SLOS930B November   2015  – November 2019 THS4541-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Single to Differential Gain of 2, 2-VPP Output
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics: (Vs+) – Vs– = 5 V
    6. 7.6 Electrical Characteristics: (Vs+) – Vs– = 3 V
    7. 7.7 Typical Characteristics
      1. 7.7.1 5-V Single Supply
      2. 7.7.2 3-V Single Supply
      3. 7.7.3 3-V to 5-V Supply Range
  8. 8 Parameter Measurement Information
    1. 8.1 Example Characterization Circuits
    2. 8.2 Frequency-Response Shape Factors
    3. 8.3 I/O Headroom Considerations
    4. 8.4 Output DC Error and Drift Calculations and the Effect of Resistor Imbalances
    5. 8.5 Noise Analysis
    6. 8.6 Factors Influencing Harmonic Distortion
    7. 8.7 Driving Capacitive Loads
    8. 8.8 Thermal Analysis
  9. 9 Detailed Description
    1. 9.1 Overview
      1. 9.1.1 Terminology and Application Assumptions
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Differential I/O
      2. 9.3.2 Power-Down Control Pin (PD)
        1. 9.3.2.1 Operating the Power Shutdown Feature
      3. 9.3.3 Input Overdrive Operation
    4. 9.4 Device Functional Modes
      1. 9.4.1 Operation from Single-Ended Sources to Differential Outputs
        1. 9.4.1.1 AC-Coupled Signal Path Considerations for Single-Ended Input to Differential Output Conversion
        2. 9.4.1.2 DC-Coupled Input Signal Path Considerations for Single-Ended to Differential Conversion
        3. 9.4.1.3 Resistor Design Equations for the Single-Ended to Differential Configuration of the FDA
        4. 9.4.1.4 Input Impedance for the Single-Ended to Differential FDA Configuration
      2. 9.4.2 Differential-Input to Differential-Output Operation
        1. 9.4.2.1 AC-Coupled, Differential-Input to Differential-Output Design Issues
        2. 9.4.2.2 DC-Coupled, Differential-Input to Differential-Output Design Issues
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 Designing Attenuators
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Interfacing to High-Performance ADCs
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
        3. 10.2.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Development Support
        1. 13.1.1.1 TINA Simulation Model Features
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

9.4.1.4 Input Impedance for the Single-Ended to Differential FDA Configuration

The designs so far have included a source impedance, Rs, that must be matched by Rt and Rg1. The total impedance at the junction of Rt and Rg1 for the circuit of Figure 63 is the parallel combination of Rt to ground, and the ZA (active impedance) presented by Rg1. The expression for ZA, assuming Rg2 is set to obtain the differential divider balance, is given by Equation 11:

Equation 11. THS4541-Q1 q_za1_los375.gif

For designs that do not need impedance matching, but instead come from the low impedance output of another amplifier for instance, Rg1 = Rg2 is the single-to-differential design used without an Rt to ground. Setting Rg1 = Rg2 = Rg in Equation 11 gives the input impedance of a simple input FDA driving from a low-impedance, single-ended source to a differential output as shown in Equation 12:

Equation 12. THS4541-Q1 q_za2_los375.gif

In this case, setting a target gain as Rf / Rg ≡ α, and then setting the desired input impedance, allows the Rg element to be resolved first, and then the required Rf to get the gain. For example, targeting an input impedance of 200 Ω with a gain of 4 V/V, Equation 13 gives the physical Rg element. Multiplying this required Rg value by a gain of 4 gives the Rf value and the design of Figure 72.

Equation 13. THS4541-Q1 q_rg_los375.gif
THS4541-Q1 dc_coupled_200_los375.gifFigure 72. 200-Ω Input Impedance, Single-Ended to Differential DC-Coupled Design with Gain of 4 V/V

After being designed, this circuit can also be AC coupled by adding blocking caps in series with the two 120-Ω Rg resistors. This active input impedance has the advantage of increasing the apparent load to the prior stage using lower resistors values, leading to lower output noise for a given gain target.