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

2.2.3.1 Analog Input Option 1

Option 1 supplies the transformer-coupled input from J6 to ADC. This configuration is the default on the EVM. The test result using this option is shown in Figure 5-2. A double-transformer input circuit is used to provide better differential to single-ended conversion than a single transformer can provide. The transformers used are both of a 1:1 turns ratio, so termination of the 50-Ω input signal path after the transformers can be two 25-Ω resistors terminated to the common-mode voltage (VCM) provided by the ADC.

Following the transformer coupling, surface-mount pads are provided for several input circuits. By default, the input circuit is configured as shown in the ADS4149 data sheet under the recommended input circuit for high-bandwidth (>100-MHz IF) inputs. However, the recommended low-bandwidth input circuit for the ADS4149 can be easily implemented on the surface-mount pads provided.