The authors present a new versatile circuit building block called a differential difference current conveyor (DDCC). An IC technique for implementing the DDCC is also presented. The DDCC-based frequency-selective circuits and nonlinear building blocks such as multiplier, squarer and square rooter are developed. Experimental results are given to demonstrate the feasibility of the proposed techniques, and they show that DDCC-based circuits offer a competitive design choice to CCIIbased and DDA-based circuits.

Aparasitic-capacitance-insensitive MOS-FET-C integrator and differentiator using operational transresistance amplifiers are proposed and experimental results demonstrated. The bandwidths of these circuits are also independent of their gains. The required capacitances are smaller than those in previous work. Two new configurations of universal current-mode biquad filters based on these circuits are presented. A secondorder bandpass filter constructed using universal biquad filters and another third-order Chebyshev lowpass filter with 0.1 dB passband ripple are breadboarded and the measured results presented.

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aspect of early vision processing. We studied the dependence of the output on the amplitude of the input in a series of simulations, which showed that the peak and the plateau values of the response are nonlinear monotonic increasing functions of J and nonlinear monotonic decreasing functions of I. Together, these results suggest that the circuit encodes the contrast rather than the absolute amplitude of the input. Fig. 3 shows that the peak and the plateau values of the response are approximately linear functions of Weber contrast on a logarithmic scale. Fig. 4 shows that the peak and the plateau values of the response are approximately linear functions of Michelson contrast on a linear scale, in particular when contrast is above 0.3.

Some new MOSFET-C integrators and CMOS current conveyors for realisations of the ladder filters are proposed. These integrators require smaller capacitance than with those currently used. The integrators also provide a better high-frequency performance in terms of gain and phase error responses. A sixth-order bandpass ladder filter, with 460 KHz centre frequency, 0.5 dB ripple, and ripple bandwidth 120 KHz, is designed and simulated. A third-order lowpass filter, with 2 dB ripple and 50 KHz ripple bandwidth, is experimentally demonstrated. The results reported in the paper will be useful in the realisation of high-frequency integrated continuous-time filters.