ZHCSJO8 May   2019 OPA818

ADVANCE INFORMATION for pre-production products; subject to change without notice.  

  1. 特性
  2. 应用
    1.     高速光学前端
  3. 说明
    1.     光电二极管电容与 3dB 带宽间的关系
  4. 修订历史记录
  5. Pin Configuration and Functions
    1.     Pin Functions
  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: VS = ±5 V
    6. 6.6 Typical Characteristics: VS = ±5 V
  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 Feedback Pin
      3. 7.3.3 Decompensated Architecture With Wide Gain-Bandwidth Product
      4. 7.3.4 Low Input Capacitance
    4. 7.4 Device Functional Modes
      1. 7.4.1 Split-Supply Operation (+4/–2 V to ±6.5 V)
      2. 7.4.2 Single-Supply Operation (6 V to 13 V)
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Wideband, Noninverting Operation
      2. 8.1.2 Wideband, Transimpedance Design Using OPA818
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Thermal Considerations
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 接收文档更新通知
    2. 11.2 社区资源
    3. 11.3 商标
    4. 11.4 静电放电警告
    5. 11.5 Glossary
  12. 12机械、封装和可订购信息
    1. 12.1 Package Option Addendum
      1. 12.1.1 Packaging Information


机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)

Wideband, Transimpedance Design Using OPA818

With high GBWP, low input voltage and current noise, and low input capacitance, the OPA818 design is optimized for wideband, low-noise transimpedance applications. The high voltage capability allows greater flexibility of supply voltages along with wider output voltage swings. Figure 13 shows an example circuit of a typical photodiode amplifier circuit. Generally the photodiode is reverse biased in a TIA application so the photodiode current in the circuit ofFigure 13 flows into the op amp feedback loop resulting 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. Input common-mode range must be considered so as not to violate it when VREF bias is used.

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

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

OPA818 SBOS940_OPA818_TIA-application.gifFigure 13. Wideband, Low-Noise, Transimpedance Amplifier

Equation 1 shows the relationship between the above mentioned three elements for a Butterworth response.

Equation 1. OPA818 SBOS940_OPA818_Eq-TIA-f3dB.gif

The feedback resistance RF and the total input capacitance CTOT cause a zero in the noise gain that 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. What You Need To Know About Transimpedance Amplifiers – Part 1 provides a link to the calculator.