Method of driving a matrix display device

A method of driving a matrix display device having an array of electro-optic display elements (12) each of which is connected in series with a two terminal non-linear device (15), such as a MIM, between associated row and column address conductors (16,17), in which the display elements are driven in a reset mode of operation by applying to the column address conductors data signals (D) and to the row address conductors selection signals (Vs) and reset signals (Va) to correct for non-uniformities in the characteristics of the non-linear devices, and in which in a row address period (T1) a data signal (D) applied to a column conductor is preceded by its inverse (D), a reset signal (Va) is applied during the application of the inverse data signal, and a selection signal (Vs+) is applied during the application of the data signal in the latter part of the row address period in order to minimize differences in ageing of the non linear devices.

BACKGROUND OF THE INVENTION 
This invention relates to a method of driving a matrix display device 
comprising sets of row and column address conductors, a row and column 
array of electro-optic display elements operable to produce a display, 
each of which is connected in series with a two terminal non-linear device 
between a row conductor and a column conductor, in which each row of 
display elements is driven by applying during a respective row address 
period a selection voltage signal to a row conductor to select the row of 
display elements and data voltage signals to the column conductors to 
drive each display element to produce a required display effect, in which, 
prior to the application of a selection voltage signal and a data voltage 
signal which are operable to charge a selected display element to a 
voltage of predetermined sign and magnitude at which the required display 
effect is obtained, the display element is charged to an auxiliary voltage 
of the same sign and greater magnitude. The invention relates also to a 
matrix display device drivable by such a method. 
The display device may be used to display alpha-numeric or video 
information and the two terminal non-linear devices can be of various 
forms, such as diode rings, back to back diodes, MIMs, etc. which are 
bidirectional and substantially symmetrical. The display elements, for 
example, liquid crystal display elements, are addressed by sequentially 
applying a selection voltage signals to each one of the first set of 
address conductors in turn and applying in synchronised manner data 
signals to the other set as appropriate to drive the display elements to a 
desired display condition which is subsequently maintained until they are 
again selected in a following field period. 
A method of driving a display device of the above kind is described in U.S. 
Pat. No. 5,159,325. In this method a five level row scanning signal is 
employed which includes a reset voltage signal in addition to the usual 
selection signals and non-selection (hold) levels. The selection and hold 
levels are polarity inverted for successive fields and, together with the 
reset voltage signal, which may be regarded as an additional selection 
signal, require a five level signal waveform. Before presenting a 
selection signal which together with the data signals provides the display 
elements of a row with a voltage of a certain sign, the display elements 
are charged through their non-linear devices having an approximately 
symmetrical I-V characteristic to an auxiliary voltage level of the same 
sign and which lies at or beyond the range of voltage levels (Vth to Vsat) 
used for display. During the application of the reset voltage the voltage 
applied to the column conductors may be set to zero volts. This method 
leads to a reduction of non-uniformities (grey variations) in the 
transmission characteristics of display elements which can otherwise occur 
when driving the rows with periodical inversion of the polarity of both 
the selection and the non-selection signals, simultaneously with inversion 
of the data signals. As described in that specification, the applied drive 
voltages can be arranged such that during a number of successive selection 
signals in successive fields applied to a row of display elements, which 
can include selection signals which are not preceded by a reset voltage 
for charging the display elements to an auxiliary voltage level, the 
current through the associated non-linear devices during selection periods 
has the same direction. 
The drive scheme of U.S. Pat. No. 5,159,325 helps to compensate for the 
effects of non-uniformities in the operating characteristics of the 
non-linear devices of the display device. 
Ideally, the non-linear devices of the display device should demonstrate 
substantially similar threshold and I-V characteristics so that the same 
drive voltages applied to any display element in the array produce 
substantially identical visual results. Differences in the thresholds, or 
turn-on points, of the non-linear devices can appear directly across the 
electro-optical material producing different display effects from display 
elements addressed with the same drive voltages. Serious problems can 
arise if the operational characteristics of the non-linear devices drift 
over a period of time through ageing effects causing changes in the 
threshold levels. The voltage appearing across the electro-optic material 
depends on the on-current of the non-linear device. If the on-current 
changes during the life of the display device then the voltage across the 
electro-optic material also changes. This change may either be in the peak 
to peak amplitude of the voltage or in the mean d.c. voltage depending on 
the actual drive scheme. The consequential change in display element 
voltages not only leads to inferior display quality but can cause an image 
storage problem and also degradation of the LC material. 
