The development of VLSI technology, together with the request of a larger number of elements on a single chip, has ledto an improvedinterest in analog circuit design, especially for what concerns integrated circuits. The main aim of analogintegrated circuits (ICs) is to satisfy circuit specifications through circuit architectureswith the required performance. They can be used either as “stand-alone” topologies or connected to the digital part to implement mixed analog-digital functions, utilised in a wide field of applications.
Even if numerous researchers havepredicted a reducedutilisation of analog architectures and anincreased development of the digital counterpart, analog circuitry continues to benecessary. In fact, analog circuits are needed in many VLSIsystems such as filters, D/A and A/D converters, voltage comparators, current andvoltage amplifiers, etc.. Moreover, new applications continue to appear where new analog topologies have to be designedto ensure the trade-off between speed and power requirements.
Finally, the recent trend towards miniaturized circuits has given a strong and decisive boost towards the design of low-voltage low-power (LV LP) analog integrated circuits, which are widely utilized in portable-system applications [1,2,3]. This has led to implement new design circuit strategies in low-cost CMOS technology.
Since the beginning of electronics, the need of new active devices has always been very important. It has driven to thebirth of transistors which have been used, then, in amplifiers, impedance converters, filters, etc.. In particular, the voltage operational amplifier (OA) has rapidly become the main analog block and has dominated the market since the advent of the first analog integrated circuits.
Nowadays, the situation is changing because there is a new impulsetowards the so calledcurrent-modecircuits [4,5,6,7], which are able to overcome the limitation of a constant gain-bandwidth product [4,8,9] and the trade-off between speed and bandwidth, so that performance is improved in terms of low-voltage characteristics and of slew-rate and bandwidth.