An addressing technique for displaying restricted patterns in rms-responding LCDs by selecting a few rows at a time

Transcription

1 An addreng technue for dplayng retrcted pattern n rm-repondng LCD by electng a few row at a tme K. G. Pan Kumar T. N. Ruckmongathan Abtract An addreng technue that wll allow rm-repondng matrx LCD to dplay retrcted pattern propoed. Th technue baed on the electon of a few row at a tme whle cannng the dplay. In applcaton uch a logc analyzer and ocllocope, motly ngle-valued functon of tme are dplayed. Th retrcton n the mage ueful n enhancng the electon rato o that good contrat achevable even wth TN-LCD. It hown that a large reducton n the hardware complexty of the column drver and the upply voltage poble when the waveform beng dplayed do not overlap each other and are eually paced. Keyword Pave-matrx LCD, addreng technue, retrcted pattern, mult-lne addreng. Background A matrx dplay uually degned to dplay general pattern. Hence, t poble to dplay N dfferent pattern n any column of a matrx dplay wth N row. However, mot of thee N combnaton do not occur n dplay for ocllocope and logc analyzer. Shank and Holland have ued the correlaton properte of peudo random bnary euence (PRBS) for dplayng a ngle waveform on a matrx LCD. An nfnte electon rato poble becaue only one waveform dplayed. An addreng technue for dplayng multple waveform on a matrx LCD wa propoed n 986. Th technue baed on cannng the matrx by electng one row at a tme. The electon rato of th technue ndependent of matrx ze and only depend on the number of waveform (w) beng dplayed. In thee dplay the number of elected pxel n each column eual to w. The number of background pxel (N-w) uually much hgher than w. The column voltage for the background pxel choen to be the ame a that for the unelected row. The column voltage for the elected pxel (.e., pont on the waveform) choen to be n-phae wth the row-elect voltage. Th euvalent to agnng data 0 to the background pxel and + to the elected pxel. Here, the rm voltage of elected pxel lower than that of the background pxel. Hence, th technue referred to a the retrcted pattern addreng technue negatve contrat (RPAT-NC). The rm voltage acro each elected pxel can alo be made greater than the background pxel by choong the column voltage for a elected pxel to be out of phae wth the row-elect voltage. Th technue referred to a the retrcted pattern addreng technue potve contrat (RPAT-PC). The electon rato of RPAT are ndependent of matrx ze and are hgher than that of the conventonal technue. 4 Hence, a good contrat rato can be acheved even n LCD wth large matrx ze. Intantaneou voltage acro any pxel n a dplay addreed wth RPAT zero durng mot of the tme nterval, and th may lead to flcker when N very large. The upplyvoltage reurement of RPAT alo ncreae wth matrx ze. In order to overcome thee problem a new flcker-free addreng technue wa propoed n 996. Th technue baed on electng all the row n the matrx dplay multaneouly, a n the cae of actve addreng. 6 Here the N row n the matrx dplay are drven wth waveform correpondng to a et of orthogonal functon derved from PRBS. The column waveform are generated by takng the orthogonal tranform of the data to be dplayed. Here, agan, the data agned to the background pxel zero whle + agned to the elected pxel. Th technue referred to a PRBS-NC. The lower rm voltage uppled to the elected pxel compared to the background pxel. In a mlar technue known a PRBS-PC, the elected pxel receve a hgher rm voltage when the data agned to the elected pxel. A hgher addre duty factor n the PRBS technue reult n the uppreon of flcker and frame repone when N large. The number of tranton n the row waveform almot the ame when orthogonal functon derved from peudo random bnary euence ued. Th reult n a good brghtne unformty of the pxel a compared to that of RPAT. The upply-voltage reurement n the PRBS technue ndependent of the matrx ze, and t lower than that of RPAT. The only dadvantage of PRBS technue that the number of voltage level n the column waveform ncreae wth w a n the cae of dplay n a logc analyzer. In ummary, both lne-by-lne addreng a well a multaneou electon of all the row ha been condered Receved 7//00; accepted 9//00. The author are wth the Raman Reearch Inttute, Lud Crytal Laboratory, Sr C. V. Raman Ave., Sadahvanagar, Bangalore, , Inda; telephone , fax , e-mal: pan@rr.ernet.n Copyrght 000 Socety for Informaton Dplay 07-09/00/080-0$.00 Journal of the SID 8/, 000

