LMH6624MFX

LMH6624/LMH6626 Single/Dual Ultra Low Noise Wideband Operational Amplifier September 2005 LMH6624/LMH6626 Single/Dual Ultra Low Noise Wideband Operational Amplifier General Description The LMH6624/LMH6626 offer wide bandwidth (1.5GHz for single, 1.3GHz for dual) with very low input noise (0.92nV/ , 2.3pA/ ) and ultra low dc errors (100µV VOS, ± 0.1µV/˚C drift) providing very precise operational amplifiers with wide dynamic range. This enables the user to achieve closed-loop gains of greater than 10, in both inverting and non-inverting configurations. The LMH6624 (single) and LMH6626’s (dual) traditional voltage feedback topology provide the following benefits: balanced inputs, low offset voltage and offset current, very low offset drift, 81dB open loop gain, 95dB common mode rejection ratio, and 88dB power supply rejection ratio. The LMH6624/LMH6626 operate from ± 2.5V to ± 6V in dual supply mode and from +5V to +12V in single supply configuration. LMH6624 is offered in SOT23-5 and SOIC-8 packages. The LMH6626 is offered in SOIC-8 and MSOP-8 packages. Features VS = ± 6V, TA = 25˚C, AV = 20, (Typical values unless specified) n Gain bandwidth (LMH6624) 1.5GHz n Input voltage noise 0.92nV/ n Input offset voltage (limit over temp) 700uV n Slew rate 350V/µs n Slew rate (AV = 10) 400V/µs n HD2 @ f = 10MHz, RL = 100Ω −63dBc n HD3 @ f = 10MHz, RL = 100Ω −80dBc ± 2.5V to ± 6V n Supply voltage range (dual supply) n Supply voltage range (single supply) +5V to +12V n Improved replacement for the CLC425 (LMH6624) n Stable for closed loop |AV| ≥ 10 Applications n n n n n n n Instrumentation sense amplifiers Ultrasound pre-amps Magnetic tape & disk pre-amps Wide band active filters Professional Audio Systems Opto-electronics Medical diagnostic systems Connection Diagrams 5-Pin SOT23 8−Pin SOIC 8−Pin SOIC/MSOP 20058951 20058952 20058961 Top View Top View Top View © 2005 National Semiconductor Corporation DS200589 www.national.com LMH6624/LMH6626 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. ESD Tolerance Human Body Model Machine Model VIN Differential Supply Voltage (V+ - V−) Voltage at Input pins Soldering Information Infrared or Convection (20 sec.) 235˚C 2000V (Note 2) 200V (Note 9) Wave Soldering (10 sec.) Storage Temperature Range Junction Temperature (Note 3), (Note 4) 260˚C −65˚C to +150˚C +150˚C Operating Ratings (Note 1) Operating Temperature Range (Note 3), (Note 4) SOIC-8 SOT23–5 MSOP-8 −40˚C to +125˚C 166˚C/W 265˚C/W 235˚C/W Package Thermal Resistance (θJA)(Note 4) ± 1.2V 13.2V V+ +0.5V, V− −0.5V ± 2.5V Electrical Characteristics Unless otherwise specified, all limits guaranteed at TA = 25˚C, V+ = 2.5V, V− = −2.5V, VCM = 0V, AV = +20, RF = 500Ω, RL = 100Ω. Boldface limits apply at the temperature extremes. See (Note 12). Symbol Parameter Conditions Min (Note 6) Typ (Note 5) 90 80 300 290 360 340 4.1 4.1 20 0.92 1.0 2.3 1.8 −60 −76 −0.75 −0.95 −1.5 −2.0 −0.25 +0.75 +0.95 +1.5 +2.0 +20 +25 ns ns ns V/µs Max (Note 6) Units Dynamic Performance fCL SR −3dB BW Slew Rate(Note 8) VO = 400mVPP (LMH6624) VO = 400mVPP (LMH6626) VO = 2VPP, AV = +20 (LMH6624) VO = 2VPP, AV = +20 (LMH6626) VO = 2VPP, AV = +10 (LMH6624) VO = 2VPP, AV = +10 (LMH6626) tr tf ts en in HD2 HD3 VOS Rise Time Fall Time Settling Time 0.1% Input Referred Voltage Noise Input Referred Current Noise 2nd Harmonic Distortion 3 rd MHz VO = 400mV Step, 10% to 90% VO = 400mV Step, 10% to 90% VO = 2VPP (Step) f = 1MHz (LMH6624) f = 1MHz (LMH6626) f = 1MHz (LMH6624) f = 1MHz (LMH6626) fC = 10MHz, VO = 1VPP, RL 100Ω fC = 10MHz, VO = 1VPP, RL 100Ω VCM = 0V VCM = 0V VCM = 0V VCM = 0V VCM = 0V VCM = 0V Common Mode Differential Mode Common Mode Differential Mode Input Referred, VCM = −0.5 to +1.9V VCM = −0.5 to +1.75V 87 85 Distortion and Noise Response nV/ pA/ dBc dBc mV µV/˚C µA nA/˚C µA nA/˚C MΩ kΩ pF Harmonic Distortion Input Characteristics Input