Very linear ramp-generators for high resolution ADC BIST and calibration

Two very linear ramp-generator designs are presented. The circuits are to be used in high-resolution ADC built-in-self-test (BIST) and on-chip calibration. The first design is used to charge a capacitor by a small current, which is linear enough to test 14-bit ADCs. The second design is in a relaxation oscillator architecture. It is linear enough to test up to 12-bit ADCs. The two designs have been fabricated in CMOS 2 /spl mu/m and 1.2 /spl mu/m processes separately.