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LMX2594: Output power at 2.5GHz

Maxplus
Prodigy 140 points
Part Number: LMX2594

Hello

I am looking for output power at 2.5GHz.

Can you please confirm? Is the power in single ended or differential?

The mixer is singled ended an takes in 0dBm +/-6dB. They recommend a series DC block cap.

Can someone please recommend which is the best balanced topology ie balanced attenuator (pi or T) , discrete LC  Balun or off the shelf Balun (please recommend in this case).

In case of balanced, when it reaches the mixer, one side of attenuator Will be gnded via cap.  Other side goes to LO

  • 0
    TI__Guru* 81250 points

    Hi Maxplus,

    The output power at 2.5GHz is approx. 8dBm with 50Ω pull-up.

    All the power measurement in the datasheet is taken with SE output. That is, we measured the power at one of the differential pins, and have the other pin terminated.

    Since the mixer accepts SE input, you don't need a balun. You can put a pi or T attenuator, 3dB, between LMX and the mixer.

  • 0 in reply to Noel Fung
    Prodigy 140 points

    Hello,

    Thank you for your reply.  The mixer is an active mixer, LTC5577.  They insist on using a series 3.9pF cap for 2.4GHz operation as DC block.  Impedance after cap is about 46-j25. So additional components after cap are required to match to 50ohm.  

    I attached two circuits.  Is this how you are perceiving? The first one is a balanced attenuator and terminate one of the side to GND via 3p9 near mixer.

    The other alternative is to terminate one of the differential port to GND via 0.01uF and the other via a SE attenuator.  Note both circuits doesn't show the additional matching components.  

    Q1 Is this how you perceive to be as reference to your last email?

    Q2. Is filtering required to attenuate harmonics from LMX2594 in addition to the attenuator?  

    Q3. Is 0.01uF used as DC block or matching?

    LO Input.pdf

  • 0 in reply to Maxplus
    TI__Guru* 81250 points

    Hi Maxplus,

    I prefer Figure 2 with some modifications.

    - put a shunt cap to GND at V2.

    - put a series 50Ω resistor between C7 and GND.

    Q2. It is up to you.

    Q3. DC block.

  • 0 in reply to Noel Fung
    Prodigy 140 points

    Hello

    Thank you for your reply.

    What's your rationale for choosing Fig.2? Fig.1  circuit is balanced so that the currents return to the LMX chip.  Is this not better?

    Fig. 2 what's the reason for series 50 between c7 and GND?

    Do you know what are be harmonics level from LMX chip in relation to fundamental power at 2.4GHz? Many thanks.

  • 0 in reply to Maxplus
    TI__Guru* 81250 points

    Hi Maxplus,

    Fig. 2 works well and is simpler, pcb layout is also easier.

    The 50Ω is required to terminate that pin.

    I guess second harmonics is around -20dBc while third harmonics is around -1xdBc.