Presented by: Shreyas Sen June 11, 2008. Paper 27.3 , DAC 08.

1. Pro-VIZOR:Process Tunable Virtually Zero Margin Low Power Adaptive RF for Wireless Systems Shreyas Sen, Vishwanath Natarajan, Rajarajan Senguttuvan, Abhijit Chatterjee Georgia Institute of Technology Presented by: Shreyas Sen June 11,2008. Paper 27.3, DAC 08.

2. Motivation • Traditional wireless circuits Designed for worst case environmental variations and worst case process corners. Involves significant built in design margin. • Waste of performance (i.e. power) under favorable condition. Goal • SAVE POWERby adapting to environment and process.

3. Baseband Baseband Transmitter Receiver Receiver Transmitter Process Tunable Virtually Zero Margin RF Worst Case System Design Adaptive System Design Base Station (BS) Mobile Station (MS) Varying channel Save Power Process adaptability

4. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

5. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

6. VIZOR: Receiver Adaptation metric is a measure of the quality of the received signal.

7. BER = V2 Adaptation metric selection Reception Channel Transmission Baseband & RF Baseband & RF 010010 010010 Demodulation Modulation • Error Vector Magnitude (EVM) • Bit Error Rate (BER) I Error in the received symbol 2 e V2 1 V1 Ne = Number of errors R = Data rate t = Test time e = - V1 Q Can be calculated in real-time Cannot be calculated in real-time

8. Adaptation Metric: EVM vs BER Channel effects • Multi-path effects • Interference • Path loss • Noise EVM vs. BER Hence EVM is chosen as the real-time adaptation metric.

9. VIZOR Operation : Constellation Normal operation VIZOR operation EVM=35% EVM=22% Channel 1 • VIZOR operation • Operation close to • error threshold Channel 2 Save power EVM=8% EVM=14%

10. Receiver hardware and Power Savings

11. Power vs. Performance locus Increasing performance P Performance Minimum power, maximum EVM locus Tuning knob 1 Tuning Knob 2 Tuning knob: Vdd, Vbias of different RF block, ADC wordsize

12. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

13. VIZOR: Transmitter Baseband DSP Power Management Channel Quality Drain Bias Control Law Gate Bias DAC Dynamic RF PA PAR Reduction Adaptive Mixer

14. Original Signal Companded Signal; PAR reduction = 5.6 dB Companding and PAR reduction Pout P1dB 5.6 dB Pin PA characteristics OFDM: High Peak to Average Ratio (PAR). Makes Power Amplifier (PA) inefficient due to high back off required. 3 dB back off halves a PA efficiency.

15. Compliance to BER threshold PAR Reduction BER moderate channel BER good channel µ : Companding Factor EVM moderate channel EVM good channel

16. PAR reduction under different channels BPSK 64 QAM 16 QAM QPSK 5% 14% 35% *EVM= 6.3 dB 7.25 dB Good Channel EVM=5.15 % Good Channel EVM=15.5 % 5.6 dB 4 dB Moderate Channel EVM=8.5 % Moderate Channel EVM=24.4 % +EVM threshold 16 QAM =12.5 % +EVM threshold QPSK=33 % *From SNR boundaries (IEEE) +From BER threshold

17. Transmitter Power Savings Pdc static PA 3X

18. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

19. Effect of Process variation Increasing performance P Performance PROCESS Minimum power, maximum EVM locus Tuning knob 1 Effect of process variations: run RF BIST to pick the “Right” locus under variation. Tuning Knob 2

20. Process Sensing *V. Natarajan et. al. “ACT: Adaptive Calibration test….” VTS 08

21. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

22. Np process instances DUT Measure Power sensitivities Measure RX process Measure TX process Find BEST MATCH with available Npprocess instances For each process instance Gain, IIP3, P/  Vdd, P/  Vb .. Gain, IIP3, P/  Vdd, P/  Vb Process tuning Production Test/Tuning Phase Design Phase Process Sensing & Process Tuning Performance Process 1 Process 2 Performance Process Np Process adaptation metric for Np instances Locus corresponding to the BEST MATCH (LMS) Minimum power & Maximum EVM locus for Np instances Perform environmental Adaptation during run time

23. Power Savings through process tuning Without tuning Without tuning With tuning Receiver Power (W) Channel Index

24. Outline • Environment Adaptability in Transceivers • - Adaptive RF receivers. • - Adaptive RF transmitters. • Process Adaptability • -Process Sensing Using Test. • -Tuning for process variation. • Experimental Results

25. VIZOR system VIZOR TX and RX

26. Runtime experimental results: Receiver Power consumption decreasing EVM increasing OFDM signal

27. System in Operation

28. Conclusion • Environment Adaptability allows transceiver operation with very less built in design margin. (i.e. Virtually Zero Margin) • - Saves significant power under favorable environmental condition. • - 3X transmitter and 4X receiver power savings could be achieved. • Process Adaptability makes this adaptation near optimal even under process variation. Significant increase in battery life.

29. Questions ?

30. Baseband Baseband Transmitter Receiver Receiver Transmitter 0: EVM > EVMthreshold 1: EVM < EVMthreshold 1 bit Encoded in MAC Header Environment Adaptability: Overview Worst Case System Design Adaptive System Design Base Station (BS) Mobile Station (MS) Varying channel conditions Power saved in MS increasing battery life

31. VIZOR Optimizer Zero-margin operation – Save more power under favorable conditions (good channel)!! Optimization • Generate different • Channels • Interference • Multi-path • Noise • Identify tunable • Parameters • LNA supply • LNA bias • Mixer supply • Mixer bias • ADC word size • Optimal values of • tunable parameters for • Different channel • conditions • Different modulations (data rates) Set EVM threshold for satisfactory operation

32. PAR reduction and compliance to BER threshold

33. Process Sensing: Adaptive Calibration Test Tuning control Tx Module BASEBAND DSP Tunedoutput Transmitter spec estimation Embedded sensor Baseband response Loopback hardware Receiver spec estimation Rx Module • Estimate transmitter specs • Tune the transmitter – Hardware + software knobs • Process variation, non-idealities • Estimate Receiver specs

34. Appendix: ACT: Tuning technique Software knobs Tuned output System under consideration Test input Hardware knob control Knob Controller Control law Envelope Detector Actual response Golden • Control law: LS error between golden and actual • Hardware knobs: Power supply, bias control • Software knobs: Reverse distortion polynomials

35. Process estimation accuracy Transmitter parameter estimation Receiver parameter estimation without transmitter tuning Receiver parameter estimation after transmitter tuning