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Generation and Conditioning of Multitone Test Signals

Generation and Conditioning of Multitone Test Signals. Agenda Linear vs. nonlinear behavior Nonlinear distortion Methods to characterize nonlinear distortion Two-tone measurements Multitone measurements Noise power ratio (NPR) measurements Summary.

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Generation and Conditioning of Multitone Test Signals

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  1. Generation and Conditioning of Multitone Test Signals

  2. Agenda Linear vs. nonlinear behavior Nonlinear distortion Methods to characterize nonlinear distortion Two-tone measurements Multitone measurements Noise power ratio (NPR) measurements Summary Generation & Conditioning of Multitone Test Signals

  3. A * Sin 360o * f (t - to) A Time t o Sin 360o * f * t A phase shift = to * 360o * f f Time Frequency 1 Output Nonlinear behavior: • output frequency may undergo frequency shift (e.g. with mixers) • additional frequencies created (harmonics, intermodulation) Time f 1 Frequency f 1 Linear versus nonlinear behavior Linear behavior: • input and output frequencies are the same (no additional frequencies created) • output frequency only undergoes magnitude and phase change DUT Output Input Frequency

  4. A A Amplifier[A] Vin = Vacos(wat) Vout = AVin Linear behavior Vs. Non-linear behavior Linear behavior 2nd harmonic A A 2A 3A 3rd harmonic Amplifier [A] Vin = Vacos(wat) Vout = AVin + A1(Vin)2 + A2(Vin)3 +… harmonic distortion Nonlinear distortion

  5. Intermodulation distortion A B 2nd harmonics 3rd harmonics Nonlinear distortion In Out Amplifier A B 3rd order IMD typical channel bandwidth 5th order IMD 3rd order IMD (2A-B) 5th order IMD (2B-A) (3A-2B) (3B-2A) 2nd order IMD (B-A) f 3A A B 2A 2B 3B

  6. Multitone Two-tone NPR Methods to characterize nonlinear distortion AM - AM AM - PM ACPR

  7. 2nd & 3rd harmonics DUT Two-tone measurements PSA performance spectrum analyzer Isolator AMP LPF Combiner PSG CW signal generators Attenuator IMD products

  8. Power source cannot supply current IOutput POutput • “Clipped” sine waves Fourier transform PInput • Rate of compression determines harmonic amplitude & IMD Tones 2nd 3rd Two-tone IMD IDS Q VGS • 1st, 2rd, 3th, etc. harmonics mix together forming IMD VInput f

  9. A B A B Amplifier linearity behavior & common metrics PowerIn PowerOut • Linear amplification • Saturated power • Gain compression • Power at 1 dB of compression • Two-tone intermodulation (IMD) • Third order intercept point (TOI) Amplifier IP3or TOI POutput Psat. P1dB “linear” P3rd P5th PInput

  10. Why use multitone 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 Multitone IMD

  11. Effect of phase relationships…on peak-to-average ratio PSG CCDF Plots Equal phase set peak-to-average17.88 dB 63-tone signal Random phase set peak-to-average6.70 dB

  12. Effect of phase relationships…on IMD performance Random phase set #1 3rd order IMD-60.22 dB Random phase set #2 3rd order IMD -48.65 dB Equal phase set 3rd order IMD -52.89 dB

  13. DUT Conventional analog test stimulus PSG CW signal generators PSA performance spectrum analyzer Isolator AMP LPF + Combiner + +

  14. Advantages of analog test approach • Well established test procedure • Common test equipment Conventional analog test stimulus 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. Internal Baseband Generator I Q Isolator DUT E8267C PSG Vector Signal Generator Vector test stimulus

  16. Multitone Number of tones: 2 to 64 Vary tone spacing: 100 Hz to 80 MHz (2-tone) Tone power: 0 to –40 dB Initial phase: fixed or random E8267C PSG vector signal generator personalities Two-tone Vary tone spacing: 100 Hz to 80 MHz

  17. E8267C PSG vector signal generator personalities …and After Before… Signal Studio for Enhanced Multitone (opt. 408) • Up to 64 tones • Vary tone power • Change phase settings • 80 MHz correction BW • CCDF plot • COM-based API LAN/GPIB • Improved IMD suppression • Correct with additional devices in the loop PSG PSA

  18. Minimize test stimulus IMD … even at the output of an external power amplifier! DUT Enhanced Multitone Measurements  Tone correction Low IMD reduces test uncertainty E8267C PSG IMD products from DUT E4440A PSA  Non-linear distortion measurement

  19. 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 • Relative tone spacing Vector test stimulus

  20. Measurement Bandwidth Noise Stimulus Noise generated By DUT NPR DUT Traditional NPR test methods PSA performance spectrum analyzer Band Stop Filter Up converter Noise Source IF RF LO PSG CW signal generators

  21. NPR challenges and alternatives • CHALLENGES: • Need signal generator + AWGN source + band stop filter • TIME & COST • AWGN is constant only if measured in a long period • REPEATABILITY • ALTERNATIVE: • Use multiple tones with a large tone density to simulate noise signal

  22. Coming Soon E8267C PSG Vector Signal Generator personalities Signal Studio for NPR wideband component and satellite test NPR • Features • Vary tone spacing and notch depth • Distortion correction • Value • Simplified test setup • Repeatable test results LAN/GPIB PSG PSA

  23. Summary • Nonlinear behavior must be characterized and addressed to minimize in-band and out-of-band interference • Distortion Measurements are typically performed using CW signals • Common test signals include two-tone, multitone, and NPR signals • Digital multi-tone generation approach provides repeatability and cost advantages over analog generation approaches • Digital generation approach uses pre-distortion to improve dynamic range, which can minimize cost and setup time

  24. [1] Kent K. Johnson, Agilent Technologies, “Predicting BER II –Measurements for Lowering Radio Cost”, http://www.agilent.com/find/BroadbandSymp/ [2] “Characterizing Digitally Modulated Signals with CCDF curves”, Agilent Technologies Application Note, literature number 5968-6875E [3] “Spectrum Analysis Basics”, Agilent Technologies Application Note 150, literature number 5952-0292 [4] “Optimizing Dynamic Range for Distortion Measurements”, Agilent PSA series Product Note, literature number 5980-3079EN [5] www.agilent.com/find/psg [6] www.agilent.com/find/signalstudio [7] www.agilent.com/find/psa Where to find additional information…

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