2 n the pat for dplayng retrcted pattern. We explored the poblty of electng a few row at a tme. Th approach analogou to mult-lne addreng (MLA) for dplayng general pattern. We have found that t poble to reduce the number of column voltage level when the number of waveform beng dplayed are large. Hence, t poble to reduce the hardware complexty of the column drver n pecal cae uch a dplay for a logc analyzer. Technue In th preent work for dplayng retrcted pattern we have opted to can the dplay by electng a few row at a tme. Th approach for drvng matrx LCD wll be referred to a mult-lne retrcted pattern addreng (MLRPA). Here, the N row to be multplexed n a dplay are dvded nto (N/) non-nterectng ubgroup, wth each ubgroup contng of addre lne. The data to be dplayed n a elected ubgroup n any one of the column an -bt word repreented d k+. Here the value of range from to and the varable k repreent the elected ubgroup and range from 0 to [(N/) ]. By agnng the data for the background pxel to be 0, the electon rato ndependent of matrx ze. Background pxel receve a hgher rm voltage compared to the elected pxel when the data for the elected pxel agned to be +. Th reult n negatve contrat. The dplay exhbt a potve contrat when the data for the elected pxel agned to be. However, the electon rato wll be lower than that for the negatve contrat mode. A n all the retrcted-pattern addreng technue, thee two varant wll be referred to a MLRPA NC and MLRPA PC, repectvely. A et of orthogonal functon are ued for electng a ubgroup of a matrx LCD. Smple orthogonal functon uch a Walh functon are preferred. Let O(,j) be the matrx repreentng the dcrete veron of the orthogonal functon. Here, the element of the matrx O(,j) are jut + or and the followng condton atfed: Â j " m n O( m, j) O( n, j), 0 " m π n wheren the calng factor whch depend on the actual orthogonal matrx elected for cannng the dplay. In the cae of Walh functon and Hadamard matrce, the total number of column n the orthogonal matrx. The column of the orthogonal matrx O(,j) are called row-elect pattern. A ubgroup elected wth voltage correpondng to one of the row elect pattern. The ampltude of thee voltage ether +V r or V r correpondng to + or n the row-elect pattern. The remanng (N ) row of the unelected ubgroup are grounded. The data n the elected ubgroup repreented by a column vector, wth element takng value of 0 or +. The column voltage the R S T () FIGURE Row-elect pule are adjacent to each other. (a) Row and column waveform for a matrx LCD and (b) correpondng row elect matrx. (Note: The ymbol + repreent a + and repreent a ). dot product of the row-elect pattern and the data vector. Th can be mathematcally repreented a Ck( j) ÂO(, j) dk+ () where C k (j) the column voltage (normalzed to V c ) correpondng to the j th row-elect pattern for the k th ubgroup. Smlarly, column voltage for all the column n the matrx are determned ndependently. Both the row and column voltage are appled multaneouly to the matrx dplay for a tme duraton τ. The proce repeated wth another rowelect pattern ether n the ame ubgroup or a dfferent ubgroup. A cycle completed when all the ubgroup (N/) are elected wth all the row-elect pattern once. The dplay refrehed contnuouly by repeatng th cycle. The cannng of the matrx can be done n a number of way. The ubgroup may be elected wth all the row-elect pattern once before electng another ubgroup. Th llutrated n Fg., for N 0 and. However, th method not 6 Kumar and Ruckmongathan / Dplayng retrcted pattern n rm repondng LCD

3 FIGURE The row-elect pule are dtrbuted n a cycle. (a) Row and column waveform for a matrx LCD and (b) correpondng row-elect matrx. (Note: The ymbol + repreent a + and repreent a ). FIGURE The row-elect pule are dtrbuted n a cycle by electng a ubgroup wth dfferent row elect pattern. (a) Row and column waveform for a matrx LCD and (b) correpondng row elect matrx. (Note: The ymbol + repreent a + and repreent a ). utable for fat-repondng LCD. Becaue the tranmon of OFF pxel ncreae due to cluterng of the uually large ampltude row-elect pule. Th may lead to the frame repone phenomena. In order to uppre the frame repone, all the ubgroup n the matrx LCD may be elected wth one row-elect pattern once before changng to another row-elect pattern, a hown n Fg.. Good brghtne unformty of the pxel can be obtaned by changng the row-elect pattern whenever a new ubgroup elected. Th llutrated n Fg.. whch the dot product of the row elect pattern and the data vector n the k th ubgroup gven by C ( j) O(, j) d, k  k+ where j range from to and k range from 0 to N/. The voltage acro any pxel the dfference between row and column voltage. The rm voltage acro the th pxel ( ) n the k th ubgroup [0 k (N/ )] gven by Analy A ubgroup elected wth voltage correpondng to one of the row-elect pattern. The voltage are +V r or V r, correpondng to + or. The row voltage zero durng the (N/ ) tme nterval when other row are beng elected. The column voltage C k (j) (normalzed to V c ) Vk+ ( rm) ( N -)  VrO(, j) - Ck( j) +   Cn( j) j n 0 j nπk () Journal of the SID 8/, 000 7

