SBOS427F June   2017  – March 2021 OPA145 , OPA2145

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information: OPA145
    5. 6.5 Thermal Information: OPA2145
    6. 6.6 Electrical Characteristics: VS = 4.5 V to 36 V; ±2.25 V to ±18 V
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Capacitive Load and Stability
      2. 7.3.2 Output Current Limit
      3. 7.3.3 Noise Performance
      4. 7.3.4 Basic Noise Calculations
      5. 7.3.5 Phase-Reversal Protection
      6. 7.3.6 Electrical Overstress
      7. 7.3.7 EMI Rejection
      8. 7.3.8 EMIRR +IN Test Configuration
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
    3. 8.3 System Examples
      1. 8.3.1 16-Bit, 100-kSPS, Fully Differential Transimpedance Imaging and Measurement
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 TINA-TI™ SImulation Software (Free Download)
        2. 11.1.1.2 WEBENCH Filter Designer Tool
        3. 11.1.1.3 TI Precision Designs
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.4 Basic Noise Calculations

Low-noise circuit design requires careful analysis of all noise sources. External noise sources can dominate in many cases; consider the effect of source resistance on overall op amp noise performance. Total noise of the circuit is the root-sum-square combination of all noise components.

The resistive portion of the source impedance produces thermal noise proportional to the square root of the resistance. This function is plotted in Figure 7-1. The source impedance is usually fixed; consequently, select the op amp and the feedback resistors to minimize the respective contributions to the total noise.

Figure 7-2 illustrates both noninverting (A) and inverting (B) op amp circuit configurations with gain. In circuit configurations with gain, the feedback network resistors also contribute noise. In general, the current noise of the op amp reacts with the feedback resistors to create additional noise components. However, the extremely low current noise of the OPAx145 means that the current noise contribution can be neglected.

The feedback resistor values can generally be chosen to make these noise sources negligible. Low impedance feedback resistors load the output of the amplifier. The equations for total noise are shown for both configurations.

GUID-E19A8FED-EE25-4667-A4D1-167F3A01923C-low.gif
Where: eN is the voltage noise of the amplifier. For the OPAx145 operational amplifier, eN = 7 nV/√Hz at 1 kHz.
Where: iN is the current noise of the amplifier. For the OPAx145 operational amplifier, iN = 0.8 fA/√Hz at 1 kHz.
NOTE: For additional resources on noise calculations visit TI's Precision Labs Series.
Figure 7-2 Noise Calculation in Gain Configurations