Practical formulation of the relation between filter specifications and the requirements for integrator circuits

The design of integrated, high-frequency, continuous-time filters has made considerable progress in the past few years. As the signal frequencies increase the design of the integrator circuits used in most of these filters becomes more critical. To give direction to the circuit design, minimum specifications for the gain and phase of the integrator circuits would be helpful. A practical method for obtaining these integrator specifications from the filter specifications is developed. The method is applied to a sixth-order Chebyshev band-pass filter, and the result is verified by computer simulatio

Automatic tuning of continuous-time filters

Integrated high-Q continuous-time filters require adaptive tuning circuits that will correct the filter parameters such as center frequency and quality factor (Q). Three different automatic tuning techniques are introduced. In all of the proposed methods, frequencyand quality factor tuning loops are controlled digitally, providing stable tuning by activating only one loop at a given time. In addition, a direct relationship between passband gain and quality factor is not required, so the techniques can be applied to active LC filters as well as Gm-C filters. The digital-tuning method based on phase comparison was verified with 1% tuning accuracy at 5.5 MHz for Q of 20. It uses phase information for both Q and center-frequency tuning. The filter output phase is tuned to the known references, which are generated by a frequency synthesizer. The core tuning circuit consists of D flip-flops (DFF) and simple logic gates. DFFs are utilized to perform binary phase comparisons. The second method, high-order digital tuning based on phase comparison, is an extension of the previous technique to high-order analog filters without depending on the master-slave approach. Direct tuning of the overall filter response is achieved without separating individual biquad sections, eliminating switches and their parasitics. The tuning system was verified with a prototype 6th order bandpass filter at 19 MHz with 0.6 MHz bandwidth, which was fabricated in a conventional 0.5 [mu]m CMOS technology. Analysis of different practical limitations is also provided. Finally, the digital-tuning method based on magnitude comparison is proposed for second-order filters for higher frequency operations. It incorporates a frequency synthesizer to generate reference signals, an envelope detector and a switched comparator to compare output magnitudes at three reference frequencies. The theoretical analysis of the technique and the simulation results are provided

A performance evaluation of oscillation based test in continuous time filters

This work evaluates the ability of OBT for detecting parametric faults in continuous-time filters. To this end, we adopt two filters with quite different topologies as cases of study and a previously reported statistical fault model. In addition, we explore the behavior of the test schemes when a particular test condition is changed. The new data reported here, obtained from a fault simulation process, reveal a lower performance of OBT not observed in previous work using single-deviation faults, even under the change in the test condition.publishedVersionFil: Romero, Eduardo Abel. Universidad Tecnológica Nacional. Facultad Regional Villa María; Argentina.Fil: Romero, Eduardo Abel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Costamagna, Marcelo. Universidad Tecnológica Nacional. Facultad Regional Villa María; Argentina.Fil: Peretti, Gabriela Marta. Universidad Tecnológica Nacional. Facultad Regional Villa María; Argentina.Fil: Peretti, Gabriela Marta. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Marqués, Carlos Alberto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Otras Ingeniería Eléctrica, Ingeniería Electrónica e Ingeniería de la Informació

Observation of chaotic behavior in automatic tuning loops for continuous–time filters

El apropiado modelizado dinámico lineal de filtros de tiempo continuo (CTFs) con lazos de sintonía automática debe llevarse a cabo para poder asegurar la estabilidad cuando queremos diseñar controladores de lazo mejorados. Con este objetivo, a partir de un análisis general y sistemático que permite obtener un modelo incremental linealizado equivalente para pequeña señal, se derivan las funciones de transferencia entre las variables de salida y las tensiones de control. Ello permite, a continuación, un posterior diseño de los compensadores de lazo con mejora en la estabilidad y en las prestaciones dinámicas. Este procedimiento sistemático permite conseguir mejores controladores para los dos lazos de control involucrados. Sin embargo, los CTFs con lazos de sintonía o ajuste automático son sistemas realimentados no lineales que tienden a ser inestables. Es más, fenómenos no lineales, que no pueden predecirse con un enfoque mediante modelos de pequeña señal orientados al diseño, pueden ser observados en este tipo de sistemas de sintonía. El propósito de este trabajo es poner de manifiesto que cuando se varían los parámetros de control, el sistema puede presentar diferentes tipos de fenómenos no lineales dinámicos tales como bifurcaciones y comportamiento caótico, que no pueden ser predichos por el modelo en pequeña señal orientado al diseño.The appropriate linear dynamic modeling of continuous–time filters (CTFs) with automatic tuning loops should be obtained to assure stability in case an improved design of the loop controllers is to be carried out. With this aim, starting from a general and systematic analysis in order to obtain an equivalent small–signal linearized incremental model, from which transfer functions between output variables and control voltages are derived, the subsequent design of compensated loops with enhanced stability and dynamic performance is required. This systematic procedure allows obtaining improved controllers for the two involved control loops. However, CTFs with automatic tuning loops are nonlinear feedback systems with potential instability. What is more, nonlinear phenomena, which cannot be predicted by a design-oriented small signal modeling approach, are observed in this kind of tuning systems. The purpose of this work is to highlight that when control parameters are varied, the system could present different kinds of dynamical nonlinear phenomena such as bifurcations and chaotic behavior, which cannot be predicted by the small signal design-oriented model.Peer Reviewe

