LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp General Description The National LMH6628 is a high speed dual op amp that offers a traditional voltage feedback topology featuring unity gain stability and slew enhanced circuitry. The LMH6628’s low noise and very low harmonic distortion combine to form a wide dynamic range op amp that operates from a single (5V to 12V) or dual ( ± 5V) power supply. Each of the LMH6628’s closely matched channels provides a 300MHz unity gain bandwidth and low input voltage noise ). Low 2nd/3rd harmonic distortion (−65/ density (2nV/ −74dBc at 10MHz) make the LMH6628 a perfect wide dynamic range amplifier for matched I/Q channels. With its fast and accurate settling (12ns to 0.1%), the LMH6628 is also an excellent choice for wide dynamic range, anti-aliasing filters to buffer the inputs of hi resolution analog-to-digital converters. Combining the LMH6628’s two tightly matched amplifiers in a single 8-pin SOIC package reduces cost and board space for many composite amplifier applications such as active filters, differential line drivers/ receivers, fast peak detectors and instrumentation amplifiers. The LMH6628 is fabricated using National’s VIP10™ complimentary bipolar process. Connection Diagram To reduce design times and assist in board layout, the LMH6628 is supported by an evaluation board (CLC730036). Features n n n n n n n Wide unity gain bandwidth: 300MHz Low noise: 2nV/ Low Distortion: −65/−74dBc (10MHz) Settling time: 12ns to 0.1% Wide supply voltage range: ± 2.5V to ± 6V High output current: ± 85mA Improved replacement for CLC428 Applications n n n n n n High speed dual op amp Low noise integrators Low noise active filters Driver/receiver for transmission systems High speed detectors I/Q channel amplifiers Inverting Frequency Response 8-Pin SOIC 20038535 Top View 20038515 © 2003 National Semiconductor Corporation DS200385 www.national.com LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp January 2003 LMH6628 Absolute Maximum Ratings (Note 1) Maximum Junction Temperature Storage Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Thermal Resistance (Note 5) 200V Supply Voltage 13.5 Short Circuit Current +300˚C Operating Ratings (Note 1) 2kV Machine Model −65˚C to +150˚C Lead Temperature (soldering 10 sec) ESD Tolerance (Note 4) Human Body Model +150˚C Package (θJC) (θJA) SOIC 65˚C/W 145˚C/W (Note 3) Common-Mode Input Voltage V + - V− Temperature Range Differential Input Voltage V + - V− Nominal Supply Voltage −40˚C to +85˚C ± 2.5V to ± 6V Electrical Characteristics (Note 2) VCC = ± 5V, AV = +2V/V, RF = 100Ω, RG = 100Ω, RL = 100Ω; unless otherwise specified. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ Max Units Frequency Domain Response GB Gain Bandwidth Product VO < 0.5VPP SSBW -3dB Bandwidth, AV = +1 VO < 0.5VPP SSBW -3dB Bandwidth, AV = +2 VO < 0.5VPP GFL Gain Flatness VO < 0.5VPP GFP GFR LPD Peaking Rolloff Linear Phase Deviation 180 DC to 200MHz 200 MHz 300 MHz 100 MHz 0.0 dB DC to 20MHz .1 dB DC to 20MHz .1 deg Time Domain Response TR Rise and Fall Time 1V Step 4 ns TS Settling Time 2V Step to 0.1% 12 ns OS Overshoot 1V Step 1 % SR Slew Rate 4V Step 550 V/µs 300 Distortion And Noise Response HD2 2nd Harmonic Distortion 1VPP, 10MHz −65 dBc HD3 3rd Harmonic Distortion 1VPP, 10MHz −74 dBc Equivalent Input Noise VN Voltage 1MHz to 100MHz 2 nV/ IN Current 1MHz to 100MHz 2 pA/ XTLKA Crosstalk Input Referred, 10MHz −62 dB 63 dB Static, DC Performance GOL Open-Loop Gain VIO Input Offset Voltage DVIO IBN DIBN IOS IOSD 56 53 ± .5 Average Drift 5 Input Bias Current ± .7 Average Drift 150 Input Offset Current 0.3 mV µV/˚C ± 20 ± 30 µA nA/˚C ±6 µA 5 nA/˚C PSRR Power Supply Rejection Ratio 60 46 70 dB CMRR Common-Mode Rejection Ratio 57 54 62 dB ICC Supply Current 7.5 7.0 9 www.national.com Average Drift ±2 ± 2.6 Per Channel, RL = ∞ 2 12 12.5 mA LMH6628 Electrical Characteristics (Note 2) (Continued) VCC = ± 5V, AV = +2V/V, RF = 100Ω, RG = 100Ω, RL = 100Ω; unless otherwise specified. