成果讲稿ni培训labview rf05phase coherent measurement systems in pxi express

1、Lesson 5 Phase Coherent RF MeasurementSystems in PXI ExpressIntroduction to Phase CoherencyPhase Coherent Clock-Sharing ArchitecturesTrigger Synchronization and Phase AlignmentPhase Coherency and RF InstrumentationNI Phase Coherency SoftwarePhase Coherency Performance VariablesA. Introduction to Pha

2、se CoherencySome Phase Coherent RF ApplicationsMultiple-Input-Multiple-Output (MIMO) SystemsBeamforming (RADAR)Direction findingAntenna-diversity receiversTxRxFree SpaceMIMO Multiple Input Multiple OutputCommon Configurations are 2x2 and 4x4Used in 802.11n, WiMAX, LTE, and evolving standardTransmitt

3、erReceiverFree SpaceBeamformingDirectional signal transmission or receptionUses an array of antennas and constructive/destructive signal interference Can be used for radio and sound wavesApplications inRADARSONARWirelessRadio astronomyDirection FindingThree or more receive antennasUnique propagation

4、 delay to each receiverDirection can be calculated through phase differenceTxRx0Rx1Rx2Phase Coherency DefinitionThe attribute of two or more waves, or parts of a wave, whose relative phase is constant during the resolving time of the observer.Usually implies a frequency lock between signals of the s

5、ame frequencyDifferent frequencies means constantly changing relative phaseCan also be interpreted for signals of different frequenciesSignals are at a specified phase relationship every N cyclesSame FrequencyDifferent FrequenciesvsPhase Coherency Performance MetricsMean Phase OffsetA channels mean

6、phase offset measured relative to a master, or reference channelPrimarily a function of LO and baseband clock propagation delaysOnce measured, can be nulled outPhase Offset Standard DeviationMeasures short-term, instantaneous variation of a channels phase around the mean offset, measured relative to

7、 a master, or reference channelMean Offset () : 0.0 degreesOffset Std Dev (): 1.0 degree Phase Coherency Performance MetricsMean Phase OffsetA channels mean phase offset measured relative to a master, or reference channelPrimarily a function of LO and baseband clock propagation delaysOnce measured,

8、can be nulled outPhase Offset Standard DeviationMeasures short-term, instantaneous variation of a channels phase around the mean offset, measured relative to a master, or reference channelMean Offset () : 0.0 degreesOffset Std Dev (): 1.0 degree B. Phase Coherent Clock-Sharing ArchitecturesAchieving

9、 Phase CoherencyInternal clock relationships determine phase coherency performanceAll clocks in RF instrument must be addressedRF Local oscillator(s) (LO)Baseband ADC/DAC sample clocksBaseband Numerically controlled oscillator (NCO)Shared Reference ClockSharing a reference clock introduces PLLs on i

10、ndividual channelsEach PLL has its own unique phase noise contributionDivider states can introduce uncertainty in mean output phase deltasFilterVCODivider10 MHzFilterVCODividerPhase DetectorPhase DetectorClock 1Clock 2Shared LO / Baseband Sample ClocksShared LO / Baseband Sample ClocksMaster device

11、generates LO and sample clocks - shares them directlyPhase noise between each channel is correlatedConstant phase relationship between each channelDependent only on propagation delayFilterVCODivider10 MHzPhase DetectorClock 1Clock 2Sharing LO and sample clocks directly is preferredClock Sharing Arch

12、itecture ComparisonShared Reference ClocksPLL count expands with channel countEach channel has uncorrelated phase noisePLL divider adds to uncertaintyShared LO / Baseband Sample ClocksOne PLL per clock (master)Uncertainty from PLL phase noise and dividers correlated, cancels outPreferred MethodExerc

13、ise 5-1: Phase Noise CorrelationUnderstand the effects of correlated vs. non-correlated phase noise upon two sine waves relative phase differencesC. Trigger Synchronization and Phase AlignmentChannels Not Synchronized or AlignedChannels are phase coherent butTime (trigger) and phase offset still pre

14、sentSynchronized trigger and phase alignment neededChannels Synchronized but not AlignedChannels are phase coherent and synchronized (trigger)Phase offset still presentPhase alignment still neededChannels Synchronized and AlignedNI Onboard Signal Processor (OSP) uses digital carrier called NCOCan be

