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LMX2820: VCO

jianjun lu
Prodigy 50 points
Part Number: LMX2820
Other Parts Discussed in Thread: LMX2594

Does the 0-191 of VCO-CAPCTRL correspond to which segment of VCO? Is its main function only for calibration, or can VCO be specified to which small range range range?

  • 0
    TI__Mastermind 29022 points

    Hello  Jianjun, 
    That is cap code. 
    Within each VCO core you have a cap code that will help decide your RFout from within the VCO core you're in. 
    LMX2820 has 7 VCO cores. 

    Are you attempting full assist? 
    Regards, 

    Vicente 

  • 0 in reply to vicente flores prado
    Prodigy 50 points

    The control word that I circled in the picture can be written as 0-191, indicating that there are only 7 sub bands used for calibrating VCO. What I am wondering is whether this 0-191 can be specified to a small cell under which VCO, or is it just a simple calibration

  • 0 in reply to jianjun lu
    TI__Mastermind 33580 points

    Each VCO has access to the full range of VCO_CAPCTRL:

    • VCO_SEL=1 and VCO_CAPCTRL=0 represents the lowest frequency on VCO1.
    • VCO_SEL=1 and VCO_CAPCTRL=191 represents the highest frequency on VCO1.
    • VCO_SEL=2 and VCO_CAPCTRL=0 represents the lowest frequency on VCO2.
    • VCO_SEL=2 and VCO_CAPCTRL=191 represents the highest frequency on VCO2.
    • etc

    The app note in the link below describes the implementation in LMX2594, but the implementation is very similar to LMX2820 (just with different VCO frequencies and total range for VCO_CAPCTRL). Read through section 1, specifically section 1.3, for a detailed explanation of VCO_SEL and VCO_CAPCTRL.

    https://www.ti.com/lit/an/snaa336a/snaa336a.pdf