Note: Descriptions are shown in the official language in which they were submitted.
CA 02678509 2009-09-09
FIELD OF THE INVENTION
The present invention generally relates to drive a display particularly light
emitting displays.
SUMMARY OF INVENTION
The disclosed technique improves the display lifetime and performance for all
gray scales by mixing
analog and digital driving schemes.
ADVANTAGES
The new techniques can improve the display lifetime and performance with
taking advantage of digital
and analog driving schemes.
CA 02678509 2009-09-09
Hybrid Driving Schemes
This driving scheme provides an innovation solution for AMOLED driver system.
1. Proposed a hybrid driving concept.
2. Proposed an area-saving GRAM structure that support hybrid driving data.
3. Provides a practical data processing system for n bits raw-grayscale data
transferring to (n+1) bits
GRAM data.
4. Introduced a Look-Up-Table for above data transferring.
5. Provides a block diagram for a real AMOLED driver.
Because the AMOLED pixel does not compensate lower grey scales very well. So
we need to increase
the applied voltage level, and reduce the frame time during which that voltage
is applied. We proposed a
new driving scheme, called hybrid driving. We divide I frame of driving into
two phase, phase 1 and
phase2, refer to Fig.1.
1. Normal Driving 1 Frame
T=T1+T2
2. Hybrid Driving
Phasel Phase2
T1 T2
Fig.1 Normal Driving vs. Hybrid Driving
As an example, assume T1=(3/4)T, T2=(1/4)T. To obtain same average luminance
for a grey scale in both
the driving schemes shown in Fig.2, the relationship for luminance between
normal driving and hybrid
driving should be given by following equations,
L2 = 4/3 * Ll
L4=4*L3
CA 02678509 2009-09-09
Normal Mode Driving -High Grey Scale Hybrid Mode Driving - High Grey Scale
Ll LZ
_! J
tire? T tire? 141T T
Avg. Luminance = Li Avg. Luminance '+' L2
IN, ortra]Mode Driving -Low Grey Scale Hybrid Mode Driving - Low Grey Scale
L4
a. n
L3 X
X 7-
J
tire? T tire? '. IT T
Avg. Luminance = L3
Avg. Luminance = 1/4 L4
Fig.2 Required Luminance for Normal Driving and Hybrid Driving
The gamma is adjusted for higher grey scales. So we cannot get the new voltage
level for the lower grey
scales merely by increasing gamma. We need to map the lower grey scales to
higher grey scales with
Look-Up-Table (LUT). As an example, this is shown in the below Fig.3. We
divide the grayscale data
into Low Grayscale and High Grayscale. If the data smaller than D(ref), we
consider it as low grayscale
data; If the data greater than or equal to D(ref), we consider it as high
grayscale data. In Fig.3,
D(ref)=64H(100).
. During phasel: If the data is located in low grayscale, the source driver
just output black level; If the
data is located in high grayscale, the source driver output the grayscale data
corresponded level.
. During phase2: If the data is located in low grayscale, the source driver
just output the grayscale data
corresponded level; If the data is located in high grayscale, the source
driver output black level.
For the high grayscale level, the data will not change, but for the low
grayscale level, because the ON
time is shorter than high grayscale (1/3 that of high grayscale). So to get
the grayscale data related
average luminance, the low grayscale data will map to high grayscale level.
CA 02678509 2009-09-09
Gammas mfor
IlannalOdvirt 1 162 I frsere .^- -,--;
Gamma<vvefa Mypim Ddvmt `- -ha=,ei lima Vhasa2 Tama
+= _ ~.r. -P10YIOk31'I~el VUfllilC rOY .
Hi tev my-le, so Hiy~Ki<;. last (It. Siad
64rimawU a Bhd .ta datatrcm LUT
falowet grey ualee
ir.IW1>riu M'Iirg qg
145
'~ ~-~~l oaeytraiet l-Nntppec 100
to*ity oaks W-245 13YT
if
r V t .._..-_._-
1 ~ 50 49 102 169 245 255
i00 255 ti,.
.................. .._._...........-._-._.._.a;
......................
st?^" Frgh?r Gv!=w scat+^. look VV aDk
i.r[VAta.
