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Optimizing the Stimulus to Maximize System Performance

Optimizing the Stimulus to Maximize System Performance. Agenda. Agenda. Overview System functionality test and troubleshooting Amplifier test Frequency conversion system test considerations Baseband system test considerations Summary. Encoder. PA. Overview. TRANSMITTER.

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Optimizing the Stimulus to Maximize System Performance

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  1. Optimizing the Stimulus to Maximize System Performance

  2. Agenda • Agenda • Overview • System functionality test and troubleshooting • Amplifier test • Frequency conversion system test considerations • Baseband system test considerations • Summary

  3. Encoder PA Overview TRANSMITTER • Superheterodyne radio architecture I Digital signal processor/FPGA x DAC Filter IF Filter FIR 0 deg x + Symbol Encoder IF LO 90 deg Q x DAC FIR Filter RF LO Baseband Frequency conversion Amplification Digital signal processor/FPGA I RECEIVER x Preselecting filter ADC IF FILTER Filter 0 deg FIR x Symbol Decoder Decoder LNA IF LO 90 deg ADC Q x FIR Filter RF LO Baseband Amplification Frequency conversion

  4. ADC ADC ADC Overview • Receiver architecture progression RF IF Baseband Superheterodyne DSP IF LO RF LO Digital Analog Direct digital conversion RF Baseband Zero IF DSP DAC RF LO Baseband to RF Analog Digital DSP Analog Digital

  5. Encoder PA Overview • Common stimuli test points TRANSMITTER I Digital signal processor/FPGA 2 1 x DAC IF Filter Filter FIR 4 3 0 deg x + Symbol Encoder IF LO 90 deg 2 1 x DAC FIR Filter Q RF LO 8 Digital signal processor/FPGA I RECEIVER 9 x Preselecting filter ADC IF FILTER Filter FIR 0 deg 7 x Symbol Decoder Decoder LNA IF LO 5 9 6 90 deg ADC Q x FIR Filter 8 RF LO Denotes test points

  6. System Functionality Test & Troubleshooting • Agenda Frequency conversion section Baseband section Amplification section • Overview • System functionality test & troubleshooting • Amplifier test • Frequency conversion system test considerations • Baseband system test considerations • Summary

  7. System Functionality Test & Troubleshooting • What is system functionality test ? Fading Transmitter Receiver transmission channel BER/PER analysis Interferers

  8. WLAN PCMCIA card Interference WLAN Tx Interference System Functionality Test & Troubleshooting • Why is system functionality testing important? • WLAN cards are inexpensive • Rework increases price • “Perfect” quality is expected • Satellites are expensive • Rework may not be possible • A/D applications must be reliable

  9. System Functionality Test & Troubleshooting • How to perform system functionality tests Field test Commercial fader DUT (Rx) DUT (Rx) Record the test signal & play it back DUT (Rx) Record Play back

  10. System Functionality Test & Troubleshooting • Field trial considerations Advantages • Real operational conditions Disadvantages • Expensive • Inefficient • Non-repeatable • Limited: cannot cycle through full range of conditions • Rework may not be possible

  11. Interference System Functionality Test & Troubleshooting • Fading considerations Multiple RF/MW channels Multiple RF/MW channels Fading Profiles & Multiple Paths Required bandwidth increases as the number of paths increase

  12. System Functionality Test & Troubleshooting • Waveform recording & streaming considerations • Memory depth • Impacts recording time (signal analyzer) • Impacts play back time (PC and signal generator) • Converter Resolution • Impacts quantization noise, fidelity, and dynamic range • Signal analyzer’s ADCs • Signal generator’s DACs • Bandwidth • Wide enough for capture & playback Amplitude Sample time Amplitude Frequency

  13. Frequency conversion section Baseband section Amplifier Test • Agenda Amplification section • Overview • System functionality test and troubleshooting • Amplifier test • Frequency conversion system considerations • Baseband system considerations • Summary Frequency conversion section Baseband section Amplification section

  14. Amplifier Test Why is amplifier characterization important? In-channel distortion PowerOut PowerIn Amplitude Amplitude Amplifier Frequency Frequency Out-of-channel distortion

  15. Stimulus Response Traditional stimulus/response test Two-tones, multitone, noise TOI, IMD, NPR Complex stimulus/response test Digitally modulated single and multicarriers ACPR, SEM, EVM Amplifier Test • How to characterize nonlinear distortion

  16. DUT Amplifier Test • Test narrow band components In-band • Two-tone • TOI & IMD 2f2-f1 2f1- f2 Amplitude . . . f2 f1 f2 f1 Frequency 3rd order IMD

