18.1 Present Status of Analogue Integrated Circuit Design

Analogue integrated circuit design has played an important role in the development of integrated circuit technology. As the level of integration increased in integrated circuit technology, digital circuit implementation became more desirable than analogue circuit implementation because of its robustness and simplicity of design. However, an all-digital implementation of complex integrated circuits is only found in certain types of applications such as memories and microprocessors and even in these integrated circuits, various types of analogue circuits are used. At the present time, a typical applications specific integrated circuit (ASIC) might contain 80% digital and 20% analogue circuits.

The focus of this book represents techniques for achieving higher performance in analogue circuits in the face of VLSI technologies. Current-mode analogue signal processing offers some important speed advantages over voltage signal processing. For example by nature, current is low impedance and therefore wider bandwidth. The various applications that have been discussed in the previous chapters give examples of how performance can be improved through the use of current signal processing techniques. One particularly important aspect of the current amplifier is found in the influence of feedback on the amplifier bandwidth. It has been shown that properly applied current feedback will cause the upper -3dB frequency to remain constant and independent of the closed loop gain [8]. This characteristic is extremely important in a circuit like a pipeline analogue-digital converter where the residue amplifier must have large bandwidth. A current amplifier having...