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ONET4291VA: Modulation Current Behavior

Part Number: ONET4291VA

I'm trying to understand the behaviour of output modulation current (IMOD+) with respect to the differential voltage input (DIN+  -  DIN-) in VCSEL Driver ONET4291VA. Specifically, when the VCSEL turns ON from OFF state, when does the modulation current begin to ramp up? In the figure below, of the possible options A1, A2, A3, I'd assume it is A1 but would like to get confirmation.

Difference between the 3 options are as follows:

A1 --> Output roughly follows the ramp up of differential input voltage (Datasheet provides relationship of output rise/fall time to input rise/fall time)

A2 --> Output ramp up starts only after the differential input voltage has increased above -200mV (200mV is the min spec for Differential Inputs. Note the negative sign.)

A3 --> Output ramp up starts only after the differential input voltage has increased above +200mV (200mV is the min spec for Differential Inputs. Note the positive sign.)

VCSELOFF_On.ppt

Thanks,

Satish

  • Hi Satish,

    Thank you for your interest in ONET4291VA.

    The MOD output roughly follows the differential input voltage. So it is option A1 from the ones you listed. The minimum spec of 2mV for the differential inputs, is to guarantee the performance metrics of the output (like jitter, o/p amplitude, rise/fall times etc) that are specified in the datasheet. If the specs listed in the DS need to be met, the input must be at least 200mV differential.

    Hope this helps. Please let us know in case of further questions.

    Regards,

    Sri