Distortion and Modulation Quality for Wideband Communications Presented by: Richard Overdorf, Agilent Technologies Aerospace & Defense Symposium © 2012 Agilent Technologies Agenda • Nonlinear Distortion • Methods to Characterize Nonlinear Distortion • Two-Tone Measurements • Multitone Measurements • CCDF Measurements • Noise Power Ratio (NPR) Measurements • Making Wideband High Frequency Measurements • Making Vector Based Measurements 2 Aerospace & Defense Symposium © 2012 Agilent Technologies Linearity Concerns Signals can interact V H V H Non-linear power amp Spectral re-growth Unusable bandwidth Need to characterize 4 Aerospace & Defense Symposium © 2012 Agilent Technologies Nonlinear Distortion: Intermodulation In Out Amplifier AB Intermodulation distortion AB typical channel bandwidth 2nd order IMD 5th order IMD 2nd harmonics 3rd order IMD 5th order IMD 3rd order IMD (2A-B) 3rd harmonics (2B-A) (3A-2B) (3B-2A) (B-A) f AB 2A 2B 3A 3B 7 Aerospace & Defense Symposium © 2012 Agilent Technologies Non-Linear Distortion: Spectral Re-Growth Pt Non-Linear Effect f Pi Spectral ‘Re Growth’ 8 Aerospace & Defense Symposium © 2012 Agilent Technologies IMD and Spectral Re-Growth Pt A+A A+B B+B B+B–A A+A–B AB f B B+B–A Pt A+A–B 1st, 2rd, 3th, etc. harmonics mix together forming IMD A TOI or IP3 Pt IMD3 Fundamental IMD3 IMD3 Distortion Pi f Aerospace & Defense Symposium © 2012 Agilent Technologies Two Tone or TOI Test Advantages • Quick test • Simple to perform • Uses common test equipment • High signal to noise Disadvantages • Essentially narrow band • Requires wideband matching • Does not simulate correct loading conditions • Probably needs components to increase source to source isolation 10 Aerospace & Defense Symposium © 2012 Agilent Technologies Traditional Two-Tone Measurements PXA performance spectrum analyzer Isolator AMP LPF Combiner PSG CW signal generators + Attenuator DUT 2nd & 3rd harmonics IMD products 11 Aerospace & Defense Symposium © 2012 Agilent Technologies Three Tone Testing Advantages 5th 3rd 7th • Reasonably quick test • Simple to perform • Uses common test equipment • Better Intermodulation test Disadvantages Note: • Essentially narrow band Uses uneven spacing for tones • Requires wideband matching • Open to interpretation • Averaging required 12 Aerospace & Defense Symposium © 2012 Agilent Technologies >10 Tone Testing In practice, using analog signal sources and combining techniques proves impractical for the majority of users. Why is this? • < +20 dBm is typically maximum out of signal sources, but usually not able to use this due to distortion due to the source levelling circuits • Combiners with good port isolation have high attenuation • Use of filters and isolators creates limited flexibility • Post combiner amplification either not available or too expensive. • Cost and physical size of signal sources 13 Aerospace & Defense Symposium © 2012 Agilent Technologies Modern Multi-tone IMD Why use multi-tone test signals? • For wideband components two-tone measurement results vary depending on tone spacing • Simulate real-world operating conditions • Stress device with higher peak-to-average ratio • Test with multiple phase sets 14 Aerospace & Defense Symposium © 2012 Agilent Technologies Conventional Analog Test Stimulus Advantages of analog test approach • Well established test procedure • Common test equipment Disadvantages of analog test approach • • • • • Complicated test setup Signal parameters are not easily modified Manual tuning Difficult to generate random phase sets Equipment and capital intensive 15 Aerospace & Defense Symposium © 2012 Agilent Technologies Analog I/Q modulation vs. digital I/Q upconversion Conventional I/Q modulation Analog I and Q signals are generated using an AWG. An I/Q modulator generates the IF or RF signal AWG Analog IQ Modulator Memory X D/A ~ 90 Memory X D/A AWG Digital upconversion – I/Q modulation is performed digitally - either in real-time (in hardware) or up-front in software Memory + Mixer / Multiplier / LO X ~ 90 Memory + D/A X ~ X Digital signal Analog signal Aerospace & Defense Symposium © 2012 Agilent Technologies Vector Test Stimulus up to 1 GHz Dual LXI arbitrary waveform generator (N8241A) PXA performance spectrum analyzer (N9030A) I Q (Differential) Isolator DUT PSG vector signal generator (E8267D) 17 Aerospace & Defense Symposium © 2012 Agilent Technologies Vector Test Stimulus Advantages of vector test approach • • • • • Simple test setup and