SBOSA14A April   2023  – November 2023 OPA814

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics:
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Input and ESD Protection
      2. 7.3.2 FET-Input Architecture With Wide Gain-Bandwidth Product
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Wideband, High-Input Impedance DAQ Front-End
      2. 8.1.2 Wideband, Transimpedance Design Using the OPA814
    2. 8.2 Typical Application
      1. 8.2.1 High-Input-Impedance, 180-MHz, Digitizer Front-End Amplifier
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Thermal Considerations
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
  • DBV|5
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.1.2 Wideband, Transimpedance Design Using the OPA814

The OPA814 design is optimized for wideband, low-noise transimpedance applications with high GBWP, low input voltage, low current noise, and low input capacitance. The high-voltage capability allows greater flexibility of supply voltages along with wider output voltage swings. Figure 8-3 shows an example circuit of a typical photodiode amplifier circuit. Figure 8-3 shows that the photodiode is generally reverse biased in a TIA application, so that the photodiode current in the circuit flows into the op-amp feedback path. This polarity of the current results in an output voltage that reduces from VREF with increasing photodiode current. In this type of configuration, and depending on the application needs, VREF can be biased closer to VS+ to achieve the desired output swing. Consider the common-mode input range when VREF bias is used so that the common-mode input voltage stays within the valid range of the OPA814.

The key design elements that determine the closed-loop bandwidth, f–3dB, of the circuit are as follows:

  1. The op amp GBWP
  2. The transimpedance gain, RF
  3. The total input capacitance, CTOT, that includes photodiode capacitance, input capacitance of the amplifier (common-mode and differential capacitance), and PCB parasitic capacitance

GUID-20230411-SS0I-9W2F-KJVG-7H1BRNN3R6SH-low.svg Figure 8-3 Wideband, Low-Noise, Transimpedance Amplifier

Equation 1 shows the relationship between the three key design elements for a Butterworth response.

Equation 1. f – 3 d B =   G B W P 2 × π × R F × C T O T

The feedback resistance (RF) and the total input capacitance (CTOT) form a zero in the noise gain, and results in instability if left uncompensated. To counteract the effect of the zero, a pole is inserted in the noise gain by adding the feedback capacitor (CF). The Transimpedance Considerations for High-Speed Amplifiers application report discusses theories and equations that show how to compensate a transimpedance amplifier for a particular gain and input capacitance. The bandwidth and compensation equations from the application report are available in a Microsoft Excel™ calculator. A link to the calculator is provided in What You Need To Know About Transimpedance Amplifiers – Part 1. The details of maximizing the dynamic range of TIA front-ends are provided in the Maximizing the Dynamic Range of Analog TIA Front-End application note.