4 V ( rm) k+ L  ( ) j NM ( N -) V O(, j) - V O(, j) O j d O j d r r  (, ) + k+    (, ) n+ n 0 j Vk+ ( rm) ( N -) Vr  O(, j) - Vr dk+  O(, j) +   dn+  O(, j) j j n 0 j Vk+ ( rm). (4) Th the general expreon for the mult-lne addreng (MLA) technue. In order to dplay w waveform n a matrx LCD, only w pxel n each column carry the nformaton, and (N-w) pxel n each column are the background pxel. Data for the w nformaton carryng pxel are agned to be +, whle the remanng (N-w) background pxel are agned to be 0. Th reult n a negatve contrat (NC) mode, wth elected pxel recevng a lower rm voltage compared to background pxel. If the V k+ (rm) n E. (4) correpond to the one for the elected pxel (.e, d k+ +), then the rm voltage acro the elected pxel (.e., OFF) after mplfcaton O QP L NM O QP ( N -) Vr - Vr dk+ +   dn+ n 0 Voff ( rm) Voff ( rm) Vr - Vr + w, Vr - Vr + w. () Th electon rato ame a that of RPAT NC and PRBS NC. Smlarly, by agnng data for the elected pxel to be for the potve contrat mode, electon rato for MLRPA PC gven by w + SR. (8) w Th ame a that obtaned for RPAT PC and PRBS PC technue. Thu, the electon rato for retrcted patternaddreng technue are ndependent of the matrx ze. 4 Supply voltage reurement of MLRPA NC The upply voltage (V up ) for the drver calculated by the maxmum wng n the addreng waveform a gven below. Cae I: If ( w), then V r > V c, where V r the maxmum wng n the row waveform and V c the maxmum wng n the column waveform. The upply voltage gven by where.e., V V, V w V, up r up c Vc N wvat, N Vup V at. (9) Smlarly, f V k+ (rm) correpond to a background pxel (.e., d k+ 0), then from E. (4) the rm voltage acro the background pxel (.e., ON) Von( rm) Vr + w, Vr w Von( rm) + (6). The electon rato defned a evon Voffj optmum when V r w. Thu, the optmum electon rato for the MLRPA NC mode gven by SR w w -. (7) FIGURE 4 Comparon of the upply voltage reurement (normalzed to V at ) for dplayng retrcted pattern ung the MLRPA NC technue when 8 wth thoe of PRBS NC and RPAT NC. 8 Kumar and Ruckmongathan / Dplayng retrcted pattern n rm repondng LCD

5 Cae II: If ( w < < w), then the maxmum wng n the addreng waveform V c, thu the upply voltage V up V, N Vup (0) w V at. Cae III: If ( w), then the maxmum wng n the addreng waveform wv c, the upply voltage gven by V up c wv, wn Vup Vat. c () Fgure 4 how a comparon graph of the upply voltage reurement for dplayng retrcted pattern for varou value of N and w by electng 8 row at tme. Reult For cae of the PRBS technue, where n all the row are elected multaneouly to dplay w waveform, (w + ) column voltage level are reured. Hardware complexty of the column drver alo ncreae a the number of waveform beng dplayed ncreaed. For the preent MLRPA technue, one can chooe < w o that maxmum number of column voltage level can be lmted to + ntead of w +. Thu, the number of column voltage level depend on the maxmum number of elected pxel n the elected ubgroup. However, uually not all the waveform wll overlap (a) (b) (c) (d) FIGURE (a) Comparon of the upply voltage reurement (normalzed to V at ) for dplayng retrcted pattern ung the MLRPA NC technue when 8 wth that of PRBS NC. (b) Comparon of the upply voltage reurement (normalzed to V at ) for dplayng retrcted pattern ung the MLRPA NC technue when 6 wth that of PRBS NC. (c) Comparon of the upply voltage reurement (normalzed to V at ) for dplayng retrcted pattern ung the MLRPA NC technue when wth that of PRBS NC. (d) Comparon of the upply voltage reurement (normalzed to V at ) for dplayng retrcted pattern ung the MLRPA NC technue when wth that of PRBS NC. Journal of the SID 8/, 000 9

