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Piotr Gawlicki MEng Thesis
 

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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    Piotr Gawlicki MEng Thesis Piotr Gawlicki MEng Thesis Presentation Transcript

    • Design of a Programmable Baseband Filter for an LTE Direct Conversion Receiver
      by Piotr Gawlicki
    • 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
    • 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
    • Evolution of telecommunications standards
      Donnerstag, 18. Juni 2009
      4
      Integrated Systems Laboratory
      GSM
      ?
      W-CDMA
      Analog Mobile Phone Service (AMPS)
    • 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
    • Direct Conversion Receiver (DCR)
      Baseband (BB) filter as an important on chip part of the DCR
      Donnerstag, 18. Juni 2009
      6
      Integrated Systems Laboratory
    • Baseband filter specifications
      Donnerstag, 18. Juni 2009
      7
      Integrated Systems Laboratory
    • Design procedure
      Donnerstag, 18. Juni 2009
      8
      Integrated Systems Laboratory
    • 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
    • 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
    • Filter type
      Elliptic
      Chebyshev
      Butterworth
      Bessel
      Butterworth Chebyshev
      Donnerstag, 18. Juni 2009
      11
      Integrated Systems Laboratory
      increasing passband phase linearity
      decreasing filter order requirements
    • 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
    • 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
    • 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
    • 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
    • Standard derivationofLeapfrogtopology
      Donnerstag, 18. Juni 2009
      16
      Integrated Systems Laboratory
      LC ladder
      Leapfrog topology
      Signal flow graph
    • 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
    • Implementation of resistors and capacitors
      Resistor network
      Capacitor network
      Donnerstag, 18. Juni 2009
      18
      Integrated Systems Laboratory
    • 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
    • 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
    • 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
    • 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.
    • Transfer function derivations
      Differential amplifier poles
      Common mode amplifier (CMA) poles
      Donnerstag, 18. Juni 2009
      23
      Integrated Systems Laboratory
    • 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
    • Final circuit
      Donnerstag, 18. Juni 2009
      25
      Integrated Systems Laboratory
    • Resultant operational amplifier
      Donnerstag, 18. Juni 2009
      26
      Integrated Systems Laboratory
      GBW = 840.7MHz PM = 64.6 ◦
    • 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
    • Resultant filter
      Donnerstag, 18. Juni 2009
      28
      Integrated Systems Laboratory
      The 1.4 MHz, 10 MHz and 20 MHz LTE bandwidth
    • Third order intercept point – iIP3
      Donnerstag, 18. Juni 2009
      29
      Integrated Systems Laboratory
      Periodic steady state analysis is Cadence
    • 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
    • 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
    • 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
    • Summary of the work
      Donnerstag, 18. Juni 2009
      33
      Integrated Systems Laboratory
    • 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
    • Final Year Project at ETH
      Many thanks to all members of the
      Integrated Systems Laboratory.