SBOS629A April   2018  – July 2018 OPA858

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      High-Speed Time-of-Flight Receiver
      2.      Photodiode Capacitance vs. Bandwidth and Noise
  4. 4 Revision History
  5. 5 Device Comparison Table
  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
    6. 7.6 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Input and ESD Protection
      2. 9.3.2 Feedback Pin
      3. 9.3.3 Wide Gain-Bandwidth Product
      4. 9.3.4 Slew Rate and Output Stage
      5. 9.3.5 Current Noise
    4. 9.4 Device Functional Modes
      1. 9.4.1 Split-Supply and Single-Supply Operation
      2. 9.4.2 Power-Down Mode
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Using the OPA858 as a Transimpedance Amplifier
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Receiving Notification of Documentation Updates
    2. 13.2 Community Resources
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.3.3 Wide Gain-Bandwidth Product

Figure 10 shows the open-loop magnitude and phase response of the OPA858. Calculate the gain bandwidth product of any op amp by determining the frequency at which the AOL is 60 dB and multiplying that frequency by a factor of 1000. The second pole in the AOL response occurs before the magnitude crosses 0 dB, and the resultant phase margin is less than 0°. This indicates instability at a gain of 0 dB (1 V/V). Amplifiers that are not unity-gain stable are known as decompensated amplifiers. Decompensated amplifiers typically have higher gain-bandwidth product, higher slew rate, and lower voltage noise, compared to a unity-gain stable amplifier with the same amount of quiescent power consumption.

Figure 50 shows the open-loop magnitude (AOL) of the OPA858 as a function of temperature. The results show minimal variation over temperature. The phase margin of the OPA858 configured in a noise gain of 7 V/V (16.9 dB) is close to 55° across temperature. Similarly Figure 51 shows the AOL magnitude of the OPA858 as a function of process variation. The results show the AOL curve for the nominal process corner and the variation one standard deviation from the nominal. The simulated results suggest less than 1° of phase margin difference within a standard deviation of process variation when the amplifier is configured in a gain of 7 V/V.

One of the primary applications for the OPA858 is as a high-speed transimpedance amplifier (TIA), as Figure 59 shows. The low-frequency noise gain of a TIA is 0 dB (1 V/V). At high frequencies the ratio of the total input capacitance and the feedback capacitance set the noise gain. To maximize the TIA closed-loop bandwidth, the feedback capacitance is typically smaller than the input capacitance, which implies that the high-frequency noise gain is greater than 0 dB. As a result, op amps configured as TIAs are not required to be unity-gain stable, which makes a decompensated amplifier a viable option for a TIA. What You Need To Know About Transimpedance Amplifiers – Part 1 and What You Need To Know About Transimpedance Amplifiers – Part 2 describe transimpedance amplifier compensation in greater detail.

OPA858 D204_SBOS629.gifFigure 50. Open-Loop Gain vs Temperature
OPA858 D205_SBOS629.gifFigure 51. Open-Loop Gain vs Process Variation