This paper presents a source-driver IC for mobile OLED displays. The proposed 3-stage-cascaded 10-bit DAC fully exploits compactness benefit of multi-step interpolation. The overlap-switch merging (OSM) method allows for a 47% size-reduction in the 2-output R-DAC. The SAR-interpolating SC (SI-SC) DAC with bit-adaptive switch size (BASS) modulation is designed to obtain 2-output without switching errors. The proposed super-OTA buffer not only offers a fast slew-rate, but it also performs accurate 1-bit true-DC interpolation The SD-IC fabricated in 180nm shows the smallest area $(132.4 \times 16.7~\mu \mathrm{m}^{2}/\mathrm{Ch})$ and the best slew-rate FoM (2470.6) reported to date.