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OPA2675: Laser Communication System

TI-CSC
Genius 9540 points
Part Number: OPA2675
Other Parts Discussed in Thread: OPA2670, STRIKE, OPA2677

Hello E2E Experts,

Good day.

I am developing a laser communication system. For the laser transmitter, we have split the project into the laser bias controller and the laser modulator. We are now developing a laser modulator.
1. I would like to know if Texas Instruments has any design/application notes for creating laser modulators with a high current output (1.5A) and a 5V output with a frequency of at least 25MHz.
2. We have reviewed several different op-amps with a high gain bandwidth product and high output current:
a. The OPA2675 has a GBP of 730 MHz and a max output current of 1000mA. Our concern is Figure 8-5, where it would appear that it may not be possible to achieve both 5V output and 1000mA of current simultaneously and stay within 2W dissipation. Will the chip limit the output to prevent it from reaching both 5V and 1000mA? Could we use two or more of these chips in parallel to reach a higher current output?
b. The OPA2670 has a 1.4GHz GBP and a max output current of 700mA. To reach 1A output, we are considering using two of these op-amps. How can we utilize both of these op amps in a circuit to create a laser modulator capable of 1A output?
c. As our laser diode heats up, the forward voltage of the diode will change. Are there any methods of accounting for this (in addition to adding a thermoelectric cooler)?

Regards,

CSC

  • 0
    TI__Mastermind 22270 points

    Hello CSC,

    1. For specifically laser drivers/modulators, we have reference designs for very low frequencies intended to drive LEDs, and we have a very high frequency reference design for optical network communication which would be overkill for this application.
      1. The TIDA-01573 is an example of very high current/fast pulse discrete laser diode driver. 
      2. The TIDA-00725 and the TIDA-060025 for a total comprehensive system optical front-end designs 
    2. That's correct on understanding of Figure 8-5. These devices would work if used in parallel which is convenient when using the dual package version such as the first one you suggested: OPA2675. 
      1. An example of this is demonstrated using another high current output amplifier: TIDA-060002.
      2. E2E thread discussion using line drivers 

    Thank you,
    Sima 

  • 0
    TI__Expert 3126 points

    Hello TI CSC , 

    i am Shreenidhi patil , product definer of the OPA2675. i would like to connect with you on helping you on the above question.

    The 2W limit is for continuous power dissipation , you can easily dissipate higher peak power if its for a smaller duration.

    Can you share your email id , i will set up a meeting you offline and we can have a better discussion for your proposal.

  • 0
    Guru 47485 points

    The OPA2677 will deliver over 1 amp, not shown in the datasheet, but later testing showed that. This was K.20 testing by Alcatel where this emulated lightning strike on a phone line showed about 1.7A supported by the OPA2677

  • 0 in reply to Michael Steffes
    Guru 47485 points

    Oh and I remember now, we went back and added the peak current spec. Still have to watch max Tj when you do this of course, use the package with the heat slug on the bottom,