An earlier paper by the authors describes an easily trimmed universal building block for active RC filters which possesses the valuable characteristic that, with suitable design, the Q -value can be made approximately independent of the gain-bandwidth product of the operational amplifiers This makes the filter usable for high frequencies, while at the same time the dependence of the Q -value on temperature variations in the operational amplifiers is drastically reduced Design formulas are presented, as well as comparative measurements which verify the theory The building block is shown to have excellent characteristics both as a universal second-order building block and as a standard block for active ladder synthesis of bandpass filters

A versatile active RC building block with inherent compensation for the finite bandwidth of the amplifier

The use of "active compensation" in precision electronic circuits employing modern IC op amps, whereby the op amps in a circuit provide "self-compensating" effects to mitigate their finite bandwidth limitations is discussed. In particular, several rather subtle applications in the field of RC active filters are presented. A number of novel integrator circuits having high performance are presented, and experimental results which support the theoretical derivations are given. Using these integrators considerably extends the useful frequency range of the "leap-frog" and "coupled-biquad" active filters, at no extra cost.

Active compensation for high-frequency effects in op-amp circuits with applications to active RC filters

A bibliography on research work related to ‘nullors’ and their applications in circuit analysis, synthesis and design, covering the period 1961–2000, is given.

Bibliography on Nullors and Their Applications in Circuit Analysis, Synthesis and Design

A sensitivity analysis for a general second-order multiamplifier RC-active network is described. The conditions for minimized sensitivity to amplifier gain-bandwidth product (GBWP) are established after first formulating the transfer function gain dependence under the assumption of a single-pole representation of the complex amplifier gain. On the basis of a perturbation technique, approximate expressions are presented for the evaluation of the selectivity and frequency sensitivities. By distinguishing a general form of denominator decomposition, the methods available for realization of high Q's with improved sensitivity are explored. Three special cases of the decomposition are identified; two of these, in common with the general case, suggest the use of twin-T null networks with their attendant high passive sensitivities, but the third gives rise to an additional group of circuits 'realizable as double first-order all-pass sections. By comparison with some previous circuits which require matched amplifiers to achieve a low sensitivity, the proposed configurations are shown to be unconditionally insensitive to variations of the GBWP of the amplifiers.

RC-active networks with reduced sensitivity to amplifier gain bandwidth product

A circuit configuration and its design formulas are presented for the realization of all the useful forms of a biquadratic voltage transfer function. The circuit employs three single-ended operational amplifiers, two capacitors, and at most eight resistors. With an additional resistor, it can realize any biquadratic voltage transfer function.

Design formulas for biquad active filters using three operational amplifiers

Four building blocks have been found that realise the biquadratic transfer function T(s)=K s2 + 2σos + σoo2/s2 + 2σps + σop2 with very low sensitivities to variations in the passive and active components, and with the possibility of trimming σo, ωoo, ωop and ωop independently each by one resistor. The networks may be manufactured in standardised integrated blocks which may be trimmed for specific applications.

Low-sensitivity easily trimmed standard building block for active rc filters

A method is described for accurate determination of the locations of poles and zeroes of a transfer function by means of phase measurements. It is especially suitable for trimming of second-degree active RC networks.

K. Mossberg

Papers

Low-sensitivity easily trimmed standard building block for active rc filters

Accurate trimming of active rc filters by means of phase measurements