Current controlled multi-step CMOS video data converters

Abstract

A method of connecting K identical parallel M bit converters to form a K-M bit converter is presented. By controlling the voltage drop over the resistor string with a current the linearity is made independent of offset voltage between the steps and high ONresistance in the switches. This connection gives DACs with linearity determined by the resistors and with a speed / power ratio of 15MHz/mW. An ADC based on the same idea has been developed for a PAL video application. This ADC uses two identical flash ADC blocks in the two-steps, making the principle suitable for monolithic integrated, hybrid and PCB solutions.