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CICC 2005 John

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A 4-bit Ultra-Wideband Beamformer with 4ps True Time Delay ResolutionJ.D. Roderick, H. Krishnaswamy, K. Newton, and H. HashemiUniversity of Southern CaliforniaCICC 2005September 21, 2005 2Outline Introduction and Applications A Prototype UWB Beamformer– Subsystems – Circuit techniques– Passive modeling UWB Beamformer Performance ConclusionCICC 2005September 21, 2005 3UWB SignalTime Domain Frequency Domain Fractional bandwidth, BF>25% Second derivative Gaussian pulse Fine time resolution in impulse radar-3dB BWCICC 2005September 21, 2005 4Potential Applications Impulse radar using UWB Beamforming– Ground or building penetrating radar– Biomedical imaging– Location, ranging and navigation– Vehicular radarDepth resolution∝Pulse widthBandwidth _________1∝CICC 2005September 21, 2005 5Narrow-Band Beamforming(((())))(((( ))))sin /( )/Lc fFLc fπϕπϕπϕπϕϕϕϕϕπϕπϕπϕπϕ====cLfεεεε====Array Beam PatternBeam WidthVGAPhaseShifterLdd / 2= λ= λ= λ= λc = Speed of lightf = Signal frequency= Signal wavelengthλλλλIncidentWaveϕϕϕϕPhase shifter is used to approximate time delay.CICC 2005September 21, 2005 6Narrow-Band BeamformingVGAϕϕϕϕ(((())))(((( ))))sin /( )/Lc fFLc fπϕπϕπϕπϕϕϕϕϕπϕπϕπϕπϕ====cLfεεεε====Array Beam PatternBeam WidthPhaseShifterPhase shifter is used to approximate time delay.CICC 2005September 21, 2005 7UWB BeamformingVariable DelaydLττττττττττττττττIncidentWaveϕϕϕϕc = Speed of light= Signal BW= Pulse width1Tf∆ =∆ =∆ =∆ =∆∆∆∆T∆∆∆∆f∆∆∆∆(((())))(((( ))))/2( )/2erf L f cAL f cπ ϕπ ϕπ ϕπ ϕϕϕϕϕπ ϕπ ϕπ ϕπ ϕ∆∆∆∆====∆∆∆∆TcLεεεε∆∆∆∆====Array Beam PatternBeam WidthTrue time delay is required in UWB beamforming!CICC 2005September 21, 2005 8UWB Beamforming(((())))(((( ))))/2( )/2erf L f cAL f cπ ϕπ ϕπ ϕπ ϕϕϕϕϕπ ϕπ ϕπ ϕπ ϕ∆∆∆∆====∆∆∆∆TcLεεεε∆∆∆∆====Array Beam PatternBeam WidthVariable DelayττττττττττττττττϕϕϕϕTrue time delay is required in UWB beamforming!CICC 2005September 21, 2005 9 Implementation requirements– Monocycle Gaussian signal– True time delay Features– Higher depth resolution– High scanning resolution– No distinct side lobes Potential applications– Impulse radar– ImagingUWB Beamforming SummaryCICC 2005September 21, 2005 10Outline Introduction and Applications A Prototype UWB Beamformer– Subsystems– Circuit Techniques– Passive Design UWB Beamformer Performance ConclusionCICC 2005September 21, 2005 11Beamformer System Diagram Gain Variation 5dB variation 1dB resolution 10dB maximumDelay 4-bit delay control 4ps resolution 64ps maximumImpedance 50 input/output  50 inter-stage CPSOne bit coarse-tuningThree bit fine-tuningSwitchingAmplifier32psCPSDelay controlGain controlCICC 2005September 21, 2005 12Trombone Structure Provides 3-bit (8 states) control with 4ps resolution Group delay variation is achieved by changing signal path Input and output are 50 matchedAmplifiersWidebandVin+-Vout+-ZoZoZoZoCICC 2005September 21, 2005 13Trombone Delay ElementsInductor Q1.0GHz = 37.5GHz = 1111.0GHz = 1370µ X 55µTrombone Line Delay vs. Bit Order0123456781 4 7 10 13Frequency (GHz)Group Delay (ps)4-bit (32 sections)3-bit (16 sections)2-bit (8 sections)1-bit (4 sections)Path “A”“Pi” Section2Delayττττ====2LCττττ====2C2cutoffLCωωωω====2C,,LCICC 2005September 21, 2005 14Wideband Amplifier Design Act like a switch Maximize bandwidth and gain Maximum Cin(12fF) set by delay resolution Maximize “Off” I/O isolation  Minimize operating input impedance difference_in inC ("Off ") C ("On")≈≈≈≈Assuming amplifier dominant pole response2tvfAπτπτπτπτ====300tf GHz≈≈≈≈ftrequired for unity gainDesign CriteriaCICC 2005September 21, 2005 15CPSWidth=4µmLength=250µmSeparation=20µmCross-routedin layoutNeutralizationDigital control enableVertical Separation=2µmAmplifier Schematic Split layout architecture−Coherent coupling CPS NeutralizationCircuit TechniquesCICC 2005September 21, 2005 16Bandwidth CompensationiiiiHiiiiHNot Cross RoutedCross RoutedDifferential OperationBandwith Enhancemnt Comparison03691215180 5 10 15Frequency (GHz)Gain (dB)Cross Routed and NeutralizationCross RoutedNot Cross RoutedNo CompensationBandwidth Enhancement ComparisonCICC 2005September 21, 2005 17MSB Delay Realization Broadband switch  Split layout architecture– CPS shunt peaking “Dummy” structures– Constant impedanceMSB CPS Delay LineLength = 4.9mmZ0 = 100Spacing = 10 mWidth = 10 meff= 5(1GHz) = 0.113dB/mm(11GHz) = 0.205dB/mmMSB Delay (32ps)CICC 2005September 21, 2005 18Variable Gain Distributed Amplifier (VGDA) 5dB gain variation Split architecture– CPS shunt peaking Compensates for propagation loss in trombone line Gain variation is achieved by manipulating current mirror referencesGain VariationControlCICC 2005September 21, 2005 19UWB Beamformer Chip MicrophotographInputTotal Chip Size: 2.5mm x 0.9mmBroadband Variable Gain AmplifierMSB Delay Element Trombone8-tap Variable Delay Element Bias Generation& Digital Control UnitOutputCICC 2005September 21, 2005 20Outline Introduction and Applications A Prototype UWB Beamformer– Subsystems – Circuit Techniques– Passive Modeling UWB Beamformer Performance ConclusionCICC 2005September 21, 2005 21Gain and Phase PerformanceGain Variation 16GHz bandwidth for lowest delay setting  5dB gain variation in 1dB stepsFrequency (GHz)dBLowest delay settingPhase VariationFrequency (GHz)DegreesHighest gain setting-3dB BWCICC 2005September 21, 2005 22Group Delay PerformanceGroup delay variation is caused by inductor Q and the differencebetween Cin(“Off”) and Cin(“On”) of the wideband amplifiers.Group Delay VariationMSB disabledMSB enabledFrequency (GHz)Highest gain settingGroup Delay (ps)Group Delay Difference (Between Adjacent Settings)Group Delay (ps)Frequency (GHz)Highest gain settingExpectedMeasuredCICC 2005September 21, 2005 23Bandwidth of Delay Settings Inductor Q results in propagation loss 13GHz worst case bandwidth for largest delay settingdBFrequency (GHz)Highest gain setting3dB BW2dB propagation lossCICC 2005September 21, 2005 24Time Domain Measurements5GHz Monocycle Signal


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