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Original question:

DS110DF111: Driver polarity inversion

DS110DF111: Can DS110DF111 Simultaneously Invert Input and Output Polarity on Channel A?

Nanjun Xu1
Intellectual 420 points

Part Number: DS110DF111

Hi everyone,

I'm designing a 10G OEO retimer board based on the DS110DF111 and encountered a signal polarity challenge.

Background:

  • The SFP+ Module's RX signal needs to be fed into the DS110DF111's INA/INB for signal regeneration
  • Due to PCB layout constraints, I had to reverse-connect my Channel A input signal (RX+ to INA-, RX- to INA+)
  • The output end also needs to be inverted to match the downstream device's expectation

Question:

According to Datasheet section 7.5.1.19, Register 0x1F bit 7 can only invert output polarity. I could not find a register to control input polarity inversion.

Please advise:

  1. Is there a register available to invert input polarity?
  2. If not, can I reverse the connections on the PCB + only invert the output via software (0x1F bit 7 = 1), so the two inversions cancel out? Will the CDR still lock properly on the reversed input signal?
  3. Are there any alternative recommended solutions?

Thanks for your insights!

Kind regards,
Nanjun

  • 0
    TI__Expert 8463 points

    Hi Nanjun,

    1. There is no register available to invert input polarity. 

    2. The input to DS110 has inverted polarity. The register write to 0x1F[7] will reverse the output polarity. The two inversions cancel out. The output of DS110 will have the original polarity. 

    The CDR should lock properly to the reversed input signal. 

    3. You could also reverse the trace routing at the output of DS110. But I see no issues with reversing polarity with the register write method.  

    Best,

    Charles