This paper considers externally linear, time-invariant systems which can be internally nonlinear and/or time-varying. Several examples of the synthesis of such systems are presented, and it is argued that they offer advantages in comparison to internally linear, time-invariant systems. In particular, their use in signal processing is considered, and it is shown that they can be designed to reduce the undesirable effects of overloading and noise corruption through the use of companding. It is shown that a variety of previously proposed schemes for this purpose are all related. Several practical problems are discussed, as are performance criteria and types of measurements needed for the evaluation of the systems discussed.

Externally linear, time-invariant systems and their application to companding signal processors

A new second-order log filter topology, which is particularly useful for RF signal processing, is introduced with a discussion of how its features meet the needs of RF design. The design concept behind log filters is reviewed. Simulation and experimental results on a test IC are presented for an electronically tunable filter which operates beyond 400 MHz, with Q's in excess of 60, using the AT&T CBIC-V2 process.

Log domain filtering for RF applications

In this paper, the design and measurement of a l-V translinear integrator and its application in a controllable second-order lowpass filter for hearing instruments is presented. A semicustom version of the filter has been integrated in a standard 2-/spl mu/m, 7-GHz, bipolar IC process and operates at voltages down to 1 V, consumes only 6 /spl mu/A, and has a dynamic range of 57 dB for a total harmonic distortion below 2%. Its cutoff frequency is linearly adjustable in octaves from 1.6 to 8 kHz.

/pdf/a-low-voltage-ultra-low-power-translinear-integrator-for-2v5te76n55.pdf

A low-voltage ultra-low-power translinear integrator for audio filter applications

As there is a growing interest in the design of so called "current-mode filters", this paper is concerned with an investigation into the general performance criteria and the speed/dynamic range limits of current-mode G/sub m/-C based filters, compared to conventional voltage-mode G/sub m/-C filters. It is shown here that, as far as speed, dynamic range, and power consumption are concerned and provided that both kinds of filter topology employ the same type of transconductors and capacitors, the result comes out in the favor of the use of the voltage-mode filter processing as a solution for realizing high performance G/sub m/-C filters.

Current-mode versus voltage-mode G/sub m/-C biquad filters: what the theory says

The general state-space synthesis of linear filters is reviewed including the use of linear transformations. Then the use of time-varying nonlinear mappings on the state variables is shown to produce equations for the synthesis of linear, linear companding, and log-domain filters. Formulas are developed which underlie the realization of log-domain filters. Design issues relating to realizability, noise, and nonideal performance are discussed using the state-space mathematical formulation.

State-space synthesis and analysis of log-domain filters : Special section on instantaneous companding in analog signal processing

A new type of electronically tunable oscillator using a cascade of two capacitorless first order log-domain all-pass filters as the frequency and the gain controlling element is proposed, where it is shown that the log-domain circuit technique is ideally suited for implementation of electronically tunable oscillators, The resulting oscillator enjoys several attractive properties, namely, low supply voltage, high oscillation frequencies, wide tuning range and relatively large oscillation levels can be obtained without excessive distortions, as oppose to previously reported forward-biased diode based electronically tunable oscillators.

A 3.3 volt high-frequency capacitorless electronically-tunable log-domain oscillator

Presents a new class of current-mode oscillators using several representative log-domain circuits both as the frequency and the gain controlling elements in electronically tunable oscillators, where the resulting oscillators enjoy the attractive properties of low supply voltages, high oscillation frequencies, wide tunable ranges and low distortion at large oscillation current amplitudes.

https://ieeexplore.ieee.org/iel3/4816/13317/00608782.pdf

Log domain oscillators

This paper demonstrates the use of the genetic algorithm to simplify both the final symbolic transfer functions and the initial equivalent circuits so that meaningful and understandable results can be obtained. The resulting simplified circuits are only as complicated as necessary to give the required accuracy in the results, which will also help in giving a better graphical insight into the circuits under consideration. This highly efficient algorithm has also been integrated into a symbolic circuit analysis package.

http://ieeexplore.ieee.org/iel3/3834/11195/00539820.pdf

Automatic circuit simplification for meaningful symbolic analysis using the genetic algorithm

A new RC current-mode oscillator using unity-gain current-mirrors is presented. Transistor-level consideration in the analysis is needed to understand some important non-ideal circuit behaviours. The proposed oscillator shows good potential for wide tuning range and high-frequency operations. Frequency tuning can be done by varying only a single resistor. >

S. Pookaiyaudom

Papers

A 3.3 volt high-frequency capacitorless electronically-tunable log-domain oscillator

Log domain oscillators

Automatic circuit simplification for meaningful symbolic analysis using the genetic algorithm

Transistor-level consideration of an RC current-mode oscillator using unity-gain current-mirrors