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Power Amplifier Nonlinearity Estimation and Predistortion with Correlation Techniques Mingyuan Li, Ian Galton, Larry Larson, Peter Asbeck University of California, San Diego La Jolla, CA 92093-0407,Outline,Nonlinearity extraction in frequency and time domain Correlation techniques for nonlinearity estimation Mathematical analysis and simulation results Application in adaptive predistortion and measured results Summary and conclusion,AM-AM and AM-PM nonlinearity,Measurement of Intersils ISL3990 Dual Band PA,Look Up Table behavioral model,Behavioral model,Complex polynomial curve fitting model,Single tone and two-tone power sweep measurement,Gain and phase vs input power,Gain and phase values vs envelope amplitude r(t),Pro: Simple to characterize and analyze nonlinearity Con: 1. Not actual signal 2. Cant test during normal operation conditions,Intermodulations vs input power,Pro: Actual signal, test during PA operation Con: 1. High resolution and speed ADC 2. Large memory 3. Considerable DSP,Time-domain CDMA envelope test,Gain vs. Pin using time-domain captured data,Phase vs. Pin using time-domain captured data,Vout (red) vs. vin(blue) (a) real part (b) imaginary part,(a),(b),Assess nonlinearity in adaptive predistortion,Correlation techniques for nonlinearity estimation,Basic idea,Nonlinearity comes from output with 3rd,5th order dependency on input. Create test signal which also has 3rd,5th order dependency on input. Extract nonlinearity by proper correlation of output and test signal,Advantages Actual signal in real operation conditions Low hardware and power consumption,Stest is uncorrelated with linear(Vin) Stest is correlated with nonliear(Vin),Correlation mathematical analysis,Assumptions Quasi-memoryless Polynomial model truncated at the 5th order,Application to IS-95 forward link transmitter,I,XI,Complex power series analysis,Real correlation value,Imag correlation value,Power correlation value,Polynomial coefficients extraction by correlation,Comparison of correlation with other techniques,Construct AM_AM and AM_PM using polynomial coefficients derived by correlations,Different order with different slopes,Comparison of two-tone and correlation,Correlation experimental measurements,Intersils ISL3990 PA 5 Channel PN with 48-tap FIR and Length is 217 Sampling rate is 4*1.2288MHz,(a)First order II,(b)Third order IQ,(c) Fifth order II,(d)Power correlation vs. Pin,Adaptive predistortion application,Predistortion architecture,Using the correlation extracted values P3corr and P5corr as an object function to adaptively change predistorters coefficients,Adaptive search algorithm(Hooke &Jeeves),Contour of correlation values vs. predistortion coefficients,Measurement results (1),Amplifier before predistortion is at (b3r,b3i,b5r,b5i=0) pointPin=-10dBm,3rd correlation values(dB) vs. b3,3rd correlation values(dB) vs. b5,Acpr750kHz(dBc) vs. b3,Acpr750kHz(dBc) vs. b5,ISL3990 PA P1db= -10dBm Psat=10dBm Pmax=24.5dBm,Measurement results (2),Magenta curve has larger correlation values and worse ACPR Green curve has smaller correlation values and better ACPR ACPR difference of 14.3dB750kHz 4.8dB1980kHz,before PD,after PD,Magenta before PD, Green after PD Pin=-10dBm,Summary and conclusion,Simple correlation techniques have been used to estimate nonlinearity Simulation and measurement results show promise of technique Application in forward link adaptive predistortion transmitter was shown experimentally Optimization algorithm was developed to adaptively change coefficients For future, expect that simple analog correlation circuit can be implemented and memory effects can be considered,
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