A class of low-sensitivity digital ladder filters may be realized in the voltage-current domain by direct analogy with the continuous resistively terminated LC ladder filter The problem of unrealizability that is implied by delay-free loops in the discrete signal flow graph is overcome by using transformations that correspond to LC elements that exhibit finite Cube factors The resultant deterioration in the passband of the transfer function is determined from the Blowstein LC ladder sensitivity theory and is, thereby, shown to be low valued at high sampling frequencies The sensitivity properties of this class of digital ladder filters are directly analogous to the LC prototype because each LC element is replaced by a digital multiplier Consequently, if maximum power transfer is approximately maintained throughout the passband of the LC prototype, then the first-order sensitivity of the corresponding digital transfer function to multiply a coefficient quantization is necessarily low valued

Low-sensitivity digital ladder filters

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 generalized approach based on signal flow graph methods for designing continuous-time active signal processing circuits with only transconductance elements and grounded capacitors is presented. For generating active simulations of LC-ladder filters, the methods result in circuits where all transconductors except possibly one are identical, making the approach extremely convenient for monolithic realization with systematic design and dense layout. Although derived for single-ended devices, it is shown how the methods can be extended to designs based on differential input or even fully balanced transconductors. SPICE simulations demonstrate the validity of the approach and practical design aspects are discussed. >

Simulating general-parameter LC-ladder filters for monolithic realizations with only transconductance elements and grounded capacitors

Active filters that derive their frequency response from internal amplifier dynamics, but use no external capacitors in their implementation, are referred to as “active R” filters. Because of their potential advantages in terms of miniaturisation (i.e. fabrication), ease of design and high-frequency performance, these circuits are receiving increasing attention in the technical literature. The paper reviews the published synthesis procedures for 1st-, 2nd- and higher-order active R filters; it is shown that the 1st- and 2nd-order circuits developed to date are special cases of a general active R topology. The paper discusses nonideal aspects and limitations of active R filter performance, which arc usually neglected in the literature; in particular, the potentially severe effect of temperature-induced drift in the amplifier's dynamic response is considered, and methods of drift compensation are discussed. Experimental results are presented to verify filter performance and the theoretical derivations

Active R filters: review of theory and practice

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

The frequency limitation of coupled-biquadratic active ladder structures is derived in terms of the gain-bandwidth products of the operational amplifiers. It is shown that the finite bandwidths of the amplifiers are analogous to finite negative Q factors of the passive inductance-capacitance LC counterpart, and a technique is proposed for the compensation of the passband deviation that is caused by this effect.

A.I.A. Salama

Papers

Frequency limitations of coupled-biquadratic active ladder structures