Signal Analysis Fundamentals

Signal Analysis Fundamentals 是德科技資深專案經理蘇千翔 SIGNAL ANALYSIS FUNDAMENTALS • Overview • Theory of Operation • Traditional Spectrum Analyzers • Modern Signal Analyzers • Specifications • Features • Wrap-up Keysight Territory Turbo Program 2 3 What is Spectrum Analysis • Passive Receiver • Display and measure amplitude versus frequency • Separate and resolve complex signals into their base components (sine waves) Signal Analysis Fundamentals 3 4 Time-Domain vs Frequency-Domain Amplitude (Power) Time Domain Frequency Domain Measurements Measurements (Oscilloscope) (Spectrum Analyzer) Signal Analysis Fundamentals 4 5 Many Measurements • Frequency, power, Tx Test Spur Search modulation, distortion, and noise • Transmitter test • Spectrum monitoring • Spurious emissions • Harmonic & intermodulation distortion • Noise figure & phase noise • Electromagnetic interference • Analog, digital, burst, & pulsed RF modulation • Wide bandwidth vector analysis • Measurement range: -172 dBm to +30 dBm • Frequency range: 3 Hz to 1.1 ACP Modulation THz Signal Analysis Fundamentals 5 6 Different Types of Analyzers Swept Analyzer Filter 'sweeps' over range of A interest LCD shows full spectral display f1 f2 f Signal Analysis Fundamentals 6 7 Different Types of Analyzers FFT Analyzer Parallel filters measured A simultaneously LCD shows full spectral display f1 f2 f Signal Analysis Fundamentals 7 8 • Spectrum Analyzer: A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to display and measure Amplitude vs. Frequency of known and unknown RF and Microwave signals. Signal Analysis Fundamentals 8 9 • Vector Signal Analyzer: A vector signal analyzer measures the magnitude and phase of an input signal at a single frequency within the IF bandwidth of the instrument. The primary use is to make in-channel measurements, such as error vector magnitude, code domain power, and spectral flatness, on known signals. Signal Analysis Fundamentals 9 10 • Signal Analyzer: A signal analyzer provides the functions of a spectrum analyzer and a vector signal analyzer. Signal Analysis Fundamentals 10 SIGNAL ANALYSIS FUNDAMENTALS • Overview • Theory of Operation • Traditional Spectrum Analyzers • Modern Signal Analyzers • Specifications • Features • Wrap-up Keysight Territory Turbo Program 11 SWEPT SPECTRUM ANALYZER BLOCK DIAGRAM RF Input IF Filter Attenuator IF Gain (RBW) Envelope Mixer Detector Input signal Log Pre-Selector or Low Amp Pass Input Filter Video Filter Local Oscillator Sweep Generator Crystal Reference Display Oscillator 12 Signal Analysis Fundamentals 13 Mixer Mixer fSIG fSIG fLO – fIF RF IF fSIG – 2*fIF LO fIF fLO fSIG - fIF Sometimes use other mix product Some use 2 mixers fLO Some mix up in frequency Signal Analysis Fundamentals 13 14 IF Filter Resolution Bandwidth (RBW) Input Spectrum IF Bandwidth (RBW) Display Wide Medium Narrow Faster Resolve in Freq See Wide Freq Reduce Noise Floor Signal Analysis Fundamentals 14 15 Detector Before detector After detector Envelope Detector Signal Analysis Fundamentals 15 16 Video Filter Video Bandwidth (VBW) Signal Analysis Fundamentals 16 17 Replaced by Analog IF Digital RBW Digital Detectors Pre-amp Filter Filter FFT ADC Attenuation Swept vs . FFT Digital Log Amp YIG Signal Analysis Fundamentals 17 18 Detector Detection Types Digitally Implemented Detector Types Bins/Buckets Positive: largest sample (Sweep Points) in bin displayed Negative: smallest sample in bin displayed Sample: middle sample in bin displayed Normal (“Rosenfell”): selects sample to display using algorithm that treats noise and signals differently ADC Samples of IF Signal Analysis Fundamentals 18 19 Detector Average Detector Type Volts Bucket / Bin Time Power Average Detector (RMS): Square-root of the sum of the squares of ALL samples in the bin, expressed as power in 50Ω Signal Analysis Fundamentals 19 20 Display Terminology Amplitude Stop Frequency Start Frequency Center Frequency Frequency Span Signal Analysis Fundamentals 20 SIGNAL ANALYSIS FUNDAMENTALS • Overview • Theory of Operation • Traditional Spectrum Analyzers • Modern Signal Analyzers • Specifications • Features • Wrap-up Keysight Territory Turbo Program 21 22 – Safe spectrum analysis – Frequency Range – Accuracy: Frequency & Amplitude – Resolution – Sensitivity – Distortion – Dynamic Range Signal Analysis Fundamentals 22 23 = ± [(time since last Accuracy: Frequency Readout Accuracy adjustment x aging rate) + temperature stability + calibration accuracy] = Frequency Readout Accuracy = 1.55 x 10-7/ year ± [(Marker Frequency x Frequency Reference Accuracy) + (0.1% x Span) + (5% x RBW) + 2Hz + (0.5 x Horizontal Resolution)] = span / (sweep points – 1) Example: 1 GHz Marker Frequency, 400 kHz Span, 3 kHz RBW, 1000 Sweep Points Calculation： (1x109Hz) x (±1.55x10–7/Year) = 155 Hz 400kHz Span x 0.1% = 400 Hz 3kHz RBW x 5% = 150 Hz 2Hz + 0.5 x 400kHz/(1000-1) = 202 Hz Total uncertainty = ±907 Hz – Utilizing internal frequency counter improves accuracy to ±155 Hz – The maximum number of sweep points for the X-Series Analyzers is 40,001 which helps to achieve the best frequency readout accuracy Signal Analysis Fundamentals 23 24 Phase Noise or Noise Sidebands Phase Noise Noise sidebands can prevent resolution of unequal signals. Signal Analysis Fundamentals 24 25 Sensitivity All active electronic circuits generate noise – including spectrum analyzers. Signal Analysis Fundamentals 25 26 Sensitivity 2.2 dB Displayed Average DANL Noise Level Sensitivity is the smallest signal that can be measured. Signal Analysis Fundamentals 26 27 Sensitivity/DANL: RBW Filter Displayed noise is a function of RBW filter bandwidth: noise decreases as bandwidth decreases. 100 kHz RBW 10 dB 10 kHz RBW 10 dB 1 kHz RBW 1 Hz RBW DANL spec’ed in 1 Hz RBW Signal Analysis Fundamentals 27 28 Dynamic Range The ratio, expressed in dB, of the largest to the smallest signals simultaneously present at the input of the spectrum analyzer that allows measurement of the smaller signal to a given degree of uncertainty. Dynamic Range Signal Analysis Fundamentals 28 29 Displayed DANL per RBW and Mixer Input Power . 0 -20 Displayed Noise in a 1 -40 kHz RBW NOISE RATIO, dBc NOISE RATIO, - -60 TO - -80 SIGNAL -100 -60 -30 0 +30 POWER AT MIXER = Displayed Noise in a INPUT - ATTENUATOR SETTING, dBm 100 Hz RBW Signal Analysis Fundamentals 29 30 Distortion: Mixers Frequency Translated Signals Resultant Signal To Be Measured Mixer Generated Distortion Signal Analysis Fundamentals 30 31 Distortion: Second and Third Order Distortion products increase as a function of fundamental's power. 3 3 2 3 Power Power in dB in dB 2f - f 1 2 f 1 f2 2f2 - f 1 f 2f 3f Two-Tone Intermod Harmonic Distortion Third Order: △3 dB/dB of Fundamental Second Order: △2 dB/dB of Fundamental Signal Analysis Fundamentals 31 32 Distortion: A Function of Mixer Level 0 -20 Second -40 Order -60 DISTORTION, dBc DISTORTION, -80 Third Order -100 -60 -30 0 +30 POWER AT MIXER = TOI SHI INPUT - ATTENUATOR SETTING dBm Signal Analysis Fundamentals 32 33 Dynamic Range (DANL, RBW, Distortion) . Dynamic range can be presented graphically. Maximum 2nd Order Dynamic Range -20 Maximum 3rd Order Dynamic Range -40 NOISE RATIO, dBc NOISE RATIO, - -60 TO - -80 SIGNAL -100 -60 -30 0 TOI SOI +30 POWER AT MIXER = INPUT - ATTENUATOR SETTING dBm Optimum Mixer Levels Signal Analysis Fundamentals 33 34 Dynamic Range vs Measurement Range +30 dBm MAXIMUM POWER LEVEL +3 dBm MIXER COMPRESSION DISPLAY RANGE 100 dB @ 10 dB/Div THIRD-ORDER DISTORTION (200 dB @ 20dB/Div) -40 dBm (Dynamic Range) MEASUREMENT SECOND-ORDER DISTORTION RANGE -50 dBm (Dynamic Range) 195 dB SIGNAL/NOISE RANGE NOISE SIDEBANDS 158 dB 0 dBc (Dynamic Range) SIGNAL /3rd ORDER DISTORTION 115 dB range SIGNAL/ 2nd ORDER INCREASING DISTORTION RBW OR 105 dB RANGE SIGNAL/NOISE SIDEBANDS ATTENUATION -129 dBc @ 10kHz OFFSET -155 dBm (1 Hz BW & 0 dB ATTENUATION) MINIMUM NOISE FLOOR (DANL) -165 dBm with preamp Signal Analysis Fundamentals 34 SIGNAL ANALYSIS FUNDAMENTALS • Overview • Theory of Operation • Traditional Spectrum Analyzers • Modern Signal Analyzers • Specifications • Features • Wrap-up Keysight Territory Turbo Program 35 36 N OISE F LOOR E XTENSION (NFE) Noise Floor Extension • Standard • Standard • With LNP • With NFE • With NFE – NFE lowers the noise floor (DANL) of the SA, by measuring its own noise (no input), and subtracting that noise power. This only works with high averaging (low variance). The improvement can be up to 8-12 dB, depending on nature of signal near noise. – NF2 is “adaptive” NFE. It applies noise subtraction gradually, in proportion to averaging and reduced variance. The trace appears less chaotic while gathering averages. Signal Analysis Fundamentals 36 37 Fast Sweep Processing RBW filter can be “over-swept”: too fast to fully respond. But in digital filters, this error is well-known, and can be corrected. ~36 seconds ~0.63 seconds Sweep without fast sweep enabled Sweep with fast sweep enabled Signal Analysis Fundamentals 37 38 Resolution: RBW Determines Sweep Time Meas Uncal Swept too fast The penalty for sweeping too fast is an uncalibrated display. Signal Analysis Fundamentals 38 39 Swept Mode Swept LO • A swept LO w/ an assigned RBW. • Covers much wider span. Freq Lost Information • Good for events that are stable in the frequency domain. Lost Information • Magnitude ONLY, no phase information (scalar info). Lost Information • Captures only events that occur at right time and right frequency point. • Data (info)

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