In European Patent Specification EP-A-0523797 there is described a similar 
display device which further includes a reference circuit which comprises 
a capacitor connected in series with a non-linear device like those of the 
display elements and to which is applied drive signals similar to those 
applied to the display elements. Changes in the way in which the 
non-linear device of the reference circuit behaves reflect behavioural 
changes in the non-linear devices of the display elements and by 
monitoring the characteristics of the non-linear device of the reference 
circuit, correction can be made so as to compensate for the corresponding 
changes in the on-current of the display element non-linear devices due to 
ageing processes. To this end, a reference voltage is applied to the 
reference circuit simulating a data signal which corresponds to a 
predetermined average data signal level or is derived from actual data 
signals applied to column conductors over a period of time. 
The effects of ageing of many non-linear devices, for example silicon 
nitride MIMs, are dependent to a large extent on the manner in which the 
device is operated. Changes in the device's operating characteristics are 
determined by the voltage levels to which the display element is driven. 
Driving a display element to higher values causes larger currents to flow 
through the non-linear device with the result that the rate of ageing is 
increased. The scheme described in EP-A-0523797 for correcting drift in 
the non-linear devices can compensate for the ageing of the non-linear 
devices driven to a single drive level. In practice, however, the ageing 
of the non-linear devices associated with picture elements which, in the 
case of LC display elements, are driven fully on (non-transmissive) and 
fully off (transmissive), e.g. black and white respectively, can be 
significantly different. Because the non-linear device of the reference 
circuit is driven at an intermediate, i.e. average, level it ages at a 
rate intermediate between the two extremes. 
SUMMARY OF THE INVENTION 
According to one aspect of the present invention a method of driving a 
matrix display device as described in the opening paragraph is 
characterised in that during a row address period the data voltage signal 
for a display element is applied during a latter part of the row address 
period and a signal comprising the inverse of the data signal is applied 
during a preceding part of the row address period with the display element 
being driven to said auxiliary voltage during the application of the 
inverse data signal in the row address period, and in that the selection 
voltage signal is applied during the application of said data signal in 
the latter part of the row address period. 
With this method the difference in ageing of non-linear devices of display 
elements driven to different levels is minimised. It has been found that 
when driving a display device using the aforementioned five level row 
waveform drive scheme the difference in the ageing rates for non-linear 
devices associated with black and white liquid crystal display elements in 
the middle of plain areas of the display is determined only by the 
difference in capacitance of these display elements. However, the 
non-linear devices associated with display elements located at the 
horizontal transitions between black and white display regions or vice 
versa may age much more or much less than those associated with other 
display elements. The method of the present invention helps to avoid this 
effect. 
In a preferred embodiment of the invention, the data signal and the inverse 
data signal are applied for substantially equal periods during a row 
address period in order to reduce cross-talk effects most effectively. The 
duration of the selection voltage signal is less than but preferably close 
to one half of the row address period, thus effectively maximising the 
time allowed for charging the display elements to the required levels. 
In order to reduce the overall flicker effects in the display image the 
array of display elements is preferably driven in a line inversion mode of 
operation in which the drive voltages applied to one row of display 
elements are shifted over one field period plus a row address period with 
respect to those for an adjacent row of display elements and the data 
signals are inverted for successive rows. 
