AWR eBooks

RF Electronics Chapter 2: Computer Simulation Page 5 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Chapter 2 Computer Simulation Introduction There are many circuit-simulation programmes available. Most of these use SPICE models, which include all relevant parameters. At lower frequencies, programmes like the commercial "Multisim" program are useful, but for RF circuits, frequency-domain computer simulation tools are much more computationally efficient for steady state analysis than SPICE based programmes. Frequency-domain computer simulation tools also allow transmission lines to be used as elements and are able to evaluate Intermodulation (IM) distortion caused by two closely spaced tones. Typical examples of RF circuit simulation software are Pathwave EDA by Keysight Technologies [1] and AWR Design Environment (AWR DE) [2]. AWR DE contains five very different simulation programs: Microwave Office (MWO), which is used for circuit simulation. This chapter describes its use for circuit simulation. The second part is Visual System Simulation (VSS), which is used to simulate whole systems. VSS is typically used to simulate communication systems to determine the performance of different modulation techniques. The third part is Analog Office, which is used for RF-IC design. The fourth part is AXIEM, which is used for 3D planar electromagnetic (EM) simulation, and the fifth part is Analyst, which is a full 3D EM simulation software. This is a very powerful computer simulation suite. During operation of the AWR DE software, all the different component MWO [3], VSS, Analog Office, AXIEM and APLAC that have valid licences, are all available. In some instances, more than one of these AWR DE components are used at the same time, the generic name AWR DE is used in this book, unless a specific component is mentioned. For the 2020 edition of this book, AWR DE version 15 is used for all the simulations. AWR DE is very good for both RF and lower frequency simulations. Many RF transistors and diodes devices models are available for both linear models and non-linear (Transient or Harmonic Balance) models. In addition, the required model parameters can often be downloaded from the device manufacturer's web site. For microwave frequencies, the device models used and the modern communication simulation programmes are very accurate, resulting in a good agreement between the computer simulations and the resulting hardware. For Terahertz frequencies, foundry models are often not accurate enough and one may have to develop their own models. The linear models treat any passive and active devices as "linear" devices and use conventional circuit analysis techniques to solve the equations for the circuit to be simulated. As a result, the simulation is fast, but it will not deal with non-linear effects such as those that occur in a mixer, oscillator or amplifier. Applying optimisation techniques to the linear simulation of the circuit allows the best performance to be obtained quickly. Simulation of non-linear circuits can be done in two ways: Firstly, Harmonic Balance is a frequency-based, steady state analysis that uses non-linear differential equations to model the devices and then uses a linear combination of excitation tones to balance currents and voltages to satisfy Kirchhoff's law. Examples of this are the simulation of the harmonics produced by an oscillator. Secondly, transient time domain simulation using SPICE models can be used to analyse the non-linear behaviour of a circuit. Examples of this are the simulation of an oscillator starting up. RF Electronics: Design and Simulation 5 www.cadence.com/go/awr

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