Offset Voltage Average Drift (Note 7) IOS Input Offset Current Average Drift (Note 7) IB Input Bias Current Average Drift (Note 7) RIN CIN CMRR Input Resistance (Note 10) Input Capacitance (Note 10) Common Mode Rejection Ratio ± 0.25 −0.05 2 13 12 6.6 4.6 0.9 2.0 90 dB www.national.com 2 LMH6624/LMH6626 ± 2.5V Electrical Characteristics Symbol Parameter (Continued) Unless otherwise specified, all limits guaranteed at TA = 25˚C, V+ = 2.5V, V− = −2.5V, VCM = 0V, AV = +20, RF = 500Ω, RL = 100Ω. Boldface limits apply at the temperature extremes. See (Note 12). Conditions Min (Note 6) 75 70 72 67 Typ (Note 5) 79 79 −75 dB Max (Note 6) Units Transfer Characteristics AVOL Large Signal Voltage Gain (LMH6624) RL = 100Ω, VO = −1V to +1V (LMH6626) RL = 100Ω, VO = −1V to +1V Xt VO Crosstalk Rejection Output Swing f = 1MHz (LMH6626) RL = 100Ω No Load RO ISC Output Impedance Output Short Circuit Current f ≤ 100KHz (LMH6624) Sourcing to Ground ∆VIN = 200mV (Note 3), (Note 11) (LMH6624) Sinking to Ground ∆VIN = −200mV (Note 3), (Note 11) (LMH6626) Sourcing to Ground ∆VIN = 200mV (Note 3),(Note 11) (LMH6626) Sinking to Ground ∆VIN = −200mV (Note 3),(Note 11) IOUT Output Current (LMH6624) Sourcing, VO = +0.8V Sinking, VO = −0.8V (LMH6626) Sourcing, VO = +0.8V Sinking, VO = −0.8V Power Supply PSRR IS Power Supply Rejection Ratio Supply Current (per channel) VS = ± 2.0V to ± 3.0V No Load 82 80 90 11.4 16 18 dB mA 90 75 90 75 60 50 60 50 Output Characteristics dB ± 1.1 ± 1.0 ± 1.4 ± 1.25 ± 1.5 ± 1.7 10 145 V mΩ 145 120 mA 120 100 75 mA ± 6V Electrical Characteristics Unless otherwise specified, all limits guaranteed at TA = 25˚C, V+ = 6V, V− = −6V, VCM = 0V, AV = +20, RF = 500Ω, RL = 100Ω. Boldface limits apply at the temperature extremes. See (Note 12). Symbol Parameter Conditions Min (Note 6) Typ (Note 5) 95 85 350 320 400 360 3.7 ns www.national.com Max (Note 6) Units Dynamic Performance fCL SR −3dB BW Slew Rate (Note 8) VO = 400mVPP (LMH6624) VO = 400mVPP (LMH6626) VO = 2VPP, AV = +20 (LMH6624) VO = 2VPP, AV = +20 (LMH6626) VO = 2VPP, AV = +10 (LMH6624) VO = 2VPP, AV = +10 (LMH6626) tr Rise Time VO = 400mV Step, 10% to 90% 3 MHz V/µs LMH6624/LMH6626 ± 6V Electrical Characteristics Symbol tf ts en in HD2 HD3 VOS Fall Time Settling Time 0.1% Input Referred Voltage Noise Input Referred Current Noise 2nd Harmonic Distortion 3 rd (Continued) Unless otherwise specified, all limits guaranteed at TA = 25˚C, V+ = 6V, V− = −6V, VCM = 0V, AV = +20, RF = 500Ω, RL = 100Ω. Boldface limits apply at the temperature extremes. See (Note 12). Parameter Conditions VO = 400mV Step, 10% to 90% VO = 2VPP (Step) f = 1MHz (LMH6624) f = 1MHz (LMH6626) f = 1MHz (LMH6624) f = 1MHz (LMH6626) fC = 10MHz, VO = 1VPP, RL 100Ω fC = 10MHz, VO = 1VPP, RL 100Ω VCM = 0V VCM = 0V (LMH6624) VCM = 0V (LMH6626) VCM = 0V VCM = 0V −1.1 −2.5 −2.0 −2.5 −0.5 −0.7 Harmonic Distortion Min (Note 6) Typ (Note 5) 3.7 18 0.92 1.0 2.3 1.8 −63 −80 Max (Note 6) Units ns ns Distortion and Noise Response nV/ pA/ dBc dBc +0.5 +0.7 1.1 2.5 2.0 2.5 nA/˚C +20 +25 µA nA/˚C MΩ kΩ pF mV µV/˚C µA Input Characteristics Input Offset Voltage Average Drift (Note 7) IOS Input Offset Current Average Drift (Note 7) ± 0.10 ± 0.2 0.05 0.1 0.7 13 12 6.6 4.6 0.9 2.0 IB Input Bias Current Average Drift (Note 7) VCM = 0V VCM = 0V Common Mode Differential Mode Common Mode Differential Mode Input Referred, VCM = −4.5 to +5.25V VCM = −4.5 to +5.0V (LMH6624) RL = 100Ω, VO = −3V to +3V (LMH6626) RL = 100Ω, VO = −3V to +3V 90 87 77 72 74 70 RIN CIN CMRR Input Resistance (Note 10) Input Capacitance (Note 10) Common Mode Rejection Ratio 95 dB Transfer Characteristics AVOL Large Signal Voltage Gain 81 80 −75 dB Xt VO Crosstalk Rejection Output Swing f = 1MHz (LMH6626) (LMH6624) RL = 100Ω (LMH6624) No Load (LMH6626) RL = 100Ω (LMH6626) No Load dB Output Characteristics ± 4.4 ± 4.3 ± 4.8 ± 4.65 ± 4.3 ± 4.2 ± 4.8 ± 