A.C.M. de Queiroz

Signal flow graph OTA-C integrated filters

Techniques are presented for the synthesis of OTA-C (operational transconductance amplifiers and capacitors) filters as leapfrog simulations of certain types of passive prototypes. Three kinds of simulations for low-pass filters are presented: for all-pole ladder filters, for ladder filters with finite transmission zeros, and for symmetrical nonladder filters obtained from unbalanced lattice structures. Problems such as dynamic range scaling, and symmetrical layout to maximize immunity to temperature and process gradients over the filter structure in fully integrated realizations, are discussed.<<ETX>>

Systematic nodal analysis of switched-current filters

An approach to the systematic analysis of switched current-filters is described. The proposed technique is based on the nodal analysis of a purely resistive network that models accurately the behavior of the filter for small signals, allowing the use of any practical topology and the inclusion of important imperfections, such as output resistances of MOS transistors. Techniques for frequency-domain analysis, z-domain transform calculation, time-domain analysis, and sensitivity analysis are discussed.<<ETX>>

Exact design of switched-current ladder filters

The authors discuss the implementation of exact simulations of passive filters by switched-current techniques, using the bilinear transformation. It is shown that the synthesis can be easily done directly, without passing through an intermediary switched-capacitor filter. The realization of the input branch, which is somewhat different from the ones usually used for switched-capacitor realizations, is detailed, with various possible forms shown. Some aspects of the proposed realizations, like sensitivity, are also discussed.<<ETX>>

Switched-current ladder band-pass filters

This work discusses the implementation of band-pass filters derived from passive ladder prototypes using switched-current techniques. The bilinear transformation is applied to a set of modified state equations derived from a conveniently modified passive prototype filter, and from the equations a switched-current circuit is derived. Two different approaches are studied and compared by simulation.<<ETX>>

Some practical problems in OTA-C filters related with parasitic capacitances

Some effects of parasitic capacitances on operational transconductance amplifier-capacitor (OTA-C) filters are studied. In particular, it is shown that serious stability problems may occur if passive filters containing capacitor loops or inductor cutsets (structures with nonobservable poles at infinity) are simulated by OTA-C structures with all the capacitors grounded. Structures that avoid these problems are proposed for realizing the filters.<<ETX>>

Switched-current filters using component simulation

This paper discusses the synthesis of switched-current filters from continuous-time prototypes by the simulation of components, particularly capacitors and transconductors in Transconductance-C filters. The obtained structures implement discrete-time versions of the prototype circuit using bilinear or Euler formulas. All the proposed structures work with doubled effective sampling rate (sampling the input and updating the output at each phase), make strict use of voltage-sampling switches and naturally admit two-phases nonoverlapping clocks.

A CCCS for high frequency filters

In this paper we propose a novel CCCS with output conductance less than 10/sup -8/ mhos and harmonic distortion less than 0.6% at 33 MHz, low sensitivity to mismatches and 0.7 mW power consumption when driven with /spl plusmn/2.5 V power, supplies. A high performance OTA (Operational Transconductance Amplifier) was designed using this CCCS and tested in a 10 MHz 5th order elliptic lowpass OTA-C filter fed with /spl plusmn/2.5 V. The filter THD was less than 1% for V/sub in/=1V(pp) at the cutoff frequency in the 8 MHz to 12 MHz range.<<ETX>>

A high performance balanced MOS transconductor

An easily tunable high frequency balanced transconductor without internal nodes and with a low output conductance is presented. The structure uses only 7 MOS transistors. The output conductance can be independently adjusted (in order to be canceled) without affecting the transconductance. The transconductor also guarantees the common-mode stability of balanced filter structures. The simulation results of a 5th order elliptic low-pass filter, using standard CMOS 2 /spl mu/m process, at 100 MHz with Q and frequency controls are shown.<<ETX>>

OTA-C filters with finite zeros and without floating capacitors

In this paper we present a novel technique for OTA-C filter realizations with finite zeros based on doubly loaded passive ladder networks. Only grounded capacitors are needed; all floating capacitors are replaced with active simulations eliminating bottom-plate parasitic capacitors and non-observable poles. Bandpass, highpass and bandstop filters are easily obtained from a lowpass OTA-C prototype applying standard frequency transformations that preserve the active simulation of floating capacitors, i,e., the finite zeros realization. Also, some stability problems of highpass and bandstop filters are briefly addressed.

Signal-flow graph OTA-C band-pass and band-reject integrated filters

A simple and straightforward method for the synthesis of OTA (operational transconductance amplifier) -C bandpass and band-reject filters is presented. The method mixes the signal-flow-graph and component-simulation techniques. The final filters have good sensitivity performance and all capacitors grounded, which are advantages for integration. The method can be applied to the OTA-C simulation of any ladder passive prototype filter. Problems related to the presence of nonobservable poles created by the structure of these filters are discussed, and solutions are proposed.<<ETX>>