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min Typ Max Units Miscellaneous Performance RIN Input Resistance Common-Mode 500 kΩ Differential-Mode 200 kΩ CIN Input Capacitance Common-Mode 1.5 pF Differential-Mode 1.5 pF ROUT Output Resistance Closed-Loop .1 Ω VO Output Voltage Range RL = ∞ ± 3.8 ± 3.5 V VOL ± 3.2 ± 3.1 RL = 100Ω CMIR Input Voltage Range IO Output Current Common- Mode ± 50 V ± 3.7 ± 85 V mA 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 Note 6 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: Output is short circuit protected to ground, however maximum reliability is obtained if output current does not exceed 160mA. Note 4: Human body model, 1.5kΩ in series with 100pF. Machine model, 0Ω In series with 200pF. Note 5: The maximum power dissipation is a function of TJ(MAX), θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJ(MAX)-TA)/ θJA. All numbers apply for packages soldered directly onto a PC board. Ordering Information Package 8-pin SOIC Part Number Package Marking LMH6628MA LMH6628MA LMH6628MAX Transport Media NSC Drawing Rails M08A 2.5k Units Tape and Reel 3 www.national.com LMH6628 Typical Performance Characteristics (TA = +25˚, AV = +2, VCC = ± 5V, Rf =100Ω, RL = 100Ω, un- less specified) Non-Inverting Frequency Response Inverting Frequency Response 20038515 20038513 Frequency Response vs. Load Resistance Frequency Response vs. Output Amplitude 20038510 20038525 Frequency Response vs. Capacitive Load Gain Flatness & Linear Phase 20038516 20038524 www.national.com 4 Channel Matching Channel to Channel Crosstalk 20038514 20038509 Pulse Response (VO = 2V) Pulse Response (VO = 100mV) 20038511 20038512 2nd Harmonic Distortion vs. Output Voltage 3rd Harmonic Distortion vs. Output Voltage 20038507 20038508 5 www.national.com LMH6628 Typical Performance Characteristics (TA = +25˚, AV = +2, VCC = ±5V, Rf =100Ω, RL = 100Ω, unless specified) (Continued) LMH6628 Typical Performance Characteristics (TA = +25˚, AV = +2, VCC = ±5V, Rf =100Ω, RL = 100Ω, unless specified) (Continued) PSRR and CMRR ( ± 5V) 2nd & 3rd Harmonic Distortion vs. Frequency 20038522 20038517 PSRR and CMRR ( ± 2.5V) Closed Loop Output Resistance ( ± 2.5V) 20038523 20038518 Closed Loop Output Resistance ( ± 5V) Open Loop Gain & Phase ( ± 2.5V) 20038519 www.national.com 20038521 6 Open Loop Gain & Phase ( ± 5V) Recommended RS vs. CL 20038520 20038526 DC Errors vs. Temperature Maximum VO vs. RL 20038545 20038546 2-Tone, 3rd Order Intermodulation Intercept Voltage & Current Noise vs. Frequency 20038544 20038547 7 www.national.com LMH6628 Typical Performance Characteristics (TA = +25˚, AV = +2, VCC = ±5V, Rf =100Ω, RL = 100Ω, unless specified) (Continued) LMH6628 Typical Performance Characteristics (TA = +25˚, AV = +2, VCC = ±5V, Rf =100Ω, RL = 100Ω, unless specified) (Continued) Settling Time vs. Accuracy 20038548 See OA-15 for more information. National suggests the 730036 (SOIC) dual op amp evaluation board as a guide for high frequency layout and as an aid in device evaluation. Application Section LOW NOISE DESIGN Ultimate low noise performance from circuit designs using the LMH6628 requires the proper selection of external resistors. By selecting appropriate low valued resistors for RF and RG, amplifier circuits using the LMH6628 can achieve output noise that is approximately the equivalent voltage input multiplied by the desired gain (AV). noise of 2nV/ ANALOG DELAY CIRCUIT (ALL-PASS NETWORK) The circuit in Figure 1 implements an all-pass network using the LMH6628. A wide bandwidth buffer (LM7121) drives the circuit and provides a high input impedance for the source. As shown in Figure 2, the circuit provides a 13.1ns delay (with R = 40.2Ω, C = 47pF). RF and RG should be of equal and low value for parasitic insensitive operation. DC BIAS CURRENTS AND OFFSET VOLTAGES Cancellation of the output offset voltage due to input bias currents is possible with the LMH6628. This is done by making the resistance seen from the inverting and noninverting inputs equal. Once done, the residual output offset voltage will be the input offset voltage (VOS) multiplied by the desired gain (AV). National Application Note OA-7 offers several solutions to further reduce the output offset. OUTPUT AND SUPPLY CONSIDERATIONS With ± 5V supplies, the LMH6628 is capable of a typical output swing of ± 3.8V under a no-load condition. Additional output swing is possible with slightly higher supply voltages. For loads of less than 50Ω, the output swing will be limited by the LMH6628’s output current capability, typically 85mA. Output settling time when driving capacitive loads can be improved by the use of a series output resistor. See the plot labeled "RS vs. CL" in the Typical Performance section. 