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

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.