A 4-bit Ultra-Wideband Beamformerwith 4ps True Time Delay Resolution by yte37472

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									 A 4-bit Ultra-Wideband
Beamformer with 4ps True
 Time Delay Resolution
J.D. Roderick, H. Krishnaswamy, K. Newton,
              and H. Hashemi
      University of Southern California
                        Outline
       Introduction and Applications
       A Prototype UWB Beamformer
        – Subsystems
        – Circuit techniques
        – Passive modeling
       UWB Beamformer Performance
       Conclusion


September 21, 2005             CICC 2005   2
                       UWB Signal
           Time Domain                     Frequency Domain


                                                     -3dB BW




             Fractional bandwidth, BF>25%
             Second derivative Gaussian pulse
             Fine time resolution in impulse radar
September 21, 2005             CICC 2005                       3
               Potential Applications
       Impulse radar using UWB Beamforming
        – Ground or building penetrating radar
        – Biomedical imaging
        – Location, ranging and navigation
        – Vehicular radar


                           ∝ Pulse width ∝
                                                 1
        Depth resolution                     _________
                                             Bandwidth


September 21, 2005             CICC 2005                 4
       Narrow-Band Beamforming
Incident
 Wave                                        c = Speed of light
               d                             f = Signal frequency
                                             λ = Signal wavelength
        ϕ

                                                      d = λ/2
               L
                                              Array Beam Pattern
                                                       sin ( Lcπϕ / f )
                                            F (ϕ ) =
                                                        ( Lcπϕ / f )
                                                     Beam Width
                     VGA Phase
                                                              c
                         Shifter                        ε=
  Phase shifter is used to approximate time delay.           Lf
September 21, 2005            CICC 2005                           5
       Narrow-Band Beamforming


        ϕ


                                              Array Beam Pattern
                                                       sin ( Lcπϕ / f )
                                            F (ϕ ) =
                                                        ( Lcπϕ / f )
                                                     Beam Width
                     VGA Phase
                                                              c
                         Shifter                        ε=
  Phase shifter is used to approximate time delay.           Lf
September 21, 2005            CICC 2005                           6
                     UWB Beamforming
Incident
                        τ
 Wave                                               c = Speed of light
                                                    ∆ f = Signal BW
               d                                    ∆ T = Pulse width

        ϕ
                        τ                               ∆T =
                                                                         1
                                                                        ∆f
                        τ
               L
                                                    Array Beam Pattern
                                                                  (   π L∆f ϕ / 2c   )
                        τ
                                                            erf
                                                  A(ϕ ) =
                                                             (    π L∆f ϕ / 2c   )
                       Variable Delay                       Beam Width
                                                                ∆Tc
True time delay is required in UWB beamforming!              ε=
                                                                 L
September 21, 2005                 CICC 2005                                 7
                     UWB Beamforming
                        τ
        ϕ
                        τ
                        τ
                                                    Array Beam Pattern
                                                                  (   π L∆f ϕ / 2c   )
                        τ
                                                            erf
                                                  A(ϕ ) =
                                                             (    π L∆f ϕ / 2c   )
                       Variable Delay                       Beam Width
                                                                ∆Tc
True time delay is required in UWB beamforming!              ε=
                                                                 L
September 21, 2005                 CICC 2005                                 8
        UWB Beamforming Summary
       Implementation requirements
        – Monocycle Gaussian signal
        – True time delay

       Features
        – Higher depth resolution
        – High scanning resolution
        – No distinct side lobes

       Potential applications
        – Impulse radar
        – Imaging


September 21, 2005              CICC 2005   9
                        Outline
       Introduction and Applications
       A Prototype UWB Beamformer
        – Subsystems
        – Circuit Techniques
        – Passive Design
       UWB Beamformer Performance
       Conclusion


September 21, 2005         CICC 2005   10
     Beamformer System Diagram
                                    32ps
                                    CPS
                                                   Switching
                                                   Amplifier



                                  One bit
                                coarse-tuning
                                                                                Three bit
                                                                               fine-tuning
                     Gain control                         Delay control




