Eldo RF FAQs
Q: Does Mentor Graphics have a solution for RF IC simulation?
A: Yes, Eldo RF extends Eldo into the RF domain. Eldo RF is a high-performance and high-capacity simulator built on top of Eldo, for large RF ICs which contain thousands of devices and/or nodes.
Q: What are the target applications for Eldo RF?
A: Eldo RF has been designed to handle complex RF ICs that are common in the 3G Telecom Wireless market. Eldo RF is more generally suited for RF IC design. The typical circuits Eldo RF is addressing are the RF transceivers found in virtually all mobile phones for example. These circuits include low noise amplifiers, mixers, filters, oscillators etc. which operate in the RF frequency range (typ. from a few 100MHz to 5 GHz)
Q: Is Eldo RF suitable for board/system designs?
A: No, Eldo RF does not support the models required by system and board designers. The focus for Eldo RF is really on the IC design side. The requirements for RF board design are currently provided by a cooperative effort with Hewlett Packard (now Agilent). The Mentor products RF Architect and RF Layout can be used in conjunction with the ADS environment, providing a solution for board level RF design and simulation.
Q: What are the prerequisites for using Eldo RF?
A: Eldo RF requires Eldo (the analog simulation kernel) and Xelga (the waveform viewer).
Technical questions – RF capabilities
Q: How is Eldo RF functionality integrated into Eldo?
A: Eldo RF includes additional analysis types for steady-state analysis. These analyses are specified through Eldo-style commands (.SST, .SSTAC, SSTNOISE and .MODSST). To support these analyses, the Fourier voltage/current source has been extended. The .EXTRACT command has also been enhanced to handle common RF measurements. The .PLOT commands have also been enhanced to support the type of output generated by the new steady-state analyses. The RF functionality represents additional commands to the users, which can be combined with any other standard Eldo analysis.
Q: Does Eldo RF require special device models?
A: No, Eldo RF, uses the same device models as Eldo, including BSIM3v3, BSIM4, BSIM3SOI, VBIC, HICUM, etc. In case proprietary models must be used, the UDM option of Eldo may be used to integrate them. However the trend is to standardize on ‘standard' models such as Bsim3v3.
Q: Which frequencies can Eldo RF handle?
A: There is no built-in limitation to the frequencies that Eldo RF can handle. The algorithms can be used at any frequency. The limitations come from the accuracy of the device models for high frequency usage. In an IC design context, which is the usage context for Eldo RF, foundries usually provide the device models, after thorough characterization of their process. The device models are ‘valid' (i.e. they accurately represent the device behavior) up to a certain frequency, which becomes the practical usage limit. The typical maximum frequencies for state-of-the-art RF processes are in the range of a few GHz.
Q: What are the analyses provided by Eldo RF?
A: The fundamentally new analyses supported by Eldo RF are the steady-state analysis and the modulated steady-state analysis. The "steady" state is defined as the state when all initial transients have vanished, and the circuit operates with periodic or quasi-periodic large signals only. This steady state is computed in the frequency domain by Eldo RF, through methods which belong to the Harmonic Balance class of algorithms. Thus the results are typically presented as a spectrum in the frequency domain. Eldo RF also automatically converts the results in the time domain. Modulated steady-state analysis is a mixed time-frequency algorithm, which efficiently handles the modulation information carried by RF signals, particularly the case of digitally modulated signals. The output of the modulated steady-state analysis is a time-varying spectrum. Other analyses are also possible, such as the steady-state small signal analysis, steady-state noise analysis and local stability analysis.
Q: Does Eldo RF support non-linear noise analysis?
A: Yes, Eldo RF supports steady-state non linear noise analysis. The noise analysis is performed in either single-tone or multi-tone conditions, which is very important for the accurate analysis of the non-linear noise in devices such as mixers. The noise models that are used are those from the (Eldo) device models. This analysis is typically used to predict the noise spectrum in low noise amplifiers, filters and mixers. Eldo RF also supports direct extraction of the noise factor of a circuit.
Q: Does Eldo RF support phase noise analysis?
A: Yes, Eldo RF supports phase noise analysis. The prediction of phase noise from voltage controlled oscillators is a critical aspect in the design of frequency synthesizers. Eldo RF includes robust and reliable algorithms, which can predict the phase noise density both close to and far from the carrier. Phase noise close to the carrier is sometimes referred as ‘close-in' phase noise.
Q: Does Eldo RF support extraction of 1dB compression point?
A: Yes, Eldo RF supports extraction of 1dB compression point through dedicated functions called ‘compress()' and ‘xcompress()', which can be used in the .EXTRACT commands.
Q: Does Eldo RF support extraction of IM3/IP3?
