Methodologies of Loop Offset voltage Trimming for Inverting-Buck-Boost for AMOLED Display Application

Methodologies of loop offset voltage trimming are presented in this paper for an inverting-Buck-Boost (IBB) having a wide output voltage (VNEG) range (-0.9V to -5.3V) used in an AMOLED display driver. Furthermore, the circuit is proposed and analyzed to meet the brightness control requirement of the AMOLED display. The error contribution from each sub-blocks of the brightness control circuit to VNEG is noted, and efficient ways of trimming the output voltage are analyzed. Achieving 0.3% of trimmed accuracy becomes challenging with the optimum number of trim bits as the magnitude of VNEG voltage reduces. Three different ways of trimming the VNEG, namely; three-step trimming, two-point trimming, and three-point trimming, are proposed and compared in terms of complexity and accuracy. The proposed methodologies of trimming are implemented for Inverting-Buck-Boost in BCD-180nm technology. Three-step trimming uses 17 bits (5-6-6 bits) resistor trimming and has the worst accuracy of ±0.17% across VNEG. Two-point trimming uses 11 bits (6-5 bits) and has the worst accuracy of ±0.3%, whereas the three-point trimming uses only 14bits (6-4-4 bits) and has the worst accuracy of ±0.21%.