ONET4291VA: modulation current vs bias current

Amir Moses

Prodigy 30 points

Part Number: ONET4291VA

Hi,

what is the difference between modulation current register 1 to bias current register 2?

I need to set the bias current to 3.8 mA , what I need to do with REG1 and REG2?

Thanks

over 2 years ago

0 Zach Dryer over 2 years ago

TI__Genius 13310 points

Hello,

We are looking into this and will get back to you shortly.

0 Nir Flysher over 2 years ago in reply to Zach Dryer

TI__Expert 3367 points

Hi Zach, Nasser,

Any feedback on this ?

Regards,

Nir.

0 Nasser Mohammadi over 2 years ago in reply to Nir Flysher

TI__Guru* 93570 points

Hi Nir,

Bias current sets the bias point where the laser would modulate - this depends on the laser type and typically is given in the laser data sheet.

Setting the bias current depends on the closed or open loop operation. If operating in closed loop, then the laser data sheet would specify the coupling ratio. On the other hand, in open loop this is completely controlled through reg 0x02. With the requested 3.8mA bias current, it means we should set reg 0x02 to about 79 decimal or 0x4E value.

Regards,Nasser

0 Amir Moses over 2 years ago in reply to Nasser Mohammadi

Prodigy 30 points

Hi, thank you for your answer.

what about modulation current sets?

I don't understand what is modulation current sets? and what value i need to set to reg1?

thx

0 Nasser Mohammadi over 2 years ago in reply to Amir Moses

TI__Guru* 93570 points

Hi Amir,

Please note ONET4291VA data sheet shown below. MODR bit sets the range while MCDC0 through 7 sets up modulation current based on the MCDR bit.

With MODR set to 1, for example, maximum modulation current is 255X68uA ~17mA. Here data sheet shows 15.4mA because of the laser efficiency.

Regards,Nasser

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ONET4291VA: modulation current vs bias current