November 2006 LMH6555 Low Distortion 1.2 GHz Differential Driver General Description Features The LMH6555 is an ultra high speed differential line driver with 50 dB SFDR at 750 MHz. The LMH6555 features a fixed gain of 13.6 dB. An input to the device allows the output common mode voltage to be set independent of the input common mode voltage in order to simplify the interface to high speed differential input ADC’s . A unique architecture allows the device to operate as a fully differential driver or as a singleended to differential converter. The outstanding linearity and drive capability (100Ω differential load) of this device is a perfect match for driving high speed analog-to-digital converters. When combined with the ADC081000/ ADC08D1500, the LMH6555 forms an excellent 8-bit data acquisition system with analog bandwidths exceeding 1 GHz. The LMH6555 is offered in a space saving 16-pin LLP package. Typical Unless Otherwise Specified: ■ −3 dB bandwidth (VOUT = 0.80PP) ■ ±0.5 dB gain flatness (VOUT = 0.80 VPP) ■ Slew rate ■ 2nd/3rd Harmonics (750 MHz) ■ Fixed gain ■ Supply current ■ Single supply operation ■ Adjustable common-mode output voltage 1.2 GHz 500 MHz 3000 V/μs −53/−54 dBc 13.6 dB 120 mA 3.3V ±10% Applications ■ Differential ADC driver ■ National Semiconductor ADC081000/ ADC08D1500 ■ ■ ■ ■ ■ driver Single ended to differential converter Differential driver Intermediate frequency (IF) amplifier Communication receivers Oscilloscope front end Block Diagram 20127704 Single Ended to Differential Conversion © 2006 National Semiconductor Corporation 201277 www.national.com LMH6555 Low Distortion 1.2 GHz Differential Driver PRELIMINARY LMH6555 Maximum Junction Temperature Storage Temperature Range Soldering Information Infrared or Convection (20 sec.) Wave Soldering (10 sec.) 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 (Note 5) Human Body Model Machine Model VS Output Short Circuit Duration (one pin to ground) Common Mode Input Voltage 2000V 200V TBD Operating Ratings 235°C 260°C (Note 1) Temperature Range (Note 4) Supply Voltage Range Infinite −1V to TBD 3.3V Electrical Characteristics +150°C −65°C to +150°C −40°C to +85°C +3.3V ±10% Package Thermal Resistance (θJA)(Note 4) 16-Pin LLP 65°C/W (Note 2) Unless otherwise specified, all limits are guaranteed for TA= 25°C, VCM_REF = 1.2V, both inputs tied to 0.3V through 50Ω (RS1 & RS2) each (Note 11), VS = 3.3V, RL = 100Ω differential, VOUT = 0.8 VPP; See Notes section for definition of terms used throughout the datasheet. Boldface limits apply at the temperature extremes. Symbol Parameter Conditions Min (Note 8) Typ (Note 7) Max (Note 8) Units Differential AC Performance SSBW −3 dB Bandwidth LSBW VOUT = 0.25 VPP 1200 VOUT = 0.8 VPP 1200 MHz GF_0.5 ±0.5 dB Gain Flatness VOUT = 0.8 VPP 500 MHz Ph_Delta Phase Delta Output Differential Phase Difference, f = 400 MHz TBD deg TRS/TRL Rise/ Fall Time VOUT = 0.4 VPP 320 pS OS Overshoot VOUT = 0.4 VPP SR Slew Rate 0.8V Step, 10% to 90%,(Note 6) ts Settling Time 0.8V Step, VOUT within ±0.1% AV_DIFF Insertion Gain (|S21|) 14 % 3000 V/µs TBD TBD TBD 13.6 ns TBD TBD dB AV_VAR Insertion Gain Variation VCM_REF Input Varied from 0.95V to 1.45V, VOUT = 0.8 VPP ±TBD ±TBD dB Distortion And Noise Response HD2_L 250 MHz (Note 12) −60 HD2_M 500 MHz (Note 12) −62 HD2_H 750 MHz (Note 12) −53 250 MHz (Note 12) −67 HD3_M 500 MHz (Note 12) −61 HD3_H 750 MHz (Note 12) −54 70 MHz (Note 12) TBD 250 MHz (Note 12) TBD f1 = 70 MHz, f2 = 70 MHz + 10 kHz, PIN = TBD (Note 12) TBD HD3_L OIP3_L 2nd Harmonic Distortion 3rd Harmonic Distortion Output 3rd Order