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Efficient Design and Analysis of Airborne Radomes
This month the Microwave Journal editors sat down to a conference call with How-Siang Yap, Agilent EEsof EDA product manager for ADS. How-Siang provided us with an update on the most recent developments in the ADS2008 product as well as an overview of the current RF, microwave and high-speed design market needs and how ADS tackles these challenges.
ADS2008 represents a major change to this leading circuit design software with a renewed focus on engineering productivity. What this apparently translates into is new features and underlying technology that will allow users to construct designs more easily, perform 3D EM analysis directly from existing physical designs (layout) within their circuit network design, and perform sophisticated simulations required by new communication systems such as WiMAX and LTE. In a nut shell, ADS2008 should be easier to use, better suited for EM-level characterization and optimization, and more capable of addressing frequency-based models in transient simulations (for high-speed signal integrity design).
The Agilent marketing people are touting “Productivity by Design”, which in terms of product development translated into three focus areas:
1. Simulation time speed up
2. Mouse click reduction
3. Reduction in activities needed to complete a design task
Quite a tall order that requires new capabilities on multiple fronts including the user interface, the 3D EM solver and modeler, system and signal processing (new wireless libraries) technology and transient convolution engine. Whew! Thus new features to ADS2008 have been rolled out in stages over the course of the past year, this recent release being the second such stage.
Cell Phone RF module and RF SiP Design The new features specifically target three types of end-users. Much of the 3D EM capability is focused on the needs of RF module, MIC, and system-in-package design groups. These are the folks who are integrating high-performance multi-functional modules into high density packages and are most likely to get burned by the parasitic behavior of miniaturized multi-layer components in close proximity. Needless to say, as consumer electronics add more features, high-density packages for address the need for multi-functional RF/microwave devices (T/R and other types of front-end modules) and are therefore receiving considerable engineering effort.
Prior to this release, these designers had to rely strictly on planar method-of-moment type analysis (i.e. Momentum) if they wanted to stay within the ADS design flow. Alternatively, they had to manage extracting the physical design over to a dedicated 3D EM tool for analysis and importing the resulting s-parameters back into the design. This second approach is very time-consuming and prone to human error. It also prevents circuit/structure optimization via co-simulation. How-Siang pointed out that the down-side of using a planar EM tool is the insufficient accuracy of this type of analysis when it comes to finite planar structures such as a QFN package. For planar tools the assumption is that all planes are infinite, which is clearly not the case for these small, highly dense packages and the result is a shift in frequency response that could lead to design failure.
Other features in ADS2008 that target module designers include 3D model parameterized libraries to handle such structures as wire bonds and ball grid arrays. The new component level Design Rule Checking (DRC) can now be selectively applied to check embedded components eliminating previous restrictions that only checked the entire design with layer based rules, which clearly doesn’t work at the module/multi-chip level.
Agilent EEsfo EDA has always benefitted from a close relationship to their colleagues over at the Test and Measurement Divisions, provided them with design software and receiving valuable insight into what it takes to build hardware. Key to building a working device is measuring its performance. Given the complexity of device characterization for wireless systems today, ADS2008 adds more “measurement” test benches to its libraries, among these one for the verification of RF modules against the Mobile WiMAX (802.16e) wireless spec.
For example, Agilent EEsof believes it would take over two weeks for an expert to set-up the appropriate test bench to measure power added efficiency for compliance to the latest 3G and 4G specifications. Now this test set-up is available straight out of the box. Another similar set-up supports verification against the LTE 4G wireless library with downlink MIMO 2/4 Antennas for Space-time coding.
Speaking of antennas, ADS2008 now links to their Antenna Modeling Design System (AMDS) allowing designers to perform adaptive matching between the phone design and the antenna. The AMDS product is based on FDTD (Finite Difference Time Domain) and specifically targets electrically large structures such as the interaction between an antenna and the human body.
Signal Integrity Design
Also in ADS2008 is a significant breakthrough in the speed of the ADS transient-convolution engine. This technology was taken from their Golden Gate product (formerly Xpedion), which typically addresses RFIC design. In this case the new transient-convolution solver, which allows frequency domain models such as s-parameters to be used in time domain simulations (including non-periodic excitations) has been demonstrated to outperform the leading SPICE engines for speed and accuracy for RF/high-speed interconnect designs. Along with the accuracy (results preserve causality and passivity), the technology takes advantage of multi-core processors to deliver up to an 18 times improvement in speed, ranking it among the fastest transient simulators on the market. Combined with the 3D EM simulator, ADS2008 is now capable of modeling the entire high-speed channel and simulating it in the time domain.
All these features should add-up to make Agilent an even stronger player in the world of high-speed design where the lines between digital, analog and RF can be as blurred as the eye diagram of a poorly matched interconnect.
So if your focus is on RF module or high-speed interconnect design, you will definitely want to consider taking a look at the latest version of ADS, especially if you have been avoiding 3D EM modeling due to poor design flow integration or you felt the previous transient simulator was lacking the horse-power for your high-speed designs.
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