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LCD Electronics Theory of Operation

LCD Electronics Theory of Operation Dick McCartney Corporate Technologist 1 Feb 2010 LCD Functional Diagram Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver W-LED RGB-LED Light Source Backlight PWR Conv

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LCD Electronics Theory of Operation

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  1. LCD Electronics Theory of Operation Dick McCartney Corporate Technologist 1 Feb 2010

  2. LCD Functional Diagram Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  3. Ernst Lueder, "Liquid Crystal Displays : Addressing Schemes and Electro-Optical Effects (Wiley Series in Display Technology)", John Wiley & Sons, 22 June, 2001.

  4. free az bound free free ax director axis bound free ay Liquid Crystal Nematic Order Nematic Order: • Free to translate in x,y and z directions • Free to rotate about the major (director) axis • Restricted rotation of the director axis

  5. Dielectrics of Nematic Order Dielectric Property eperpendicular-2 eperpendicular eparallel eparallel eperpendicular-1 director axis director axis Nematic Order reduces a 3-dimensional dielectric property to two dimensions. eperpendicular-1 eperpendicular-2 + eperpendicular Due to spin about the director axis. = 2

  6. Torque Depends on VRMS RMS dependency Temperature dependency dielectric anisotropy

  7. Order Depend on Springs Nematic order is maintained by intermolecular forces which are macroscopically characterized as spring constants for the material. The bend, twist and splayspring constants restore order in a perturbed system. E-field inducted torque works against these springs. The spring constants also depend on temperature

  8. LCD Monitor Block Diagram Display Electronics Scaler RGB (VGA) DVI Power Converter Backlight WALL PWR L Audio AMP AUDIO IN R

  9. LCD TV Block Diagram Display Electronics Tuner Video Processor CABLE CVBS Y/C YUV YPbPr Power Converter RGB (VGA) DVI/HDMI Backlight WALL PWR L Audio AMP Audio Processor AUDIO IN AUDIO OUT R

  10. RepresentativeSmart Phone System Radio Section Including: carrier modem, Bluetooth, WiFi, GPS PMU LED Driver Application Processor Key pad Key Pad Cntlr Level Shifter Memory Stick Battery Charging & Protection Processor/ Main Unit Camera LED Driver LED Flash Display Audio Subsystem Micro- phone Display Driver & Power Audio Amplifier Audio/Video

  11. LTPS LCD Functional Diagram Display Driver Chip Timing Controller Application Processor or Graphic Controller DSI MPL Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver Integrated into the LTPS display panel W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  12. LCD Device Operation Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver CCFL W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  13. Active Matrix source or column driver (row) gate NMOS FET source drain (column) (subpixel) gate or row driver common backplane driver (Vcom)

  14. Serial Data Scan Pattern Converted to Row-by-Row pixel 1 Serial input R:G:B new frame old frame

  15. Vcom Function Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver CCFL W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  16. Gate Line Charge Injection Gate bus Cgd Cstore Clc

  17. V Alternating Voltage Drive Normally-White Operation Alternating polarity is used to keep the average voltage value across the LC at zero. This prevents electroplating of ion impurities in the liquid crystal onto the electrodes. Electroplating of contaminants is a major source of image retention (sticking image). Brightness RMS Voltage

  18. Subpixel Voltage Translation Gate Bus Voltage Subpixel Voltage DV + Polarity Translated Source Bus Voltage DV - Polarity Row Select Time

  19. Vcom Equivalent Circuit at the Subpixel Level real transistor with its charge injection modeled as a series voltage drop. ideal transistor without charge injection operating as a voltage controlled switch. V Vsource Vsource Vgate Vgate Clc Cstore Clc Cstore Vcom

  20. Static and Dynamic Vcom Cgd Vsource Clc Vgate Cstore Vcom dynamic(GL) Vcom static

  21. Grayscale Dependent Offset Cgd Column Driver Vsource Clc Vgate Cstore Vcom dynamic (GL) Vcom static

  22. Adding Dynamic Vcom to each gray level of the Column Driver Voltage pair for one particular gray level normally black behavior offset +V Dynamic Range -V GL 255 0 255 0 GL Asymmetric Inverse Gamma Curve Correcting for DV Symmetric Inverse Gamma Curve

  23. Vcom (GL) Vcom (GL) Vcom (GL) V V V Vcom Corrected Matrix V(GL) V(GL) V(GL) Vgate Clc Clc Cstore Cstore Clc Cstore Vcom column line or source bus

  24. Row Driver Operation Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver CCFL W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  25. Gate and Source Voltages Select Voltage Gate Bus Voltage ON Center of the driving waveform Valid Source Bus Range OFF De-Select Voltage Row Select Time

  26. D D D D D D D D Q Q Q Q Q Q Q Q LS LS LS LS LS LS LS LS Row Driver Block Diagram Start Out Start in CLK OE Outputs

  27. AMLCD Address Signal Propagation Column Drivers Row Signal Delay Worst Corner (column driver changes immediately but row fall is delayed) Row Signal Delay Column Delay Column Delay Column Delay Row Drivers Row Signal Delay Best Corner (column line changes well after row line changes)

