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What is the proper input impedance matching network for a single ended input to DS30BA101

Other Parts Discussed in Thread: DS30BA101, DS30EA101, LMH0303, LMH0366, LMH0346

The DS30BA101 states that is capable of receiving single ended inputs, yet all reference diagrams have differential inputs. We would like to use this chip in a couple locations which require single ended inputs (of 50Ω and 75Ω), however, I’m not certain as to which method I should use to match the input impedance expected by the chip.

- Should I treat the input pair as 100Ω differential (like DS30EA101), or each input as an independent 50Ω network?

- Is it better to terminate the unused input, or leave it floating?

 

Furthermore, we hope to use these for trace conversions of SMPTE 929/424 (3G & HD-SDI) signals, so any additional design suggestions for optimal operation in these bandwidths would be very helpful.

 

As always, your help and insight is much appreciated.  Thank you.

  • Hi Jay,

    Please treat DS30BA101 as 100Ω differential input(like DS30EA101 as you indicated). DS30BA101 is from our LMH0303 family of devices and these require differential 100Ω input. You can refer to the LMH0303 data sheet to see how we use two 49.9Ω with 0.1uF on their junction to GND(for terminating the 100Ω differential line).

    Regards,,nasser
  • Hi Nasser,

        Thank you very much for that clarification.

    In mentioning the LMH0303, you have me wondering if this wouldn’t be a better fit for my application, any thoughts?

    Design Requirements:

    - (3G/HD-SDI signals) Single ended input conversion to Differential Outputs.

               - Differential Outputs feed into LMH0366 (Reclocker) via: ≥4 Successive Board Stack headers (25GHz rated, 100Ω differential impedance), minimal trace lengths ≤1”

    My only concern with using a cable driver is the potential for overpowering the inputs to the LMH0366, or potentially causing large reflections given the lack of any actual cable.

    Once again, thank you for your help and your insight.

     

       Jay H.

  • Hi Jay,

    LMH0303 and DS30BA101 are pin compatible. The main difference is that LMH0303 drives 75 ohm coax while DS30BA101 drives 100 Ohm differential line.

    Please note LMH0366 is very sensitive to PCB layout especially when you have multiple LMH0366 devices. LMH0346 is more immune to this issue. Perhaps it would be good to consider LMH0346(if power consumption is not a main concern).

    Regards,,nasser