According to another aspect of the present invention, there is provided a 
matrix display device comprising sets of row and column address 
conductors, a row and column array of electro-optic display elements for 
producing a display, each of which display elements is connected in series 
with a two terminal non-linear device between a row conductor and a column 
conductor and a drive circuit connected to the sets of row and column 
address conductors for applying a selection voltage signal to each row 
address conductor during a respective row address period to select the row 
of display elements and data voltage signals to the column conductors to 
drive each display element to produce a required display effect, and in 
which the drive circuit is arranged also to charge a display element to an 
auxiliary voltage prior to the application to that display element of a 
selection voltage signal and a data voltage signal for driving the 
selected display element to a voltage of predetermined sign and magnitude 
to obtain the required display effect, which auxiliary voltage is of the 
same sign and greater magnitude, characterised in that the drive circuit 
is arranged to apply in a a row address period the data voltage signal for 
a display element and the inverse of the data signal to its associated 
column address conductor during respectively a latter part of the row 
address period and a preceding part of the row address period, the drive 
circuit being operable to charge the display element to said auxiliary 
voltage during the application of the inverse data signal in the row 
address period and to apply the selection voltage signal during the 
application of said data signal in the latter part of the row address 
period.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, the display device is intended for datagraphic display 
and comprises an active matrix addressed liquid crystal display panel 10 
of conventional construction and consisting of m rows (1 to m) with n 
picture elements 12 (1 to n) in each row. Each picture element 12 consists 
of a twisted nematic liquid crystal display element 14 connected 
electrically in series with a bidirectional non-linear resistance device 
15, which exhibits a threshold characteristic and acts as a switching 
element, between a row conductor 16 and a column conductor 17. The display 
elements 12 are addressed via sets of row and column conductors 16 and 17 
carried on respective opposing faces of two, spaced, glass supporting 
plates (not shown) also carrying the opposing electrodes of the liquid 
crystal display elements. The devices 15 are provided on the same plate as 
the set of row conductors 16 but could instead be provided on the other 
plate and connected between the column conductors and the display 
elements. 
The row conductors 16 serve as scanning electrodes and are addressed by a 
row driver circuit 20 which applies a scanning signal, comprising a 
selection voltage signal component, to each row conductor 16 sequentially 
in turn. In synchronism with the scanning signals, data signals are 
applied to the column conductors 17 from a column driver circuit 22 to 
produce the required display from the rows of display elements associated 
with the row conductors 16 as they are scanned. The selection voltage 
signal component occurs in a row address period in which the optical 
transmissivity of the display elements 14 of the row are set to produce 
the required visible display effects according to the data signals present 
on the conductors 17. The individual display effects of the display 
elements 14, addressed one row at a time, combine to build up a complete 
picture in one field, the display elements being refreshed in a subsequent 
field. Using the transmission/voltage characteristics of a liquid crystal 
display element grey scale levels can be achieved. The display elements 
are addressed using a line inversion mode of drive to reduce perceived 
flicker. In addition the polarity of the data signal voltages for any 
given row of display elements is reversed in successive fields to reduce 
image sticking effects. 
The row and column driver circuits 20 and 22 are controlled by a timing and 
control circuit, generally referenced at 25, to which a video signal is 
applied and which comprises a video processing unit, a timing signal 
generation unit and a power supply unit. The row drive circuit 20, like 
known row drive circuits, comprises a digital shift register circuit and 
switching circuit to which timing signals and voltages determining the 
scanning signal waveforms are applied. The column driver circuit 22, again 
like known column drive circuits, comprises one or more shift 
register/sample and hold circuits and is supplied from the video 
processing unit with video data signals derived from an input video signal 
containing picture and timing information. Timing signals are supplied to 
the circuit 22 in synchronism with row scanning to provide serial to 
parallel conversion appropriate to the row at a time addressing of the 
panel 10. 
In this embodiment the non-linear devices 15 comprise MIMs. However other 
forms of bidirectional non-linear resistance devices exhibiting a 
threshold characteristic, for example diode rings, back to back diodes, or 
other diode structures such as n-i-n or p-i-p structures may be used 
instead. All such non-linear devices have an approximately symmetrical I-V 
characteristic. 
The display device is driven using a method involving a five level row 
signal waveform which is similar to the method described in U.S. Pat. No. 
5,159,325, to which reference is invited and whose disclosure is 
incorporated herein, but with certain differences as will be described 
later. In addition to the usual selection voltage signals followed by 
non-selectional voltages, this waveform further includes a reset voltage 
signal which immediately precedes a selection signal, and which can be 
regarded as an additional selection signal, for the purpose of correcting 
for the effects of non-uniformities in the behaviour of the non-linear 
devices across the array. As a result of the reset voltage, a display 
element is, in alternate fields, charged (this term being used herein to 
include discharge where appropriate) to an auxiliary voltage level beyond 
one end of the range of display element voltages used for display just 
before the display element is set to the required voltage level of the 
same sign, but of lower magnitude than the auxiliary voltage level, by the 
application of a selection voltage signal and the data voltage signal. In 
intermediate fields, the display element is driven with a single selection 
signal and an inverted data voltage signal. 
Examples of waveforms present in the known drive scheme according to U.S. 
