The matching of small capacitors for analog VLSI

The capacitor has become the dominant passive component for analog circuits designed in standard CMOS processes. Thus, capacitor matching is a primary factor in determining the precision of many analog circuit techniques. In this paper, we present experimental measurements of the mismatch between square capacitors ranging in size from 6 /spl mu/m/spl times/6 /spl mu/m to 20 /spl mu/m/spl times/20 /spl mu/m fabricated in a standard 2 /spl mu/m double-poly CMOS process available through MOSIS. For a size of 6 /spl mu/m/spl times/6 /spl mu/m, we have found that those capacitors that fell within one standard deviation of the mean matched to better than 1%. For the 20 /spl mu/m/spl times/20 /spl mu/m size, we observed that those capacitors that fell within 1 standard deviation of the mean matched to about 0.2%. Finally, we observed the effect of nonidentical surrounds on capacitor matching.