A CALIBRATION ALGORITHM FOR ABSOLUTE AND RELATIVE TOLERANCES IN CMOS AND BiCMOS INTEGRATED RESISTORS
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2002-Apr-15
Precision analog IC functions such as filtering and signal conversion (A/D and D/A converters) require precise component matching for their reali- zations in silicon. However, the hmdamental limita- tions associated with analog integrated circuits such as the poor tolerance and mismatch of integrated resistors and capacitors limits, considerably, the achievable level of precision. To circumvent these limitations, expensive hybrid circuits combining two or more different and costly technologies are used. Complex thin-film resistor processing and laser trim- ming are still used to provide the necessary compo- nent matching. To reduce the cost associated with these process related solutions, CMOS circuit tech- nique solutions such as switched-capacitor and g,-C filtering [l-2] and self-calibrating A/D converters  have been proposed. All ofthese circuit related solu- tions makes exclusive use of integrated capacitors as the precision element to set pole/zero position in filters, for bandwidth definition, and to obtain pre- cise fractions of a reference voltage in A/D and D/A converters. On the other hand, integrated resistors typically have poor absolute accuracy (20-50%) and relatively high temperature coefficients (200-2000 ppm/"C) which limits the accuracy of data convert- $1 "REF ers to the &bit level and makes impractical the real- ization of conventional active filters since the -3dB bandwidth can vary by a full order of magnitude. Furthermore, only moderate resistance values can be obtained due to the relatively low sheet resist- ance of CMOS and BiCMOS processes (l-2.5 kQ/sq). These drawbacks have limited the use of integrated resistors as precision components.