Pat. No. 5,159,325 are illustrated schematically in FIG. 2 for the case in 
which a plain field is displayed and in which the reset pulse is positive. 
FIG. 2A shows an example of row signal waveform, V.sub.R, applied to a 
typical row conductor 16 together with an example of a data signal 
waveform in this known drive scheme, designated V.sub.C, applied to a 
column conductor 17 associated with a particular display element in that 
row, for the case of a plain field display in which the display elements 
are all driven to a fully transmissive, white, display state corresponding 
to the lower end of the range of operational voltages used for display. 
The waveforms of FIG. 2B are similar except that they illustrate the case 
of a plain field display where the display elements are driven to their 
opaque, black, display state, corresponding to the upper end of their 
range of operational voltages. 
In one field period a selection voltage V.sub.S - is presented to a row 
conductor during a row address period while a data voltage (Vd) is 
presented to a column conductor, with respective data voltages being 
applied to each of the other column conductors, as a result of which the 
display element at the intersection of the row and column conductors 
concerned is charged through the non-linear device to, for example, a 
positive voltage according to the level of the data signal. Upon 
termination of the selection signal, a non-selection, hold, level V.sub.h 
- is applied to the row conductor until just before the next selection of 
the row. To reduce visible flicker effects, information having an 
alternating sign is presented to a display element in successive fields. 
In the next field, therefore, the display element is charged to a negative 
voltage by presenting a selection signal. Immediately before this next 
selection, and in a row address period of the preceding row of display 
elements, a reset voltage Va is applied as a result of which the display 
element is charged negatively through the non-linear device to an 
auxiliary voltage, dependent on the reset voltage level, which lies at or 
beyond the range of operating voltages used for display (i.e. up to a 
value less than or equal to Vsat, its black level). The display element is 
then charged, in the next field period, to the desired value by means of a 
selection voltage signal Vs+ applied to the row conductor in the 
subsequent row address period while an inverted data voltage, (-Vd), is 
presented to the column conductor. Upon termination of this selectional 
signal, a non-selection, hold, level Vh+ is applied. In this way, the 
voltage across the display elements is inverted every field. The selected 
display elements are then charged to the required voltages, at which a 
desired display state is obtained, by passing current in the same 
direction through the non-linear devices, while the passage of current 
when the display elements are charged to the auxiliary level is in the 
opposite direction. 
The duration Ts of each of the selection pulse signals Vs- and Vs+ is 
slightly less than the line period T1 of the incoming video signal, e.g. 
32 microseconds for a datagraphic display, which corresponds to the row 
address period. The duration of the reset voltage pulse signal Va is also 
slightly less than T1. Tf in FIG. 2 represents a field period, e.g. 
approximately 16 ms. 
In this drive scheme, the display elements are driven in a line inversion 
mode of operation in which, in addition to the column drive voltages 
applied to a display element being reversed in polarity every field, the 
drive voltages applied to one row of display elements are shifted over one 
field period plus a row address period with respect to those for an 
adjacent row and the data signals are inverted for successive rows. This 
is illustrated in FIG. 3 which shows the row signal waveforms for four 
successive row conductors, R1 to R4. The data signals on the column 
conductors are inverted correspondingly, as shown in FIGS. 2A and 2B. 
In these example waveforms, the reset voltage pulse Va is positive. The 
sign of all the operating voltages, including the reset pulse and the data 
signals, applied to a row of display elements can periodically be changed 
if desired, for example after a fixed number of frames as described in 
U.S. Pat. No. 5,159,325. 
In this known drive scheme there are three transitions in the row signal 
waveform during which large peak current flows can occur in the non-linear 
devices, namely the leading edges of the negative selection pulse Vs-, in 
one field and the reset pulse Va, and the positive selection pulse 
V.sub.S+ in the succeeding field. These transitions are denoted in FIG. 2 
at T1, T2 and T3 respectively. The peak current is determined by the value 
of the column signal V.sub.C at the time of the relevant transition and 
the voltage on the display element immediately prior to the transition. 
The situation is summarised in Table 1 below for the case where the reset 
pulse voltage level is set exactly at its ideal theoretical value. The 
total charge which must be transferred onto the display element during the 
transition is an indication of the peak current. This charge is 
proportional to both the change in the display element voltage during the 
transition and the display-element capacitance. Voltages are expressed in 
terms of V.sub.W and V.sub.B which are the voltages on the display 
elements required to drive the LC fully white and fully black. The 
corresponding display element capacitances are C.sub.W and C.sub.B. 
