EE 186 LAB 2 FALL Network Analyzer Fundamentals and Two Tone Linearity

Transcription

1 Network Analyzer Fundamentals and Two Tone Linearity Name: Name: Name: Objective: To become familiar with the basic operation of a network analyzer To use the network analyzer to characterize the in-band response of filters To characterize the effects of over-driving an amplifier using two tone methods Reference: Class notes and Agilent Network Analyzer Basics (available on WebCT) Lab 1 single carrier distortion data and report. Equipment: Network/Impedance/Spectrum Analyzer (Agilent 4396B) and User s Guide Transmission/Reflection Test Jig (Agilent 87512A) RF Signal Generator (Agilent E4422B) Digital Signal Generator (R&S SMIQ-03B) Vector Signal Analyzer - VSA (HP 89441A) Power Supply (HP E3631A) Multimeter (HP 34401A) Oscilloscope (Agilent Infinium) Two filters A and B and test cables 1 and 2 RF Power Splitter/Adder (0 ), adapters, switchable attenuator and cables Device Under Test (DUT) ( Low Performance Amplifier ) with 3 db attenuator at input Prelab: 1. In your own words, discuss the difference between a spectrum analyzer and a network analyzer. 2. To perform the procedure in Part I of this lab, calibration of the network analyzer is performed repeatedly. Why? 3. For Part II of this lab, determine the frequencies (in MHz) for the IMD products and enter them in the orange boxes of Table 3b. PART I: Network Analyzer Basics For this part of the lab you will be working on the ANALOG RF AND DEVICE CHARACTERIZATION BENCH. Setup: Configure the 4396B to Network Analyzer mode. Measure > Analyzer Type > Network > B/R Set the start and stop frequencies to capture the full range of the instrument: 100 khz 1.8 GHz. Configure the scale to 10 db/div [Scale/Ref > Scale/div > 10 > x1]. Connect cable No. 1 to the test jig and cable No. 2 to the B port of the network analyzer. Connect cable No. 1 and No. 2 together using the male-to-male BNC adapter. 1 of 6

2 Procedure: 1. S 21 or Transmission Response of Filter A. Perform the response and calibration procedure found on page 3-10 of the 4396B user s guide. Connect Filter A to the test setup. Capture this image to disk [Save > Graphic > type filename > Enter]. Zoom in on the inband response to capture the response to 20 db down from the peak [Maker> Search> Max ; Marker > Search > Peak Center]. Change the setting to 5 db/div. Repeat the calibration and response procedure and capture the detailed image. Determine the minimum loss and its frequency (Search > Peak). Use the 0 marker (Marker > scroll) to determine the ± 3 db and ± 10 db frequencies and record these values in Table 1. Observation: Ideally, what would be the loss at the peak frequency? What is the reality at this point? 2. S 21 or Transmission Response of Filter B. Repeat the above procedure for Filter B. Rotate the team member functions so all get experience performing the calibration and measurement functions. Observation: Why is it important to repeat the calibrations procedure again after zooming in on the frequencies of interest? 3. S 21 or Transmission Response of the DUT You may recall that the amplifier, the device under test (DUT), used for this experiment is of simple design (single transistor, common emitter configuration) and was quick to build. Significant distortion begins to occur with fairly low input signal levels, but for this experiment that is just what is needed. Set the power supply to 12 Volts and verify with the multimeter. Connect the voltage source to the DUT. Note: for this lab, we will assume the 3 db attenuator to be part of the DUT. Set the analyzer s start frequency to 1 MHz and the stop frequency to 51 MHz. Set the scale to 10 db/div. Connect cable No. 1 and No. 2 together. Configure the source power to -50 dbm (Source > Power > -50 > x1). Perform the calibration procedure. Observation: Do you think this calibration is valid? Why or why not? Increase the source power to -30 dbm and recalibrate the setup. Connect cable No. 1 to the input of the DUT and cable No. 2 to the output. Determine the point of peak gain (Search > Peak) and record its frequency (MHz) and gain (db) in Table 2. Determine the gain of the device at 5 MHz by scrolling the marker. Record this value in Table 2. 2 of 6

