A WIDE-BAND LCD SEGMENT DRIVER IC WITHOUT SACRIFICING LOW OUTPUT-OFFSET VARIATION

This paper describes a segment driver IC for high-quality liquid-cryst al-displays (LCDs). Major design issues in the segment driver IC are a wide signal bandwidth and excessive output-offset variation both with in a chip and between chips. After clarifying the trade-off relation b etween the signal bandwidth and the output-offset variation originated from conventional sample-and-hold (S/H) circuits, two wide-band S/H c ircuits with low output-offset variation have been introduced. The bas ic ideas for the proposed S/H circuits are to improve timing of the sa mpling pulses applied to MOS analog switches and to prevent channel ch arge injection onto a storage capacitor when the switches turn off. Th e inter-chip offset-cancellation technique has been also introduced by using an additional S/H circuit. Two test chips were implemented usin g the above S/H circuits for demonstration purposes. The intra-chip ou tput-offset standard deviation of 9.5 mV(rms) with a -3dB bandwidth of 50 MHz was achieved. The inter-chip output-offset standard deviation was reduced to 5.1 mV(rms) by using the inter-chip offset-cancellation technique. The evaluation of picture quality of an LCD using the chip s shows the applicability of the proposed approaches to displays used for multimedia applications.