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Freescale Reference Design for WCDMA Base Station
From the Freescale Technical Data Sheet for the MRF21125 Device:
Frequency of operation 2110-2170 MHz. Suitable for TDMA, CDMA and multi-carrier amplifier applications. To be used in Class AB for PCN-PCS/cellular radio and WLL applications.Capable of Handling up to 125 Watts (CW) Output Power in the linear range of operation.
For more information see the Freescale Technical Data Sheet for the MRF21125 Device. The Freescale data sheet can be accessed online (via www) by selecting the part through Microwave Office's XML element browser (under Nonlinear Devices/Freescale/LDMOS) and selecting "Element Help".
This example uses both the Visual System Simulator and the Circuit Simulator (either MWO or AO) so you can view single tone and modulated signal results of this amplifier. If you don’t have both a VSS feature and a MWO or ANO, this project won't run correctly.
VSS System Analysis
This example uses the NL_F block in VSS to import the AM/AM AM/PM device characteristics of an amplifier designed in MWO. The input signal is two WCDMA channels seperated by 10 MHz as shown in the spectal plot "WCDMA signal before and after amp".
The AM/AM and instantaneous operating point of the amplifier are shown in the "AM_AM" graph. ACPR is shown in the "Input Power Output Power and ACPR" tabular graph.
The current draw of the amplifier is monitored by the use of the 'powervscurrent' data file in the look-up table. The instantaneous power of the source is measured and converted to current by the subcircuit 'Voltage to Power _ dBm'. This is then used to feed a look-up table to determine the instantaneous, peak and average current. The measure of the peak to average power ratio (PAR) is displayed in the "CCDF" graph. The instantaneous power and current are also shown.
MWO Circuit Analysis
Please look at the "DC Bias Network" graph to see the load lines of the output of the device super-imposed on the IV curves for the device. Then look at the "Total Power and Efficiency Graph" to see what is happening versus swept power.
This design was created by entering the values of transmission lines from the data sheet. The capacitor at the output (C4) was then adjusted to maximize the output power.
However, just entering these transmission line dimensions will not give you an accurate answer. There are very big steps in line widths and narrow TEE geometries which can give rise to closed form model inaccuracies. Also many of the discontinuities are too close together to get an accurate answer from the closed form models. When you first run this simulation notice all of the geometry warnings from this simulation.
The EM Extraction section below details the procedure of verifying the Transmission Line models by extracting these models into the built in EMsight solver. EM analysis should be used when the circuit models won’t be accurate. There are several warnings in this project about models with out of valid range values and thus EM should be used.
Note: It is interesting to look at the load line of the amplifier superimposed on the IV curves for the device in the "DC Bias Network" graph. With the initial project settings, this graph shows the load lines at all of the input power levels. Double click on the 2nd measurement on that graph to modify the graph settings. For the Port_1 settings in the lower right of the dialog box, change the setting from Plot all traces to Select with tuner. Now open the tuner and change the input power level and watch what the load line looks at the different input power levels.
Many other characteristics of this amplifier are plotted on the graphs, such as the device drain currents and large signal input match.
There is a schematic called "IMD_Test" that will simulate the intermodulation performance of this amplifier. The "Intermodulation Distortion" graph is initially disabled. Right click on the graph and select Enable All Measurements and re-simulate to watch this simulation run. This exercise shows how AWR is a measurement driven simulation system. Simulations only run when required by an output such as a Graph, Annotation or Equation.
There are two Extract blocks in "Power_Amplifier" that are disabled. To use EM Extraction, enable one or both of these elements and run the simulation. You will now see new EM structures automatically created called "Input_Extract_Doc" and "Output_Extract_Doc" when you run the simulation. The results from this EM simulation are automatically used in the simulation (no changing subcircuit names required). Note, by just toggling the Extract block, you switch between the circuit models and the EM results.