6 TABLE MLRPA-NC Technue PRBS-NC Technue RPAT-NC N w No. of voltage level reured Supply voltage (normalzed to V at ) No. of voltage level reured Supply voltage (normalzed to V at ) No. of column voltage level reured (4) Supply voltage (normalzed to V at ) each other n a elected ubgroup, and thu the number of column voltage level may be le than +. In applcaton uch a logc analyzer, the waveform generally do not overlap wth each other and are eually paced. One can chooe N/ w, then only one elected pxel wll be preent n each ubgroup. Hence, only two column voltage level (+V c and V c ) are reured. If (N/) > w, then n ome ubgroup none of the elected pxel may be preent. Thu, only three column voltage level (+V c, 0 and V c ) are needed. Hence, the number of column voltage level can be reduced conderably for a gven applcaton. Supply voltage for the drve electronc gven by the maxmum wng n the addreng waveform. Lower ampltude pule reduce the upply voltage of the drve electronc. Fgure how the upply voltage reurement (normalzed to V at ) of MLRPA NC n comparon wth PRBS-NC for varou value of. Table ummarze the number of column voltage level a well a the upply voltage reurement of MLRPA NC n comparon wth that of the RPAT-NC and PRBS NC technue. A computer program ha been developed to generate the data of row and column waveform for a 6-row matrx LCD to dplay eght waveform. The data from the program wa loaded nto the waveform FIGURE 6 Supply voltage (normalzed to V at ) of the MLRPA NC technue for varou value of. generator WFG 00, and typcal row and column waveform were appled to a ngle pxel. The upply-voltage reurement wa meaured ung an electro-optc meaurement etup. Fgure 6 how the upply-voltage reurement 60 Kumar and Ruckmongathan / Dplayng retrcted pattern n rm repondng LCD

7 TABLE N w [V up (MLRPA NC)/ V up (PRBS NC)] 00 No of voltage level reured (MLRPA NC)/ (PRBS NC) / / / / / / / / / / / / 0.00 / / / (normalzed to V at ) for the cae of the MLRPA NC technue n dplayng eght waveform n a 6-row matrx LCD by electng varou value of. The upply voltage obtaned from the meaurement agree wthn ±.% of the theoretcal value. The rm voltage acro the ON and OFF pxel were meaured ung the HP 467A, a loggng multmeter capable of meaurng true-rm voltage. Fgure 7 how the plot of V on (rm) and V off (rm) for varou value of the upply voltage. Fgure 8 how the plot of the electon rato meaured expermentally. The electon rato obtaned from meaurement agree wthn ±0.% of the theoretcal value of.47. Table how the value of leadng to a large reducton n the upply voltage a well a FIGURE 8 Selecton rato veru upply voltage. the number of column voltage level for varou value of N and w n comparon wth the PRBS NC technue. The addreng technue dcued above ha been mplemented ung a matrx TN-LCD. A photograph of a dplay addreed by electng eght row at a tme hown n Fg. 9. Four waveform are dplayed wth jut three voltage level n both row and column waveform. 6 Concluon We have demontrated the feablty of a new addreng technue to dplay retrcted pattern wth TN-LCD. The hgher electon rato of the retrcted-pattern addreng technue allow for the ue of relatve fat TN-LCD rather than STN-LCD wth low repone tme. The FIGURE 7 RMS voltage acro a pxel veru upply voltage. FIGURE 9 Photograph of a TN-LCD dplayng four waveform and addreed ung MLRPA NC by electng eght row at a tme. Journal of the SID 8/, 000 6

8 electon rato whch ndependent of the matrx ze an added advantage of ung retrcted-pattern addreng to can the pave-matrx LCD. The electon rato of th mult-lne approach ame a that for other retrcted-pattern addreng technue uch a RPAT and PRBS. However, t poble to reduce the hardware complexty of the column drver a well a the upply-voltage reurement whle ung MLRPA by a careful choce of for a gven matrx ze (N) and the number of waveform (w). Acknowledgment The author are thankful to S. Sehachala and H. Subramonyam for the fabrcaton of the dplay. Reference I A Shank and P A Holland, Addreng method for non-multplexed lud crytal ocllocope dplay, SID Intl Symp Dget Tech Paper, - (979). T N Ruckmongathan, An LCD for multtrace ocllocope, SID Intl Symp Dget Tech Paper, 8- (986). T N Ruckmongathan, the ubmtted to department of electrcal communcaton engneerng, Indan Inttute of Scence, Bangalore, Inda, P M Alt and P Plehko, Scannng lmtaton of lud crytal dplay, IEEE Tran Electron Devce ED-, 46- (974). T N Ruckmongathan, Flcker free retrcted pattern addreng technue wth low upply voltage, SID Intl Symp Dget Tech Paper, 6-6 (996). 6 T J Scheffer and B Clfton, Actve addreng method for hgh-contrat vdeo-rate STN dplay, SID Intl Symp Dget Tech Paper, 8- (99). 6 Kumar and Ruckmongathan / Dplayng retrcted pattern n rm repondng LCD