Scientists in Europe have pooled their knowledge and ideas to develop and deploy integrated simulation algorithms and prototype tools to overcome the barriers in both existing and future radio frequency design flows. The result is part of the ICESTARS ('Integrated circuit/EM simulation and design technologies for advanced radio systems-on-chip') project, which is funded under the 'Information and communication technologies' (ICT) Theme of the EU's Seventh Framework Programme (FP7) to the tune of EUR 2.8 million. RFIC (integrated circuits for radio frequency) design is currently integrated with digital and analogue modules on the same die, posing severe challenges to existing simulation tools. Driven by the market demand for higher bandwidth and more end-product capability, radio frequency designs are moving into higher frequency ranges and growing in complexity.
The processes to develop both electronic design automation (EDA) and computer aided design (CAD) - indispensable to design integrated circuits for radio frequency design - and their underlying mathematics are themselves complex. Solutions to these problems therefore need new modelling approaches, new mathematical solution procedures and numerical simulations with mixed analogue and digital signals. That is where ICESTARS, a consortium of five leading European mathematical institutes, two semiconductor companies and two software providers, stepped in. 'Advancing radio frequency design in super high and extremely high frequencies necessitates new transceiver architectures and CAD tools as today's EDA tools are functionally not adequately addressing the simulation challenges of high-frequency designs,' said Jan ter Maten from NXP Semiconductors, a Dutch semiconductor company and ICESTARS partner.
'The project's research areas have been the efficient connection between the frequency domain, where the radio frequency part of wireless transceiver systems is usually designed, and the time domain, where the digital signal processing and control logic are developed,' he explained, adding that 'in electromagnetic (EM) analysis and coupled EM circuit analysis we deal with the 'communication' of the physical layer (such as mapping of devices) and the mathematical one'. The team used modified algorithms to tackle these issues. Mathematical equations, such as ordinary differential equations (ODEs), differential-algebraic equations (DAEs) and partial differential-algebraic equations (PDAEs), are the basis of time- and frequency-domain analyses.
However, the researchers modified these to cover extended functionalities to develop new algorithms to meet the simulation demands of circuits operating in frequency beyond 3 Gigahertz (GHz). For example, when it comes to the mutual simulation of digital and analogue radio frequency parts, standard time-domain techniques alone are far from sufficient. Therefore, the ICESTARS partners developed and successfully tested a prototype of adaptive wavelet-based analysis, an entirely new circuit simulation algorithm. In circuit-envelope simulation, input waveforms are represented as radio frequency carriers with modulation envelopes. By embedding the system of DAEs into partial DAEs the project succeeded in formulating a general mathematical framework that can be adapted to different classes of radio frequency circuits. An optimal dynamic time splitting allows efficient simulation of frequency or amplitude modulated signals.
Adaptivity - the dynamic simulator adjustment to the frequency response of, for instance, amplifiers, filters or mixers, in terms of network parameters or frequency-dependent noise - was core to the frequency-domain research in the project. The researchers achieved reasonable estimates for the initial conditions for distortion analysis of free-running oscillators, and for the first time, in ICESTARS, a truly generic multi-device, a so-called VoHB algorithm, was coded and tested for circuits that are larger than plain single-transistor power amplifiers. To prove that these and other concepts dreamed up by the researchers worked, they have been put to the test successfully by the industrial partners and Upper Austria University.
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