    Delay                                  Gain Variation                 Impedance
     4-bit delay control                    5dB variation                   50 input/output
     4ps resolution                         1dB resolution                  50 inter-stage CPS
     64ps maximum                           10dB maximum


September 21, 2005                            CICC 2005                                      11
                  Trombone Structure
      +
    Vout                                                    Zo
      -                                                Zo

     Wideband
     Amplifiers


       +
    Vin                                                     Zo
       -                                               Zo



      Provides 3-bit (8 states) control with 4ps resolution
      Group delay variation is achieved by changing signal path
      Input and output are 50 matched

September 21, 2005           CICC 2005                           12
        Trombone Delay Elements
                                                                                 Trombone Line Delay vs. Bit Order
                                                                         8
                                                                                                                Path “A”
                                                                         7




                                                  G rou p D elay (p s)
                                                                         6
                                                                         5
                                                                         4
                                                                         3          4-bit (32 sections)
                                                                         2          3-bit (16 sections)
                                                                         1          2-bit (8 sections)
                                                                         0          1-bit (4 sections)
 “Pi” Section          L                                                     1        4         7          10        13
                                                                                             Frequency (GHz)

          C                     C
                                                                                                    Inductor Q
          2                     2
                                                                                                     1.0GHz = 3
          τ                             2                                                            7.5GHz = 11
Delay =       , τ =2   LC , ωcutoff =                                                                11.0GHz = 13
          2                             LC                               70µ X 55µ

September 21, 2005                           CICC 2005                                                                13
       Wideband Amplifier Design
                                             Design Criteria
                                             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
                                              _
                                                  Cin ("Off ") ≈ Cin ("On")
       Assuming amplifier dominant
             pole response                    ft required for unity gain

                 f tπ τ                           f t ≈ 300 G H z
            Av =
                    2
September 21, 2005               CICC 2005                                 14
            Amplifier Schematic
                                        CPS
                             Vertical Separation=2µm
                                Separation=20µm
                                  Length=250µm
                                    Width=4µm


                                                       Cross-routed
                                                         in layout

                                                       Neutralization
Circuit Techniques
Split layout architecture
  −Coherent coupling CPS
Neutralization               Digital control enable

September 21, 2005          CICC 2005                            15
          Bandwidth Compensation
Not Cross Routed                                  Bandw ith Enhancem nt Com parison
                                              Bandwidth Enhancement Comparison
           H                         18
 i              i
                                     15

  i             i        Gain (dB)   12

                                      9
                                               No Compensation
      Cross Routed                    6        Not Cross Routed
           H
                                      3
                                               Cross Routed
 i              i                              Cross Routed and Neutralization
                                      0
 i              i                         0                5                     10        15
                                                               Frequency (GHz)

Differential Operation

September 21, 2005                             CICC 2005                              16
              MSB Delay Realization
                                  MSB Delay (32ps)
                                  Broadband switch
                                  Split layout architecture
                                   – CPS shunt peaking
                                  “Dummy” structures
                                   – Constant impedance

                                  MSB CPS Delay Line
                                     Length = 4.9mm
                                     Z0 = 100
                                     Spacing = 10 m
                                     Width = 10 m
                                      eff = 5
                                      (1GHz) = 0.113dB/mm
                                      (11GHz) = 0.205dB/mm

September 21, 2005    CICC 2005                           17
              Variable 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 references
Gain Variation
   Control


September 21, 2005      CICC 2005                  18
                     UWB Beamformer Chip
                       Microphotograph
                                              Output



Input




          Broadband       MSB Delay       Trombone       Bias Generation
         Variable Gain     Element      8-tap Variable           &
           Amplifier                    Delay Element     Digital Control
                                                               Unit
                     Total Chip Size: 2.5mm x 0.9mm
September 21, 2005                CICC 2005                                 19
                        Outline
       Introduction and Applications
       A Prototype UWB Beamformer
        – Subsystems
        – Circuit Techniques
        – Passive Modeling
       UWB Beamformer Performance
       Conclusion


