PLL Phase Resync


I want to set up a fractional-N PLL with a deterministic phase relationship between RF out and REFin. Specifically, REFin will be 49.92 MHz and RFout will be 38.4 MHz. If REFin drops out momentarily, RFout needs to be lined up with REFin when REFin resumes. REFin may change over the life of the project by up to +/- 40 kHz.
I tried this out with a competitor's product who claimed a deterministic relationship but we found that only worked when integer-N division was being used. I believe you refer to it as "Phase Resync"? I know some of your PLLs have this feature but before I start searching through them I need to know if your phase resync applies to fractional-N as well. I'm perfectly ok with using an external VCO if necessary.
Thank you

  • There's been a lot of PM traffic with Chris on this subject, and great progress has been made. It's been suggested that I post my most recent development back to this Forum:

    "We've set up our phase measurement system, based around the ADF4351 eval board. As per the attached block diagram, we provide 49.92 MHz to the PLL ref input, and use the '4351 to convert to 38.4 MHz.
    The 49.92 MHz ref signal is provided by a stable, fixed remote PLL  which gets its reference from a 38.4 MHz TCXO. The same TCXO provides a reference signal against which the ADF4351 is phase-compared.
    S1 is used to interrupt the 49.92 MHz Ref signal for random periods of about 1/2 second. The intent is that the '4351 will resume output at the same phase position as when the input was turned off. I'm finding that this works about 75% of the time. I've attached my ADF4351 config file in case I've made a mistake in configuring this part.
    Your comments would be appreciated.
    Thank you"

    •  Analog Employees 
    on Dec 2, 2020 8:44 AM in reply to fossil

    Hi,

    Block diagram and config file is not attached. Can you try to share them again? 

    •  Analog Employees 
    on Dec 2, 2020 1:20 PM in reply to kudret.unal

    ADF4351_settings (1).txt
    CheckBox: BandSelectClockAutosetBox.Checked = True
    CheckBox: RefD2Box.Checked = True
    CheckBox: RefDoublerBox.Checked = False
    CheckBox: SweepReturnStartBox.Checked = False
    RadioButton: ADF4351.Checked = True
    RadioButton: ADF4350.Checked = False
    RadioButton: USBselector.Checked = False
    RadioButton: SDPSelector.Checked = False
    ComboBox: LDPinModeBox.SelectedIndex = 1
    ComboBox: RFOutputPowerBox.SelectedIndex = 3
    ComboBox: AuxOutputEnableBox.SelectedIndex = 0
    ComboBox: RFOutputEnableBox.SelectedIndex = 1
    TextBox: BandSelectClockFrequencyBox.Text = 124.800
    NumericUpDown: BandSelectClockDividerBox.Value = 200
    ComboBox: AuxOutputPowerBox.SelectedIndex = 0
    ComboBox: AuxOutputSelectBox.SelectedIndex = 0
    ComboBox: MTLDBox.SelectedIndex = 0
    ComboBox: VCOPowerdownBox.SelectedIndex = 0
    NumericUpDown: ClockDividerValueBox.Value = 150
    ComboBox: CLKDivModeBox.SelectedIndex = 2
    ComboBox: ABPBox.SelectedIndex = 0
    ComboBox: CSRBox.SelectedIndex = 0
    ComboBox: BandSelectClockModeBox.SelectedIndex = 0
    ComboBox: ChargeCancellationBox.SelectedIndex = 0
    ComboBox: CounterResetBox.SelectedIndex = 0
    ComboBox: LDPBox.SelectedIndex = 0
    ComboBox: CP3StateBox.SelectedIndex = 0
    ComboBox: LDFBox.SelectedIndex = 0
    ComboBox: PowerdownBox.SelectedIndex = 0
    ComboBox: ChargePumpCurrentBox.SelectedIndex = 7
    ComboBox: PDPolarityBox.SelectedIndex = 1
    ComboBox: DoubleBuffBox.SelectedIndex = 0
    ComboBox: MuxoutBox.SelectedIndex = 0
    ComboBox: LowNoiseSpurModeBox.SelectedIndex = 0
    NumericUpDown: PhaseValueBox.Value = 1
    NumericUpDown: RcounterBox.Value = 1
    TextBox: OutputDividerBox.Text = 64
    TextBox: VCOChannelSpacingBox.Text = 640
    TextBox: OutputChannelSpacingBox.Text = 10
    TextBox: VCOFreqBox.Text = 2457.6
    TextBox: RFOutFreqBox.Text = 38.4
    TextBox: RefFreqBox.Text = 49.92
    TextBox: RFoutBox.Text = 38.4
    TextBox: DivBox.Text = 64
    TextBox: PFDBox.Text = 24.96
    TextBox: MODBox.Text = 13
    TextBox: FRACBox.Text = 6
    TextBox: INTBox.Text = 98
    ComboBox: FeedbackSelectBox.SelectedIndex = 1
    ComboBox: PhaseAdjustBox.SelectedIndex = 0
    ComboBox: PrescalerBox.SelectedIndex = 0
    TextBox: PFDFreqBox.Text = 24.96
    NumericUpDown: ChannelUpDownButton.Value = 0
    NumericUpDown: RandomCurrentBox.Value = 100
    NumericUpDown: RandomTimeDelayBox.Value = 100
    NumericUpDown: RandomMinStepBox.Value = 10
    NumericUpDown: RandomStopBox.Value = 2000
    NumericUpDown: RandomStartBox.Value = 1000
    TextBox: HopCurrent.Text = 
    TextBox: HopDelayBox.Text = 100
    TextBox: HopFBBox.Text = 1010
    TextBox: HopFABox.Text = 1000
    TextBox: SweepSpacingBox.Text = 1
    TextBox: SweepCurrent.Text = 
    TextBox: SweepDelayBox.Text = 100
    TextBox: SweepStopBox.Text = 1010
    TextBox: SweepStartBox.Text = 1000
    TextBox: R5HexBox.Text = 580005
    TextBox: R4HexBox.Text = EC803C
    TextBox: R3HexBox.Text = 4B3
    TextBox: R2HexBox.Text = 1004E42
    TextBox: R1HexBox.Text = 8008011
    TextBox: R0HexBox.Text = 310008
    ComboBox: ReadSelBox.SelectedIndex = 0
    TextBox: ReadbackComparatorBox.Text = 0
    TextBox: ReadbackVCOBox.Text = 0
    TextBox: ReadbackVCOBandBox.Text = 0
    TextBox: ReadbackVersionBox.Text = 0
    ComboBox: VCOSelBox.SelectedIndex = 0
    ComboBox: BandSelectBox.SelectedIndex = 0
    ComboBox: ExtBandEnBox.SelectedIndex = 0
    ComboBox: PDSynthBox.SelectedIndex = 0
    ComboBox: PLLTestmodesBox.SelectedIndex = 0
    ComboBox: SDTestmodesBox.SelectedIndex = 0
    ComboBox: ICPADJENBox.SelectedIndex = 3
    TextBox: DirectWriteBox.Text = 
    

  • This may be grasping at straws, but in looking at the Phase Resync section of the data sheet, they make the comment that Tsync must be at least as long as the worst-case lock time. In ADIsimPLL, it looks like the lock time on the '4351 eval board might be around 200 us. At present, my Tsync is about 78 us. I'll go try this out in the morning - changing Clock Divider value from current 150 to maybe 500 or more. Would you expect that to improve the situation, ie better than 75%?
    thanks
    regards,
    Bob