Intercept OIP3_H OIM3 Third Order Intermodulation Distortion eno Output Referred Voltage Noise >1 MHz NF Noise Figure Relative to Differential Inputs dBc dBc dBm dBc 24 nV/ TBD dB Input Characteristics RIN Input Resistance Single Ended Input Drive TBD RIN_DIFF Differential Input Resistance Differential Input Drive TBD CIN Input Capacitance Each Input to GND www.national.com 2 50 TBD 80 TBD 0.3 Ω Ω pF Parameter Conditions Min (Note 8) Typ (Note 7) Max (Note 8) Units TBD V Output Characteristics CMVR Input Common Mode Voltage Range AV_DIFF – AV_CM ≥ 30 dB VOOS Output Offset Voltage Differential Mode TBD ±100 TBD mV TCVOOS Output Offset Voltage Average Drift (Note 9) ±200 TBD μV/°C RO Output Resistance RT1 and RT2 TBD 50 TBD VOUT Differential Output Voltage Swing ΔAV_DIFF ≤ 1 dB TBD TBD 800 VO_CM Output Common Mode Voltage Range 0.95 TBD BAL_Error_DC Output Balance Error VCM_REF Input Varied, VOUT = 0.80 VPP 0 BAL_Error_AC AV_CM 1.45 TBD TBD DC, ΔVO_CM/ΔVI_CM TBD TBD V TBD dB TBD Common Mode Gain Ω mV TBD TBD TBD dB VCM_REF Characteristics VOS_CM Output CM Offset Voltage VOS_CM = VO_CM – VCM_REF TBD ±50 mV IB_CM VCM_REF Bias Current 0.95V ≤ VCM_REF ≤ 1.45V (Note 10) −100 TBD μA RIN_CM VCM_REF Input Resistance Gain_VCM_REF VCM_REF Input Gain to Output ΔVO_CM/ΔVCM_REF TBD 0.99 TBD V/V IS Supply Current RS1 & RS2 Open (Note 3) TBD TBD 120 TBD TBD mA PSRR Differential Power Supply Rejection Ratio DC, ΔVS = ±0.3V, ΔVOUT/ΔVS TBD TBD 76 PSRR_CM Common Mode PSRR DC, ΔVS = ±0.3V, ΔVO_CM/ΔVS TBD TBD TBD TBD kΩ Power Supply dB dB 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. Note 3: Total supply current is affected by the input voltages connected through RS1 and RS2. Supply current tested with input removed. 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 package soldered directly into a 2 layer PC board with zero air flow. Note 5: Human Body Model, applicable std. MIL-STD-883, Method 3015.7. Machine Model, applicable std. JESD22-A115-A (ESD MM std. of JEDEC) Field-Induced Charge-Device Model, applicable std. JESD22-C101-C (ESD FICDM std. of JEDEC). Note 6: Slew Rate is the average of the rising and falling edges. Note 7: Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material. Note 8: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Note 9: Drift determined by dividing the change in parameter at temperature extremes by the total temperature change. Note 10: Positive current is current flowing into the device. Note 11: Quiescent device common mode input voltage is 0.3V. Note 12: Distortion data taken under single ended input condition. 3 www.national.com LMH6555 Symbol LMH6555 Ordering Information Package 16-Pin LLP Part Number LMH6555SQ LMH6555SQX Package Marking Transport Media 1k Units Tape and Reel L6555SQ 4.5k Units Tape and Reel NSC Drawing SQA16A Definition of Terms and Specifications (Alphabetical order) Unless otherwise specified, VCM_REF = 1.2V 1. 1. AV_CM (dB) Change in the output common mode voltage (ΔVO_CM ) with respect to the change in input 2. AV_DIFF (dB) Insertion gain from a single ended 50Ω (or 100Ω differential) source to the differential output (ΔVOUT) 3. ΔAV_DIFF (dB) Variation in insertion gain (AV_DIFF) with input signal change (ΔVIN ) 4. AV_VAR (dB) Variation of insertion gain (AV_DIFF) with VCM_REF input change (ΔVCM_REF). Calculated as the change in AV_DIFF (dB) at various VCM_REF 5. CMVR (V) Range of input common mode voltage (VI_CM) where the insertion gain (AV_DIFF) is 30 dB larger than common mode gain (AV_CM) and hence the amplifier’s output is dominated by its differential output 