SBOS301C May   2004  – December 2025 LOG114

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics (±5V)
    6. 5.6 Electrical Characteristics (5V)
    7. 5.7 Typical Characteristics: VS = ±5V
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Logarithmic and Difference Amplifier
      2. 6.3.2 COM Voltage Range
      3. 6.3.3 VCM IN
      4. 6.3.4 Auxiliary Operational Amplifier
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Applications Information
      1. 7.1.1 Transfer Function
      2. 7.1.2 Input Current Range
      3. 7.1.3 Setting the Reference Current
      4. 7.1.4 Negative Input Currents
      5. 7.1.5 Voltage Inputs
      6. 7.1.6 High-Current Linearity Correction
      7. 7.1.7 Error Sources
        1. 7.1.7.1 Accuracy
        2. 7.1.7.2 Total Error
        3. 7.1.7.3 Errors RTO and RTI
        4. 7.1.7.4 Log Conformity
        5. 7.1.7.5 Individual Error Components
    2. 7.2 Typical Applications
      1. 7.2.1 Design Example for Dual-Supply Configuration
      2. 7.2.2 Design Example for Single-Supply Configuration
      3. 7.2.3 Advantages of Dual−Supply Operation
      4. 7.2.4 Log Ratio
      5. 7.2.5 Data Compression
      6. 7.2.6 3.3V Operation
      7. 7.2.7 Erbium-Doped Fiber Optic Amplifier (EDFA)
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Device Nomenclature
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
      2. 8.2.2 PSpice® for TI
      3. 8.2.3 TINA-TI™ (Free Software Download)
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.7 Erbium-Doped Fiber Optic Amplifier (EDFA)

The LOG114 is designed for optical networking systems. Figure 7-14 shows a block diagram of the LOG114 in a typical EDFA application. This application uses two logarithmic amplifiers to measure the optical input and output power of the amplifier. A difference amplifier subtracts the log output signals of both logarithmic amplifiers and applies an error voltage to the proportional-integral-derivative (PID) controller. The controller output adjusts a voltage-controlled current source (VCCS), which then drives the power operational amplifier and pump laser. The desired optical gain is achieved when the error voltage at the PID is zero.

The log ratio function is the optical power gain of the EDFA. This circuitry forms an automatic power level control loop.

An alternate design of the system shown in Figure 7-14 is possible because the LOG114 inherently takes the log ratio. Therefore, one log amp can be eliminated by connecting one of the photodiodes to the LOG114 I1 input, and the other to the I2 input. The differential amplifier can then be eliminated.

The fast rise and fall times of the LOG114 are designed for most EDFA applications (typically less than 1μs for a 100:1 current input step). The device also measures a very wide dynamic range of up to eight decades.

LOG114 Erbium-Doped Fiber Optic Amplifier (EDFA) Block DiagramFigure 7-14 Erbium-Doped Fiber Optic Amplifier (EDFA) Block Diagram