Michael B. Steer

Demystifying 3D ICs: the pros and cons of going vertical

This article provides a practical introduction to the design trade-offs of the currently available 3D IC technology options. It begins with an overview of techniques, such as wire bonding, microbumps, through vias, and contactless interconnection, comparing them in terms of vertical density and practical limits to their use. We then present a high-level discussion of the pros and cons of 3D technologies, with an analysis relating the number of transistors on a chip to the vertical interconnect density using estimates based on Rents rule. Next, we provide a more detailed design example of inductively coupled interconnects, with measured results of a system fabricated in a 0.35-/spl mu/m technology and an analysis of misalignment and crosstalk tolerances. Lastly, we present a case study of a fast Fourier transform (FFT) placed and routed in a 0.18-/spl mu/m through-via silicon-on-insulator (SOI) technology, comparing the 3D design to a traditional 2D approach in terms of wire length and critical-path delay.

An electronically tunable microstrip bandpass filter using thin-film Barium-Strontium-Titanate (BST) varactors

A tunable third-order combline bandpass filter using thin-film barium-strontium-titanate varactors and fabricated on a sapphire substrate is reported. Application of 0-200-V bias varied the center frequency of the filter from 2.44 to 2.88 GHz (16% tuning) while achieving a 1-dB bandwidth of 400 MHz. The insertion loss varied from 5.1 dB at zero bias to 3.3 dB at full bias, while the return loss exceeded 13 dB over the range. The third-order intercept of the filter was found to be 41 dBm.

Characterization of spectral regrowth in microwave amplifiers based on the nonlinear transformation of a complex Gaussian process

A statistical technique is presented for the characterization of spectral regrowth at the output of a nonlinear amplifier driven by a digitally modulated carrier in a digital radio system. The technique yields an analytical expression for the autocorrelation function of the output signal as a function of the statistics of the quadrature input signal transformed by a behavioral model of the amplifier. The amplifier model, a baseband equivalent representation, is derived from a complex radio-frequency envelope model, which itself is developed from readily available measured or simulated amplitude modulation-amplitude modulation and amplitude modulation-phase modulation data. The technique is used in evaluating the spectral regrowth for a CDMA signal.

Demystifying Surrogate Modeling for Circuits and Systems

In this article, grey-box and black-box surrogate modeling are described, with some key findings. The important point is that surrogate modeling has a solid mathematical basis leading to what has become a dramatic increase in our ability to develop engineering models and to engineer systems. In Section 2, a systematic approach to constructing surrogate models is provided. Each step is explained using published methods. Section 3 presents surrogate modeling examples from the domain of circuits and systems.

A novel envelope-termination load-pull method for ACPR optimization of RF/microwave power amplifiers

A novel load-pull method for envelope-termination characterization is presented. The method enables the source and load envelope terminations to be easily evaluated to further optimize the linearity/efficiency tradeoff of RF/microwave power transistors used in digital wireless communication systems with time-varying envelopes. Results are presented for a 53 mm low-voltage LDMOS transistor at 850 MHz. It is shown that the optimal envelope termination may in general be complex, in contrast to the commonly held belief that the envelope-termination must be approximately zero. A simplified Volterra series analysis is used to qualitatively explain how the envelope termination impacts linearity.

Electrothermal CAD of power devices and circuits with fully physical time-dependent compact thermal modeling of complex nonlinear 3-d systems

An original, fully analytical, spectral domain decomposition approach is presented for the time-dependent thermal modeling of complex nonlinear (3-D) electronic systems, from metallized power FETs and MMICs, through MCMs, up to circuit board level. This solution method offers a powerful alternative to conventional numerical thermal simulation techniques, and is constructed to be compatible with explicitly coupled electrothermal device and circuit simulation on CAD timescales. In contrast to semianalytical, frequency space, Fourier solutions involving DFT-FFT, the method presented here is based on explicit, fully analytical, double Fourier series expressions for thermal subsystem solutions in Laplace transform s-space (complex frequency space). It is presented in the form of analytically exact thermal impedance matrix expressions for thermal subsystems. These include double Fourier series solutions for rectangular multilayers, which are an order of magnitude faster to evaluate than existing semi-analytical Fourier solutions based on DFT-FFT. They also include double Fourier series solutions for the case of arbitrarily distributed volume heat sources and sinks, constructed without the use of Greens function techniques, and for rectangular volumes with prescribed fluxes on all faces, removing the adiabatic sidewall boundary condition. This combination allows treatment of arbitrarily inhomogeneous complex geometries, and provides a description of thermal material nonlinearities as well as inclusion of position varying and non linear surface fluxes. It provides a fully physical, and near exact, generalized multiport network parameter description of nonlinear, distributed thermal subsystems, in both the time and frequency domains. In contrast to existing circuit level approaches, it requires no explicit lumped element, RC-network approximation or nodal reduction, for fully coupled, electrothermal CAD. This thermal impedance matrix approach immediately gives rise to minimal boundary condition independent compact models for thermal systems. Implementation of the time-dependent thermal model as N-port netlist elements within a microwave circuit simulation engine, Transim (NCSU), is described. Electrothermal transient, single-tone, two-tone, and multitone harmonic balance simulations are presented for a MESFET amplifier. This thermal model is validated experimentally by thermal imaging of a passive grid array representative of one form of spatial power combining architecture.

Frequency-domain nonlinear circuit analysis using generalized power series

The authors present details of the generalized power series technique for the analysis of analog nonlinear circuits. The method uses generalized power series descriptions of the nonlinear elements and a spectral balance techniques to operate entirely in the frequency domain. It is therefore suited to the analysis of analog nonlinear circuits with large-signal multifrequency excitation of arbitrary frequency separation. The analysis of a low-frequency mixer is used here as a vehicle to illustrate the concepts of large-signal frequency-domain analysis and the generalized power series analysis technique. >

Computer-aided design of RF and microwave circuits and systems

The history of RF and microwave computer-aided engineering is documented in the annals of the IEEE Microwave Theory and Techniques Society. The era began with elaborate analytically based models of microwave components and simple computer-aided techniques to cascade, cascode, and otherwise connect linear component models to obtain the responses of linear microwave circuits. Development has become rapid with computer-oriented microwave practices addressing complex geometries and with the ability to globally model and optimize large circuits. The pursuit of accurate models of active devices and of passive components continues to be a key activity.

Accurate estimation of digital communication system metrics - SNR, EVM and /spl rho/ in a nonlinear amplifier environment

A nonlinear spectral analysis technique that enables digital communication system metrics; SNR, EVM and the waveform quality factor (/spl rho/) to be related to in-band distortion spectrum is presented. System metrics are estimated from the measured output power and in-band distortion power. The estimated metrics are verified by direct measurements of each metric using a vector signal analyzer (VSA) performed on a forward-link IS-95 signal. Estimated system metrics are in excellent agreement with measured values.

Electro-Thermal Theory of Intermodulation Distortion in Lossy Microwave Components

An analytic formulation of dynamic electro-thermally induced nonlinearity is developed for a general resistive element, yielding a self-heating circuit model based on a fractional derivative. The model explains the 10 dB/decade slope of the intermodulation products observed in two-tone testing. Two-tone testing at 400 MHz of attenuators, microwave chip terminations, and coaxial terminations is reported with tone spacing ranging from 1 to 100 Hz.