  28. OE Required Row Select Pulse for both Near and Far Column row line signal column line signal TFT off Far column

  29. Conventional Solution Row and Column Signals OE adjustable width Row N Row N + 1 Row N + 2 Row N + 3 Line N Line N+1 Line N+2 Line N+3

  30. Column Driver Operation Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver CCFL W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  31. Simplified, 6-bit (64:1), R-DAC analog voltage references Analog output Gray level voltage digital code (input)

  32. Decoder Decoder Decoder Decoder Column Driver Block Diagram gamma references in large format drivers there are two separate banks of reference busses, one for each polarity. in small format drivers the reference busses are usually shared between polarities. Digital Gray Levels Output Strobe Outputs

  33. Column Driver Direct Drive Column Driver Column Driver Row Driver Vcom Driver

  34. Column Driver Direct Drive Column Driver Column Driver Row Driver Vcom Driver

  35. Normally-White Direct Drive Graylevel

  36. Gamma References

  37. Column Driver Vcom Modulation (AC Vcom) Row Driver Vcom Driver

  38. Vcom Modulation Inverse Gamma Negative Positive Graylevel

  39. LTPS Active Matrix LTPS Display Driver multiplexer integrated into glass gate or row driver integrated into glass

  40. Rotated, LTPS Active Matrix LTPS Display Driver rotation permits fewer column outputs for the same h x v format

  41. Frame M+1 Frame M E O E O E O E O Rows E + + + + E - - - - O + + + + O - - - - E + + + + E - - - - O + + + + O - - - - - - + + Frame Inversion • Low Power Operation • Sensitive to Flicker Due to Lack of spatial Averaging and Slight Transmissivity Mismatches for + and - Polarities • Sensitive to Horizontal and Vertical Cross-talk

  42. Frame M+1 Frame M E O E O E O E O Rows E + + + + E - - - - O - - - - O + + + + E + + + + E - - - - O - - - - O + + + + - + - + Line Inversion • Reduced Flicker Due to Spatial Averaging • Reduced Vertical Cross-talk • Compatible with Vcom Modulation Scheme • High Power Operation: 480X Higher Power than Frame or Column Inversion • Sensitive to Horizontal Cross-talk

  43. Frame M+1 Frame M E O E O E O E O Rows E + - + - E - + - + O + - + - O - + - + E + - + - E - + - + - - + + O + - + - O - + - + Column Inversion • Low Power Operation • Further Flicker Reduction Due to Spatial Averaging • Greatly Reduced Horizontal Cross-talk • Requires High Voltage Source Driver • Reduces component count and complexity • Incompatible with Vcom Modulation

  44. Frame M+1 Frame M E O E O E O E O Rows E + - + - E - + - + O - + - + O + - + - E + - + - E - + - + O - + - + O + - + - - + - + Pixel Inversion • Highest Quality Image Due to Reduction in Both Horizontal and Vertical Cross-talk • No Flicker Due to Spatial Averaging • Requires High Voltage Source Driver • Incompatible with Vcom Modulation • Higher Power Due to Line Inversion Component

  45. Pixel Inversion Frame 1 + - + - + - - + - + - + - + - + - + Frame 2 + - + - + -

  46. N-Line Inversion (N=2) Frame 1 + - + - + - + - + - + - - + - + - + Frame 2 - + - + - +

  47. ó ó ó l l l l l l P( P( ) ) f f ( ( ) d ) d K ó ó ó y y Video System Intensity Transformations (Gamma) Irradiance from source (spectral density function) (watts/steradian) Simultaneous contrast Effect in dark surround = (x)1/125 CRT or other display device = (x)2.5 Human Lightness Perception (Brightness) Contrast boost as Pre-correction for Dark surround (assumed = (x)1/1.125 Pre-correction for display device (assumed = (x)2,5 (Y) L (Y’) L0.45 (L0.4) L1.125 L (x)2.5 (x)1/1.125 (x)1/2.5 116(x/xn)0.33 -16 (x)1.125 P(l) Camera (video source) TV Display Human Visual System These two spaces are reasonably linear with each other. Enough so that image processing in the Luma domain is close enough to be uniform in perception. www.poynton.com Charles Poynton, A Technical Introduction to Digital Video. New York: Wiley, 1996.

  48. Advanced Features Timing Controller Video Source Gamma DAC Ref Column Drivers Electronics DC/DC Conv Display Vcom Buffer Row Driver CCFL W-LED RGB-LED Light Source Backlight PWR Conv Controller Driver

  49. Dynamic Contrast Expansion Reduced Backlight (x1/N) LCD limited contrast Bright Images Amplified Grayscale (xN) Dark Image When the Image is Dark… Ideal Contrast Scale the Transmission up by N Dark Images While scaling The Backlight Down by N Ideal Contrast Experience

  50. LCD Lighting Modes

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