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LMX2595EVM: LMX2595EVM

singam vamshi krishna
Intellectual 775 points
Part Number: LMX2595EVM
Other Parts Discussed in Thread: LMX2595

Hello. I need to design 17GHz frequency synthesizer with a bandwidth of 200 MHz and phase noise of -85 dBc @ 1KHz. Initially I thought of generating 8.5GHz and later by using the built in VCO doubler from the LMX2595 IC I can obtain the required objective. For generating 8.5 GHz the feedback divider is to be kept at 21.25 where in the 0.25 fraction is been obtained by changing the numerator and denominator coefficients. But as per our design in the TICS pro software the block N Divider is red coloured which I thought it might result in error and moreover while changing the numerator and denominator coefficients the block N Divider turned to yellow in colour. Even I tried of using large numerator and denominator coefficients but the bug haven't fixed. How to program this register DBLR_IBIAS_CTRL1=3115 in order to make use of VCO doubler and are there any particular set of registers to synchronize phase noise and adjust output power levels. I am new to this TICS pro software. Can anyone help me out to fix this error and meet the above mentioned objective

Thanks in advance    

  • 0
    TI__Guru** 110530 points

    Hi Singam,

    Whenever you see yellow or red box in TICS Pro, you can mouse-over the box to see what when wrong.

    In this case, I think your fpd is 400MHz and therefore N=21.25, which is too small. Every fractional-N pll has min. N requirement, see datasheet for details.

    Set fpd to 200MHz, VCO = 8.5GHz and enable VCO doubler to get 17000MHz output.

    DBLR_IBIAS_CTRL1 is used to increase the current biasing for the VCO doubler. Make this value to 3115 can extend the doubled VCO frequency to 20GHz.