Improving toggle rate in a rail-to-rail comparator output stage

Abstract

The demand for high-speed components has driven an increase in the speed of analog comparators, a building block for many analog circuits. This paper describes the modification of one of Linear Technology's low-cost, high-speed comparators to increase the output toggle rate beyond the one hundred megahertz range. The essential modifications to the output stage mainly relate to overcoming quasi-saturation of the output devices by extracting unwanted, stored base charge. Additional features were added into a dual comparator package with a tiny footprint to increase consumer interest and to diversify it from other comparators in Linear Technology's line. A final circuit design and physical silicon layout were designed using computer design tools, and the IC was fabricated and tested. The first silicon was tested extensively and worked successfully with only minor undesired discrepancies that were deemed acceptable. The LT1715 design was successful since the design itself accomplished all the desired specifications and the part is now available for sale.