15、 manually adjusted per channel (VSA and VSG)Compensates for channel-to-channel phase offset0.0055 phase adjust resolution2 phase aligned channelsNational Instruments T-Clock (TClk)Patent-pending technology for multiple device synchronizationApplies to baseband devices (digitizers/AWGs) of RF VSA/VSG

16、Performs sample clock alignment when sharing ref clocksNot performed when sharing sample clocksEnables accurate triggering of multiple devicesPerformed regardless of clock sharing methodImplemented via NI-TClk software APIOnly two function calls neededNo additional external cabling needed Downconver

17、ter + DigitizerD. RF Instrumentation for Phase Coherency Two Phase Coherent Single Stage VSAsLO SourceDigitizerADC DigitizerRx0Rx1OSPADCOSPVector Signal AnalyzerShared LOShared ADC Sample ClockDownconverterDownconverterTwo Phase Coherent Single Stage VSGsMaster device generates LO and DAC sample clo

18、ck from referenceLO and DAC sample clock shared with remaining channelsPXI-5652PXI-5611PXI-545090DACDAC+ PXI-5611PXI-545090DACDAC+Shared LOShared DAC sample clockNI Phase Coherent RF Measurement SystemsNI PXIe-5663E 6.6 GHz RF Vector Signal AnalyzerPXIe-5652 LO SourcePXIe-5601 RF DownconverterLO IN

19、/ LO OUT portsPXIe-5622 IF DigitizerClkIn / ClkOut portsNI PXIe-5673E 6.6 GHz RF Vector Signal GeneratorPXIe-5652 LO SourcePXIe-5611 RF UpconverterLO IN / LO OUT portsPXIe-5450 Dual Channel AWGClkIn / ClkOut portsNI Phase Coherent RF Measurement SystemsNI PXIe-5663E 6.6 GHz RF Vector Signal Analyzer

20、PXIe-5652 LO SourcePXIe-5601 RF DownconverterLO IN / LO OUT portsPXIe-5622 IF DigitizerClkIn / ClkOut portsNI PXIe-5673E 6.6 GHz RF Vector Signal GeneratorPXIe-5652 LO SourcePXIe-5611 RF UpconverterLO IN / LO OUT portsPXIe-5450 Dual Channel AWGClkIn / ClkOut portsLocal OscillatorDownconvertersDigiti

21、zersShared LOShared ADC ClockFour Channel Phase Coherent AcquisitionUpconvertersShared LOAWGsLocal OscillatorShared DAC ClockTwo Channel Phase Coherent GenerationE. NI Phase Coherency SoftwarePhase Coherency Configuration in MAXNI-RFSA and NI-RFSG use single resource nameEach instrument comprised of

22、 multiple modulesMeasurement and Automation Explorer (MAX) configuration links modules togetherMaster device LO source is the PXIe-5652Slave device LO source is set to ExternalNI Phase Coherency Software OverviewNormal NI-RFSA (VSA) and NI-RFSG (VSG) drivers usedProgramming approach essentially the

23、same as single channel use casePhase coherent specifics:Must enable PXIe-5673 VSG LO OUTPXIe-5663 VSA LO OUT always enabledMust export / import sample clocks via SW callsShould disable PXIe-5663 dither for high IQ ratesNI-TClk technology used for synchronized triggerInitiate slave channels first / m

24、aster channel lastNI Phase Coherency Software OverviewNormal NI-RFSA (VSA) and NI-RFSG (VSG) drivers usedProgramming approach essentially the same as single channel use casePhase coherent specifics:Must enable PXIe-5673 VSG LO OUTPXIe-5663 VSA LO OUT always enabledMust export / import sample clocks

25、via SW callsShould disable PXIe-5663 dither for high IQ ratesNI-TClk technology used for synchronized triggerInitiate slave channels first / master channel lastNI Phase Coherent Software ConclusionVSA / VSG Reference Architecture (LV) software availableUses scalable channel count architecture with F

26、OR loopsScales to N channelsVSA software has phase Auto Adjust featureF. Phase Coherency Performance VariablesSignal to Noise Ratio (SNR)Sample Rate / Input BandwidthRF FrequencyTemperaturePhase Coherency Performance VariablesSignal to Noise Ratio (SNR)Sample Rate / Input BandwidthRF FrequencyTemperaturePhase Coherency Performance Plots VSAsFull scale input to two PXIe-5663 VSAs (0 dBm CW, 0 dBm ref level)Increasing IQ Rate reduces SNR (noise floor increases)Zoom in for next plotPhase Coherency Performance Plots VS