1. All Rights Reserved © Alcatel-Lucent 2006, 2008 Enabling high efficiencies Digital signal conditioning in modern RF transmitters Thomas BOHN June 2008

2. All Rights Reserved © Alcatel-Lucent 2006, 2008 2 | Enabling high efficiencies | June 2008 Agenda 1.Overview 2.Peak-to-Average-Power-Ratio (PAPR) Reduction 3.Power amplifier linearisation 4.Image suppression and DC-offset compensation 5.Conclusions

3. All Rights Reserved © Alcatel-Lucent 2006, 2008 3 | Enabling high efficiencies | June 2008 1 Overview Architecture of a modern RF transmitter

4. All Rights Reserved © Alcatel-Lucent 2006, 2008 4 | Enabling high efficiencies | June 2008 Transmitter architecture  Digital-in analogue-out RF amplifier –Signal conditioning right in front of the analogue PA chain  Easiest (cheapest) possible analogue design  Highest possible power efficiency ClippingPredistortion Digital-Module D/A- conv. Conversion-Module Image- & Carrier- Suppr. PA chain PA-Module Wide band Down- conversion A/D- conv. Time Delay Compens. Modulation & Wide band Up-conversion

5. All Rights Reserved © Alcatel-Lucent 2006, 2008 5 | Enabling high efficiencies | June 2008 2 PAPR Reduction

6. All Rights Reserved © Alcatel-Lucent 2006, 2008 6 | Enabling high efficiencies | June 2008 PAPR Reduction What is PAPR reduction ? Clipping ! Reducing signal power peaks to a certain threshold –increasing the EVM Power @ Soft ClippingPower @ Hard Clipping

7. All Rights Reserved © Alcatel-Lucent 2006, 2008 7 | Enabling high efficiencies | June 2008 PAPR Reduction Why do we perform PAPR reduction ?  PA has to be designed for the signal peak  driving into saturation produces intermodulation  PA delivers an average output power  Black:  PAPR: 10.9 dB  43dBm (12% efficiency)  Blue:  PAPR: 5.5 dB  45.2 dBm (16% efficiency) Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes)

8. All Rights Reserved © Alcatel-Lucent 2006, 2008 8 | Enabling high efficiencies | June 2008 3 PA linearisation Digital predistortion for higher efficiencies

9. All Rights Reserved © Alcatel-Lucent 2006, 2008 9 | Enabling high efficiencies | June 2008 PA linearisation How to linearise a PA ? With (digital) predistortion ! Principle of PA linearisation:  Amplitude distortions can be compensated up to the PA’s saturation point  Phase distortion can be compensated for arbitrary input amplitudes

10. All Rights Reserved © Alcatel-Lucent 2006, 2008 10 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the PA Complex baseband model for the PA:  Quasi-static nonlinear model (static in the complex baseband)  AM-AM and AM-PM distortions  Complex gain model: –x, y:Complex envelope of RF input and output signal –  PA (|x|)Complex gain depending on the magnitude of the input signal –G(|x|)Magnitude of the gain – (|x|)Phase shift –a i Complex coefficients

11. All Rights Reserved © Alcatel-Lucent 2006, 2008 11 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the linearisation PA linearisation with inverse PA characteristic:  Linear PA transfer characteristics up to saturation point: –x, y:Complex envelope of RF input and output signal – Constant real gain  Linearised PA transfer characteristics up to saturation point: –G(|x|)Magnitude of the gain – (|x|)Phase shift –a i Complex coefficients

12. All Rights Reserved © Alcatel-Lucent 2006, 2008 12 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the non-linearity (1) The intervals over the input signal power: P out  PA transfer characteristic just for illustration  The “r” depicts the power of the current input sample in the 2 nd interval r1 r r2 r3 (max.) P IN

13. All Rights Reserved © Alcatel-Lucent 2006, 2008 13 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the non-linearity (2) In the interval :

14. All Rights Reserved © Alcatel-Lucent 2006, 2008 14 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the non-linearity (3) Block diagram of the PIPOP:   PD calculation for each input sample  Predistortion of each input sample  Issues to ease the implementation:  f(x) (= 1 ?)  Base functions granularity  Interval widths (equal ?)

