Multiport, Multichannel Transmission Line: Modeling and Synthesis - PowerPoint PPT Presentation

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Multiport, Multichannel Transmission Line: Modeling and Synthesis

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Title: Multiport, Multichannel Transmission Line: Modeling and Synthesis


1
Multiport, Multichannel Transmission Line
Modeling and Synthesis
  • Based on the research paper J. Chen and L. He,
    Modeling and Synthesis of Multi-Port
    Transmission Line for Multi-Channel
    Communication, IEEE Transactions on
    Computer-Aided Design of Integrated Circuits and
    Systems, Sept 2006
  • Presented by Pratyush Singh
  • Course EE201C

2
Overview
  • Introduction
  • Basics of transmission line
  • Frequency domain models for multi-port
    transmission lines
  • Voltage response
  • SNR model
  • Signal distortion metrics
  • Synthesis of RF interconnects
  • Conclusion

3
Introduction
  • Traditional approach
  • On-board or in-package communication
    Transmission lines
  • On-chip communication Traditional interconnects
    (limited by inherent signal distortion and large
    RC delays)
  • On-chip communication via transmission lines
  • Transmit baseband digital signals
  • Transmit digital signals via high frequency
    carriers (modulate base-band signals with high
    frequency carriers before transmission and let
    the analog receivers recover the signal) like RF
    interconnects.

4
RF Interconnects
  • Transmission via high-frequency carrier signals
  • Composition
  • CPW/MTL
  • Analog modulators and demodulators
  • Capacitive couplers
  • Advantages
  • Multiple accesses possible (FDMA, CDMA)
  • Reconfigurable
  • High speed (close to speed of light)
  • Lower distortion and losses
  • Immune to digital switching noise

5
This work
  • Develops closed-form SNR models that are
    effective for a generic network with multiple
    discontinuities (i.e ports, junctions,
    terminations)
  • Presents signal distortion FOMs in terms of
    amplitude and phase delay
  • Brings up automatic synthesis of RF
    interconnects with high quality results showing
    the advantages and significance of the same (as
    against the manual designs presented in some
    earlier works)

6
Why automatic synthesis?
  • Because the earlier efforts involving manual
    designs were inherently limited by the level of
    complexity
  • Limitations in manual design
  • Overdesign lead to large interconnect area
  • Hard to consider multiple ports and branches
  • Long design cycle

7
Transmission line basics
  • A transmission line can be described as
  • R,L,C,G unit length parameters
  • Characteristic impedance
  • So the solution
  • Reflection ratio at terminations

8
How circuit is modeled?
  • Between any two discontinuities, a uniform
    transmission line model has been employed
  • Transceivers have been modeled as linear elements
    with an impedance and a voltage source
  • Model each frequency channel in frequency domain
  • Multiple frequency channels

9
Port Voltage Response
  • Each segment between adjacent discontinuities is
    a transmission line
  • At each port
  • At each branching point

10
Port Voltage Response (contd.)
  • At each termination
  • Zt Impedance of the termination
  • System matrix sparse band
  • 2n2b variables with n ports and b branches
  • Complexity of O(nb)
  • Example for a two-port line,

11
Model v/s SPICE simulation
  • Voltage comparison shows high accuracy of the
    model voltage response

12
SNR model
  • Isolated communication channel
  • Approx. to first order, neglecting reflections
    from other discontinuities

13
SNR model (contd.)
  • Effect of Multiple ports
  • Transmission and reflection rates at port k
  • Zpk Impedance of port k
  • Z0 Characteristic impedance of transmission line
  • Termination reflection rate

14
SNR model (contd.)
  • Reflection rate of branch i
  • Z0i Characteristic impedance of line i.
  • Transmission rate to other branches

15
SNR model (contd.)
  • With transmission and reflection from all
    discontinuities coming into picture, SNR can be
    expressed as
  • Vs signal received by the receiver r
  • Vn first-order reflection noise from the
    discontinuities
  • Pn Intrinsic noise power

16
FOMs
  • Distortion depends upon attenuation and phase
    delay. If both are uniform over the frequency
    band of the channel, the communication is
    distortionless
  • To ensure small distortion following metrics are
    defined
  • Phase delay metric
  • Attenuation metric

17
Multiband CPW RF Interconnect
  • Digital signal ? Modulation (by transmitter)? RF
    carrier signal? Interconnect (coupled via a
    capacitive coupler) ? Receivers (via capacitive
    couplers) ?Demodulation ? Original digital signal

18
Automatic Synthesis of RF Interconnect
  • Target
  • Minimize total area of interconnects and coupler
    sizes
  • Constraints
  • SNR (lower bound)
  • Distortion (upper bound)
  • Freedom to decide
  • w (signal wire width), g (shielding wire width),
    s (spaces), coupler sizes (defined by the
    capacitive density)
  • Given
  • Transceiver sizes, locations, intrinsic noise,
    interconnect topology

19
Algorithm
  • Simulated Annealing method
  • Objective function
  • Where
  • A area
  • FSi, FPi and FAi penalty function of violation
    of SNR, phase delay variation and amplitude
    variation
  • Ka, Ks, Kpd and Kad weight factors

20
Synthesis Results
  • Synthesis of 2-port-2-channel interconnect gave
    80 reduction in the area as against the manual
    design Chang et al. 01
  • In general, total area depends on design and
    varies up to 3x

21
Other observations
  • Coupler sizes vary up to 20x even in same design
    as against the assumption of uniform sizes in
    manual designs.
  • Receiver couplers are much smaller than
    transmitter couplers when multiple ports are
    there.
  • Mismatched interconnects lead to violation of
    constraints
  • Termination mismatch leads to increase in
    interconnect area and coupler sizes.

22
Conclusions
  • RF interconnects are very effective multichannel
    multiport interconnects used for high speed high
    bandwidth communications
  • In this work, an efficient multi-port
    transmission line model was developed for RF
    interconnects
  • An accurate closed-form SNR model was developed
  • Highly area efficient interconnect designs were
    synthesized using these models
  • The effectiveness and necessity of these models
    and automatic synthesis process is observable
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