JAJU648A November   2018  – April 2022 TLV3601 , TLV3601-Q1 , TLV3603 , TLV3603-Q1

 

  1.   概要
  2.   Resources
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Amplifier and Comparator
      2. 2.2.2 Digital Processing and Control
      3. 2.2.3 Optical Components
        1. 2.2.3.1 Laser Driver and Laser Diode
        2. 2.2.3.2 Photodiode
      4. 2.2.4 Power Supply
    3. 2.3 Highlighted Products
      1. 2.3.1 OPA858 Operational Amplifier
      2. 2.3.2 TLV3501 and TLV3601/3 High-Speed Comparators
      3. 2.3.3 TDC7201 Time-to-Digital Converter
    4. 2.4 System Design Theory
      1. 2.4.1 Transimpedance Amplifier
        1. 2.4.1.1 Bandwidth
        2. 2.4.1.2 Stability Considerations
        3. 2.4.1.3 Noise Performance
      2. 2.4.2 Time-of-Flight Measurement
      3. 2.4.3 Simulations
        1. 2.4.3.1 Bandwidth Simulation
        2. 2.4.3.2 Noise Simulation
        3. 2.4.3.3 OPA858 Loop-Gain and Phase Margin Simulation
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Software
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
        1. 3.2.1.1 Getting Started: System Setup
          1. 3.2.1.1.1 Laser-Driver Setup
          2. 3.2.1.1.2 Receiver and Optical Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Verification and Measured Performance
          1. 3.2.2.1.1 Pulse Response Measurements
            1. 3.2.2.1.1.1 Pulse Response Settling
            2. 3.2.2.1.1.2 Pulse Response vs Output Pulse Width
            3. 3.2.2.1.1.3 Rise and Fall Time
            4. 3.2.2.1.1.4 Overdriven Response
          2. 3.2.2.1.2 Time-of-Flight Test
          3. 3.2.2.1.3 Time-of-Flight Measurement Error Sources
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
  10. 5Related Documentation
    1. 5.1 Trademarks
  11. 6About the Author
  12. 7Revision History

1 System Description

This reference design showcases the capabilities of Texas Instruments high-speed amplifiers, comparators, and time-to-digital converters (TDCs) to demonstrate a high-accuracy, low-power, time-of-flight (ToF) measurement system. The receive path consists of a PIN photodiode receiver biased with a
5-V reference coupled into the OPA858 amplifier in a transimpedance configuration with a gain of 10 kΩ. The OPA858 amplifier is a decompensated, 5.5-GHz, operational amplifier with low bias current complementary metal oxide semiconductor (CMOS) inputs. The design uses the OPA858 5.5-GHz amplifier by default, but can be easily configured to use the OPA855 8-GHz, bipolar input amplifier or the OPA859 900-MHz, CMOS input, unity-gain stable amplifier. The OPA858 output is connected to the TLV3501 4.5-ns comparator to amplify and propagate the signal to the next stage.

The received signal is measured using the TDC7201 time-to-digital converter in its short-time measurement mode. The TDC7201 internally calculates the time difference between the start and stop pulses to determine a ToF measurement. In this design, the start signal is provided by the microcontroller or by the built-in monitor diode packaged in the laser diode and the stop signal is the received signal from the TLV3501. By default, the TDC7201 has a minimum measurement time of 12 ns that limits the minimum measurement distance to 3.6 meters. However, the short-time mode of the device allows the two measurement cores to work in conjunction to reduce the minimum measurement time to 250 ps, which reduces the minimum measurement distance to 7.5 centimeters in a vacuum. The digital output of the TDC7201 is connected to the MSP430 microcontroller that calculates the actual distance measurement and sends the information to the computer graphical user interface (GUI).

The transmit path of the design is also controlled by the MSP430, which commands the laser driver to fire and also starts the TDC7201 measurement based on inputs from the computer GUI. The laser driver is connected to a laser diode that features an onboard monitoring photodiode. When the diode transmits, the onboard photodiode outputs a current signal that is converted to a simple voltage using a resistor. Optionally, the measurement start of the TDC7201 can be triggered by the laser diodes onboard the photodiode instead of the MSP430 to provide a connection with less latency. For this design, the optical signal is transmitted through an optical fiber for ease of measurement and setup. The design can be modified to an over-the-air measurement using alternate diodes and lenses in place of the fiber optics.