procedure Easily modify signal parameters Apply pre-distortion to improve signal quality Repeatable and accurate test results Save time and capital equipment cost Disadvantages of vector test approach • • • Available output power Carrier feed through Images 18 Aerospace & Defense Symposium © 2012 Agilent Technologies N7621A Signal Studio for Multi-tone Distortion …and After Before… Option 203 • • • • • • • Improved IMD suppression LAN/GPIB Up to 4097 tones Vary tone power Change phase settings Randomly spaced tones CCDF plot COM-based API PSG PXA • Correct with additional devices in the loop • 80 MHz correction BW (internal AWG) • 1 GHz correction BW (Agilent’s WB AWG) 19 Aerospace & Defense Symposium © 2012 Agilent Technologies Achieving the Right Signal Statistics Average t Average random power? Noise vs. pseudo noise v % Time % Time v2 P 2 Peak to average ratio Power % Time 2 CCDF signal statistic Power PSG NPR adjustable % Time 10 log 1 cdf 1 cdf Power Generator seed selectable Power CCDF 20 Aerospace & Defense Symposium © 2012 Agilent Technologies Complementary Cumulative Distribution Function Link- CCDF demo video Aerospace & Defense Symposium © 2012 Agilent Technologies Enhanced Multi-tone Measurements Tone correction Minimize test stimulus IMD… even at the output of an external power amplifier! Low IMD reduces test uncertainty E8267D PSG DUT IMD products from DUT N9030A PXA Non-linear distortion measurement 22 Aerospace & Defense Symposium © 2012 Agilent Technologies Complicated Loading Scenarios: NPR ? f Multiple signal bandwidths, amplitudes & modulation types 3rd’s, 5th’s, etc… Can add together Difficult to predict, so measure with NPR test Aerospace & Defense Symposium © 2012 Agilent Technologies NPR Measurement Overview Amplitude Amplitude Notch Bandwidth Broadband Noise Notch Notch Depth Notch Depth NPR Frequency Frequency Spectral Re-Growth Aerospace & Defense Symposium © 2012 Agilent Technologies Traditional NPR Test Setup Spectrum analyzer Up converter Noise Source IF RF LO Band stop filter DUT CW signal generator Aerospace & Defense Symposium © 2012 Agilent Technologies Traditional NPR Test Problems Notch filter shape issues Depth & bandwidth Band Stop Filter Power Filter Q requirement Cavity filters Notch Bandwidth Fixed center frequency NPR Notch Depth Noise flatness Test station correlation Frequency Aerospace & Defense Symposium © 2012 Agilent Technologies Arbitrary Waveform Generator for NPR Dual LXI arbitrary waveform generator (N8241A) PXA Performance Spectrum Analyzer (N9030A) I Q (Differential) DUT PSG Vector Signal Generator (E8267D) 27 Aerospace & Defense Symposium © 2012 Agilent Technologies Using a Vector Signal Generator and an AWG for NPR Conventional Analog NPR Stimulus Digitally Synthesized NPR Stimulus Repeatable, flat noise power, square notch…. Deeper notch with easily adjusted center frequency Up to 80 MHz bandwidth in PSG & 1 GHz with the N8241A! Aerospace & Defense Symposium © 2012 Agilent Technologies Signal Studio for Multitone Distortion Option 204 Synthesize NPR stimulus Vary notch depth Vary notch bandwidth LAN/GPIB Vary notch frequency Distortion correction Digitally Synthesized NPR Stimulus Vary stimulus’ CCDF PSG PXA Aerospace & Defense Symposium © 2012 Agilent Technologies NPR Measurement Using Noise and Band Power Markers Notch Creation Amplifier Measurement 38 GHz! 30 Aerospace & Defense Symposium © 2012 Agilent Technologies Arbitrary Waveform Generator Requirements N6030A (PXI) • • • • • • N8241A (LXI) Wide bandwidth (1 GHz) High dynamic range Low distortion products Flatness Repeatability IF and IQ generation capabilities 31 Aerospace & Defense Symposium © 2012 Agilent Technologies New ARB – M8190A 16 QAM Example with Analog IQ Modulation using Vector Signal Generator Aerospace & Defense Symposium © 2012 Agilent Technologies High-Precision AWG Example: Analog IQ Modulation, Fc=10GHz Wideband digital modulation: QAM16, 1.76G Sym/s Fs = 7.2 GHz with amplitude correction EVM=1.17% Aerospace & Defense Symposium © 2012 Agilent Technologies High-Precision AWG Example: Digital Upconversion, Fc= 1GHz (without PSG RF Sig Gen) Wideband digital modulation: QAM16, 1G Sym/s Fs = 7.2 GHz with amplitude correction EVM=0.89% Aerospace & Defense Symposium © 2012 Agilent Technologies Vector Modulation Analysis - 89600 VSA Software Use the SAME measurement tool at ALL stages of your block diagram!!! DUT DSP Digital (SSI) Logic Analyzer BB (I-Q) Oscilloscope IF/RF Signal