Paper 11.3Wavelets for Displaying Gray Shades

in LCDs

T.N. Ruckmongathan

Raman Research Institute, Bangalore

Wavelets for

DisplayingGray Shades

in LCDs

ByT.N. Ruckmongathan,

Nanditha Rao P and Ankita Prasad

Raman Research Institute, Bangalore

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)

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)

• 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 2k gray shades

Same as Row pulse modulation, Para-unitary matrices and Successive approximation

Haar Wavelets

Energies of the Wavelets are equal

Principle

Wavelets are used to deliver energies that are proportional

to the weight of the gray shade data bits

Modified Haar Wavelets

Orthogonal matrices

Matrices for eight gray shades

Typical waveforms

Distributed select pulses

Multiplier in the column signal generator

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

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

Block diagram

Typical waveforms- pixel

Plot: RMS vs. Supply voltages

Photographs

Further work…• Find wavelets for displaying

large number of gray shades

Example for displaying 32 gray

Shades (Not necessarily the best !)

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

Acknowledgment

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

Thank you

For

Your attention