A: Yes, Eldo RF supports extraction of 3 rd order intermodulation and intercept points. Users can either enter the appropriate .EXTRACT commands to obtain the values, or use built-in functions (OIPx and IIPx). This provides the adequate level of flexibility.
Q: Is Eldo RF able to handle S parameters?
A: Yes. Eldo RF can extract S parameters from a steady state analysis (i.e. large signal ). These S parameters can be displayed in Smith charts within Xelga, the waveform viewer. Eldo and Eldo RF can also simulate blocks defined by their small-signal S parameters. For Eldo, it means AC and transient simulations. For Eldo RF, it means steady-state (SST) simulations. The S parameters are given using a ‘de facto' standard format, used by all measurement equipments. Any RF equipment may have measured them. This can be useful to incorporate a representation of an antenna or any block with a linear behavior, without having to provide a transistor level representation
Q: Can Eldo RF use other Eldo commands during analysis?
A: Yes, since Eldo RF uses Eldo, all the common Eldo commands are available. Eldo RF can take advantage of Eldo's parametric sweeping, temperature sweeping, .EXTRACT, .DEFMAC, etc.
Q: Can Eldo RF perform parametric analyses (design parameter sweeping)?
A: Yes. Again, since Eldo RF leverages on Eldo, all the common Eldo commands are available. Eldo RF can take advantage of Eldo's parametric sweeping, temperature sweeping. For RF analysis, the input power and the frequency are the commonly ‘swept' parameters. Furthermore, the Harmonic Balance algorithm used in Eldo RF is very efficient at parametric sweeps. Indeed, information from the previous point can be reused at each point of a sweep, leading to considerable CPU time savings when doing a 1dB compression point analysis for example (this analysis requires sweeping the input power).
Q: Can Eldo RF handle oscillators and VCOs?
A: Yes. Eldo RF provides efficient analysis of VCOs (LC-tuned, ring oscillators, etc.). It is not necessary to ‘start' the oscillator in the time domain, everything is directly computed in the frequency domain.
Q: Can Eldo RF handle frequency dividers?
A: Yes. Eldo RF may efficiently handle dividers.
Q: Can Eldo RF handle modulated signals?
A: Yes. Eldo RF supports digitally modulated sources and an analysis called ‘modulated steady-state'. The types of modulation supported are GMSK, GFSK, OQPSK,P/4QPSK, MPSK and MQAM. The sources incorporate a low-pass filter (Gaussian, Square Root Raised Cosine or Raised Cosine), and they are driven with either an explicit pattern (user-defined bit stream), or a pseudo-random sequence (using a built-in pseudo-random pattern generator). The outputs can be analyzed both in the time and the frequency domain. Some of the typical applications is the prediction of standard figures such as ACPR or NPR for Power Amplifiers.
Performance considerations
Q: What is the capacity (circuit size) limitation of Eldo RF?
A: Eldo RF has been designed for high capacity. We have successfully simulated a full chip with 5000 nodes using 3 tones (fundamental frequencies) each with 5 harmonics. A customer reported a successful test case using 15,000 elements (mixers).
Q: I heard that Harmonic Balance has memory problems. What about Eldo RF?
A: Indeed, ‘brute force' implementation of the harmonic balance algorithm does not allow handling large circuits with many harmonics. Memory usage has been thoroughly optimized in Eldo RF to overcome this limitation. The tool has successfully simulated circuits with 10,000 devices and 5 harmonics. Eldo RF also uses multi-threading to further improve the performance on multi-proessor machines.
Q: Is Eldo RF able to handle the parasitics from a RC or RLC extraction?
A: Yes. Again, Eldo RF has been designed for high capacity. The RC or RLC parasitic extractions from layout tend to produce large netlists with thousands of elements, which in very challenging for simulators. Eldo RF can simulate full chips with thousands of nodes and elements.
Q: What is the speed advantage of Eldo RF over competitors?
A: As for ‘regular' analog simulation, this question has unfortunately no straightforward answer. The speed ratio can vary widely depending on the circuit under analysis. What is consistently observed with Eldo RF, is a much faster simulation (typically 10x to 100x) for really large circuits – those in the range of several thousands elements – under multi-tone conditions.
Flow and integration considerations
Q: Is Eldo RF integrated in the Mentor flow ?
A: Yes. Eldo RF, like Eldo and ADVance MS are integrated into Design Architect IC. The integration is called the Mentor IC Flow. It uses efficient hierarchical netlisting, and a choice of waveform viewers (Xelga or DA-IC View).
Q: Is Eldo RF integrated in the Cadence flow?
A: Yes. Artist Link supports Eldo RF. Forms dedicated to Eldo RF are included in Artist Link, to support RF source parameterization (FOUR sources), analysis control (steady-state analysis etc.). Both the original Cadence waveform viewer and Mentor's viewer Xelga can be used to post-process the results. Cross-probing is supported with both viewers.