Network Transfer Functions Using the Concept of Frequency-Dependent Negative Resistance

A study of the limitations of active CMOS filters at high frequencies suggests automatic means to compensate imperfections in the filter response introduced by active devices. The effects of nonzero FET output conductance, limited frequency response and noise on the filter characteristics, and dynamic range are analyzed, particularly for filters with high Q components. These are used to demonstrate a 3- mu m CMOS realization of a fourth-order bandpass filter with a 250-kHz passband centered at 12.5 MHz. The filter demonstrates that the maximum frequency of filter operation is not as seriously limited by device f/sub T/ as was previously thought, but that automatic means may be used to tune out the imperfections introduced in the filter elements by the limited voltage gain and frequency response of transistors. >

CMOS active filter design at very high frequencies

The technique of designing inductorless filters by replacing the inductors in conventional LC filters with gyrators and capacitors is considered for the special case of the high-quality channel bandpass filters used in multiplex telephony. One particular gyrator circuit, which has been found to be very satisfactory, using two operational amplifiers and four resistors, is analyzed in some detail. The difficulties of simulating floating inductors are discussed, and ways of designing filters to avoid the necessity of such simulations are proposed. The dynamic range of a filter is defined and the factors controlling it are described. Detailed measured results of two specific channel filter designs are included.

Inductorless bandpass filters

Improved sensitivity performance of active filters in multiloop feedback (coupled) topologies is well known. Of the numerous design procedures available in the literature, in this paper those methods are reviewed which are based on first- or second-order building blocks in a feedback configuration. A statistical sensitivity measure is given which results in a realistic performance measure for the filters and which can be used to compare circuits and to optimize their design to achieve minimum sensitivity. Design procedures are provided for each topology, which result in realizations having minimum sensitivity and maximum dynamic range. Also, design tables for several examples are given, and the performance of some filters is demonstrated experimentally.

Multiple-loop feedback topologies for the design of low-sensitivity active filters(Invited Paper)

Positive-impedance converting networks may be used to realize driving-point inductance and frequency-dependent negative resistance. The Q factors of these immittances are evaluated over a wide frequency range in terms of the relevant parameters. Three distinct types of Q- factor behavior are derived and it is shown that extended wide-band operation may be achieved such that Q factor is virtually independent of amplifier phase shift. The use of design-value asymptotes is explained as a means of determining the behavior of practical circuits.

http://ieeexplore.ieee.org/iel5/8147/23408/01083160.pdf

Nonideal performance of two-amplifier positive-impedance converters

An integratable high-performance direct-coupled gyrator circuit which is capable of being used in the simulation of floating inductors for lowpass filters is presented, and some of the peculiarities of practical floating gyrators are discussed.

Direct-coupled gyrators with floating ports

Two new integratable high-performance direct-coupled gyrator circuits are presented, and some aspects of their design are discussed. Simulated inductances of up to 200H have been realised, with stable Q factors of up to several thousands. Without special compensation, the temperature coefficients were 20×10−6 per deg C for inductance and 800×10−6 per deg C for Q.

S. Gruetzmann

Papers

Direct-coupled gyrators with floating ports

High-performance direct-coupled gyrators