Fig.3 Grayscale Data Transformation with LUT
To achieve the hybrid driving, we need to store the grayscale data in the GRAM
of AMOLED driver in a
special format. So we proposed following data processing scheme.
Here assume the grayscale data from the controller is 8-bit. We can use 9-bit
RAM instead of 8-bit RAM
to store "8-bit grayscale data" plus " 1-bit indicator". In this way, all the
input data is divided into two kind
of 8-bit grayscale data.
If it is high grayscale data, then D[8]=1, D[7:0]=original data (Get from
LUT);
If it is low grayscale data, then D[8]=0, D[7:0] =relaxation data (Get from
LUT).
The LUT with this scheme is shown in following table. Note the data in the LUT
is hexadecimal data, the
input data is same as that in Fig.3. Fig.4 shows the data processing from the
8-bit raw grayscale data to 9-
bit GRAM data.
Input Data 1H ... 32H ... 63H 64H ... FFH
GRAM Data 066H ... OA8H ... OF5H 164H ... 1FFH
In this way,
1. The GRAM size will be only 1/8 larger than the normal. It is cost efficient
for driver chip IC.
2. The LUT is kept in front of the GRAM input, the input 8-bit data is
transferred to 9-bit by LUT and
then stored into the GRAM one by one.
CA 02678509 2009-09-09
C Start
2
Input from
Data Interface
8-bit Data
D[7:0]
Normal or Normal Driving
Hybrid?
T Hybrid
Driving
256x9 bit 8-bit Normal
Look-Up-Table Data, D_N[7:0]
9-bit Relaxation
Data, D_R[8:0]
GRAM[8:0]
END
Fig.4 Flowchart from Grayscale Data to GRAM Data (Example of 8-bit Grayscale
Data)
For the output side, present row of data is controlled by local D[8] and
normal/relaxation control signal
only. It will be simple for circuit design and layout of the IC.
. For Normal driving period (Relaxation=OFF), if D[8]=1, then D[7:0]-=DAC; if
D[8]=0, then Black
(VSL)]-=DAC.
CA 02678509 2009-09-09
For Relaxation driving period (Relaxation=ON), if D[8]=1, then Black (VSL) -
*DAC; if D[8]=0, then
D[7:0]-=DAC.
Detail flowchart for between GRAM and DAC is shown in Fig.5.
,::Start
Normal or Normal Driving
brid Drivin 9
Hybrid
Driving
Program Time rogra
or Relaxation
Time?
Relaxation
Time
Yes GRAM[8]=1 ? GRAM[8]=1 ? No
No Yes
GRAM[7:0]
-.D[7:0]
#00-DAC D[7:0]--*DAC
C End D
Fig. 5 Flowchart from GRAM Data to DAC Input (Example of 8-bit Grayscale Data)
CA 02678509 2009-09-09
C Start
D
Normal or Normal Driving
brid Drivin
Hybrid
Driving
Program Time rogra
or Relaxation
Time?
T Relaxation
Time
Yes GRAM[81=1 ? GRAM[8]=1 ? No
No Yes
= GRAM[7:4]
D[7:O]
, GK -:~.r~-.4+ Ift>1Mi D :O)---oAC
C End D
Fig. 6: Another flowchart for hybrid driving scheme.
To avoid contorting effect during the transition one can use a smoothening
function for different part of
frame. These functions can be but not limited to offset, shift, and partial
inversion. This data flow is
shown in Fig. 6.
Also, one can use multi LUTs for implementation of hybrid driving schemes as
shown in Fig. 7. Here,
each set of gray scales has its own LUT and so can help implementation of
smoothening function.
CA 02678509 2009-09-09
LUT (1)
LUT(m)
Fig. 7: Multi look-up table implementation of hybrid driving scheme.
Figure 8 highlights a system implementation for accommodating multiple gamma
curves for different
applications and brightness control. Here, to change the display peak
brightness or to change the gamma
curves, different set of voltages is applied to the source driver DACs. At the
same time, one can change
the hybrid look up table to get a more solid gamma curve despite changing the
peak brightness.
CA 02678509 2009-09-09
C
N
e-I
M .....
E M L
E DACS
M
U
.Q ~
Fig. 8: system implementation of multiple gamma curve for brightness control.
