SBOS849B December   2017  – February 2019 LMH5401-SP

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      LMH5401-SP Small Signal Frequency Response
      2.      LMH5401-SP Driving an ADC12D1620QML
  4. 4 Revision History
  5. 5 Description (continued)
  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 = 5 V
    6. 7.6 Electrical Characteristics: VS = 3.3 V
    7. 7.7 Typical Characteristics: 5 V
    8. 7.8 Typical Characteristics: 3.3 V
  8. 8 Parameter Measurement Information
    1. 8.1  Output Reference Nodes and Gain Nomenclature
    2. 8.2  ATE Testing and DC Measurements
    3. 8.3  Frequency Response
    4. 8.4  S-Parameters
    5. 8.5  Frequency Response with Capacitive Load
    6. 8.6  Distortion
    7. 8.7  Noise Figure
    8. 8.8  Pulse Response, Slew Rate, and Overdrive Recovery
    9. 8.9  Power Down
    10. 8.10 VCM Frequency Response
    11. 8.11 Test Schematics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Fully-Differential Amplifier
      2. 9.3.2 Operations for Single-Ended to Differential Signals
        1. 9.3.2.1 AC-Coupled Signal Path Considerations for Single-Ended Input to Differential Output Conversion
        2. 9.3.2.2 DC-Coupled Input Signal Path Considerations for SE-DE Conversions
        3. 9.3.2.3 Resistor Design Equations for Single-to-Differential Applications
        4. 9.3.2.4 Input Impedance Calculations
      3. 9.3.3 Differential-to-Differential Signals
        1. 9.3.3.1 AC-Coupled, Differential-Input to Differential-Output Design Issues
        2. 9.3.3.2 DC-Coupled, Differential-Input to Differential-Output Design Issues
      4. 9.3.4 Output Common-Mode Voltage
    4. 9.4 Device Functional Modes
      1. 9.4.1 Operation With a Split Supply
      2. 9.4.2 Operation With a Single Supply
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Stability, Noise Gain, and Signal Gain
      2. 10.1.2 Input and Output Headroom Considerations
      3. 10.1.3 Noise Analysis
      4. 10.1.4 Noise Figure
      5. 10.1.5 Thermal Considerations
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Driving Matched Loads
        2. 10.2.2.2 Driving Unmatched Loads For Lower Loss
        3. 10.2.2.3 Driving Capacitive Loads
        4. 10.2.2.4 Driving ADCs
          1. 10.2.2.4.1 SNR Considerations
          2. 10.2.2.4.2 SFDR Considerations
          3. 10.2.2.4.3 ADC Input Common-Mode Voltage Considerations—AC-Coupled Input
          4. 10.2.2.4.4 ADC Input Common-Mode Voltage Considerations—DC-Coupled Input
        5. 10.2.2.5 GSPS ADC Driver
        6. 10.2.2.6 Common-Mode Voltage Correction
        7. 10.2.2.7 Active Balun
      3. 10.2.3 Application Curves
    3. 10.3 Do's and Don'ts
      1. 10.3.1 Do:
      2. 10.3.2 Don't:
  11. 11Power Supply Recommendations
    1. 11.1 Supply Voltage
    2. 11.2 Single Supply
    3. 11.3 Split Supply
    4. 11.4 Supply Decoupling
  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 Device Nomenclature
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10.1.4 Noise Figure

Noise figure (NF) is a helpful measurement in an RF system design. The basis of this calculation is to define how much thermal noise the system (or even on the component) adds to this input signal. All systems are assumed to have a starting thermal noise power of –174 dBm/√Hz at room temperature calculated from P(dBW) = 10 × log (kTB), where T is temperature in Kelvin (290k), B is bandwidth in Hertz (1 Hz), and k is Boltzmann's constant 1.38 × 10–23 (J / K). Whenever an element is placed in a system, additional noise is added beyond the thermal noise floor. The noise factor (F) helps calculate the noise figure and is the ratio between the input SNR and the output SNR. Input SNR includes the noise contribution from the resistive part of the source impedance, ZS. NF is relative to the source impedance used in the measurement or calculation because ideal capacitors and inductors are known to be noiseless. NF can be calculated by Equation 9:

Equation 9. NF = 10 log (eno2 / enZs)

where

  • en(Zs) is the thermal noise of the source resistance and equal to 4 kTRS (GDT)2,
  • G is the voltage gain of the amplifier.

From Equation 10, NF is roughly equal to 10 dB which is the just above the actual value of 9.6 dB measured on the bench at 200 MHz when referenced to 50 Ω and as illustrated in Figure 29.

Equation 10. LMH5401-SP q_dt_sbos710.gif

For thermal noise calculations with different source resistance, Equation 11 can be used to calculate the NF change with a new source resistance. For example, Equation 9 uses a source resistance of 50 Ω. By using a source of 100 Ω, the new noise figure calculation (Equation 11) yields an NF with a 3-dB improved. This is intuitive as the noise of source increases, the noise of the amplifier becomes less noticeable, and, hence, the NF improves.

Equation 11. en(Zs) = kTRs