4.65 ± 4.9 ± 5.2 ± 4.8 ± 5.2 10 mΩ V RO Output Impedance f ≤ 100KHz www.national.com 4 LMH6624/LMH6626 ± 6V Electrical Characteristics Symbol ISC Parameter Output Short Circuit Current (Continued) Unless otherwise specified, all limits guaranteed at TA = 25˚C, V+ = 6V, V− = −6V, VCM = 0V, AV = +20, RF = 500Ω, RL = 100Ω. Boldface limits apply at the temperature extremes. See (Note 12). Conditions (LMH6624) Sourcing to Ground ∆VIN = 200mV (Note 3), (Note 11) (LMH6624) Sinking to Ground ∆VIN = −200mV (Note 3), (Note 11) (LMH6626) Sourcing to Ground ∆VIN = 200mV (Note 3), (Note 11) (LMH6626) Sinking to Ground ∆VIN = −200mV (Note 3), (Note 11) Min (Note 6) 100 85 100 85 65 55 65 55 Typ (Note 5) 156 Max (Note 6) Units 156 120 mA 120 IOUT Output Current (LMH6624) Sourcing, VO = +4.3V Sinking, VO = −4.3V (LMH6626) Sourcing, VO = +4.3V Sinking, VO = −4.3V 100 80 mA Power Supply PSRR IS Power Supply Rejection Ratio Supply Current (per channel) VS = ± 5.4V to ± 6.6V No Load 82 80 88 12 16 18 dB 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 and the test conditions, see the Electrical Characteristics. Note 2: Human body model, 1.5kΩ in series with 100pF. Note 3: Applies to both single-supply and split-supply operation. Continuous short circuit operation at elevated ambient temperature can result in exceeding the maximum allowed junction temperature of 150˚C. Note 4: 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. Note 5: Typical Values represent the most likely parametric norm. Note 6: All limits are guaranteed by testing or statistical analysis. Note 7: Average drift is determined by dividing the change in parameter at temperature extremes into the total temperature change. Note 8: Slew rate is the slowest of the rising and falling slew rates. Note 9: Machine Model, 0Ω in series with 200pF. Note 10: Simulation results. Note 11: Short circuit test is a momentary test. Output short circuit duration is 1.5ms. Note 12: 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. Absolute maximum ratings indicate junction temperature limits beyond which the device may be permanently degraded, either mechanically or electrically. Ordering Information Package SOT23-5 SOIC-8 SOIC-8 MSOP-8 Part Number LMH6624MF LMH6624MFX LMH6624MA LMH6624MAX LMH6626MA LMH6626MAX LMH6626MM LMH6626MMX A98A LMH6626MA LMH6624MA Package Marking A94A Transport Media 1k Units Tape and Reel 3k Units Tape and Reel 95 Units/Rail 2.5k Units Tape and Reel 95 Units/Rail 2.5k Units Tape and Reel 1k Units Tape and Reel 3.5k Units Tape and Reel MUA08A M08A M08A NSC Drawing MF05A 5 www.national.com LMH6624/LMH6626 Typical Performance Characteristics Voltage Noise vs. Frequency Current Noise vs. Frequency 20058962 20058963 Inverting Frequency Response Inverting Frequency Response 20058989 20058988 Non-Inverting Frequency Response Non-Inverting Frequency Response 20058904 20058903 www.national.com 6 LMH6624/LMH6626 Typical Performance Characteristics Open Loop Frequency Response Over Temperature (Continued) Open Loop Frequency Response Over Temperature 20058966 20058964 Frequency Response with Cap. Loading Frequency Response with Cap. Loading 20058984 20058986 Frequency Response with Cap. Loading Frequency Response with Cap. Loading 20058987 20058985 7 www.national.com LMH6624/LMH6626 Typical Performance Characteristics Non-Inverting Frequency Response Varying VIN (Continued) Non-Inverting Frequency Response Varying VIN 20058906 20058905 Non-Inverting Frequency Response Varying VIN (LMH6624) Non-Inverting Frequency Response Varying VIN (LMH6626) 20058908 20058981 Non-Inverting Frequency Response Varying VIN (LMH6624) Non-Inverting Frequency Response Varying VIN (LMH6626) 20058907 20058980 www.national.com 8 LMH6624/LMH6626 Typical Performance Characteristics Sourcing Current vs. VOUT (LMH6624) (Continued) Sourcing Current vs. VOUT (LMH6626) 20058957 20058972 