TABLE 1 
__________________________________________________________________________ 
Plain Field 
Display 
Display 
Row Signal 
Initial 
Final 
Voltage 
Element 
Element 
Transition 
Voltage 
Voltage 
change 
Capacitance 
Charge 
__________________________________________________________________________ 
White 
T.sub.1 
+V.sub.W 
-V.sub.W 
-2V.sub.W 
C.sub.W 
-2C.sub.W V.sub.W 
White 
T.sub.2 
-V.sub.W 
2V.sub.B - V.sub.W 
+2V.sub.B 
C.sub.W 
+2C.sub.W V.sub.B 
White 
T.sub.3 
2V.sub.B - V.sub.W 
+V.sub.W 
-2V.sub.B + 2V.sub.W 
C.sub.W 
-2C.sub.W (V.sub.B - V.sub.W) 
Black 
T.sub.1 
+V.sub.B 
-V.sub.B 
-2V.sub.B 
C.sub.B 
-2C.sub.B V.sub.B 
Black 
T.sub.2 
-V.sub.B 
+V.sub.B 
+2V.sub.B 
C.sub.B 
+2C.sub.B V.sub.B 
Black 
T.sub.3 
+V.sub.B 
+V.sub.B 
0 C.sub.B 
0 
__________________________________________________________________________ 
The total charges, Q, flowing through the non-linear device, irrespective 
of direction, are: 
EQU Q (white display element)=4C.sub.W V.sub.B and 
EQU Q (black display element)=4C.sub.B V.sub.B (1) 
This shows that for a five level level row signal drive scheme the 
difference in the total charge through the non-linear device in each 
complete cycle between black and white picture elements is due only to the 
difference in capacitance and not to any difference in column voltage. In 
practice the reset pulse voltage may be set to a slightly higher value 
than the simple ideal value which drives a picture element just to black 
when the column voltage is V.sub.B. This alters the total charge passing 
through the non-linear device but the difference between black and white 
picture elements still depends only on the difference in their capacitance 
and not on the difference between V.sub.B and V.sub.W. 
The above discussion applies to a plain field display. The situation for a 
display having black and white regions will now be considered. 
At the junction between a region of black display elements and a region of 
white display elements the charge balance is different from that described 
above. This situation is illustrated in the lower parts of FIGS. 2A and 2B 
by the new column voltage signal V.sub.C' now present, respectively, for 
a white display element just below a black region of the display and a 
black display element just below a white region of the display. In this 
case the voltage changes and charges are as indicated in the following 
Table: 
TABLE 2 
__________________________________________________________________________ 
Black/White Edge Regions 
Display 
Display 
Row Signal 
Initial 
Final 
Voltage 
Element 
Element 
Transition 
Voltage 
Voltage 
change 
Capacitance 
Charge 
__________________________________________________________________________ 
White 
T.sub.1 
+V.sub.W 
-V.sub.W 
-2V.sub.W 
C.sub.W 
-2C.sub.W V.sub.W 
White 
T.sub.2 
-V.sub.W 
+V.sub.B 
V.sub.B + V.sub.W 
C.sub.W 
C.sub.W (V.sub.B + V.sub.W) 
White 
T.sub.3 
+V.sub.B 
+V.sub.W 
V.sub.W - V.sub.B 
C.sub.W 
-C.sub.W (V.sub.B - V.sub.W) 
Black 
T.sub.1 
+V.sub.B 
-V.sub.B 
-2V.sub.B 
C.sub.B 
-2C.sub.B V.sub.B 
Black 
T.sub.2 
-V.sub.B 
2V.sub.B - V.sub.W 
3V.sub.B - V.sub.W 
C.sub.B 
C.sub.B (3V.sub.B - V.sub.W) 
Black 
T.sub.3 
2V.sub.B - V.sub.W 
+V.sub.B 
V.sub.W - V.sub.B 
C.sub.B 
-C.sub.B (V.sub.B - V.sub.W) 
__________________________________________________________________________ 
If the total charge flowing through the non-linear device is considered, 
irrespective of direction, then the values are: 
EQU Q(White display element)=(2V.sub.B +2V.sub.W)CW and 
EQU Q(Black display element)=(6V.sub.B -2V.sub.W)CB (2) 
It is apparent, therefore, that in this case the charges for the black and 
white display elements are significantly different and are also different 
from the plain field case. It is clear that the non-linear devices 
associated of picture elements at the edges of black and white zones in 
the image will tend to age at a different rate from those in the middle of 
plain areas of the image. Thus, when line inversion and a five-level row 
signal waveform are used, the differences in ageing rate for the 
non-linear devices of black and white display elements in the middle of 
plain areas of the image are determined only by the differences in 
capacitance of these display elements, but the non-linear devices of 
picture elements at the horizontal transitions between black and white 
regions, or vice versa, may age much more or much less than those of other 
picture elements. In display panels aged by displaying a chequerboard 
pattern this effect has been observed as a series of darker and lighter 
lines at the horizontal edges of the chequerboard when the display is 
subsequently examined using a conventional 4-level row drive waveform. In 
5-level drive these areas show greater flicker levels. 