  17. Amplifier Test Test broad band components Multitone test Noise power ratio test Amplitude Amplitude Frequency Frequency Out-of-band tests In-band tests

  18. Amplifier Test • Complementary cumulative distribution curves AWGN (reference) Before: Non-compressed signal Probability After: Compressed signal from distortion Peak/Average dB

  19. Amplifier Test • Multitone: phase relationship impacts CCDF Equal phase set: crest factor = 17.88 dB Random phase set: crest-factor = 6.70 dB

  20. DUT Amplifier Test Multitone test setup: CW sources • 1 CW source needed for each tone Spectrum analyzer CW source Isolator AMP LPF + CW source Combiner + CW source + Denotes isolators

  21. Amplifier Test Multitone test considerations: CW sources Advantages • Established test procedure • Common test equipment Disadvantages • Complicated test setup • Time-consuming to change signal parameters • Difficult to generate repeatable random tones • Expensive

  22. Isolator DUT Amplifier Test Multitone test setup: vector signal generator • 1 vector signal generator creates many tones • Reduce cost • Simplify test procedure • Save time • Repeatable test setup • Accurate test results • Control signal parameters • Utilize digital predistortion (DPD) capabilities of the multitione signal creation software Vector signal generator Spectrum analyzer

  23. DUT Amplifier Test Multitone: example Signal Studio for enhanced multitone software Minimize test stimulus IMD … even at the output of an external power amplifier! Low IMD reduces test uncertainty Vector signal generator IMD products from DUT Spectrum analyzer Non-linear distortion measurement

  24. Amplifier Test • Before & after digital predistortion 25 dB improvement Before… …and After

  25. I/Q skew of baseband waveform v I Q Time, ns time skew, Q leads I Amplifier Test • Images Images resulting from I/Q skew Minimize images by adjusting the I/Q skew

  26. Amplifier Test Multitone test considerations: vector signal generator Advantages • Simple test setup and procedure • Easy to modify signal parameters • Improved signal quality • Repeatable and accurate test results • Save time and test equipment cost Disadvantages • Output power distributed • Carrier feedthrough

  27. Amplifier Test What is noise power ratio (NPR)? Noise Stimulus DUT Amplitude Amplitude Frequency Frequency Notch Noise generated By DUT

  28. DUT Amplifier Test NPR test setup: CW and noise source NPR stimulus requirements Band Stop Filter Up converter Noise Source IF RF LO • CW source • Spectrum analyzer

  29. DUT Amplifier Test NPR test setup: vector signal generator NPR stimulus requirements LAN or GPIB • Vector signal generator • Signal Studio for NPR software • Save time with simplified test setup • Accurate test results • Movable notch without analog filters • Better dynamic range • Repeatable results • Phase and CCDF • Spectrum analyzer

  30. Amplifier Test Advantages of pseudo-random tones over analog noise Pseudo-random tones Analog noise Better dynamic range Amplitude Amplitude Frequency Frequency • Better signal-to-noise ratio • Steeper filter • Flatter amplitude

  31. Amplifier Test • Complex stimulus/response • Digitally modulated single and multicarrier • ACPR, SEM, EVM PowerIn PowerOut Amplitude Amplitude Amplifier Frequency Frequency

  32. Amplifier Test • Timing and phase offsets impacts the crest factor AWGN signal (used as a reference) Multicarrier W-CDMA with no offsets applied 18 dB crest factor! • Apply timing & phase offsets for CDMA • Randomize code channels for CDMA • Apply phase offsets for multicarrier

  33. Amplifier Test • Use clipping to limit the signal peaks Signal after clipping Signal before clipping Gaussian noise

  34. Amplifier Test Common techniques to clip waveforms Rectangular Clipping Circular Clipping Peak power without clipping (clipping set to 100%) Peak power without clipping Vector representation of clipped I & Q I waveform Baseband waveform Vector representation of clipped peak Clipping set to 80% Clipping applied Q waveform

  35. Baseband section Frequency Conversion System • Agenda Frequency conversion section Amplification section • Overview • System functionality test and troubleshooting • Amplifier test • Frequency conversion system considerations • Baseband system test considerations • Summary Frequency conversion section Baseband section Amplification section

  36. Frequency Conversion System • Frequency conversion system impacts measurements Vector signal generator Amplification section Baseband section Level accuracy Spectral Purity Bandwidth Baseband section Amplification section Vector signal generator

