Presentation on Digital Predistortion of Power Amplifiers - Agilent ...

More documents

Recommendations

Info

The cartesian feedback technique [1] has the virtue of simplicity; the amplifier input complex envelope is proportional to the difference between the desired and measured amplifier output. This negative feedback technique is constrained in the amount of reduction in distortion achievable. Both the linearity as well as the bandwidth are critically dependent on the feedback loop delay. The negative feedback gain adjusts the level of nonlinear distortion. Another issue is that of stability, where precise adjustment is required of the RF phase shifter. Digital Predistortion - 11
Digital Predistortion - 12 Complex Vector Mapping LUT Digital Domain Analog Domain Data Modulating Signal Generator V m (t) V d (t) D A C Quadrature Modulator Power Amplifier RAM Look-up Table V c (t) Local Oscillator Delay 1/a phase shift V e (t) A D C Quadrature Demodulator Delay Adjust V a (t) Digital Predistortion of Power Amps June, 01 Page 12 The complex vector mapping LUT [6] approach compares the measured signal Va(t) with the reference signal Vm(t), the resultant error signal is used to update the RAM Look-Up Table. There exists some delay in the feedback path that needs to be compensated for by delaying the reference signal before a comparison is made. The delay adjusting circuit can use the modulation characteristics to continuously track the delay . Typically is the delay is controlled to within 1/64 th of a symbol duration this will keep sufficient linearization. This technique also requires a phase shifter in the feedback path for stability in the adaptation update and tends to slow the convergence time. This particular configuration uses the linear convergence approach where “a” is the updating gain parameter. The compensating vectors Vc(t) are stored in the RAM look-up table and indexed by the instantaneous input vectors. Thus the requirement for a large random access memory for storing all the possible input vector states. Typically a 10 bit A/D and D/A is sufficient for achieving -60 dBc intermodulation levels.
Page 1 and 2: Agilent EEsof EDA This document is
Page 3 and 4: About the Author Shawn P. Stapleton
Page 5 and 6: Digital Predistortion - 4 Introduct
Page 7 and 8: Digital Predistortion - 6 Power Amp
Page 9 and 10: Digital Predistortion - 8 Digital P
Page 11: Design Techniques Digital Predistor
Page 15 and 16: The complex gain function F{x} is i
Page 17 and 18: Digital Predistortion - 16 ADS RF P
Page 19 and 20: Digital Predistortion - 18 ADS Digi
Page 21 and 22: Digital Predistortion - 20 Complex
Page 23 and 24: Digital Predistortion - 22 Feedback
Page 25 and 26: Digital Predistortion - 24 Clock Ti
Page 27 and 28: Digital Predistortion - 26 Optimize
Page 29 and 30: Summary Digital Predistortion ● A
Page 31 and 32: Digital Predistortion - 30 Resource
Page 33: For more information about Agilent

Presentation on Digital Predistortion of Power Amplifiers - Agilent ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?