Frequency-Based Measurement of Mismatches Between Small Capacitors

The mismatch between two capacitors can be measured by alternately switching each into an oscillator and measuring the change in the oscillation frequency. Three-stage differential ring oscillators can provide multiple mismatch data points for capacitances as small as 8 fF. Experimental results obtained from test circuits fabricated in 0.13-?m CMOS technology also reveal lower mismatches for metal sandwich capacitors than for lateral fringe structures.