A fully integrated circuit design of a general complex function is developed. It is realised in log-domain since this technology shows good potential for design of low-power, high frequency and high-dynamic range networks. A number of transistor-level networks are developed and extensive examination of these networks is carried out with the intention of determining key design properties of general complex-valued networks.

Approximation and design methods of a general class of IIR complex functions without any required symmetrical property are examined. A set of routines has been developed to allow arbitrary amplitude approximation of such asymmetrical functions. Approximation routines will include such features as high-order touch points in both passband and stopband regions, fixed poles and zeros and arbitrary frequency template shaping. These features, in conjunction with a Remez approximation algorithm, will permit the development of functions that realise any reasonable arbitrary shape and form of the transfer function. Approximation routines have been implemented in the XFILTER design software and a number of examples, demonstrating efficiency and flexibility of the proposed approximation method.

In this paper, an accurate semi-symbolic analysis method based on polynomial interpolation techniques for large non-ideal switched linear networks (SC and SI) is presented. For the computation of frequency responses, the semi-symbolic method demonstrates significant improvements in speed over direct numerical methods and this increases with circuit size. It is shown that semi-symbolic techniques can be used in the computation of noise for circuits containing a limited number of clock waveforms, but the performance rapidly deteriorates with network size. Examples demonstrate the comparative speed and accuracy performance over a range of circuits.

Strategies and algorithms for multirate SC and SI filter design are presented in this paper. By using analogue multirate signal processing techniques, much more efficient SI or SC circuit realisations can be obtained. The paper shows how multirate systems can be synthesized within the filter design system XFILT.

The speed at which a digital sigma-delta modulator can operate is limited by the latency of the loop filter. A digital sigma-delta modulator is presented which overcomes the problem of long adder carry propagation delays. The design is sixth order and implemented using a single pipelined resonator section.>

A fully general and efficient noise analysis method is presented for both switched capacitor and switched-current circuits. The fold back effects and non-ideal effects such as parasitic resistive time constant have been taken into account. The thermal noise and flicker noise generated by MOS transistors are considered. By utilising the adjoint network technique, only one system solution is needed for noise analysis. In addition, numerical inversion of the Laplace transformation, the Hessenberg technique, extensive sparse matrix routines and interpretable code generation have been used to improve the efficiency of noise analysis. The method has been implemented in SCNAP4 and numerical results are given in the last section.>

A comparison for SC filter realisation based on different biquads is given. The total capacitance, capacitance spread, sensitivity, non-idealities and dynamic range of the designed filters are presented. Some conclusions are obtained as very useful guidelines for the choice of a suitable biquad structure according to the nature of the filter problem.>

In this paper, the canonical transconductor-C realisation definition is given. Two approaches to realise a canonical structure for ladder based transconductor-capacitor filters are proposed. Examples are given to demonstrate the application of these techniques.>

A unified investigation is presented for low-sensitivity, limit-cycle-free filter structures. It is shown that important properties like boundedness and pseudopassivity are closely related to the symmetry of the system matrix description. Implementations by digital circuits are considered. It is demonstrated that symmetric matrix systems can be designed for optimal circuit performance. Sensitivity can be minimized if the deviation of component values is kept symmetric, which can be achieved for a digital filter design by carefully selecting the coefficient truncations.>

A previous attempt at realizing an adaptive circulator for telephone applications suffered from limitations due to voice switching problems, resistive part matching only, and some difficulties with adaptive operation for broadband signals. The use of pilot tones enables the circuit to be free from voice switching problems and to accomplish a close impedance match with that of a telephone line. Analysis of the circuit in an adaptive hybrid configuration produces the theoretical bounds on performance. Experimental results display the performance characteristics of the adaptive circuits and various other hybrid circuits on a selection of subscriber lines with a range of terminations.

A design for an adaptive three-port electronic circulator is presented. The circuit has particular use in telephone work and this model can provide isolation when the terminating load varies over the range200 \Omega - 1 k\Omega. The whole circuit is realizable in microelectronic form.