6. Gain_VCM_REF (V/V) Variation in output common mode voltage (ΔVO_CM) with respect to change in VCM_REF input 7. Pin (dBm referenced to 50Ω) Input power associated with each of the tones for OIM3 testing 8. PSRR (dB) Differential output change (ΔVOUT) with respect to the power supply voltage change (ΔVS) with nominal differential output 9. PSRR_CM (dB) Output common mode voltage change (ΔVO_CM) with respect to the change in the power 10. RIN (Ω) Single ended input impedance to ground 11. RIN_DIFF (Ω) Differential input impedance 12. RL (Ω) Differential output load 13. RO (Ω) Equivalent to RT1 & RT2 14. RS1, RS2 (Ω) Source impedance to VIN+ and VIN− respectively 15. RT1, RT2 (Ω) Output impedance looking into each output 16. VCM_REF (V) Device input pin voltage which controls output common mode 17. ΔVCM_REF (V) Change in the VCM_REF input voltage 18. VI_CM (V) DC average of the inputs (VIN+, VIN−) 19. ΔVI_CM (V) Variation in input common mode voltage (VI_CM) 20. VIN+, VIN− (V) Device input pin voltages 21. ΔVIN (V) Terminated (50Ω for single ended and 100Ω for differential) generator voltage 22. VO_CM (V) Output common mode voltage (DC average of VOUT+ and VOUT−) 23. ΔVO_CM (V) Variation in output common mode voltage (VO_CM) common mode voltage (ΔVI_CM) (ΔVCM_REF) with maximum differential output supply voltage (ΔVS) 24. Balance Error. Measure of the output swing balance of VOUT+ and VOUT−, as reflected on the output common mode voltage (VO_CM), relative to the differential output swing (VOUT). Calculated as output common mode voltage change (ΔVO_CM) divided into the output differential voltage change (ΔVOUT) 25. AC version of the DC balance error 26. VOOS (V) www.national.com test DC Offset Voltage. Differential output voltage measured with both inputs grounded through 50Ω 4 VOS_CM (V) Difference between the output common mode voltage (VO_CM) and the voltage on the VCM_REF input, for the allowable VCM_REF range 28. VOUT (V) Differential Output Voltage (VOUT+ - VOUT−) (Corrected for DC offset (VOOS)) 29. ΔVOUT (V) Change in the differential output voltage (Corrected for DC offset (VOOS)) 30. VOUT+, VOUT− (V) Device output pin voltages 31. VS (V) Supply Voltage (V+ - V−) 32. ΔVS (V) Change in VCC supply voltage Connection Diagram 16-Pin LLP 20127705 of most differential high speed ADC’s will be tied to the VCM_REF input of the LMH6555 for direct output common mode control. In some cases, the output drive capability of the ADC VCMO output may need an external buffer (not shown) to increase its current capability in order to drive the VCM_REF pin. The LMH6555 Electrical Characteristics table shows the gain (AV_CM) and the offset (VOS_CM) from the VCM_REF to the device output common mode. Application Information The LMH6555 consists of three individual amplifiers: The VOUT+ driver, VOUT− driver, and the common mode amplifier. Being a differential amplifier, the LMH6555 will not respond to the input common mode input (as long as it is within its input common mode range) and instead the output common mode is forced by the built-in common mode amplifier with VCM_REF as its input. As shown in Figure 1 below, the VCMO 20127704 FIGURE 1. Single Ended to Differential Conversion 5 www.national.com LMH6555 27. LMH6555 The single ended AC input and output impedance of the LMH6555 I/O pins are close to 50Ω and are also specified in the Electrical Characteristics table (RIN and RO). With differential input drive, the differential input impedance (RIN_DIFF) will be close to 80Ω. The device nominal input common mode voltage is close to 0.3V at VIN+ and