can serve as an example layout for the final production printed circuit board. Care must also be taken with the LMH6715’s layout in order to achieve the best circuit performance, particularly channelto-channel isolation. The decoupling capacitors (both tantalum and ceramic) must be chosen with good high frequency characteristics to decouple the power supplies and the physical placement of the LMH6715’s external components is critical. Grouping each amplifier’s external components with their own ground connection and separating them from the external components of the opposing channel with the maximum possible distance is recommended. The input (RIN) and gain setting resistors (RF) are the most critical. It is also recommended that the ceramic decoupling capacitor (0.1µF chip or radial-leaded with low ESR) should be placed as closely to the power pins as possible. POWER DISSIPATION Follow these steps to determine the Maximum power dissipation for the LMH6715: 1. Calculate the quiescent (no-load) power: PAMP = ICC (VCC - VEE) 2. Calculate the RMS power at the output stage: PO = (VCC -VLOAD)(ILOAD), where VLOAD and ILOAD are the voltage and current across the external load. 3. Calculate the total RMS power: Pt = PAMP + PO The maximum power that the LMH6715, package can dissipate at a given temperature can be derived with the following equation: Pmax = (150o - Tamb)/ θJA, where Tamb = Ambient temperature (˚C) and θJA = Thermal resistance, from junction to ambient, for a given package (˚C/W). For the SOIC package θJA is 145˚C/W. MATCHING PERFORMANCE With proper board layout, the AC performance match between the two LMH6715’s amplifiers can be tightly controlled as shown in Typical Performance plot labeled “Small-Signal Channel Matching”. The measurements were performed with SMT components using a feedback resistor of 300Ω at a gain of +2V/V. The LMH6715’s amplifiers, built on the same die, provide the advantage of having tightly matched DC characteristics. SLEW RATE AND SETTLING TIME One of the advantages of current-feedback topology is an inherently high slew rate which produces a wider full power bandwidth. The LMH6715 has a typical slew rate of 1300V/ µs. The required slew rate for a design can be calculated by the following equation: SR = 2πfVpk. Careful attention to parasitic capacitances is critical to achieving the best settling time performance. The LMH6715 20042921 Both plots show the value of RF approaching a minimum value (dashed line) at high gains. Reducing the feedback resistor below this value will result in instability and possibly oscillation. The recommended value of RF is depicted by the solid line, which begins to increase at higher gains. The reason that a higher RF is required at higher gains is the need to keep RG from decreasing too far below the output impedance of the input buffer. For the LMH6715 the output resistance of the input buffer is approximately 160Ω and 50Ω is a practical lower limit for RG. Due to the limitations on RG the LMH6715 begins to operate in a gain bandwidth limited fashion for gains of ± 5V/V or greater. RF vs. Inverting Gain 20042922 When using the LMH6715 as a replacement for the CLC412, identical bandwidth can be obtained by using an appropriate value of RF . The chart “Frequency Response vs. RF” shows that an RF of approximately 700Ω will provide bandwidth very close to that of the CLC412. At other gains a similar increase in RF can be used to match the new and old parts. CIRCUIT LAYOUT With all high frequency devices, board layouts with stray capacitances have a strong influence over AC performance. The LMH6715 is no exception and its input and output pins are particularly sensitive to the coupling of parasitic capaci9 www.national.com LMH6715 Application Introduction (Continued) Applications Circuits SINGLE-TO-DIFFERENTIAL LINE DRIVER The LMH6715’s well matched AC channel-response allows a single-ended input to be transformed to highly matched push-pull driver. From a 1V single-ended input the circuit of Figure 3 produces 1V differential signal between the two outputs. For larger signals the input voltage divider (R1 = 2R2) is necessary to limit the input voltage on channel 2. has a typical short term settling time to 0.05% of 12ns for a 2V step. Also, the amplifier is virtually free of any long term thermal tail effects at low gains. When measuring settling time, a solid ground plane should be used in order to reduce ground inductance which can cause common-ground-impedance coupling. Power supply and ground trace parasitic capacitances and the load capacitance will also affect settling time. Placing a series resistor (Rs) at the output pin is recommended for optimal settling time performance when driving a capacitive load. The Typical Performance plot labeled “RS and Settling Time vs. Capacitive Load” provides a means for selecting a value of Rs for a given capacitive load. DC & NOISE PERFORMANCE A current-feedback amplifier’s input stage does not have equal nor correlated bias currents, therefore they cannot be canceled and each contributes to the total DC offset voltage at the output by the following equation: The input resistance is the resistance looking from the noninverting input back toward the source. For inverting DCoffset calculations, the source resistance seen by the input resistor Rg must be included in the output offset calculation as a part of the non-inverting gain equation. Application note OA-7 gives several circuits for DC offset correction. The noise currents for the inverting and non-inverting inputs are graphed in the Typical Performance plot labeled “Equivalent Input Noise”. A more complete discussion of amplifier inputreferred noise and external resistor noise contribution can be found in OA-12. DIFFERENTIAL GAIN & PHASE The LMH6715 can drive multiple video loads with very low differential gain and phase errors. The Typical Performance plots labeled “Differential Gain vs. Frequency” and “Differential Phase vs. Frequency” show performance for loads from 1 to 4. The Electrical Characteristics table also specifies performance for one 150Ω load at 4.43MHz. For NTSC video, the performance specifications also apply. Application note OA-24 “Measuring and Improving Differential Gain & Differential Phase for Video”, describes in detail the techniques used to measure differential gain and phase. I/O VOLTAGE & OUTPUT CURRENT The usable common-mode input voltage range (CMIR) of the LMH6715 specified in the Electrical Characteristics table of the data sheet shows a range of ± 2.2 volts. Exceeding this range will cause the input stage to saturate and clip the output signal. The output voltage range is determined by the load resistor and the choice of power supplies. With ± 5 volts the class A/B output driver will typically drive ± 3.9V into a load resistance of 100Ω. Increasing the supply voltages will change the common-mode input and output voltage swings while at the same time increase the internal junction temperature. 20042945 FIGURE 3. Single-to-Differential Line Driver DIFFERENTIAL LINE RECEIVER Figure 4 and Figure 5 show two different implementations of an instrumentation amplifier which convert differential signals to single-ended. Figure 5 allows CMRR adjustment through R2. 20042946 FIGURE 4. Differential Line Receiver www.national.com 10 LMH6715 Applications Circuits (Continued) LOW NOISE WIDE-BANDWIDTH TRANSIMPEDANCE AMPLIFIER Figure 7 implements a low noise transimpedance amplifier using both channels of the LMH6715. This circuit takes advantage of the lower input bias current noise of the noninverting input and achieves negative feedback through the second LMH6715 channel. The output voltage is set by the value of RF while frequency compensation is achieved through the adjustment of RT. 20042947 FIGURE 5. Differential Line Receiver with CMRR Adjustment NON-INVERTING CURRENT-FEEDBACK INTEGRATOR The circuit of Figure 6 achieves its high speed integration by placing one of the LMH6715’s amplifiers in the feedback loop of the second amplifier configured as shown. 20042950 FIGURE 7. Low-Noise, Wide Bandwidth, Transimpedance Amp. 20042949 FIGURE 6. Current Feedback Integrator 11 www.national.com LMH6715 Dual Wideband Video Op Amp Physical Dimensions unless otherwise noted inches (millimeters) 8-Pin SOIC NS Package Number M08A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 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