Characterization and Compensation of Non-Linear Effects in Components. Dr. Florian Ramian

Transcription

1 Characterization and Compensation of Non-Linear Effects in Components Dr. Florian Ramian

2 Agenda ı Introduction: What Is a Non-Linear Device ı Characterization of Non-Linear Devices Characterization Parameters Traditional CW level swept measurement Modulated Measurement ı Compensation of Linear and Non-Linear Effects Equalizer Digital Predistortion (DPD) ı Summary A&D Symposium 2

3 Introduction ı What is a non-linear device? DUT A&D Symposium 3

4 Agenda ı Introduction: What Is a Non-Linear Device ı Characterization of Non-Linear Devices Characterization Parameters Traditional CW level swept measurement Modulated Measurement ı Compensation of Linear and Non-Linear Effects Equalizer Digital Predistortion (DPD) ı Summary A&D Symposium 4

5 Characterization of Non-Linear Devices Characterization Parameters ı Distortion: AM/AM, AM/PM ı Gain ı Compression A&D Symposium 5

6 Characterization of Non-Linear Devices CW Stimulus ı Measurement of amplitude dependent effects sweep input amplitude ı Level swept CW signal A&D Symposium 6

7 Measurement Instruments ı VNA ı Signal Generator / Signal Analyzer CW Measurement Modulated Measurement A&D Symposium 7

8 Modulated Measurements Distortion CW distortion measurement describes DUT behavior, but does not indicate whether the DUT will distort the modulated signal significantly Line Width: Memory Effect Stimulus: Ramp AM/AM is a line as expected Stimulus: Modulated signal AM/AM is a cloud A&D Symposium 8

9 Modulated Measurements Gain Measurement ı Gain at specified frequency / level can be precisely measured with CW 2 GHz / 0 dbm input level: 17.9 db ı But: a real word signal looks like this A&D Symposium 9

10 Modulated Measurements Gain Measurement ı Measurement on a modulated signal is equivalent to multiple gain measurements across the input power range A&D Symposium 10

11 Modulated Measurements Principle Data / Control Connection (LAN) VSG (play waveform) DUT RF connection VSA (capture RF signal) Measured signal (Meas) Reference signal (Ref) DSP A&D Symposium 11

12 Measurement Principle (DSP) DSP Measured signal (Meas) Reference signal (Ref) Sync Synchronized Meas signal Reference signal (Ref) Compare Gain, Distortion, EVM, A&D Symposium 12

13 Modulated Measurements All Characterization Results from a Single Measurement ACLR Numeric Results, modulation accuracy: EVM I/Q Imbalance Distortion A&D Symposium 13

14 Modulated Measurements Modulation Accuracy ı EVM Measurement based on a sample-bysample comparison ı Depending on oversampling and distortion of DUT, EVM may differ from demodulation EVM measurements A&D Symposium 14

15 Agenda ı Introduction: What Is a Non-Linear Device ı Characterization of Non-Linear Devices Characterization Parameters Traditional CW level swept measurement Modulated Measurement ı Compensation of Linear and Non-Linear Effects Equalizer Digital Predistortion (DPD) ı Summary A&D Symposium 15

16 Compensation of Linear and Non-Linear Effects ı Frequency response ı Non-linear effects A&D Symposium 16

17 Compensation of Frequency Response Equalizer ı Frequency response can be compensated by a filter, often referred to as equalizer ı Flattened magnitude / phase vs. frequency Equalizer A&D Symposium 17

18 Compensation of Non-Linearities Digital Predistortion (DPD) EVM DPD ACLR A&D Symposium 18

19 Model Based DPD Characterization of DUT Apply (inverse) model to signal, i.e. in the TX chipset DUT TX Chipset BB z 1 n DUT Inverse A&D Symposium 19

20 Waveform Based DPD DPD on Individual Samples ı Each sample is predistorted to a new value ı Since each sample is individually predistorted, any memory effect can be compensated Original Signal Measured Signal Predistorted Signal samples of equal level may have different predistorted levels compensation is limited to measured bandwidth A&D Symposium 20

21 Waveform Based DPD Iterative Approach Measure DUT Upload new WV to SigGen Compensate each individual sample A&D Symposium 21

22 Agenda ı Introduction: What Is a Non-Linear Device ı Characterization of Non-Linear Devices Characterization Parameters Traditional CW level swept measurement Modulated Measurement ı Compensation of Linear and Non-Linear Effects Equalizer Digital Predistortion (DPD) ı Summary A&D Symposium 22

23 Summary ı Linear and non-linear effects contribute significantly to signal quality ı Non-linear effects may vary significantly, depending on the stimulus (input signal) ı Characterization of these effects is vital to understand limitations to system design ı With effects understood, compensation methods can be contemplated ı R&S FSW-K18 Amplifier Measurement Personality characterizes signal and evaluated different compensation methods A&D Symposium 23