Analyzer Aerospace & Defense Symposium © 2012 Agilent Technologies Wideband High-Frequency Vector Measurement Options PXA 160MHz @78 dB Dynamic Range MXA 25MHz @78 dB Wide Band VSA (PXA + Infiniium) 900 MHz @ 40 dB* X93204A Infiniium scope 32 GHz @ 40 dB Bandwidth Aerospace & Defense Symposium © 2012 Agilent Technologies Instrument and System Calibration Amplitude error Calibration Amplitude Flatness Q Phase linearity Measured signal Ideal Signal θ Phase linearity error I Minimum Error Vector Magnitude EVM The goal is to measure the EVM of the DUT not the EVM introduced by the measuring system Aerospace & Defense Symposium © 2012 Agilent Technologies 140 MHz BW (option B1X) PXA Simplified Block Diagram 2Gbyte SDRAM 140 MHz Front End FPGA ADC 3.5-26.5 GHz high band Low noise path YIG filter with bypass relay 8.3-14 GHz LO 40 MHz BW (option B40) 40 MHz μW converters 6 10 20 30 μW preamp X1 3.6-13.6 GHz X2 13.6-26.5 GHz ADC F0=250 MHz 200 MHz CK 25 MHz 10.9M Cal input .3M F0=322.5 MHz 4 GHz Switched filters, F0=322.5 MHz 4.8 GHz LO 1 dB-step electronic atten RF converter 140 MHz Linearity Corrections 966K F0= 5.1225 GHz RF preamp ASIC 400 MHz CK 3 Hz-26.5 GHz Input 2 dB-step mech atten 2 2 F0=300 MHz 303K 2nd converter 2Gbyte SDRAM ADC FPGA 79K 3.8-8.73 GHz LO 9K 100 MHz CK ASIC 300 MHz LO 0-3.6 GHz low band Switched filters, F0=22.5 MHz Swept IF & 10 MHz BW & 25 MHz BW (option B25) Aerospace & Defense Symposium © 2012 Agilent Technologies Example of Quality of Magnitude and Phase Corrections on 140 MHz BW EVM Results for 138 MHz OBW QPSK Signal vs. Center Frequency in Band 0 Aerospace & Defense Symposium © 2012 Agilent Technologies PXA Simplified Block Diagram (900 MHz IF Path) Low noise path Front End 13.6 - 26.5 GHz Path YIG filter with bypass relay 3.5-26.5 GHz high band Aux IF out 3 Hz-26.5 GHz Input μW preamp Option CR3 Option MPB 3.6-13.6 GHz Path Rear Panel 8.3-14 GHz 900 MHz IF BW centered at 600 MHz Aerospace & Defense Symposium © 2012 Agilent Technologies Setting up the Vector Signal Analyzer 1. Connect a source to the PXA 2. Connect the VSA the scope over the LAN, and the PXA’s wideband IF output to channel 1 of the scope’s input Aerospace & Defense Symposium © 2012 Agilent Technologies Setting up the Vector Signal Analyzer 3. Configure the VSA for use with a downconverter. Aerospace & Defense Symposium © 2012 Agilent Technologies Correcting Downconverter Frequency Response 1. Configure your source for a 0 dBm CW at the desired carrier 2. Set VSA averaging to “continuous peak hold” Aerospace & Defense Symposium © 2012 Agilent Technologies Correcting Downconverter Frequency Response 1. Program your source to slowly sweep across the desired band 2. Be sure that the ADC is not being overdriven during the sweep. 3. Use an external leveling loop if necessary Aerospace & Defense Symposium © 2012 Agilent Technologies Applying Frequency Response Corrections 1. 2. Aerospace & Defense Symposium © 2012 Agilent Technologies Applying Frequency Response Corrections Aerospace & Defense Symposium © 2012 Agilent Technologies Amplitude Corrections Aerospace & Defense Symposium © 2012 Agilent Technologies Vector Analysis with Wideband QPSK, APSK, and SOQPSK Agilent 89601B VSA 10 GHz QPSK signal BW = 900 MHz and EVM = 1.4% APSK and SOQPSK Aerospace & Defense Symposium © 2012 Agilent Technologies Digital Waveform Creation Agilent’s SystemVue Modulation models • BPSK, SBPSK, QPSK, OQPSK, 8PSK, pi/4 DQPSK, SOQPSK, Pi/4 CQPSK, MSK, GMFSK, CPM, CPFSK • FHSS, DSSS FEC – forward error correction • • Convolutional Coding Turbo Coding • LDPC Multiple Access Scheme • • FDMA TDMA • CDMA Satellite Channel Model Transponder Aerospace & Defense Symposium © 2012 Agilent Technologies Summary Nonlinear behavior must be characterized and addressed Common test signals include two-tone, multitone, and NPR signals Digital signal generation approach provides repeatability and cost advantages over analog generation approaches including notch depth, bandwidth, and adjustability Multiple techniques and measurements non-linear behaviors in the PXA Using the PXA as a down-converter is a technique for lower cost high-frequency wideband measurement VSA software enabled is a flexible platform that allows for easy input of corrections as well as a platform to make a large amount of vector/modulation quality measurements 53 Aerospace & Defense Symposium © 2012 Agilent Technologies Thank You! 54 Aerospace & Defense Symposium © 2012 Agilent Technologies