Analog IC Design at the University of Twente

This article describes some recent research results from the IC Design group of the University of Twente, located in Enschede, The Netherlands.\ud \ud Our research focuses on analog CMOS circuit design with emphasis on high frequency and broadband circuits. With the trend of system integration in mind, we try to develop new circuit techniques that enable the next steps in system integration in nanometer CMOS technology. Our research funding comes from industry, as well as from governmental organizations. We aim to find fundamental solutions for practical problems of integrated circuits realized in industrial Silicon technologies.\ud \ud CMOS IC technology is dictated by optimal cost and performance of digital circuits and is certainly not optimized for nice analog behavior. As analog designers, we do not have the illusion to be able to change the CMOS technology, so we have to "live with it" and solve the problems by design. In this article several examples will be shown, where problematic analog behavior, such as noise and distortion, can be tackled with new circuit design techniques. These circuit techniques are developed in such a way that they do benefit from the modern technology and thus enable further integration. This way we can improve various analog building blocks for wireless, wire-line and optical communication. Below some examples are given.\ud \u

Architectures for RF Frequency synthesizers

Frequency synthesizers are an essential building block of RF communication products. They can be found in traditional consumer products, in personal communication systems, and in optical communication equipment. Since frequency synthesizers are used in many different applications, different performance aspects may need to be considered in each case. The main body of the text describes a conceptual framework for analyzing the performance of PLL frequency synthesizers, and presents optimization procedures for the different performance aspects. The analysis of the PLL properties is performed with the use of the open-loop bandwidth and phase margin concepts, to enable the influence of higher-order poles to be taken into account from the beginning of the design process. The theoretical system analysis is complemented by descriptions of innovative system and building block architectures, by circuit implementations in bipolar and CMOS technologies, and by measurement results. Architectures for RF Frequency Synthesizers contains basic information for the beginner as well as in-depth knowledge for the experienced designer. It is widely illustrated with practical design examples used in industrial products.\ud Written for:\ud Electrical and electronic engineer

Systematic Comparison of HF CMOS Transconductors

Transconductors are commonly used as active elements in high-frequency (HF) filters, amplifiers, mixers, and oscillators. This paper reviews transconductor design by focusing on the V-I kernel that determines the key transconductor properties. Based on bandwidth considerations, simple V-I kernels with few or no internal nodes are preferred. In a systematic way, virtually all simple kernels published in literature are generated. This is done in two steps: 1) basic 3-terminal transconductors are covered and 2) then five different techniques to combine two of them in a composite V-I kernel. In order to compare transconductors in a fair way, a normalized signal-to-noise ratio (NSNR) is defined. The basic V-I kernels and the five classes of composite V-I kernels are then compared, leading to insight in the key mechanisms that affect NSNR. Symbolic equations are derived to estimate NSNR, while simulations with more advanced MOSFET models verify the results. The results show a strong tradeoff between NSNR and transconductance tuning range. Resistively generated MOSFETs render the best NSNR results and are robust for future technology developments

Analog/RF Circuit Design Techniques for Nanometerscale IC Technologies

CMOS evolution introduces several problems in analog design. Gate-leakage mismatch exceeds conventional matching tolerances requiring active cancellation techniques or alternative architectures. One strategy to deal with the use of lower supply voltages is to operate critical parts at higher supply voltages, by exploiting combinations of thin- and thick-oxide transistors. Alternatively, low voltage circuit techniques are successfully developed. In order to benefit from nanometer scale CMOS technology, more functionality is shifted to the digital domain, including parts of the RF circuits. At the same time, analog control for digital and digital control for analog emerges to deal with current and upcoming imperfections

Spectral Purity Enhancement via Polyphase Multipath Circuits

The central question of this paper is: can we enhance the spectral purity of nonlinear circuits by using polyphase multipath circuits? The basic idea behind polyphase multipath circuits is to split the nonlinear circuits into two or more paths and exploit phase differences between these paths to cancel undesired distortion products.\ud It turns out that it is very well possible to use polyphase multipath circuits to cancel distortion products produced by a nonlinear circuit. Unfortunately, there are also some spectral components that cannot be canceled with the polyphase multipath circuits