Agenda. Spectrum Analyzer Basics.

Transcription

1 Agenda Overview: What do we use to measure distortion What is spectrum analysis? Theory of Operation: Spectrum analyzer hardware Specifications: Which are important and why? Features Making the analyzer more effective Demo of Intermodulation and Harmonic Meas ts Using a Spectrum Analyzer Fixed freq and power Using a Network Analyzer Swept freq and power Gain Compression

2 What are Distortion Measurements Principally, we measure the distortion in terms of the products (signals) that are produced when an active device (amplifier or mixer) is driven in a non-linear mode Non-linear means the output power is not a linear function of the input power: The gain is not constant with drive level Products (distortion signals) are harmonics (usually tested with a single tone input), or inter-modulation signals, tested with twotones (or more). We might want to test the distortion while changing: Frequency Power Tone-spacing

3 Amplifiers Measurement Requirements Small Signal Amplifiers Critical Measurements Gain S-Parameters (S 11, S 21, S 12, S 22 ) Output 1 db Compression (P1dB) Output 3 rd Order Intercept Point (OIP3) Harmonics Load Pull Hot S22 Noise Figure

4 Overview Frequency versus Time Domain Amplitude (power) frequency time Time domain Measurements Frequency Domain Measurements

5 Lets first look at the effect of change in gain with power level Non-linear gain means that the gain changes with power level You can test this by sweeping the frequency response, at several different power levels. OR you can see the gain compression effect at one frequency, by holding the frequency constant, and measuring the gain, or the output power, while sweeping the input power A key figure of merit is P-1dB, or the power that causes the apparent gain to be reduced by 1 db

6 Gain Compression CW Power Sweep What can be measured with a CW Power Sweep? Gain Vs. Drive Requires an Enhanced Response (ER) or a 2-Port Calibration. ER is recommended since amplifier is being driven into compression and the 2-Port correction math does not hold true under non-linear conditions. Input Power at P1dB Strictly speaking, this only requires a source power cal on the input port and receiver cal for the reference receiver. If corrected Gain numbers are also required, then an ER cal should also be done. Output Power at P1dB Again strictly speaking, this only requires a receiver power cal on measurement receive port, but this also requires a calibrated source. Also again if corrected Gain numbers are required, then an ER cal should be done. Phase Vs. Drive This also requires an ER or a 2-port cal. Again, an ER Cal is recommended. Combination of All of The Above This requires a combination of an ER cal and a measurement receiver cal done in a particular way. The following slides will explain the procedure.

7 CW Gain Compression Results DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz Linear Gain Gain vs. Drive Pout OP1dB IP1dB Deviation From Linear Phase Pin Phase vs. Drive

8 Finding The 1 db Compression Point With Markers On the gain trace add a reference marker. Move the Ref marker to the linear region of the gain trace. Add a regular marker to the gain trace and set its property to coupled. With the marker selected, go to the Marker Search dialog and choose target search. Set the target to -1 and turn tracking on. Your marker will now show the point on the gain trace where the gain is 1 db less than the linear gain. On the other traces in the window add the same marker and choose Coupled Markers from the marker dialog. Now all those markers also point to the 1 db Compression point.

9 SPECTRUM ANALYZER 9 khz GHz Other distortion characteristics can be viewed using a Spectrum Analyzer 8563A

10 Overview Types of Tests Made. Modulation Noise Distortion

11 Overview Different Types of Analyzers Swept Analyzer A Filter 'sweeps' over range of interest LCD shows full spectral display f 1 f 2 f

12 Theory of Operation Spectrum Analyzer Block Diagram RF input attenuator mixer IF gain IF filter detector Input signal Pre-Selector Or Low Pass Filter local oscillator Log Amp video filter sweep generator Crystal Reference CRT display

13 Theory of Operation Mixer input MIXER f sig RF LO IF f sig f LO - f sig f LO f LO + f sig f LO

14 Theory of Operation IF Filter IF FILTER Input Spectrum IF Bandwidth (RBW) Display

15 Theory of Operation Detector DETECTOR amplitude "bins" Positive detection: largest value in bin displayed Negative detection: smallest value in bin displayed Sample detection: last value in bin displayed

