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LMX2594EVM: Inductor value

Sultan Weatherspoon
Prodigy 20 points

Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

On the LMX2594EVM what tool or formula should I use to determine the L1 pullup inductor in single output mode for 9.4GHz & 9.8GHz?

is it okay to just put a 50-ohm end cap on RFoutAM to enable single mode out on RFoutAP?

Should I remove R38 in single output mode when only using RFoutAP?

  • 0
    TI__Mastermind 28031 points

    Sultan,

    For the inductor pull-up, it should be high impedance at the frequency of interest.   For instance, we use 18 nH for some designs.   In terms of impedance, 18 nH is 1108 ohm.  But at high frequecy, there are some parasitics, so maybe it makes sense to make smaller.  At 15 GHz for the LMX2594, we have used 1 nH, but 1 nH at 9.8 GHz is about 62 ohm, so maybe not high enough.  So maybe something closer to 3.3 nH or so.  I don't have an exact formula,but the idea is that this is high impedance but balance this with potential real-world issues of the inductor at higher frequency.

    If using only single-ended, terminate the unused side the same way as the used side, except put a series capacitor and 50 ohm load to ground.

    Regards,

    Dean