Yannis Tsividis

Integrated continuous-time filter design /spl minus/ an overview

The state of the art of continuous-time filter design is reviewed. Several techniques are discussed and compared in terms of performance and implementation feasibility in different fabrication technologies. This review does not aim at historical completeness, but rather emphasizes techniques that have proven their worth in commercial applications. Brief mention is also made of experimental work which, in the opinion of the author, shows promise for the future. >

Externally linear, time-invariant systems and their application to companding signal processors

This paper considers externally linear, time-invariant systems which can be internally nonlinear and/or time-varying. Several examples of the synthesis of such systems are presented, and it is argued that they offer advantages in comparison to internally linear, time-invariant systems. In particular, their use in signal processing is considered, and it is shown that they can be designed to reduce the undesirable effects of overloading and noise corruption through the use of companding. It is shown that a variety of previously proposed schemes for this purpose are all related. Several practical problems are discussed, as are performance criteria and types of measurements needed for the evaluation of the systems discussed.

Fully integrated active RC filters in MOS technology

Fully integrated voiceband continous-time active RC filters in CMOS technology will be discussed. With ±5V supplies, 6V p-p signals can be handled in less than 1% THD and 96dB dynamic range.

Design considerations for high-frequency continuous-time filters and implementation of an antialiasing filter for digital video

An approach that has made possible the integration of video frequency continuous-time filters with wide dynamic range is discussed. The tuning scheme necessary to maintain the stable and accurate frequency response in the presence of temperature variations, process tolerance, and aging is described. Detailed design techniques specific to high-frequency operation are introduced to implement a 5-V, seventh-order elliptic analog magnitude filter for antialiasing in digital video applications. The filter, based on a G/sub m/-C technique, exhibits a dynamic range of 61 dB and dissipates a power of 75 mW. Ninety-two chips from various wafers and two different process runs were tested. Seventy-five percent of the fabricated chips were functional, and 63% of them met the commercial-grade specifications in spite of an error in the layout which forced the phase control circuitry to perform suboptimally. >

MOSFET modeling for analog circuit CAD: problems and prospects

The requirements for good MOSFET modeling as they apply to usage in analog and mixed analog-digital design are discussed. A set of benchmark tests that can be easily performed is given, and it is argued that most CAD (computer-aided design) models today fail such tests even for simple, long-channel devices at room temperature. A number of other problems are discussed, and in certain cases specific cures are suggested. The issue of parameter extraction is addressed. Finally, the context of model development and usage is considered, and it is argued that some of the factors responsible for the problems encountered in the modeling effort are of a nontechnical nature.

A reconfigurable VLSI neural network

Due to the variety of architectures that need be considered while attempting solutions to various problems using neural networks, the implementation of a neural network with programmable topology and programmable weights has been undertaken. A new circuit block, the distributed neuron-synapse, has been used to implement a 1024 synapse reconfigurable network on a VLSI chip. In order to evaluate the performance of the VLSI chip, a complete test setup consisting of hardware for configuring the chip, programming the synaptic weights, presenting analog input vectors to the chip, and recording the outputs of the chip, has been built. Following the performance verification of each circuit block on the chip, various sample problems were solved. In each of the problems the synaptic weights were determined by training the neural network using a gradient-based learning algorithm which is incorporated in the experimental test setup. The results of this work indicate that reconfigurable neural networks built using distributed neuron synapses can be used to solve various problems efficiently. >

Fully differential operational amplifiers with accurate output balancing

Design considerations are presented for attaining accurate output balancing in fully differential operational amplifiers over the useful operating frequency of the differential signals. Such output balancing is obtained by merging the common-mode feedback and the differential gain paths as close to the front end of the amplifier as possible, ensuring maximum sharing of circuit components. Two circuit designs implemented in a 5-V, 1.75- mu m process are presented, one based on a two-stage topology and one based on a folded cascode topology. Experimental results for both designs are given. >

A Si 1.8 GHz RLC filter with tunable center frequency and quality factor

A second-order active bandpass filter using integrated inductors was implemented in Si bipolar technology. The filter uses special techniques to make the quality factor and the center frequency tunable. For a nominal center frequency of 1.8 GHz and a quality factor of 35, the filter has 1 dB compression dynamic range of 40 dB, and draws 8.7 mA from a 2.8 V supply.

An integrated NMOS operational amplifier with internal compensation

An internally compensated differential operational amplifier is described which has been fabricated using n-channel Al-gate MOS technology. Only enhancement mode devices are used, and the circuit has been designed so that its performance is insensitive to process parameters.

A CMOS voltage reference

A method for developing a reference voltage in CMOS integrated circuits is described. The circuit uses MOS devices operating in the weak inversion region, as well as a bipolar device formed without process modifications. A brief description of this region of operation is given. Then, the principle of the suggested voltage reference is explained and the final implementation is presented. Higher order effects are discussed, and results from an integrated prototype given.