16 Theory of Operation Video Filter VIDEO FILTER

17 Theory of Operation Other Components RF INPUT ATTENUATOR IF GAIN LO SWEEP GEN frequency LCD DISPLAY

18 Theory of Operation How it all works together f s Signal Range LO Range (GHz) f LO - f s f LO f LO +f s f s IF filter input mixer f s detector 3.6 sweep generator f IF A LO f LO (GHz) LCD display (GHz) f

19 SPECTRUM ANALYZER 9 khz GHz Softkeys Theory of Operation Front Panel Operation Primary functions (Frequency, Amplitude, Span) 8563A Control functions (RBW, sweep time, VBW) RF Input Numeric keypad

20 Specifications Accuracy Absolute Amplitude in dbm Relative Amplitude in db Frequency Relative Frequency

21 Specifications Resolution What Determines Resolution? Resolution Bandwidth Residual FM RBW Type and Selectivity Noise Sidebands

22 Specifications Resolution: Resolution Bandwidth Mixer 3 db BW 3 db Detector Input Spectrum LO IF Filter/ Resolution Bandwidth Filter (RBW) Sweep RBW Display

23 Demo - Theory: IF filter 8447F Amplifier out in Spec An Spectrum Analyzer Setup fc=170 Mhz RBW=1 MHz VBW=300 khz Span=10 MHz ESG-D or DP Sigl Gen ESG-D or DP Sigl Gen Signal Generator Setup f1=170 MHz, F2= MHz A=-25 dbm On Filter Bandpass filter (center frequency = 170 MHz) On Power Splitter (used as combine)

24 Specifications Resolution: Resolution Bandwidth 10 khz RBW 3 db 10 khz

25 Specifications Resolution: RBW Type and Selectivity 3 db 3 db BW 60 db 60 db BW Selectivity = 60 db BW 3 db BW

26 Specifications Resolution: RBW Type and Selectivity RBW = 1 khz Selectivity 15:1 RBW = 10 khz 3 db 7.5 khz Distortion Products 60 db 60 db BW = 15 khz 10 khz 10 khz

27 Specifications Resolution: Residual FM Residual FM "Smears" the Signal

28 Specifications Resolution: Noise Sidebands Phase Noise Noise Sidebands can prevent resolution of unequal signals

29 Specifications Resolution: RBW Determines Measurement Time Swept too fast Penalty For Sweeping Too Fast Is An Uncalibrated Display

30 Specifications Resolution: Digital Resolution Bandwidths ANALOG FILTER Typical Selectivity Analog 15:1 Digital 5:1 DIGITAL FILTER RES BW 100 Hz SPAN 3 khz

31 Specifications Sensitivity/DANL RF Input Mixer RES BW Filter Detector LO Sweep A Spectrum Analyzer Generates and Amplifies Noise Just Like Any Active Circuit

32 Specifications Sensitivity/DANL Effective Level of of Displayed Noise is is a Function of of RF Input Attenuation signal level 10 db Attenuation = 10 db Attenuation = 20 db Signal -To -Noise Ratio Decreases as RF Input Attenuation is Increased

33 Specifications Sensitivity/DANL: IF Filter (RBW) Displayed Noise is is a Function of of IF IF Filter Bandwidth 100 khz RBW 10 db 10 db 10 khz RBW 1 khz RBW Decreased BW = Decreased Noise

34 Specifications Sensitivity/DANL: VBW Video BW Smoothes Noise for Easier Identification of of Low Level Signals

35 Specifications Sensitivity/DANL Sensitivity is is the Smallest Signal That Can Be Measured Signal Equals Noise 2.2 db

36 Specifications Distortion Most Influential Distortion is the Second and Third Order < -50 dbc < -40 dbc < -50 dbc Two-Tone Intermod Harmonic Distortion

37 Specifications Distortion Distortion Products Increase as a Function of Fundamental's Power Power in db 2f - f f f 3 2f - f 2 1 Third-order distortion Second-order distortion Two-Tone Intermod Second Order: 2 db/db of Fundamental Third Order: 3 db/db of Fundamental Power in db 2 3 f 2f 3f Harmonic Distortion

