Piotr Gawlicki MEng Thesis

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

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Piotr Gawlicki MEng Thesis

  1. 1. Design of a Programmable Baseband Filter for an LTE Direct Conversion Receiver<br />by Piotr Gawlicki <br />
  2. 2. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />2<br />Integrated Systems Laboratory<br />
  3. 3. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />3<br />Integrated Systems Laboratory<br />
  4. 4. Evolution of telecommunications standards<br />Donnerstag, 18. Juni 2009<br />4<br />Integrated Systems Laboratory<br />GSM<br />?<br />W-CDMA<br />Analog Mobile Phone Service (AMPS)<br />
  5. 5. LTE specifications<br />Variable bandwidth:<br />1.4MHz , 3MHz , 5MHz , 10MHz , 15MHz , 20MHz<br />Two modulation schemes:<br />Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink<br />Single Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink<br />Anticipated speed of data transfer:<br />100 Mbit/s in the downlink<br />50 Mbit/s in the uplink<br />Donnerstag, 18. Juni 2009<br />5<br />Integrated Systems Laboratory<br />
  6. 6. Direct Conversion Receiver (DCR)<br />Baseband (BB) filter as an important on chip part of the DCR<br />Donnerstag, 18. Juni 2009<br />6<br />Integrated Systems Laboratory<br />
  7. 7. Baseband filter specifications<br />Donnerstag, 18. Juni 2009<br />7<br />Integrated Systems Laboratory<br />
  8. 8. Design procedure<br />Donnerstag, 18. Juni 2009<br />8<br />Integrated Systems Laboratory<br />
  9. 9. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />9<br />Integrated Systems Laboratory<br />
  10. 10. Reasons for using MATLAB simulations:<br />Filter type:<br />Chebyshev<br />Butterworth<br />Elliptic<br />Bessel<br />Filter order determination<br />Donnerstag, 18. Juni 2009<br />10<br />Integrated Systems Laboratory<br />Methods used:<br />3GPP test cases simulations with a predefined maximal residual blocker<br />Error Vector Magnitude simulations<br />
  11. 11. Filter type<br />Elliptic<br />Chebyshev<br />Butterworth<br />Bessel<br /> Butterworth Chebyshev<br />Donnerstag, 18. Juni 2009<br />11<br />Integrated Systems Laboratory<br />increasing passband phase linearity<br />decreasing filter order requirements<br />
  12. 12. LTE test cases: maximal residual blocker<br />Donnerstag, 18. Juni 2009<br />12<br />Integrated Systems Laboratory<br />Maximal residual blocker taken as 24 dB<br />5th order Chebyshev filter with 0.2dB ripple in the passband<br /> 6th order Chebyshev filter with 0.2dB ripple in the passband<br />
  13. 13. EVM simulations<br />Donnerstag, 18. Juni 2009<br />13<br />Integrated Systems Laboratory<br /> QPSK signal imitating the 1.4MHz LTE signal <br />EVM = 5.18%<br />for fc 8% higher than the bandwidths<br />
  14. 14. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />14<br />Integrated Systems Laboratory<br />
  15. 15. Leapfrog filter implementation<br />Required: an active filter to be implemented on an IC<br />Cascade of 1st/2nd order networks<br />Multiple loop feedback<br />LC Ladder simulation<br />Leapfrog structure <br />derived from an LC ladder and <br />takes the form of a multiple loop feedback<br />Donnerstag, 18. Juni 2009<br />15<br />Integrated Systems Laboratory<br />
  16. 16. Standard derivationofLeapfrogtopology<br />Donnerstag, 18. Juni 2009<br />16<br />Integrated Systems Laboratory<br />LC ladder<br />Leapfrog topology<br />Signal flow graph<br />
  17. 17. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />17<br />Integrated Systems Laboratory<br />
  18. 18. Implementation of resistors and capacitors <br />Resistor network <br />Capacitor network<br />Donnerstag, 18. Juni 2009<br />18<br />Integrated Systems Laboratory<br />