CMOS circuits for analog signal processing

Design choices in CMOS analog signal processing circuits are presented. Special attention is focussed on continuous-time filter technologies. The basics of MOSFET-C continuous-time filters and CMOS Square Law Circuits are explained at the hand of a graphical MOST characteristics representation

Chaotic behaviour in on-chip automatic tuning loops for continuous-time filters

Postprint (published version

Continuous time filter design using stochastic logic

Stochastic logic is based on digital processing of random pulse stream. In this paper we propose a stochastic approach to the digital implementation of continuous time filters. The similarity between probability and Boolean algebras is exploited to obtain simple realizations. A design of a fourth order filter is presented

High frequency integrated MOS filters

Several techniques exist for implementing integrated MOS filters. These techniques fit into the general categories of sampled and tuned continuous-time filters. Advantages and limitations of each approach are discussed. This paper focuses primarily on the high frequency capabilities of MOS integrated filters

High performance continuous-time filters for information transfer systems

Vast attention has been paid to active continuous-time filters over the years. Thus as the cheap, readily available integrated circuit OpAmps replaced their discrete circuit versions, it became feasible to consider active-RC filter circuits using large numbers of OpAmps. Similarly the development of integrated operational transconductance amplifier (OTA) led to new filter configurations. This gave rise to OTA-C filters, using only active devices and capacitors, making it more suitable for integration. The demands on filter circuits have become ever more stringent as the world of electronics and communications has advanced. In addition, the continuing increase in the operating frequencies of modern circuits and systems increases the need for active filters that can perform at these higher frequencies; an area where the LC active filter emerges. What mainly limits the performance of an analog circuit are the non-idealities of the used building blocks and the circuit architecture. This research concentrates on the design issues of high frequency continuous-time integrated filters. Several novel circuit building blocks are introduced. A novel pseudo-differential fully balanced fully symmetric CMOS OTA architecture with inherent common-mode detection is proposed. Through judicious arrangement, the common-mode feedback circuit can be economically implemented. On the level of system architectures, a novel filter low-voltage 4th order RF bandpass filter structure based on emulation of two magnetically coupled resonators is presented. A unique feature of the proposed architecture is using electric coupling to emulate the effect of the coupled-inductors, thus providing bandwidth tuning with small passband ripple. As part of a direct conversion dual-mode 802.11b/Bluetooth receiver, a BiCMOS 5th order low-pass channel selection filter is designed. The filter operated from a single 2.5V supply and achieves a 76dB of out-of-band SFDR. A digital automatic tuning system is also implemented to account for process and temperature variations. As part of a Bluetooth transmitter, a low-power quadrature direct digital frequency synthesizer (DDFS) is presented. Piecewise linear approximation is used to avoid using a ROM look-up table to store the sine values in a conventional DDFS. Significant saving in power consumption, due to the elimination of the ROM, renders the design more suitable for portable wireless communication applications

High frequency and high dynamic range continuous time filters

Many modern communication systems use orthogonal frequency division multiplexing (OFDM) and discrete multi-tone (DMT) as modulation schemes where high data rates are transmitted over a wide frequency band in multiple orthogonal subcarriers. Due to the many advantages, such as flexibility, good noise immunity and the ability to be optimized for medium conditions, the use of DMT and OFDM can be found in digital video broadcasting, local area wireless network (IEEE 802.11a), asymmetric digital subscriber line (ADSL), very high bit rate DSL (VDSL) and power line communications (PLC). However, a major challenge is the design of the analog frontend; for these systems a large dynamic range is required due to the significant peak to average ratio of the resulting signals. In receivers, very demanding high-performance analog filters are typically used to block interferers and provide anti-aliasing before the subsequent analog to digital conversion stage. For frequencies higher than 10MHz, Gm-C filter implementations are generally preferred due to the more efficient operation of wide-band operational transconductance amplifiers (OTA). Nevertheless, the inherent low-linearity of open-loop operated OTA limits the dynamic range. In this dissertation, three different proposed OTA linearity enhancement techniques for the design of high frequency and high dynamic range are presented. The techniques are applied to two filter implementations: a 20MHz second order tunable filter and a 30MHz fifth order elliptical low-pass filter. Simulation and experimental results show a spurious free dynamic range (SFDR) of 65dB with a power consumption of 85mW. In a figure of merit where SFDR is normalized to the power consumption, this filter is 6dB above the trend-line of recently reported continuous time filters