38 Specifications Distortion Relative Amplitude Distortion Changes with Input Power Level 1 db 21 db 1 db 20 db 2 db 3 db f 2f 3f

39 Specifications Distortion RF INPUT ATTENUATOR Distortion Test: Is it Internally or Externally Generated? IF GAIN 1 Change Input Attn by 10 db Watch Signal on Screen: No change in amplitude = distortion is part of input signal (external) Change in amplitude = at least some of the distortion is being generated inside the analyzer (internal) 2

40 Specifications Dynamic Range Dynamic Range for Spur Search Depends on Closeness to Carrier Dynamic Range Limited By Noise Sidebands dbc/hz Dynamic Range Limited By Compression/Noise Noise Sidebands Displayed Average Noise Level 100 khz to 1 MHz

41 Specifications Dynamic Range Actual Dynamic Range is the Minimum of: Maximum dynamic range calculation Maximum dynamic range calculation Calculated from: distortion sensitivity Noise sidebands at the offset frequency Noise sidebands at the offset frequency

42 Specifications Dynamic Range +30 dbm MAXIMUM POWER LEVEL -10 dbm MIXER COMPRESSION LCD-DISPLAY RANGE 80 db INCREASING BANDWIDTH OR ATTENUATION -35 dbm MEASUREMENT RANGE 145 db SIGNAL/NOISE RANGE 105 db SIGNAL /3rd ORDER DISTORTION 80 db RANGE THIRD-ORDER DISTORTION -45 dbm SECOND-ORDER DISTORTION 0 dbc NOISE SIDEBANDS SIGNAL/ 2nd ORDER DISTORTION SIGNAL/NOISE 70 db RANGE SIDEBANDS 60 dbc/1khz -115 dbm (1 khz BW & 0 db ATTENUATION) MINIMUM NOISE FLOOR

43 Features Modulation Measurements: Time Domain (use Zero Span) LIN MARKER 10 msec X CENTER 100 MHz SPAN 0 Hz RES BW 1 MHz VBW 3 MHz SWP 50 msec

44 Features Modulation Measurements: Time-Gating Time-Gated Measurements in the Frequency Domain "time gating" Envelope Detector GATE time Video Filter Frequency

45 Advanced Measurements with a VNA You can use Frequency Offset mode to do swept power OR swept frequency distortion measurements with a VNA The dual-source PNA allows you to do swept TOI measurements Lets see how the block diagram works to enable this.

46 OUT 1 PNA-X Block Diagram 4 Port Option 419, 423 Source Pulse modulator 1 OUT 2 OUT 1 Pulse modulator Source 2 (standard) OUT 2 LO To receivers Rear panel Pulse generators J11 J10 J9 J8 J7 J4 J3 J2 J R1 SW1 SW3 SW4 SW2 R3 R4 R2 A C D B 65 db 35 db 35 db 35 db 65 db 65 db 65 db 35 db Test port 1 Test port 3 Test port 4 Test port 2 RF jumpers Receivers Mechanical switch

47 Setting Up FOM Activate FOM Setup the primary stimulus Setup the source(s) & receiver frequencies Choose the range to display on the X-Axis Enable Frequency Offset FOM is the enabling technology that is the key to many critical measurements, such as Harmonics and Intermodulation Distortion

48 Power as You Like it Port powers in the PNA can be controlled together or individually. The primary output of each source in the PNA-X can support both Internal or Open Loop Leveling. Through the use of FOM, one source can be set to sweep power while the other sweeps frequency. State: Auto = turn on when dictated by the parameters in the channel. ON = Turn on whenever this channel is sweeping OFF = Turn off whenever this channel is sweeping

49 If You Can t Measure it, Compute It!! The Equation Editor is a powerful and convenient tool to add computation results as a new trace to your measurement display. Equations can be based on any combination of existing traces or underlying channel parameters or memory traces along with any user defined constants. You can use any of the basic operators or choose from an extensive library of functions and standard constants. Equations can be stored for later use.