Sourcing Current vs. VOUT (LMH6624) Sourcing Current vs. VOUT (LMH6626) 20058954 20058969 VOS vs. VSUPPLY (LMH6624) VOS vs. VSUPPLY (LMH6626) 20058967 20058968 9 www.national.com LMH6624/LMH6626 Typical Performance Characteristics Sinking Current vs. VOUT (LMH6624) (Continued) Sinking Current vs. VOUT (LMH6626) 20058958 20058971 Sinking Current vs. VOUT (LMH6624) Sinking Current vs. VOUT (LMH6626) 20058956 20058970 IOS vs. VSUPPLY Crosstalk Rejection vs. Frequency (LMH6626) 20058953 20058979 www.national.com 10 LMH6624/LMH6626 Typical Performance Characteristics Distortion vs. Frequency (Continued) Distortion vs. Frequency 20058944 20058946 Distortion vs. Frequency Distortion vs. Gain 20058945 20058978 Distortion vs. VOUT Peak to Peak Distortion vs. VOUT Peak to Peak 20058943 20058977 11 www.national.com LMH6624/LMH6626 Typical Performance Characteristics Non-Inverting Large Signal Pulse Response (Continued) Non-Inverting Large Signal Pulse Response 20058973 20058974 Non-Inverting Small Signal Pulse Response Non-Inverting Small Signal Pulse Response 20058975 20058976 PSRR vs. Frequency PSRR vs. Frequency 20058948 20058949 www.national.com 12 LMH6624/LMH6626 Typical Performance Characteristics Input Referred CMRR vs. Frequency (Continued) Input Referred CMRR vs. Frequency 20058901 20058902 Amplifier Peaking with Varying RF Amplifier Peaking with Varying RF 20058983 20058982 13 www.national.com LMH6624/LMH6626 Application Section 20058918 20058919 FIGURE 1. Non-Inverting Amplifier Configuration INTRODUCTION The LMH6624/LMH6626 are very wide gain bandwidth, ultra low noise voltage feedback operational amplifiers. Their excellent performances enable applications such as medical diagnostic ultrasound, magnetic tape & disk storage and fiber-optics to achieve maximum high frequency signal-tonoise ratios. The set of characteristic plots in the "Typical Performance" section illustrates many of the performance trade offs. The following discussion will enable the proper selection of external components to achieve optimum system performance. BIAS CURRENT CANCELLATION To cancel the bias current errors of the non-inverting configuration, the parallel combination of the gain setting (Rg) and feedback (Rf) resistors should equal the equivalent source resistance (Rseq) as defined in Figure 1. Combining this constraint with the non-inverting gain equation also seen in Figure 1, allows both Rf and Rg to be determined explicitly from the following equations: Rf = AVRseq and Rg = Rf/(AV-1) When driven from a 0Ω source, such as the output of an op amp, the non-inverting input of the LMH6624/LMH6626 should be isolated with at least a 25Ω series resistor. As seen in Figure 2, bias current cancellation is accomplished for the inverting configuration by placing a resistor (Rb) on the non-inverting input equal in value to the resistance seen by the inverting input (Rf||(Rg+Rs)). Rb should to be no less than 25Ω for optimum LMH6624/LMH6626 performance. A shunt capacitor can minimize the additional noise of Rb. FIGURE 2. Inverting Amplifier Configuration TOTAL INPUT NOISE vs. SOURCE RESISTANCE To determine maximum signal-to-noise ratios from the LMH6624/LMH6626, an understanding of the interaction between the amplifier’s intrinsic noise sources and the noise arising from its external resistors is necessary. Figure 3 describes the noise model for the non-inverting amplifier configuration showing all noise sources. In addition to the intrinsic input voltage noise (en) and current noise (in = in+ = in−) source, there is also thermal voltage noise (et = √(4KTR)) associated with each of the external resistors. Equation 1 provides the general form for total equivalent input voltage noise density (eni). Equation 2 is a simplification of Equation 1 that assumes 20058920 FIGURE 3. Non-Inverting Amplifier Noise Model www.national.com 14 LMH6624/LMH6626 