SLWU067D November   2009  – March 2022 ADS4122 , ADS4125 , ADS4126 , ADS4128 , ADS4129 , ADS4142 , ADS4145 , ADS4146 , ADS4149 , ADS41B25 , ADS41B29 , ADS41B49 , ADS58B18 , ADS58B19

 

  1.   Trademarks
  2. 1Overview
    1. 1.1 Purpose
    2. 1.2 EVM Quick-Start Procedure
  3. 2Circuit Description
    1. 2.1 Schematic Diagram
    2. 2.2 Circuit Function
      1. 2.2.1 Power
        1. 2.2.1.1 Power Supply Option 1
        2. 2.2.1.2 Power Supply Option 2
        3. 2.2.1.3 Power Supply Option 3
      2. 2.2.2 Clock Input
        1. 2.2.2.1 Clock Option 1
        2. 2.2.2.2 Clock Option 2
        3. 2.2.2.3 Clock Option 3
      3. 2.2.3 Analog Inputs
        1. 2.2.3.1 Analog Input Option 1
        2. 2.2.3.2 Analog Input Option 2
      4. 2.2.4 Digital Outputs
  4. 3TI ADC SPI Control Interface
    1. 3.1 Installing the ADC SPI Interface
    2. 3.2 Setting Up the EVM for ADC SPI Control
    3. 3.3 Using the TI ADC SPI Interface Software
      1. 3.3.1 SPI Register Writes
  5. 4Quick Start Setup
  6. 5Evaluation
    1. 5.1 Register Programming
    2. 5.2 Quick-Test Results

2.2.3.2 Analog Input Option 2

Option 2 allows the use of an amplifier to provide input to the ADC. TI has a range of wideband operational amplifiers such as THS4508/09/11/13/20. On this EVM, THS4509 is used as an example to amplify the input from J8. The THS4509 is powered up by applying 5 V to J9 and GND to J11. A differential power supply also may be used to power up the amplifier if common-mode biasing is an issue for DC-coupled applications. See the THS4509 data sheet (SLOS547). The output of the THS4509 is filtered through a band-pass filter before ADC input. The band-pass filter can be designed depending on the end application. By default, the band-pass filter components are not populated as the filter design depends on the end application. The TI schematic provides an example of a filter that is designed for the frequency band of 10 MHz to 58 MHz. When using the suggested filter, be sure to consider the proper value for R23 and R24 resistors, as the ADC may impose limits on how large these resistors may be while the amplifier may impose limits on how low an impedance it can drive. A key point when designing a filter is to design it for proper load termination. Care must be taken when supplying the input to the board, and ensure that the source impedance is 50 Ω. Results can vary due to mismatching of the various source and termination impedances.