3 Repeat the above steps for the power levels noted in Table 2. At the point at which you are overdriving the analyzer (warning on screen), take out the DUT and put in the switchable attenuator set to 20 db. Recalibrate the setup with the attenuator in place. Put in the DUT prior to the switchable attenuator and complete the measurements for Table 2. Collect one frequency response curve of the device operating in its linear region and one of operation in the nonlinear region. Observation: Why is the attenuator put in after the DUT? PART II. Two-tone linearity test For this part of the lab, you will be working on the WIRELESS AND DIGITAL COMMUNICATIONS BENCH (as in Lab 1). 1. Two-Tone Distortion Measurements Set the VSA for a center frequency of 10 MHz, span of 8 MHz, resolution bandwidth of 10 khz, and a reference level of -10 dbm. Configure the R&S SMIQ for a frequency of 9.5 MHz and the Agilent RF signal generator for a frequency of 10.5 MHz. Set the output power of each generator to -37 dbm. Connect each source to one port of the 0º splitter (1 and 2) and the S-port of the splitter to the input of the VSA. Record the power of each signal off the PSA (use RF on/off to enable/disable sources) in Table 3a. Disconnect the splitter output from the VSA and connect it to the input of the DUT. Connect the DUT output to the PSA. Turn off the 10.5 MHz carrier and record the single carrier power of the 9.5 MHz source. Repeat, switching sources. Record this info in Table 3a. Enabling both sources, record the output power of the two carriers and the 3 rd, 5 th, and 7 th IMD products (from spectrum analyzer). Record all this information in Table 3b. Capture one image off the VSA showing the device operating in its linear region and one image showing the device in saturation. Repeat this procedure for all power levels noted in Table 3. Should the VSA become overdriven (as noted by the flashing OVI ), place the selectable attenuator at the VSA input (be sure to record attenuator settings). Connect the DUT output to the oscilloscope and note your observations. Note whether the oscilloscope is providing meaningful information in this experiment. Capture at least one oscilloscope trace to backup your observations (File > Save > Screen > A: drive; use JPEG format). Observation: Is the oscilloscope useful for the two-carrier test? Why or why not? 3 of 6

4 Laboratory Report: Your lab report should include the following: 1. A two to three page discussion of the laboratory experiment including the key concepts demonstrated in the lab, what difficulties (if any) did the team have in performing the experiments (and why?), what was learned that was especially intriguing. The discussion should be written to discuss the experiment step by step. The discussion should embed your captured figures appropriately. Finally, the discussion should address the following questions: What are the 3 db and 10 db bandwidths and center frequencies of the two filters? In your conclusion discuss both the advantages and disadvantages of using the network analyzer to characterize the frequency response of devices. Use the results of Part I.3 to generate a Gain vs. P in and a P out vs. P in curve. Discuss the usefulness of both representations. Use your results of Part II (i.e., Table 3) to and plot C/3IM and C/5IM vs. total input power. Use these plots to form your discussion as to the regions of linear vs. non-linear operation. Be sure to utilize the captured images in your discussion. Why was the signal generator output set 3 db higher than what you expected at the input to the 3dB attenuator/dut combination? Use your single tone test data (from Lab 1) and the dual tone results from this lab to discuss how each measurement quantifies the linear and non-linear operation regions of the DUT. Are the results of the various techniques consistent? What are the advantages and disadvantages of each technique? Note: techniques that should be discussed are (1) single tone data: THD%, oscilloscope and TOI, (2) network analyzer data and (3) and dual tone data: C/XIM. Why didn t the oscilloscope yield useful information when performing the dual tone tests? Why was the resolution bandwidth set so narrow (10 khz) during Part II of this lab? 2. Your filled in original data sheet and your prelab assignment. 3. Attached and well-labeled tables, figures and calculations containing all the data from your experiments. Please note any corrections to the procedure and give them to the instructor or TA. Thanks. 4 of 6

5 Table 1. Filter Characteristic Data data Filter A Filter B MHz dbm MHz dbm peak -3 db +3 db -10 db + 10 db 10 db bandwidth 3 db bandwidth Center frequency Table 2. DUT Gain data Pin Peak freq (MHz) Peak gain (db) Gain at 5 MHz of 6

6 Table 3a. Two Tone Measurements Test Setup Data Signal Generator Out MHz power in 10.5 MHz power in Total input power 9.5 MHz power out 10.5 MHz power out Attenuator setting (db) Table 3b. Two Tone Measurements Intermodulation Data Signal Generator Out f1,0 IM 0, 1 f IM f1, 2 IM f 2, 1 IM f 3, 2 IM f 2, 3 IM f IM 4, 3 f 3,4 IM TA prelab signature: 6 of 6