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Paper 11.3 Wavelets for Displaying Gray Shades in LCDs T.N. Ruckmongathan Raman Research Institute, Bangalore

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Wavelets for Displaying Gray Shades in LCDs By T.N. Ruckmongathan, Nanditha Rao P and Ankita Prasad Raman Research Institute, Bangalore

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Displaying Gray Shades Frame modulation Suzuki et.al., SID Digest, pp 32-33, (1983) Pulse width modulation H Kawakami et.al., SID Digest, pp28-29, (1980) Amplitude (pulse height) modulation T.N. Ruckmongathan, Japan Display, pp 77-80, (1992) Row pulse height modulation H. Mono et. a.l. SID ‘93 Digest, pp 93-96,(1993) Para-unitary orthogonal matrices S.Young, Proceedings of IDW, pp 257-260,(1999) Successive approximation Pani Kumar et. Al., Proc. ASID, pp229-232, (2002)

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Do we need one more technique??? Frame mod: Flicker for more gray shades Pulse width: Poor brightness uniformity why? Number of time intervals is proportional to the number of gray shades (Both are simple techniques)

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Amplitude modulation: highly complex data waveforms, four time intervals Row pulse modulation: complex data waveforms, low selection ratio Para-unitary matrix: complex data waveforms The new wavelet based technique needs just k time intervals to display 2 k gray shades Same as Row pulse modulation, Para-unitary matrices and Successive approximation

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Haar Wavelets Energies of the Wavelets are equal

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Principle Wavelets are used to deliver energies that are proportional to the weight of the gray shade data bits

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Modified Haar Wavelets

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Orthogonal matrices

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Matrices for eight gray shades

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Typical waveforms

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Distributed select pulses

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Multiplier in the column signal generator Output of three such multipliers are added to get the column signal

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Multiplier Cont. …. Truth table Input code 000 (0) d 001 (+1) 010 (+2) 111 (-1) 110 (-2) Data = +1 000 (0) 001 (+1) 010 (+2) 111 (-1) 110 (-2) Data = -1 000 (0) 111 (-1) 110 (-2) 001 (+1) 010 (+2) 2’s complement notation

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Block diagram

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Typical waveforms- pixel

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Plot: RMS vs. Supply voltages

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Photographs

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Further work… Find wavelets for displaying large number of gray shades Example for displaying 32 gray Shades (Not necessarily the best !)

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Conclusion Opens up the possibility of displaying large number of gray shades with limited number of voltage levels in the addressing waveforms Wavelets can be tailor made to meet the design criteria 32 and 64 gray shades soon

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Acknowledgment A. R. Shashidhara for fabricating the display and preparing the figures

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Thank you For Your attention

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