Application Section (Continued) (1) Rf||Rg = Rseq for bias current cancellation. Figure 4 illustrates the equivalent noise model using this assumption. Figure 5 is a plot of eni against equivalent source resistance (Rseq) with all of the contributing voltage noise source of Equation 2. This plot gives the expected eni for a given (Rseq) which assumes Rf||Rg = Rseq for bias current cancellation. The total equivalent output voltage noise (eno) is eni*AV. Rf||Rg should be as low as possible to minimize noise. Results similar to Equation 1 are obtained for the inverting configuration of Figure 2 if Rseq is replaced by Rb and Rg is replaced by Rg + Rs. With these substitutions, Equation 1 will yield an eni referred to the non-inverting input. Referring eni to the inverting input is easily accomplished by multiplying eni by the ratio of non-inverting to inverting gains. NOISE FIGURE Noise Figure (NF) is a measure of the noise degradation caused by an amplifier. (3) The Noise Figure formula is shown in Equation 3. The addition of a terminating resistor RT, reduces the external thermal noise but increases the resulting NF. The NF is increased because RT reduces the input signal amplitude thus reducing the input SNR. 20058921 FIGURE 4. Noise Model with Rf||Rg = Rseq (2) As seen in Figure 5, eni is dominated by the intrinsic voltage noise (en) of the amplifier for equivalent source resistances below 33.5Ω. Between 33.5Ω and 6.43kΩ, eni is dominated by the thermal noise (et = √(4kT(2Rseq)) of the external resistor. Above 6.43kΩ, eni is dominated by the amplifier’s current noise (in = √(2) inRseq). When Rseq = 464Ω (ie., en/√(2) in) the contribution from voltage noise and current noise of LMH6624/LMH6626 is equal.. For example, configured with a gain of +20V/V giving a −3dB of 90MHz and driven from Rseq = 25Ω, the LMH6624 produces a total 1.57*90MHz) of equivalent input noise voltage (eni x 16.5µVrms. (4) The noise figure is related to the equivalent source resistance (Rseq) and the parallel combination of Rf and Rg. To minimize noise figure. • Minimize Rf||Rg • Choose the Optimum RS (ROPT) ROPT is the point at which the NF curve reaches a minimum and is approximated by: ROPT ≈ en/in SINGLE SUPPLY OPERATION The LMH6624/LMH6626 can be operated with single power supply as shown in Figure 6. Both the input and output are capacitively coupled to set the DC operating point. 20058926 20058922 FIGURE 6. Single Supply Operation LOW NOISE TRANSIMPEDANCE AMPLIFIER Figure 7 implements a low-noise transimpedance amplifier commonly used with photo-diodes. The transimpedance gain is set by Rf. Equation 4 provides the total input current 15 www.national.com FIGURE 5. Voltage Noise Density vs. Source Resistance If bias current cancellation is not a requirement, then Rf||Rg need not equal Rseq. In this case, according to Equation 1, LMH6624/LMH6626 Application Section (Continued) noise density (ini) equation for the basic transimpedance configuration and is plotted against feedback resistance (Rf) showing all contributing noise sources in Figure 8. This plot indicates the expected total equivalent input current noise density (ini) for a given feedback resistance (Rf). The total equivalent output voltage noise density (eno) is ini*Rf. 20058929 FIGURE 9. Low Noise Integrator HIGH-GAIN SALLEN-KEY ACTIVE FILTERS 20058927 FIGURE 7. Transimpedance Amplifier Configuration The LMH6624/LMH6626 are well suited for high gain SallenKey type of active filters. Figure 10 shows the 2nd order Sallen-Key low pass filter topology. Using component predistortion methods discussed in OA-21 enables the proper selection of components for these high-frequency filters. 