Adel S. Sedra

A second-generation current conveyor and its applications

A recent publication [l] introduced the concept of current conveying and an implementation in the form of a circuit building block termed the current conveyor (CC). This block has proven to be useful in many inst.rumentation applications, some of which have already been test)ed and reported [2], [3], while others are still under investigation. This correspondence introduces another new building block embodying the current conveying concept, but with different and more versatile terminal characteristics. This new block is considered to be a secondgeneration current conveyor,1 and h.ence is termed CC II.2 Application of CC II to the areas of active network synthesis and analog computation will be considered..

The current conveyor—A new circuit building block

A new circuit concept applicable to a basic building block in a variety of instrumentation and communication systems is introduced. The new concept is called current conveying and its implementation a current conveyor.

A general class of current amplifier-based biquadratic filter circuits

A general class of current amplifier-based biquadratic filter circuits capable of realizing arbitrary filter functions including the low-pass, high-pass, and bandpass transfer functions is presented. These realizations are derived from a class of well-known low sensitivity single amplifier biquadratic (SAB) filter circuits using the principle of adjoint networks. The salient features of the proposed circuits are that they are synthesized using the same procedure as their op-amp-based SAB circuit counterparts, and they possess the same sensitivities to component variations as the original SAB circuits. However, it is demonstrated experimentally that unlike op-amp-based SAB realizations whose effective operating bandwidth is much less than the unity-gain bandwidth of the op-amp, these current-based filter circuits are effective over the entire bandwidth of the current amplifier. >

Continuous-time LMS adaptive recursive filters

An approach for implementing continuous-time adaptive recursive filters is presented. The resulting filters should be capable of operating on much higher signal frequencies than their digital counterparts since no sampling is required. With respect to implementation problems, the effects of DC offsets are investigated and formulas derived so that these effects can be estimated and reduced. It is shown that the DC offset performance is strongly affected by the choice of structure for the adaptive filter. Experimental results from a discrete prototype are given where accurate adaption is observed and DC offset effects are compared to theoretical predictions. >

Exact design of switched-capacitor bandpass filters using coupled-biquad structures

A method is presented for the design of switched-capacitor bandpass filters using the bilinear z -transform. The filters are realized in low-sensitivity coupled-biquad structures and employ biquad circuits which are completely insensitive to stray capacitances between any node and ground. Geometrically symmetric (both all-pole and finite-transmissionzeros) as well as general-parameter filters are treated.

Exact design of strays-insensitive switched-capacitor.ladder.filters

This paper presents a systematic solution to the problem of designing a stray-insensitive switched-capacitor filter based on the exact simulation of the operation of an LC ladder prototype. A complete procedure is given for the design of low-pass and bandpass filters with and without transmission zeros.

A Q-enhanced active-RLC bandpass filter

The passive elements R, L, and C are combined with an amplifier to realize a high-Q bandpass filter. Positive feedback is used to enhance the finite Q of the lossy integrated inductors, and design equations are given that take into account the finite gain and finite bandwidth of the amplifier. It is shown that a quality factor of 20 at 1 GHz is possible with 10-GHz transistors. Preliminary noise analysis indicates promising results.<<ETX>>

Automatic tuning of continuous-time integrated filters using an adaptive filter technique

An adaptive filter technique for tuning continuous-time integrated filters is presented. This technique is based on the model-matching configuration and tunes both the poles and zeros of the transfer function. Circuit details of an experimental prototype are given. The experimental prototype consists of an integrated third-order filter that is automatically tuned by off-chip circuitry realizing the adaptive tuning system. Both experimental and simulation results are presented to confirm the viability of the proposed approach. >

The current conveyor: history and progress

To create a better voltage-to-current converter, it seemed natural to use another junction, that of a matched pnp transistor connected as a diode, to compensate for the V/sub EB/ of the current-source transistor. However, for this compensation to be effective it was necessary to arrange that the current in the additional pnp transistor track that in the current-source transistor, which was supposed to vary over a number of decades. A five-transistor circuit that provides a nice solution to the problem of creating a precise voltage-to-current converter is proposed. It was incorporated into the circuit for a controlled oscillator with good results. The circuit and its applications are described.<<ETX>>

Adaptive recursive state-space filters using a gradient-based algorithm

To aid in the search for better adaptive filter structures, a method is presented to obtain the gradients required to adapt general state-space filters. Unfortunately, the number of computations for this general case is quite high. To reduce the number of computations, two new state-space adaptive filters are introduced. One application where these new structures are shown to be useful is in oversampled filtering where an estimate of the final pole locations is known and the adaptive filter is required only to fine-tune the transfer function. It is shown that for this type of application, the new adaptive structures can have much improved adaptation rates and roundoff noise performance as compared to the corresponding direct-form realizations. >