  37. Frequency Conversion System What is level accuracy? 1 2 Absolute Amplitude (dBm) Repeatability (dB) -10 dBm -10 dBm A B Amplitude Amplitude f1 f1 f2 Frequency Frequency 3 4 Relative level accuracy (dB) Linearity (dB) -10 dBm 1 dB Amplitude Amplitude 24 dB Amplitude -100 dBm Frequency f1 Frequency f1 Attenuator hold on Frequency

  38. Why is level accuracy important? Frequency Conversion System -110dBm spec. -110dBm spec. -110.5dBm actual -111dBm setting Power Output Power Output -114dBm actual -115dBm setting Frequency Frequency Case 1: Source has +/-5 dB of output power accuracy. Case 2: Source has +/-1 dB of output power accuracy. Passes test Should pass but fails Fails test

  39. ALC/Burst Modulator Output Attenuator from frequency conversion section ALC Driver ALC Detector Frequency Conversion System • What impacts level accuracy? • Automatic level control (ALC) • Flatness • Crest factor Power Flatness Frequency Entire frequency range

  40. Frequency Conversion System • How to control level accuracy? ALC/Burst Modulator Output Attenuator • For non-bursted signals • Use the ALC • For bursted signals • Use ALC hold • Use ALC hold with RF blanking • Use power search from frequency conversion section ALC Driver ALC Detector

  41. ALC/Burst Modulator Output Attenuator from frequency conversion section ALC Driver ALC Detector Frequency Conversion System • ALC considerations • ALC degrades EVM • Depends on loop bandwidth chosen and bandwidth of modulated signal • ALC detector bandwidth • smaller than what it is trying to detect, otherwise level accuracy suffers ALC BW =100 Hz The smaller the ALC BW, the less it impacts EVM ALC BW =10 kHz ALC BW =1 kHz Amplitude Modulated signal frequency

  42. Frequency Conversion System • Level control for bursted signals using the ALC Bursted signal 1 Amplitude, V time ALC on: ALC will try to correct the power of the off period RF power envelope of the bursted signal 2 Power, dBm Average power time Marker ALC is on during this time Logic level 3 ALC hold: ALC power is held for this duration time Pulse/RF blank: ALC is held for this duration and the RF output is blanked, thus resulting in a greater on/off ratio Marker route to ALC hold or Pulse/RF blank

  43. Frequency Conversion System • Power flatness affects accuracy of wideband signals As bandwidth increases, the more power flatness impacts level accuracy BW=200 MHz f1=2500 f2=2700

  44. Frequency Conversion System Absolute level accuracy • Flatness varies by frequency & I/Q source type Flatness Power Frequency Entire frequency range

  45. Frequency Conversion System • How level accuracy is impacted by the crest factor Crest factor = 10.5 dB Peak power –13 dBm Average (RMS) power –23.5 dBM Amplitude time

  46. Frequency Conversion System • What is spectral purity? Harmonic Spur CW signal Phase Noise Non-Harmonic Spur Amplitude Broadband noise f0 2f0 frequency Phase noise is expressed as jitter in the time domain Amplitude time

  47. Frequency Conversion System • Why is phase noise important? Channel Separation Impacts ACPR tests Adjacent Channel Amplitude Phase noise frequency Blocking signal Impacts blocking tests Amplitude Desired signal Phase noise frequency

  48. Frequency Conversion System • Phase noise degrades signal quality Phase Noise I Test Signal Error Vector Q f Ideal Signal RMS Phase Error Constellation Phase noise results in rotation of the constellation

  49. Frequency Conversion System • Phase noise versus offset frequency from carrier 4 10 ó ô 7 A= - - C= 10 B= 10 d f 9.9 10 = ´ ô õ 2 10 7 10 ó 4 ô 10 10 6 -70 - - ô 10 d f 6.868 10 = ´ A f ô B õ 4 10 10 dB/decade L(f) ,SSB phase noise (dBc,/Hz) -100 D Digital modulation on 30 dB/decade CW only C -130 -140 20 dB/decade 10 102 103 104 105 106 107 Frequency, offset from carrier

  50. Frequency Conversion System • What does the source’s phase noise do to my signal? f2 ½ RMS = RMS= (2•L(f)•df ) radians (9.87 x 10-2 °)  f1 • Root mean square angular deviation -70 A B Test Signal L(f) ,SSB phase noise (dBc,/Hz) -100 Error Vector ideal low pass filter f Ideal Signal RMS -140 102 10 104 106 103 105 Frequency, offset from carrier

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