20038501 FIGURE 1. LAYOUT Proper power supply bypassing is critical to insure good high frequency performance and low noise. De-coupling capacitors of 0.1µF should be placed as close as possible to the power supply pins. The use of surface mounted capacitors is recommended due to their low series inductance. A good high frequency layout will keep power supply and ground traces away from the inverting input and output pins. Parasitic capacitance from these nodes to ground causes frequency response peaking and possible circuit oscillation. 20038502 FIGURE 2. Delay Circuit Response to 0.5V Pulse www.national.com 8 LMH6628 Application Section (Continued) The circuit gain is +1 and the delay is determined by the following equations. (1) Td = 1 dφ 360 df ; (2) where Td is the delay of the op amp at AV = +1. The LMH6628 provides a typical delay of 2.8ns at its −3dB point. 20038531 FULL DUPLEX DIGITAL OR ANALOG TRANSMISSION FIGURE 4. Simultaneous transmission and reception of analog or digital signals over a single coaxial cable or twisted-pair line can reduce cabling requirements. The LMH6628’s wide bandwidth and high common-mode rejection in a differential amplifier configuration allows full duplex transmission of video, telephone, control and audio signals. In the circuit shown in Figure 3, one of the LMH6628’s amps is used as a "driver" and the other as a difference "receiver" amplifier. The output impedance of the "driver" is essentially zero. The two R’s are chosen to match the characteristic impedance of the transmission line. The "driver" op amp gain can be selected for unity or greater. Receiver amplifier A2 (B2) is connected across R and forms differential amplifier for the signals transmitted by driver A2 (B2). If RF equals RG, receiver A2 (B1) will then reject the signals from driver A1 (B1) and pass the signals from driver B1 (A1). POSITIVE PEAK DETECTOR The LMH6628’s dual amplifiers can be used to implement a unity-gain peak detector circuit as shown in Figure 5. 20038505 FIGURE 5. The acquisition speed of this circuit is limited by the dynamic resistance of the diode when charging Chold. A plot of the circuit’s performance is shown in Figure 6 with a 1MHz sinusoidal input. 20038503 FIGURE 3. The output of the receiver amplifier will be: (3) Care must be given to layout and component placement to maintain a high frequency common-mode rejection. The plot of Figure 4 shows the simultaneous reception of signals transmitted at 1MHz and 10MHz. 9 www.national.com LMH6628 Application Section (Continued) (4) To build a boost circuit, use the design equations Eq. 6 and Eq. 7. (5) (6) Select R2 and C using Eq. 6. Use reasonable values for high frequency circuits - R2 between 10Ω and 5kΩ, C between 10pF and 2000pF. Use Eq. 7 to determine the parallel combination of Ra and Rb. Select Ra and Rb by either the 10Ω to 5kΩ criteria or by other requirements based on the impedance Vin is capable of driving. Finish the design by determining the value of K from Eq. 8. 20038537 FIGURE 6. A current source, built around Q1, provides the necessary bias current for the second amplifier and prevents saturation when power is applied. The resistor, R, closes the loop while diode D2 prevents negative saturation when VIN is less than VC. A MOS-type switch (not shown) can be used to reset the capacitor’s voltage. The maximum speed of detection is limited by the delay of the op amps and the diodes. The use of Schottky diodes will provide faster response. (7) Figure 8 shows an example of the response of the circuit of Figure 9, where fo is 2.3MHz. The component values are as follows: Ra =2.1kΩ, Rb = 68.5Ω, R2 = 4.22kΩ, R = 500Ω, KR = 50Ω, C = 120pF. ADJUSTABLE OR BANDPASS EQUALIZER A "boost" equalizer can be made with the LMH6628 by summing a bandpass response with the input signal, as shown in Figure 7. 20038506 20038543 FIGURE 7. FIGURE 8. The overall transfer function is shown in Eq. 5. www.national.com 10 LMH6628 Dual Wideband, Low Noise, Voltage Feedback Op Amp Physical Dimensions inches (millimeters) unless otherwise noted 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: [email protected] Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: [email protected] 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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