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Piotr Gawlicki MEng Thesis

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Design of a Programmable Baseband Filter for an LTE Direct Conversion Receiver - Thesis presentation

Design of a Programmable Baseband Filter for an LTE Direct Conversion Receiver - Thesis presentation


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  • 1. Design of a Programmable Baseband Filter for an LTE Direct Conversion Receiver
    by Piotr Gawlicki
  • 2. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    2
    Integrated Systems Laboratory
  • 3. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    3
    Integrated Systems Laboratory
  • 4. Evolution of telecommunications standards
    Donnerstag, 18. Juni 2009
    4
    Integrated Systems Laboratory
    GSM
    ?
    W-CDMA
    Analog Mobile Phone Service (AMPS)
  • 5. LTE specifications
    Variable bandwidth:
    1.4MHz , 3MHz , 5MHz , 10MHz , 15MHz , 20MHz
    Two modulation schemes:
    Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink
    Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink
    Anticipated speed of data transfer:
    100 Mbit/s in the downlink
    50 Mbit/s in the uplink
    Donnerstag, 18. Juni 2009
    5
    Integrated Systems Laboratory
  • 6. Direct Conversion Receiver (DCR)
    Baseband (BB) filter as an important on chip part of the DCR
    Donnerstag, 18. Juni 2009
    6
    Integrated Systems Laboratory
  • 7. Baseband filter specifications
    Donnerstag, 18. Juni 2009
    7
    Integrated Systems Laboratory
  • 8. Design procedure
    Donnerstag, 18. Juni 2009
    8
    Integrated Systems Laboratory
  • 9. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    9
    Integrated Systems Laboratory
  • 10. Reasons for using MATLAB simulations:
    Filter type:
    Chebyshev
    Butterworth
    Elliptic
    Bessel
    Filter order determination
    Donnerstag, 18. Juni 2009
    10
    Integrated Systems Laboratory
    Methods used:
    3GPP test cases simulations with a predefined maximal residual blocker
    Error Vector Magnitude simulations
  • 11. Filter type
    Elliptic
    Chebyshev
    Butterworth
    Bessel
    Butterworth Chebyshev
    Donnerstag, 18. Juni 2009
    11
    Integrated Systems Laboratory
    increasing passband phase linearity
    decreasing filter order requirements
  • 12. LTE test cases: maximal residual blocker
    Donnerstag, 18. Juni 2009
    12
    Integrated Systems Laboratory
    Maximal residual blocker taken as 24 dB
    5th order Chebyshev filter with 0.2dB ripple in the passband
    6th order Chebyshev filter with 0.2dB ripple in the passband
  • 13. EVM simulations
    Donnerstag, 18. Juni 2009
    13
    Integrated Systems Laboratory
    QPSK signal imitating the 1.4MHz LTE signal
    EVM = 5.18%
    for fc 8% higher than the bandwidths
  • 14. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    14
    Integrated Systems Laboratory
  • 15. Leapfrog filter implementation
    Required: an active filter to be implemented on an IC
    Cascade of 1st/2nd order networks
    Multiple loop feedback
    LC Ladder simulation
    Leapfrog structure
    derived from an LC ladder and
    takes the form of a multiple loop feedback
    Donnerstag, 18. Juni 2009
    15
    Integrated Systems Laboratory
  • 16. Standard derivationofLeapfrogtopology
    Donnerstag, 18. Juni 2009
    16
    Integrated Systems Laboratory
    LC ladder
    Leapfrog topology
    Signal flow graph
  • 17. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    17
    Integrated Systems Laboratory
  • 18. Implementation of resistors and capacitors
    Resistor network
    Capacitor network
    Donnerstag, 18. Juni 2009
    18
    Integrated Systems Laboratory
  • 19. Unit resistance/capacitance
    Have resistance and capacitances derived from the same unit value
    Problematic for both feed-forward (Rf) and feedback (Rb) resistors:
    Either found to be too big for sensible IC implementation
    Or the values were never ideally multiples
    Also, some other solutions required too large capacitors
    Donnerstag, 18. Juni 2009
    19
    Integrated Systems Laboratory
  • 20. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    20
    Integrated Systems Laboratory
  • 21. Derivation of op-amp specifications
    Simulated with gain bandwidth product (GBW)
    Required op-amp with GBW of at least 500MHz
    Phase Margin (PM)
    Decided on a value of 60 ◦ for stability reasons
    Donnerstag, 18. Juni 2009
    21
    Integrated Systems Laboratory
    Group delay
    Filter response
  • 22. Chosen design
    Donnerstag, 18. Juni 2009
    22
    Integrated Systems Laboratory
    Banu M., Khoury J.M., Tsividis J., Fully differential Operational Amplifier with Accurate Output Balancing, IEEE Journal of Solid-State Circuits, vol. 23, no. 6, December 1988.
  • 23. Transfer function derivations
    Differential amplifier poles
    Common mode amplifier (CMA) poles
    Donnerstag, 18. Juni 2009
    23
    Integrated Systems Laboratory
  • 24. Alterations to the circuit
    Donnerstag, 18. Juni 2009
    24
    Integrated Systems Laboratory
    Transfer functions helped to explain:
    Instability of the CMA
    Choice of compensation capacitance and resistance
    As a result, minor alterations:
    Addition of capacitance between the pMOS current mirror node and rail
    Decision to keep only one feedback connection from the CMA
  • 25. Final circuit
    Donnerstag, 18. Juni 2009
    25
    Integrated Systems Laboratory
  • 26. Resultant operational amplifier
    Donnerstag, 18. Juni 2009
    26
    Integrated Systems Laboratory
    GBW = 840.7MHz PM = 64.6 ◦
  • 27. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    27
    Integrated Systems Laboratory
  • 28. Resultant filter
    Donnerstag, 18. Juni 2009
    28
    Integrated Systems Laboratory
    The 1.4 MHz, 10 MHz and 20 MHz LTE bandwidth
  • 29. Third order intercept point – iIP3
    Donnerstag, 18. Juni 2009
    29
    Integrated Systems Laboratory
    Periodic steady state analysis is Cadence
  • 30. Compression point of the wanted signal
    Again, periodic steady state analysis in Cadence
    iCP is -44.20 dBm
    Donnerstag, 18. Juni 2009
    30
    Integrated Systems Laboratory
  • 31. Noise and maximal blocker revisited (black text)
    Theoretical noise
    20 MHz LTE:
    1.4 MHz LTE:
    In practice, Cadence simulation showed 8.59 and 31.60
    Relative attenuation of wanted signal and interferer
    Donnerstag, 18. Juni 2009
    31
    Integrated Systems Laboratory
  • 32. Overview of the presentation
    Long Term Evolution (LTE) & Baseband filter requirements
    MATLAB simulations
    Filter topology
    Implementation in Cadence software
    Operational amplifier design
    Final filter simulations
    Conclusions and possible improvements
    Donnerstag, 18. Juni 2009
    32
    Integrated Systems Laboratory
  • 33. Summary of the work
    Donnerstag, 18. Juni 2009
    33
    Integrated Systems Laboratory
  • 34. Conclusions, possible improvements
    The filter follows the specifications, but…
    There is always room for improvement:
    Reduction of current consumption
    Unit resistance
    Simulations with an actual OFDMA signal would be welcome
    Donnerstag, 18. Juni 2009
    34
    Integrated Systems Laboratory
  • 35. Final Year Project at ETH
    Many thanks to all members of the
    Integrated Systems Laboratory.