15. All Rights Reserved © Alcatel-Lucent 2006, 2008 15 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the adaptation Coefficient update formula:  For each of the four ( 0  k  3) coefficients within one interval  c- coefficient   - step width of the algorithm   - hermite base function  y’*- complex conjugated PD output signal (y’ is the delayed y)  e- error (y’ - w)   - PD gain

16. All Rights Reserved © Alcatel-Lucent 2006, 2008 16 | Enabling high efficiencies | June 2008 PA linearisation Digital predistortion - the system Schematic view:

17. All Rights Reserved © Alcatel-Lucent 2006, 2008 17 | Enabling high efficiencies | June 2008 PA linearisation Efficiency and spectral distortions in case of 1 carrier UMTS (1)  Blue: 46.0 dBm  18.2% efficiency  out of spec  Black: 43.0 dBm  11.9% efficiency  in spec  Green: 40.6 dBm  8.35% efficiency  in spec Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)

18. All Rights Reserved © Alcatel-Lucent 2006, 2008 18 | Enabling high efficiencies | June 2008 PA linearisation Efficiency and spectral distortions in case of 1 carrier UMTS (2)  Green: 46.0 dBm  18.2% efficiency  out of spec  Blue: 46.0 dBm  memory-less PD  in spec with 5dB margin Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)

19. All Rights Reserved © Alcatel-Lucent 2006, 2008 19 | Enabling high efficiencies | June 2008 PA linearisation Efficiency and spectral distortions in case of 1 carrier UMTS (3)  Green: 47.0 dBm  20.4% efficiency  out of spec  Blue: 47.0 dBm  memory-less PD  in spec Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)

20. All Rights Reserved © Alcatel-Lucent 2006, 2008 20 | Enabling high efficiencies | June 2008 PA linearisation Efficiency and spectral distortions in case of 4 carrier UMTS (1)  Blue: 46.0 dBm  17.8% efficiency  out of spec  Black: 31.7 dBm  1.2% efficiency  out of spec  Green: 25.5 dBm  0.3% efficiency  out of spec Set-up: PA rated for 46.0 dBm; 4 x 3GPP test model 1 (64 codes, 5.5 dB PAPR)

21. All Rights Reserved © Alcatel-Lucent 2006, 2008 21 | Enabling high efficiencies | June 2008 PA linearisation Efficiency and spectral distortions in case of 4 carrier UMTS (2)  Green: 46.0 dBm  17.8% efficiency  out of spec  Black  memory-less PD  out of spec  Green  PD with memory effect compensation  in spec Set-up: PA rated for 46.0 dBm; 4 x 3GPP test model 1 (64 codes, 5.5 dB PAPR)

22. All Rights Reserved © Alcatel-Lucent 2006, 2008 22 | Enabling high efficiencies | June 2008 4 Image suppression and DC-offset compensation

23. All Rights Reserved © Alcatel-Lucent 2006, 2008 23 | Enabling high efficiencies | June 2008 Image suppression and DC-offset compensation Zero-IF transmitter and efficiency  Simple architecture with small amount of analogue components: –1 analogue quadrature modulator (QM, also known as IQ modulator) –1 local oscillator (LO)  Half of the signal bandwith @ DACs, Performance of DACs is best around 0 Hz  No frequency selective filters  But: QM has imperfections resulting in DC feed trough and image DC I DC Q r(t) 90°+p k QM Modulator DAC v LO(t) z(t) I Q

24. All Rights Reserved © Alcatel-Lucent 2006, 2008 24 | Enabling high efficiencies | June 2008 Image suppression and DC-offset compensation Spectral distortions in case of 1 carrier UMTS (1)  Green: 46.0 dBm  18.2% efficiency  out of spec –ACP both –ALT low  Blue:  memory-less PD  out of spec –DC @ ACP low –Image @ ALT low Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR) @ 5MHz

25. All Rights Reserved © Alcatel-Lucent 2006, 2008 25 | Enabling high efficiencies | June 2008 Image suppression and DC-offset compensation Spectral distortions in case of 1 carrier UMTS (2)  Green : 46.0 dBm  18.2% efficiency  out of spec  Black:  memory-less PD  out of spec  Blue:  memory-less PD  Image suppression and DC-offset compensation  in spec Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR) @5MHz

26. All Rights Reserved © Alcatel-Lucent 2006, 2008 26 | Enabling high efficiencies | June 2008 5 Conclusion

27. All Rights Reserved © Alcatel-Lucent 2006, 2008 27 | Enabling high efficiencies | June 2008 Conclusion  We are working hard on increasing the energy efficiency of our products !  What about the energy efficiency of our workshop ?

28. All Rights Reserved © Alcatel-Lucent 2006, 2008 28 | Enabling high efficiencies | June 2008 www.alcatel-lucent.com