  19. 19. Unit resistance/capacitance<br />Have resistance and capacitances derived from the same unit value<br />Problematic for both feed-forward (Rf) and feedback (Rb) resistors:<br />Either found to be too big for sensible IC implementation<br />Or the values were never ideally multiples<br />Also, some other solutions required too large capacitors<br />Donnerstag, 18. Juni 2009<br />19<br />Integrated Systems Laboratory<br />
  20. 20. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />20<br />Integrated Systems Laboratory<br />
  21. 21. Derivation of op-amp specifications<br />Simulated with gain bandwidth product (GBW)<br />Required op-amp with GBW of at least 500MHz<br />Phase Margin (PM)<br /> Decided on a value of 60 ◦ for stability reasons<br />Donnerstag, 18. Juni 2009<br />21<br />Integrated Systems Laboratory<br />Group delay<br />Filter response<br />
  22. 22. Chosen design<br />Donnerstag, 18. Juni 2009<br />22<br />Integrated Systems Laboratory<br />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. <br />
  23. 23. Transfer function derivations<br />Differential amplifier poles<br />Common mode amplifier (CMA) poles<br />Donnerstag, 18. Juni 2009<br />23<br />Integrated Systems Laboratory<br />
  24. 24. Alterations to the circuit<br />Donnerstag, 18. Juni 2009<br />24<br />Integrated Systems Laboratory<br />Transfer functions helped to explain:<br />Instability of the CMA<br />Choice of compensation capacitance and resistance<br />As a result, minor alterations:<br />Addition of capacitance between the pMOS current mirror node and rail<br />Decision to keep only one feedback connection from the CMA<br />
  25. 25. Final circuit<br />Donnerstag, 18. Juni 2009<br />25<br />Integrated Systems Laboratory<br />
  26. 26. Resultant operational amplifier<br />Donnerstag, 18. Juni 2009<br />26<br />Integrated Systems Laboratory<br />GBW = 840.7MHz PM = 64.6 ◦<br />
  27. 27. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />27<br />Integrated Systems Laboratory<br />
  28. 28. Resultant filter<br />Donnerstag, 18. Juni 2009<br />28<br />Integrated Systems Laboratory<br />The 1.4 MHz, 10 MHz and 20 MHz LTE bandwidth<br />
  29. 29. Third order intercept point – iIP3<br />Donnerstag, 18. Juni 2009<br />29<br />Integrated Systems Laboratory<br />Periodic steady state analysis is Cadence<br />
  30. 30. Compression point of the wanted signal<br />Again, periodic steady state analysis in Cadence<br />iCP is -44.20 dBm<br />Donnerstag, 18. Juni 2009<br />30<br />Integrated Systems Laboratory<br />
  31. 31. Noise and maximal blocker revisited (black text)<br />Theoretical noise<br />20 MHz LTE:<br />1.4 MHz LTE:<br />In practice, Cadence simulation showed 8.59 and 31.60<br />Relative attenuation of wanted signal and interferer<br />Donnerstag, 18. Juni 2009<br />31<br />Integrated Systems Laboratory<br />
  32. 32. Overview of the presentation<br />Long Term Evolution (LTE) & Baseband filter requirements<br />MATLAB simulations<br />Filter topology<br />Implementation in Cadence software<br />Operational amplifier design<br />Final filter simulations<br />Conclusions and possible improvements<br />Donnerstag, 18. Juni 2009<br />32<br />Integrated Systems Laboratory<br />
  33. 33. Summary of the work<br />Donnerstag, 18. Juni 2009<br />33<br />Integrated Systems Laboratory<br />
  34. 34. Conclusions, possible improvements<br />The filter follows the specifications, but…<br />There is always room for improvement:<br />Reduction of current consumption<br />Unit resistance<br />Simulations with an actual OFDMA signal would be welcome<br />Donnerstag, 18. Juni 2009<br />34<br />Integrated Systems Laboratory<br />
  35. 35. Final Year Project at ETH<br />Many thanks to all members of the <br />Integrated Systems Laboratory. <br />

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