20058930 20058928 FIGURE 8. Current Noise Density vs. Feedback Resistance FIGURE 10. Sallen-Key Active Filter Topology LOW NOISE MAGNETIC MEDIA EQUALIZER The LMH6624/LMH6626 implement a high-performance low noise equalizer for such application as magnetic tape channels as shown in Figure 11. The circuit combines an integrator with a bandpass filter to produce the low noise equalization. The circuit’s simulated frequency response is illustrated in Figure 12. (5) LOW NOISE INTEGRATOR The LMH6624/LMH6626 implement a deBoo integrator shown in Figure 9. Positive feedback maintains integration linearity. The LMH6624/LMH6626’s low input offset voltage and matched inputs allow bias current cancellation and provide for very precise integration. Keeping RG and RS low helps maintain dynamic stability. www.national.com 16 LMH6624/LMH6626 Application Section (Continued) 20058931 the PCB layout is mandatory. Generally, a good high frequency layout exhibits a separation of power supply and ground traces from the inverting input and output pins. Parasitic capacitances between these nodes and ground may cause frequency response peaking and possible circuit oscillations (see Application Note OA-15 for more information). Use high quality chip capacitors with values in the range of 1000pF to 0.1F for power supply bypassing. One terminal of each chip capacitor is connected to the ground plane and the other terminal is connected to a point that is as close as possible to each supply pin as allowed by the manufacturer’s design rules. In addition, connect a tantalum capacitor with a value between 4.7µF and 10µF in parallel with the chip capacitor. Signal lines connecting the feedback and gain resistors should be as short as possible to minimize inductance and microstrip line effect. Place input and output termination resistors as close as possible to the input/output pins. Traces greater than 1 inch in length should be impedance matched to the corresponding load termination. Symmetry between the positive and negative paths in the layout of differential circuitry should be maintained to minimize the imbalance of amplitude and phase of the differential signal. These free evaluation boards are shipped when a device sample request is placed with National Semiconductor. Component value selection is another important parameter in working with high speed/high performance amplifiers. Choosing external resistors that are large in value compared to the value of other critical components will affect the closed loop behavior of the stage because of the interaction of these resistors with parasitic capacitances. These parasitic capacitors could either be inherent to the device or be a by-product of the board layout and component placement. Moreover, a large resistor will also add more thermal noise to the signal path. Either way, keeping the resistor values low will diminish this interaction. On the other hand, choosing very low value resistors could load down nodes and will contribute to higher overall power dissipation and high distortion. Device Package SOT23–5 SOIC-8 SOIC-8 MSOP-8 Evaluation Board Part Number CLC730216 CLC730227 CLC730036 CLC730123 FIGURE 11. Noise Magnetic Media Equalizer 20058932 FIGURE 12. Equalizer Frequency Response LAYOUT CONSIDERATION National Semiconductor suggests the copper patterns on the evaluation boards listed below as a guide for high frequency layout. These boards are also useful as an aid in device testing and characterization. As is the case with all highspeed amplifiers, accepted-practice RF design technique on LMH6624MF LMH6624MA LMH6626MA LMH6626MM 17 www.national.com LMH6624/LMH6626 Physical Dimensions inches (millimeters) unless otherwise noted 5-Pin SOT23 NS Package Number MF05A 8-Pin SOIC NS Package Number M08A www.national.com 18 LMH6624/LMH6626 Single/Dual Ultra Low Noise Wideband Operational Amplifier Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 8-Pin MSOP NS Package Number MUA08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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