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)

Decompensated Architecture With Wide Gain-Bandwidth Product

Figure 10 shows the open-loop gain and phase response of the OPA818. The GBWP of an op amp is measured in the 20 dB/decade constant slope region of the AOL magnitude plot. The open-loop gain of 60 dB for the OPA818 is along this 20 dB/decade slope and the corresponding frequency intercept is at 2.7 MHz. Converting 60 dB to linear units (1000 V/V) and multiplying it with the 2.7 MHz frequency intercept gives the GBWP of OPA818 as 2.7 GHz. As can be inferred from the AOL Bode plot, the second pole in the AOL response occurs before AOL magnitude drops below 0 dB (1 V/V). This results in phase change of more than 180° at 0 dB AOL indicating that the amplifier will not be stable in a gain of 1 V/V. Amplifiers like OPA818 that are not unity-gain stable are referred to as decompensated amplifiers. The decompensated architecture typically allows for higher GBWP, higher slew rate, and lower noise compared to a unity-gain stable amplifier with equivalent quiescent current. The additional advantage of the decompensated amplifier is better distortion performance at higher frequencies in high gain applications for comparable quiescent current to a unity-gain stable amplifier.

OPA818 is stable in noise gain of 7 V/V (16.9 dB) or higher in conventional gain circuits as shown in Figure 6 and Figure 7. It has 790 MHz of SSBW in this gain configuration with approximately 50° phase margin.

The high GBWP and low voltage and current noise of OPA818 make it a very suitable amplifier for wideband moderate to high transimpedance gain applications. Transimpedance gains of 50kΩ or higher benefit from the low current noise JFET input. In a typical transimpedance (TIA) circuit as shown in Figure 13, unity-gain stable amplifier is not a requirement. At low frequencies, the noise gain of TIA is 0 dB (1 V/V) and at high frequencies the noise gain is set by the ratio of the total input capacitance (CTOT) and the feedback capacitance (CF). To maximize TIA closed-loop bandwidth, the feedback capacitance is generally smaller than the total input capacitance. This results in the ratio of total input capacitance to the feedback capacitance to be greater than 1, which is ultimately the noise gain of the TIA at higher frequencies. The blog series, What you need to know about transimpedance amplifiers – part 1 and What you need to know about transimpedance amplifiers – part 2 describe TIA compensation techniques in greater detail.

OPA818 D027_10V_Aol_Phase.gif
RL = 100 Ω Simulation
Figure 10. Open-Loop Gain Magnitude and Phase Vs Frequency
OPA818 D106_10V_Aol-over-temp.gif
RL = 100 Ω Simulation
Figure 11. Open-Loop Gain Magnitude vs Temperature