+ Post New Thread
Results 1 to 7 of 7
  1. #1
    Member level 1
    Points: 2,507, Level: 11
    akrcal's Avatar
    Join Date
    Aug 2006
    Posts
    38
    Helped
    3 / 3
    Points
    2,507
    Level
    11

    Calculation of Phase noise at the mixer output

    Hello All,

    What is the difference between correlated and uncorrelated phase noise? How to calculate phase noise at the output of a mixer when the phase noise of the input signals are specified for the following cases:

    Case (A) Mixer is operating as downconverter:(Output frequency = RF frequency - LO frequency)
    (1) the input signals are coherent (i.e. phase noise are related to each other because they are phase locked to a single OCXO)
    (2) the input signals are non-coherent.(i.e. the two signals are independent and not phase locked)

    Case (B) Mixer is operating as upconverter: (Output frequency = IF frequency + LO frequency)
    (1) the input signals are coherent (i.e. phase noise are related to each other because they are phase locked to a single OCXO)
    (2) the input signals are non-coherent.(i.e. the two signals are independent and not phase locked)

    Regards,
    akrcal

    •   AltAdvertisment

        
       

  2. #2
    Full Member level 1
    Points: 700, Level: 5

    Join Date
    Jun 2018
    Posts
    118
    Helped
    10 / 10
    Points
    700
    Level
    5

    Re: Calculation of Phase noise at the mixer output

    -- https://www.keysight.com/upload/cmc_...ast19Jul12.pdf

    -- http://www.ab4oj.com/test/docs/5990-7529EN.pdf

    -- http://www.ti.com/lit/an/scaa113/scaa113.pdf

    Phase noise is essentially the probability of your signal being in that specific frequency away from the carrier given by a pdf function.

    If it says @100 Khz -90dbc, you can interpret it as probability of being 100 KHz away from the carrier at a given time instance is 1e-9.
    Above links are Keysight and TI phase noise documents about a PLL and Crystal Oscillator systems. Phase noise is created at VCO or Crystal Osc, then carried all along the way, and it depends on multiple factors such as Loop BW, PLL being fractional or integer etc.



    •   AltAdvertisment

        
       

  3. #3
    Advanced Member level 5
    Points: 33,513, Level: 44

    Join Date
    Oct 2001
    Posts
    4,795
    Helped
    1416 / 1416
    Points
    33,513
    Level
    44

    Re: Calculation of Phase noise at the mixer output

    Usually the uncorrelated noise sources (with similar phase noise) at the input of the mixer, gives lower phase noise at the output of the mixer than correlated sources.

    http://micro.apitech.com/pdf/whitepa...lculations.pdf



    •   AltAdvertisment

        
       

  4. #4
    Member level 1
    Points: 2,507, Level: 11
    akrcal's Avatar
    Join Date
    Aug 2006
    Posts
    38
    Helped
    3 / 3
    Points
    2,507
    Level
    11

    Re: Calculation of Phase noise at the mixer output

    Quote Originally Posted by vfone View Post
    Usually the uncorrelated noise sources (with similar phase noise) at the input of the mixer, gives lower phase noise at the output of the mixer than correlated sources.

    http://micro.apitech.com/pdf/whitepa...lculations.pdf
    HI vfone,

    Generally in RADAR systems, various LO signals are locked with a single OCXO i.e. their phase noises are correlated. So how the statement "uncorrelated noise sources (with similar phase noise) at the input of the mixer, gives lower phase noise at the output of the mixer than correlated sources" is justified.

    akrcal



  5. #5
    Advanced Member level 5
    Points: 33,513, Level: 44

    Join Date
    Oct 2001
    Posts
    4,795
    Helped
    1416 / 1416
    Points
    33,513
    Level
    44

    Re: Calculation of Phase noise at the mixer output

    The reason that many RF systems use a single common OCXO reference is NOT to reduce the phase noise at the output of their mixers.



  6. #6
    Member level 1
    Points: 2,507, Level: 11
    akrcal's Avatar
    Join Date
    Aug 2006
    Posts
    38
    Helped
    3 / 3
    Points
    2,507
    Level
    11

    Re: Calculation of Phase noise at the mixer output

    Quote Originally Posted by vfone View Post
    The reason that many RF systems use a single common OCXO reference is NOT to reduce the phase noise at the output of their mixers.
    Hi vfone,

    In the document you have attached there are the following figures:

    Click image for larger version. 

Name:	2.png 
Views:	5 
Size:	11.6 KB 
ID:	150719

    Fig 1.

    Click image for larger version. 

Name:	1.png 
Views:	7 
Size:	16.8 KB 
ID:	150720
    Fig 2.

    In the fig. 1, the phase noise of multipliers D2 and D3 are also taken into account in calculation of overall phase noise but in fig. 2 they are not incorporated. Can you elaborate at this point?



    •   AltAdvertisment

        
       

  7. #7
    Advanced Member level 5
    Points: 34,083, Level: 45

    Join Date
    Dec 2004
    Location
    New England, USA
    Posts
    4,794
    Helped
    1339 / 1339
    Points
    34,083
    Level
    45

    Re: Calculation of Phase noise at the mixer output

    to op, 3 db



--[[ ]]--