LTC6948 - impedance of the RF+/- differential lines?

Hello,

We plan to use the LTC6948-3 with a 5GHz output, using a balun to produce a single-ended output.

I have a few questions regarding this:

- The HHM1570B1 is out of stock and we have decided to go for the HHM1595A1 which has a wider band at the price of a ~-20dB insertion loss. Any restriction on this?

- In Figure 18 (see below), there is no indication on the impedance of the lines connecting RF+/- to the balanced inputs of the balun. Which impedance do you recommend? Or should be use the single ended matching circuit from Figure 16 on both branch?

Thank you in advance for your support!

Thomas

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  • +1
    •  Analog Employees 
    on Mar 1, 2021 7:41 PM

    Hi Thomas,  the DC feed (pin 2 of the Balun's)  behaves as the two inductors in figure 16.  So you don't need to copy figure 16.  The lines between 6948 and the Balun can either be routed 100 differential or two 50 ohm single ended traces.  

    The 1595 pin 2&5 is listed as GND only.  Where the 1570 has pin 2 listed as GND or DC feed. I'm not sure why that is?  You may want to clarify this point with the balun manufacturer, as figure 18 requires the DC feed on pin 2.  Other than that possible issue, the 1595 specs look ok.  And it looks like the pin outs are compatible so you inherently have a back up plan once the 1570Bs are in stock.

Reply
  • +1
    •  Analog Employees 
    on Mar 1, 2021 7:41 PM

    Hi Thomas,  the DC feed (pin 2 of the Balun's)  behaves as the two inductors in figure 16.  So you don't need to copy figure 16.  The lines between 6948 and the Balun can either be routed 100 differential or two 50 ohm single ended traces.  

    The 1595 pin 2&5 is listed as GND only.  Where the 1570 has pin 2 listed as GND or DC feed. I'm not sure why that is?  You may want to clarify this point with the balun manufacturer, as figure 18 requires the DC feed on pin 2.  Other than that possible issue, the 1595 specs look ok.  And it looks like the pin outs are compatible so you inherently have a back up plan once the 1570Bs are in stock.

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