ADS学习第四章 S参数仿真

ADS学习第四章 S参数仿真 OBJECTIVES · Measure gain and impedance with S-parameters · Use a sweep plans, parameter sweeps, and equation based impedances · Plot and manipulate data in new ways About this lab: This lab continues the mixer testing by making various S-parameter measurements to determine circuit performance: gain and impedance. PROCEDURE 1. Copy the last lab and save it as a new design named: s_params. After saving the schematic as s_params, continue modifying the design to match the schematic shown here, according to the following steps: a. Delete the AC sources and simulations. Also delete the measurement equations, parameters sweep, etc. – These are components you will not use for S-parameter simulations. b. Insert an S-Parameter simulation controller (Simulation-S_Param palette) and set: Start=100 MHz, Stop=2 GHz, and Step=100 MHz. c. Insert S-parameter port terminations (Term) instead of a source and load. The Node Names are the same as before: Vin and Vout 2. Simulate and display results: use the data display options The following steps will compare the S21 measurement to the AC simulation data and show you more about plots, traces, markers and text. a. Be sure the name of the dataset is: s_params and then simulate. It is a good idea to always check dataset names before simulating. b. When the simulation is finished, open a new Data Display window and save it as s_params. Then insert a rectangular plot of S-21 (dB). c. On the same plot, insert the trace the db of Vout from the ac_sim dataset from the last lab. NOTE on S-21 vs dB gain from AC simulation: The dB values of gain are the same because the AC simulation uses the standing wave voltage only. But the S-parameter simulation uses output power divided by incident power (V and I). In addition, the Sparameter source impedance is 50 ohms and the V_AC source 0 ohms. d. Edit the plot (double click). Go to Plot Options and try adjusting both axes by deactivating the autoscale and setting: Min, Max and Step. e. Reset the axes to Auto Scale and try the plot-zooming icons. Reset to Auto Scale when finished. f. Also, click on the Grid button and try changing the grid as desired 3. Add the LO impedance: series R-C to ground a. In the schematic, insert the following components to represent the impedance of the local oscillator: C=1.0 pF and R=50 Ohms and ground. Insert onto the transistor base. b. Simulate S-21 again with the frequency range from 100 MHz to 2 GHz (100 MHz steps) and name the dataset: s_lo. c. Deactivate the LO components, and simulate again with the dataset name: s_nolo to compare results. d. In the data display window, insert a new plot with the two S-21 traces: with the LO and without the LO impedance. The display should look similar to the one shown here. Select the two markers and click Marker > Delta Mode On. The delta S-21 is about 0.9 dB. Delta marker mode shows difference in impedance. e. Save the data display window as s_params. Remember the data display windows are .dds files and the datasets are .ds files in the data directory. 4-5 Lab 4: S-parameter Simulations 4. Plot the S11 impedance a. In the same data display window, insert a Smith chart with the S-11 trace from the s_lo dataset. Insert a marker at 900 MHz and notice that the marker shows the reflection coefficient (magnitude/ angle) and also the impedance (real and imaginary). For the design, there is an obvious mismatch here. b. Edit the marker readout (double click on the marker readout). When the dialog appears, change Zo to 50 and click OK. The marker will now give you the real and imaginary value of S-11 in ohms: c. Change the Zo setting to PortZ(1) as shown and you will get the same answer as setting Zo to 50. However, if you did have a different port impedance (for example Z=75 Ohm) then the PortZ setting would calculate the readout using 75. 4-6 Lab 4: S-parameter Simulations d. Insert a list. Then select S data and PortZ and add them. Then use Plot Options to Suppress Table Format. This will display all four Sparameters in a tabular format as opposed to selecting only one of the S values. In addition, the port impedance of the termination is given too. e. In the Data Display window, use the scroll buttons or zoom icons to view the data. Also, try changing the font type and size in the list (you may need this for a presentation) by clicking the command: Text > Font.