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Compiler/LMX2594EVM: LMX2594EVM output power and ramp

Tony Hanna
Prodigy 30 points
Part Number: LMX2594EVM
Other Parts Discussed in Thread: LMX2594

Tool/software: TI C/C++ Compiler

Hello,

I have 2 questions concerning the LMX2594EVM board.

Just for information, we are testing the board in order to use the LMX2594 in an industrial level probing FMCW radar.

 

In fact, the output power is not adequate with the datasheet of the LMX2594 synthesizer (as shown in the attached figure outputpower.jpg).

As 7 GHz is the default frequency of the TICS software, I find it curious that the power at 7 GHz is the same as the datasheet. So is there something I am doing wrong with the configuration of the output frequency ? (I attached a screenshot of the TICS software configuration for 10 GHz).

 

The second question is concerning the ramp.

Generally, if we “zoom in” the ramp we see that it is not perfectly linear and it is a stair (attached figure ramp.jpg). Is this the case with the LMX2594 ?

If yes can you give us how to calculate the ‘dt’ ? It is very important for us to decrease ‘dt’ as possible (< 1 ns) in order to get the highest precision for the FMCW radar we are designing.  

 

Thanks,

Best regards,

Tony Hanna Ph.D.

  • 0
    TI__Guru* 96830 points

    Hi Tony,

    The output power we specified in the datasheet has the trace loss de-embedded. 

    If you want higher output power, we recommend use one of the differential output pins and has the complementary pin terminated. The trace connecting the output pin and the following device should be as short as possible. 

    We can do linear automatic ramp, but the ramp range is very limited, usually it is around or below 100MHz.

    If the ramp range is big, calibration is required. As a result, it becomes a staircase ramp.

    In either cases, the frequency will be incremented once at a rate of 1/fpd. For example, if fpd = 100MHz, dt = 10ns.

  • 0 in reply to Noel Fung
    Prodigy 30 points

    Hello,

    Thank you for your reply.

    The board is connected as shown in the attached photo (no cable at the output and the other pins are terminated with 50 ohm).

    Maybe it is the dispersion of the boards ? I just wanted to make sure that there is no error made on my part while programming the device.

    Concerning the ramp, is there an application note on how to program an automatic ramp with TICS pro ? ( or an example screenshot for 9490 - 9510 MHz).

    Finally, can we generate a pluse frequency with a duration of 10 ns with the LMX2594, if yes how ?

    Tony

  • 0 in reply to Tony Hanna
    TI__Guru* 96830 points

    Hi Tony,

    Your test setup is good. Please note datasheet output power plot was with power setting (OUTA_PWR) of 50. Secondly, datasheet has the trace loss de-embedded. 

    In the EVM user's guide, there is a linear ramp example.

    To generate a 10ns pulse, we can use SYSREF PULSE mode with sysref frequency = 50MHz. 

  • 0 in reply to Noel Fung
    Prodigy 30 points

    Hello,

    Ok thank you for the clarifications on the ramp and the output power.

    For the pulse I guess the question wasn't clear. Is it possible to output a pulsed RF signal ? For example a 9.5 GHz signal for a duration of 10 ns (illustration image attached).

    Thanks again,

    Best regards,

    Tony  

  • 0 in reply to Tony Hanna
    TI__Guru* 96830 points

    Hi Tony,

    No, pulsed RF is not possible. I think you need a RF switch to toggle on/off.