SNOA565 Datasheet, PDF (1/13 Pages) Texas Instruments – AN-2177 Using the LMH6554 as a ADC Driver

Application Report
SNOA565 – July 2011
AN-2177 Using the LMH6554 as a ADC Driver
Vannavong Philavanh .......................................................................................................................
ABSTRACT
National Semiconductor’s latest family of ultra-high-speed data converters are capable of sampling
frequencies in the low end of the GHz range and are designed to work with a fully differential signal. The
combination of high frequencies and fully differential inputs translates into special requirements in terms of
amplitude, phase match and high frequency hardware performance for single to differential conversion.
The LMH6554 is part of the LMH™ high speed amplifier family.
Contents
1 General Description ......................................................................................................... 2
2 Single-to-Differential Conversion .......................................................................................... 2
3 Common-Mode Level Considerations .................................................................................... 3
4 LMH6554 DC-Coupled Configurations ................................................................................... 4
5 LMH6554 AC-Coupled Configuration .................................................................................... 6
6 LMH6554 Gain Compression at GHz Frequencies ..................................................................... 7
7 Interconnect at GHz Frequencies ......................................................................................... 7
8 LMH6554 Driving a High-Speed 12-Bit ADC ............................................................................ 8
9 Conclusion .................................................................................................................. 12
List of Figures
1 Single-Ended Input with Differential Output ............................................................................. 2
2 Balance Error ................................................................................................................ 3
3 LMH6554 Pinout ............................................................................................................ 3
4 LMH6554 SE-Input ADC Driver Circuit With A=6dB ................................................................... 4
5 Previous Circuit with VCM = 1.25V....................................................................................... 4
6 Fully DC-Coupled Configuration with Shifted Dual Supplies (VCM=1.25V)......................................... 5
7 AC-Coupled Source Configuration (VCM=1.25V) ...................................................................... 6
8 Fully AC-Coupled Single Supply Configuration (VCM=2.5V) ......................................................... 6
9 1dB compression point of the LMH6554 at 750MHz and 1GHz. ..................................................... 7
10 LMH6554 RF Test Setup .................................................................................................. 8
11 ADC performance, Pin=1.5 dBm AC-coupled mode (LMH6554 is entering compression range)................ 9
12 ADC performance, Pin=-1.5 dBm AC-coupled mode (LMH6554 is well below 1dB compression point)........ 9
13 ADC performance, Pin=1.5 dBm AC-coupled mode with 1.6GHz LP filters between the LMH6554 and
the ADC’s input port (LMH6554 is entering compression range) ................................................... 10
14 ADC performance at Pin=-1.5dBm and Fully DC-coupled configuration. .......................................... 11
List of Tables
1 Gain Component Values for 50Ω System ............................................................................... 3
2 ADC Test Parameters ...................................................................................................... 8
3 LMH6554 ADC System Performance................................................................................... 11
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SNOA565 – July 2011
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AN-2177 Using the LMH6554 as a ADC Driver
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