September 21, 2005         CICC 2005   20
     Gain and Phase Performance
           Gain Variation                           Phase Variation
             Lowest delay setting                     Highest gain setting




                                          Degrees
dB




               -3dB BW

              Frequency (GHz)                        Frequency (GHz)


                     16GHz bandwidth for lowest delay setting
                     5dB gain variation in 1dB steps


September 21, 2005                  CICC 2005                                21
                       Group Delay Performance
                   Group Delay Variation                                    Group Delay Difference
                                                                            (Between Adjacent Settings)
                           Highest gain setting                                     Highest gain setting
                        MSB disabled                                                                Expected
Group Delay (ps)




                                                         Group Delay (ps)
                        MSB enabled                                                                 Measured




                          Frequency (GHz)                                          Frequency (GHz)


                   Group delay variation is caused by inductor Q and the difference
                   between Cin(“Off”) and Cin(“On”) of the wideband amplifiers.


September 21, 2005                                CICC 2005                                                22
      Bandwidth of Delay Settings
                               Highest gain setting

                     2dB propagation loss
          dB




                                 3dB BW



                             Frequency (GHz)

      Inductor Q results in propagation loss
      13GHz worst case bandwidth for largest delay setting

September 21, 2005                 CICC 2005            23
     Time Domain Measurements
5GHz Monocycle                 Oscilloscope          Laptop
Signal Generator
                                                     Digital
                                                     Control
                                         Trigger
                     DUT




                                              32ps


September 21, 2005         CICC 2005                       24
           -1dB Compression Point
            Normalized Output Power   Highest gain setting
                                      1GHz
                                      3GHz
                                      7GHz
                                      9GHz
                                      11GHz




                                      Input Power (dBm)

       1GHz : P-1dB = -28dBm                     7GHZ : P-1dB = -21dBm
       9GHz : P-1dB = -21dBm                     11GHz: P-1dB = -20dBm
September 21, 2005                           CICC 2005                   25
       Expected NB Array Performance
         with Measured Beamformer
 Input                             Ideal Antennas                       Output
                                N = 4, d = /2 @ 7.0GHz


                            d
-100          0           100                            -100       0            100



         Time (ps)                                              Time (ps)
                     Ideal beamformer          Measured beamformer
         0o                   3.5o                  7o                  17.5o




September 21, 2005                      CICC 2005                           26
       Expected UWB Array Performance
          with Measured Beamformer
                                 Ideal Antennas
 Input                           N = 4, d = 10mm                      Output

                             d

-100           0           100                            0     100    200       300

         Time (ps)                                             Time (ps)
                      Ideal beamformer          Measured beamformer
          0o                     7o                  14o              35o




 September 21, 2005                      CICC 2005                          27
             Performance Summary
                           Parameter                       Result
                      UWB delay resolution                  4ps
                      Total achievable delay                64ps
                Worst case -3dB bandwidth                  13GHz
               Gain peaking over bandwidth                  1dB
            Gain difference over delay settings             2dB
               Maximum system power gain                   10dB
                     Power gain tuning range         5dB in 1dB steps
                     UWB steering resolution          7° (4 elements)
             Narrow band steering resolution          3.5° (4 elements)
                       Power consumption               87.5mW (2.5V)
                              Area                        2.25mm2
                           Technology               0.18 m BiCMOS SiGe


September 21, 2005                      CICC 2005                         28
                     Conclusion
       A prototype silicon UWB beamformer
       has been demonstrated that is suitable
       for high-resolution scanning radar and
       imaging applications.

       Several system and circuit level
       techniques are implemented to
       maintain flat gain and group delay over
       an ultra-wide bandwidth.
September 21, 2005      CICC 2005            29
                     Acknowledgements

   • Boeing Phantom Works
   • Ryan Stevenson, Andrew Stapleton, Ali
     Medi, Sanghyun Chang and Dr. John
     Choma from USC.




September 21, 2005         CICC 2005         30

								
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