DETERMINATION OF STABILITY USING RETURN RATIOS IN BALANCED FULLY DIFFERENTIAL FEEDBACK-CIRCUITS

This paper describes SPICE [1] simulation techniques that can be used to find the return ratios for the differential and common-mode feedbac k loops in balanced, fully differential circuits, Since each of these loops may contain multiple feedback paths, conditions under which thes e two return ratios are sufficient for determining stability of the ba lanced feedback circuit are described, To allow the use of these techn iques with switched-capacitor common-mode feedback circuits, a special simulation technique is presented that finds the de bias for the retu rn-ratio simulations.