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Question about PLL from PLL Performance Simulation and Design Handbook - 5th Edition

Ee Wen Quek
Intellectual 300 points

Hi, 

I was studying on this book http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=snaa106&fileType=pdf where I have a doubt from the explanation on the book on Chapter 1 page 5 for third paragraph. I dont understand how to get the output frequency range as mentioned, can someone show me the steps on that?

From my understanding,

VCO=4-5GHz, Div 1=1-20; so frequency coverage should be 200MHz-5GHz 

Divide by 1 and divide by 2, frequency range become 100MHz, 5GHz?

Continue divide with Div 3=1-32; frequency range=3.125MHz-5GHz

This is not same as provided in the book. Did I missed out anything or make wrong assumption on that? 

Thanks.

  • 0
    TI__Mastermind 33620 points

    Greetings,

    I spoke to the author, and we both agree that the numbers for the frequency range are not correct.

    For VCO=4-5GHz:

    Divider Minimum Frequency Maximum Frequency
    1 4GHz 5GHz
    2 2GHz 2.5GHz
    3 1.33GHz 1.66GHz
    4 1GHz 1.25GHz

    Starting with divide by 4 and increasing, the frequency ranges for each divider are continuous or overlap. The intent of this paragraph in the book is to show that a VCO with a restricted frequency range can also be used with a divider to generate a continuous frequency range, but there will be frequency "holes" (regions where the divider and VCO combination cannot generate the desired frequency) between the VCO frequency and the ultimate continuous range. The holes in this example are between 2.5GHz to 4GHz, 1.66GHz to 2GHz, and 1.25GHz to 1.33GHz. This is in contrast to the VCO in the paragraph before, which spans from 2GHz to 4GHz and can generate continuous output frequencies all the way to the maximum VCO frequency.

    Summarizing: For a VCO with tuning range equal to the minimum frequency, it is possible to use dividers to achieve any frequency between the maximum VCO frequency and the minimum VCO frequency divided by the maximum divider value. Meanwhile, for a VCO with tuning range that is less than the minimum frequency, the range in which continuous frequency can be achieved will be less than the minimum VCO frequency, and there will be one or more frequency gaps between the continuous range and the minimum VCO frequency.

    We will update the book as soon as possible to correct the ranges and clarify the intent of this paragraph. Thank you for bringing it to our attention!

    Regards,

  • 0 in reply to Derek Payne
    Intellectual 300 points
    Thanks for the inform very much. Appreciate the explanation.