Development of General-Purpose LSI for Sensor Signal Processing

Abstract

This paper describes how to develop a general-purpose LSI for analog signal processing for the signal obtained by variety of sensors. The LSI system includes eight independent elements and variety of signal processing circuit can be realized just by properly combining some of the elements functions. The eight elements are input-output full swing operational amplifiers, low noise operational amplifiers, monitor circuits, an absolute detector, filters, a current generate to adjust the filter cut-off frequency, an AGC, and reference voltage and current circuits. Among those, the input-output full swing operational amplifiers, the filters, and the absolute detector were newly designed by applying the special circuit techniques to make the circuits highly accurate. The conventional simple full swing operational amplifiers were mostly realized by C-MOS transistors, whereas the proposed circuits cannot help using the bi-polar transistors because variety of circuit elements are realized in the LSI. The LSI realized both by bi-polar and C-MOS transistors are more expensive than the LSI simply realized by bi-polar transistors. The gyrator techniques were newly employed to realize the filters by which the type of filters, i.e., HPF or LPF can be easily selected by the external connection of elements and the cut-off frequency can be easily adjusted by controlling the current to the circuit. The absolute detector does not include diodes from which the detector circuit is less-influenced by the temperatures and has the less-distortion characteristics.