AWR eBooks

RF Electronics Chapter 2: Computer Simulation Page 6 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Nonlinear circuit simulation is described in detail later in this chapter, using example 2.4: Buck DC-DC Converter. Computer simulation is a powerful tool for ensuring that a circuit has been designed to perform correctly. It is best practice for commercial designs to firstly check the circuit under the ideal design conditions and then check that the circuit still performs correctly for all realistic component tolerances variations. Since the production of a PCB, containing an RF circuit is quite expensive it is always good practice to first fully simulate the circuit using both EM and circuit simulation. Inadequate simulation may result in a design fault being discovered in the hardware after it is built, resulting in costly delays. Even though modern computer simulation tools are very good, they are no substitute for good design by an experienced designer. Even then, one will often find something that was not known and was not considered in the simulation, especially at RF and microwave frequencies, that can seriously affect the circuit's performance. The computer simulation process is illustrated by some examples. Basic Operation Example 2.1: Low-Pass Filter Design a 4 th order low-pass filter and a high-pass filter to have a cut off frequency of 250 MHz and an impedance level of 75 Ω, and in the second example combine these filters to form a VHF-UHF TV antenna diplexer. The Coaxial cables used for TV antennae are 75 Ω impedance. Hence, 75 Ω is used for the impedance of this diplexer. For Butterworth filters [4] the design equations for L and C are well known and obtained using the Cauer topology realisation for Butterworth polynomials and are used for the filter tables of [5] for these filters. The components are [4]: � � � �� � � ��� � ������� �� � � � 1����� � Eqn. 2.1 � � � �� � ��� � ������� �� � � � 2����� � Eqn. 2.2 Where R is the desired load impedance and F c is the cut off frequency. Later in this chapter, it is shown how these equations can be used directly in AWR DE. The high-pass filter is obtained using the standard low-pass to high-pass transformation described in most filter textbooks, such as section 5.4 of Zverev [5] and section 2.6 of Huelsman [6]. The low-pass to high-pass transformation simply results in the normalised L and C values being swapped and replacing L with C and C with L in the circuit. As can be seen by comparing figures 2.3 or 2.7 with figure 2.8. These equations can easily be entered into a spreadsheet, to give the results for the 250 MHz filter shown in table 2.1. This spreadsheet is also included in the zip file containing all the AWR DE project files used in this chapter. We now enter these values into MWO. To do this we must create the required project as follows: Open AWR DE. This will then open up a blank project as shown in figure 2.1. Select Project Add Schematic New Schematic and name the Schematic "LowPass". Then type CNTL+L or select the Element window at the bottom left of the Design Environment window and select Lumped Elements Capacitor and drag the CAP symbol into the circuit schematic as shown in figure 2.2. RF Electronics: Design and Simulation 6 www.cadence.com/go/awr

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