VIN− with a weak relationship to the VCM_REF voltage. Thus, the input source will experience a DC current which is dependant on its DC voltage. Because of this, the differential output offset voltage is influenced by the matching between RS1 and RS2 under DC and AC conditions. So, for example, in a single ended input condition, if the signal source is AC coupled to one input, the undriven input needs to also be AC coupled. In applications where very low output offset is required, adjusting the value of RS2 (the input which is not driven) can be an effective method of trimming the output offset voltage of the LMH6555 in a single ended input configuration. The nominal value of RS1 and RS2 on the other hand will affect the insertion gain. The LMH6555 can also be used with the input signal AC coupled. In this case, the coupling capacitors need to be large enough to not block the frequency content below (1/2πRINC)Hz. The single ended output impedance of the LMH6555 is 50Ω. The LMH6555 Electrical Characteristics shows the device performance with 100Ω differential output load, as would be the case if a device such as the ADC081000 were being driven. As shown in Figure 2 below, some applications can benefit from using the LMH6555 to interface a Class A type differential output device (U1) to a high speed ADC. In this application, the LMH6555 performs the task of buffering and amplifying the signal to properly drive the 100Ω differential input impedance of the ADC. 20127706 FIGURE 2. Differential Buffering and Amplification In this application, U1’s DC common mode output will be affected by the LMH6555 input common mode voltage through RG and RL. The equivalent load to the driver Collector within U1 would be the combination of R L and RIN_DIFF (≅80Ω). Series isolation resistors (not shown) between U1 outputs and LMH6555 input pins would offer additional isolation at the expense of more signal loss. Alternatively, input AC coupling could have been used to alleviate the common mode concerns. pins. It is recommended, but not necessary, that the exposed pad be connected to the supply ground plane. The thermal dissipation of the device is largely dependent on the connection of this pad. The exposed pad should be attached to as much copper on the circuit board as possible, preferably external copper. However, it is very important to maintain good high speed layout practices when designing a system board. Here is a link to more information on the National 16 pin LLP package: http://www.national.com/packaging/folders/sqa16a.html EXPOSED PAD LLP PACKAGE The LMH6555 is packaged in a thermally enhanced package. The exposed pad (device bottom) is connected to the GND www.national.com 6 LMH6555 Physical Dimensions inches (millimeters) unless otherwise noted 16-Pin LLP NS Package Number SQA16A 7 www.national.com LMH6555 Low Distortion 1.2 GHz Differential Driver Notes THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. NATIONAL MAKES NO REPRESENTATIONS OR WARRANTIES WITH RESPECT TO THE ACCURACY OR COMPLETENESS OF THE CONTENTS OF THIS PUBLICATION AND RESERVES THE RIGHT TO MAKE CHANGES TO SPECIFICATIONS AND PRODUCT DESCRIPTIONS AT ANY TIME WITHOUT NOTICE. NO LICENSE, WHETHER EXPRESS, IMPLIED, ARISING BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. TESTING AND OTHER QUALITY CONTROLS ARE USED TO THE EXTENT NATIONAL DEEMS NECESSARY TO SUPPORT NATIONAL’S PRODUCT WARRANTY. EXCEPT WHERE MANDATED BY GOVERNMENT REQUIREMENTS, TESTING OF ALL PARAMETERS OF EACH PRODUCT IS NOT NECESSARILY PERFORMED. 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