The edge effects are significant for datagraphic displays where fixed 
geometric patterns can be present for long periods. 
These effects are significantly reduced by using the method of driving the 
display device according to the present invention. The method is similar 
to that described above but with certain modifications to the row and 
column drive signals. In particular, it involves alterations to the timing 
of the presentations of data and inverted data signals. By appropriate 
adjustment of these timings and the timings of the selection and reset 
voltages of the row waveform it can be arranged that data inversion is 
used to reduce the problem of differential ageing of non-linear devices of 
the display elements at the edge of black and white regions to be 
overcome. The data inversion is then such that the ageing behaviour of 
these non-linear devices is the same as for the plain field case 
illustrated in FIGS. 2A and 2B since each data signal is followed by its 
inverse. 
An embodiment of this method of driving the display device is illustrated 
by FIG. 4 which shows examples of the row signal waveform and data signal 
waveform, V.sub.R and V.sub.C, applied to typical row and column 
conductors of the array for the case of a plain field (white) display. 
In this method the column drive circuit 22 is arranged to provide data 
inversion in a row address period, that is, the output signal to a column 
conductor 17 is first applied to the column conductor for a predetermined 
period with one polarity and is then re-applied for a, preferably, equal 
period with the inverse polarity. As before, T.sub.1 represents a row 
address period, corresponding to a line period of the applied video 
signal. D and D respectively are the data and inverse data signal. Each 
polarity of the data signal is applied in this example for half the 
overall row address period, T.sub.1. The duration of each of the selection 
and reset signals, Vs-, Vs+ and Va, is slightly less than one half of the 
row address period, i.e. Ts=Ta&lt;T1/2. 
The selection pulse signal Vs- occurs during the second half of the data, 
row address period, that is, after the column signal has carried inverted 
data signal D and while the normal data signal D is present. 
Also, the timing of the reset pulse signal Va is such that its leading edge 
occurs during the first half of the column data period, that is, while the 
column conductor is carrying the inverted data signal D. The selection 
signal Vs+ then occurs during the application of the data signal D to the 
column conductor. 
It is preferred to use data and inverted data signals of substantially 
equal duration as this is most effective for reducing cross-talk effects. 
Using this approach the ageing of all non-linear devices, no matter what 
the displayed image, will depend only on the display element capacitance 
and not on the current drive voltage. As a result the difference in ageing 
between the non-linear devices will be much less dependent on image 
content than that normally encountered using 5-level row drive signals and 
line inversion. This enables much more accurate compensation of the ageing 
effects by means of the kind of technique described in European Patent 
Specification EP-A-0523797 using a reference non-linear device driven at 
an appropriate reference level. In particular, if storage capacitors are 
incorporated in the display so that the display element capacitance is 
only very slightly dependent on the drive level, the non-linear devices of 
all display elements will age substantially equally and very accurate 
compensation is possible. 
The matrix display device may be a colour display device and references in 
the preceding description to black and white display elements should be 
construed accordingly. Moreover, although the method has been described in 
relation to a display device comprising a liquid crystal display device, 
it is envisaged that the method can be used with display devices employing 
other kinds of electro-optic materials, for example, electrochromic or 
electrophoretic materials. 
From reading the present disclosure, other modifications will be apparent 
to persons skilled in the art. Such modifications may involve other 
features which are already known in the field of matrix display apparatus 
and their methods of driving and which may be used instead of or in 
addition to features already described herein.