SNOA569 Datasheet, PDF (1/6 Pages) Texas Instruments – AN-2195 Driving High Speed ADCs With the LMH6521 DVGA for High IF AC-Coupled Applications

Application Report
SNOA569 – November 2011
AN-2195 Driving High Speed ADCs With the LMH6521
DVGA for High IF AC-Coupled Applications
Loren Siebert ..................................................................................................................................
ABSTRACT
Sampled data systems can be categorized into two main types. The first and simplest is the baseband
system known as the “1st Nyquist-zone” system. The second is a more complex under-sampled system,
often referred to as the sub-sampled system or Intermediate frequency (IF)-sampled system. Baseband
system applications are generally DC-coupled while the IF-sample systems applications tend to be AC-
coupled. In this application report, the LMH6521 is combined with National Semiconductor's high-speed
analog-to-digital convertor (ADC), the ADC16DV160, that is optimized for an IF frequency of 192 MHz.
Contents
1 Introduction .................................................................................................................. 2
2 Circuit Description ........................................................................................................... 2
3 Tapped Inductor Band-pass Filter ........................................................................................ 2
4 IF-Sampling Frequency Plan .............................................................................................. 3
5 System Performance ....................................................................................................... 4
6 Optimal Performance ....................................................................................................... 5
List of Figures
1
Tapped-L Band-pass Filter For fc=192 MHz With a 20 MHz Bandwidth Designed for 100Ω Impedance ...... 2
2 Single-Ended Tapped-L Band-pass Filter Segments .................................................................. 3
3 192 MHz Tapped-L Filter Profile .......................................................................................... 3
4 Using Impedance Transform To Realize Voltage Gain ................................................................ 4
5 SFDR Performance vs. Input Signal Frequency ........................................................................ 4
6 SNR Performance vs. Input Signal Frequency.......................................................................... 4
7 Output Inductors at 90 degrees ........................................................................................... 5
List of Tables
1 SNR and SFDR Results ................................................................................................... 5
All trademarks are the property of their respective owners.
SNOA569 – November 2011
Submit Documentation Feedback
AN-2195 Driving High Speed ADCs With the LMH6521 DVGA for High IF
1
AC-Coupled Applications
Copyright © 2011, Texas Instruments Incorporated