50 Harmonic Measurements Setup Example Use the multiplier to make a quick job of setting the receiver frequencies for the desired harmonics

51 Harmonic Measurement Results DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz Window 1 = Fundamental + 2 nd, 3 rd, and 4 th harmonic absolute levels Window 2 = 2 nd, 3 rd, and 4 th harmonics relative to carrier

52 Harmonic Measurement Results Swept Power DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz Window 1 = Fundamental + 2 nd, 3 rd, and 4 th harmonic absolute levels Window 2 = 2 nd, 3 rd, and 4 th harmonics relative to carrier Note: To change from swept frequency to swept power, simply change the sweep type of each channel to power sweep and set the power levels and the CW Frequency. If the frequency is already within the calibrated range of the swept frequency setup, no further calibration is required.

53 Setting Up the 2-Tone Stimulus & the Receiver We will use the Frequency Offset dialog to configure the source and receiver frequencies:

54 CW Fixed Power IMD Results DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz 5 th Order Products

55 Swept Center Frequency Fixed Power IMD Measurements Channel Setup A swept frequency IMD measurement requires multiple channels. A Calibration Channel This is for convenience. It allows for 1 set of source power calibrations (1 for each tone) and 1 B receiver cal and 1 Enhanced Response Cal [optional] to be later shared among all the other channels. An [optional] channel to measure the device gain at the center frequency of the IMD sweep. A channel to measure the input and output power levels of tone 1. A channel to measure the input and output power levels of tone 2. A channel to measure the output level of the lower 3 rd order product. A channel to measure the output level of the higher 3 rd order product.

56 Setting Up Channels to Measure the IMD Products Channels to Measure the lower and higher 3 rd order IMD products Using Copy Channel copy the tone 2 channel to a new unused channel. In the FOM dialog change the receiver frequencies to measure the lower 3 rd order IMD product. Relative to the primary that is an offset of -1.5 MHz. In the Power & Attenuation dialog turn on Port 1 and turn on Port 1 Src 2. Change the S11 measurement to B,1. Follow the same process in a new channel and set the receiver to measure the higher 3 rd order IMD product. IMD = 2F1 F 2 + IMD = 2F2 F1 ToneSpacing F1 = F 2 = Pr imary.5 MHz Pr imary +.5 MHz IMD = 2(Pr imary.5) (Pr imary +.5 ) = Pr imary = 1 MHz 1.5 MHz + IMD = 2(Pr imary +.5) (Pr imary.5) = Pr imary MHz Continued

57 Setting Up Channels to Compute the IP3 Computing the 3 rd Order Intercept points. Input & Output, High & Low IP3 values can be computed based on all the existing measurements in the channels we have already setup. Use one of the existing channels (other than the cal channel) * and create enough traces for each of the IP3 measurements that you want. IP3 is typically expressed in db, so choose S-Parameters as the base trace for your equations. Use the equation editor and use the equations on the right for the desired IP3 result. Remember that in the equation editor, each of the variables are referred by trace number in order to user the error corrected result in the equation. IM3 = Output power level of the lower 3rd order IMD product + IM3 = Output power level of the higher 3rd order IMD product OF1= Output power level of the lower fundamental tone IF1= Input power level of the lower fundamental tone OF2 = Output power level of the higher fundamental tone IF2 = Input power level of the higher fundamental tone IIP3 IIP3 + OIP3 + OIP3 = Higher input referred IP3 - IIP3 = Lower input referred IP3 + = IF2 - IIP3 = IF1 + = Higher output referred IP3 - OIP3 = Lower output referred IP3 In Complex Form: = OF2 - OIP3 = OF1 OF1 + IM3 OF2 IM3 = = OF1 + IM3 OF2 IM3 + OIP3 Gain OIP3 Gain This is where having an optional gain (S21) measurement at the center frequencies may be useful. * Equation traces have to be in a channel that has the same number of points as the equation s constituent traces.

58 Swept Frequency IMD Measurement Results DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz

59 Swept Power IMD Measurement Results DUT = Hittite HMC452ST89 Power Amplifier tuned for 900 MHz