Pixel circuit and driving method thereof
View Patent ↗Disclosed are a pixel circuit and a driving method thereof. The pixel circuit includes: a data writing unit configured to control an input of a data signal; a first energy storage unit configured to store the data signal output by the data writing unit; a second energy storage unit configured to store the data signal together with the first energy storage unit; a light-emitting unit configured to emit light for display; a driving unit, where an input end of the driving unit is connected with the high level VDD, a control end of the driving unit is input with a control signal, and an output end of the driving unit is configured to provide a light-emitting current to the light-emitting unit; a light-emitting control transistor configured to control conduction of the driving unit and the light-emitting unit; and a compensation unit.
1 . A pixel circuit, comprising:
a data writing unit, configured to control an input of a data signal into the pixel circuit;
a first energy storage unit, configured to store the data signal output by the data writing unit, wherein a first end of the first energy storage unit is connected with an output end of the data writing unit;
a second energy storage unit, configured to store the data signal together with the first energy storage unit, wherein a first end of the second energy storage unit is connected with a high level VDD, and a second end of the second energy storage unit is connected with a second end of the first energy storage unit;
a light-emitting unit, configured to emit light for display;
a driving unit, wherein an input end of the driving unit is connected with the high level VDD, a control end of the driving unit is input with a control signal, and an output end of the driving unit is configured to provide a light-emitting current to the light-emitting unit;
a light-emitting control transistor, configured to control conduction of the driving unit and the light-emitting unit, wherein an input end of the light-emitting control transistor is connected with the output end of the driving unit, a control end of the light-emitting control transistor is connected with the first end of the first energy storage unit, and an output end of the light-emitting control transistor is connected with the light-emitting unit; and
a compensation unit, wherein an output end of the compensation unit is connected with the first end of the first energy storage unit, an input end of the compensation unit is connected with the output end of the light-emitting control transistor, and a control end of the compensation unit is input with a compensation control signal.
2 . The pixel circuit according to claim 1 , further comprising: a reset unit configured to reset the light-emitting unit; wherein the reset unit is connected with an input end of the light-emitting unit.
3 . The pixel circuit according to claim 2 , wherein the reset unit comprises: a third PMOS transistor;
wherein a source electrode of the third PMOS transistor is connected with the output end of the compensation unit, a gate electrode of the third PMOS transistor is input with a reset signal, and a drain electrode of the third PMOS transistor is grounded.
4 . The pixel circuit according to claim 1 , wherein the data writing unit comprises: a first Positive channel Metal Oxide Semiconductor (PMOS) transistor;
wherein a source electrode of the PMOS transistor is input with the data signal.
5 . The pixel circuit according to claim 1 , wherein the first energy storage unit comprises: a first capacitor;
wherein a first end of the first capacitor is connected with the output end of the data writing unit.
6 . The pixel circuit according to claim 5 , wherein the second energy storage unit comprises:
a second capacitor;
wherein a first end of the second capacitor is connected with the high level VDD, and a second end of the second capacitor is connected with a second end of the first capacitor.
7 . The pixel circuit according to claim 6 , wherein the driving unit comprises: a second PMOS transistor;
wherein a source electrode of the second PMOS transistor is connected with the high level VDD, and a gate electrode of the second PMOS transistor is connected with the second end of the first capacitor and the second end of the second capacitor.
8 . The pixel circuit according to claim 7 , wherein the compensation unit comprises: a fourth PMOS transistor;
wherein a drain electrode of the fourth PMOS transistor is connected with the first end of the first capacitor, and a gate electrode of the fourth PMOS transistor is input with the compensation control signal.
9 . The pixel circuit according to claim 8 , wherein the light-emitting control transistor is a PMOS transistor;
wherein a source electrode of the light-emitting control transistor is connected with a drain electrode of the second PMOS transistor, and a gate electrode of the light-emitting control transistor is connected with the first end of the first capacitor.
10 . The pixel circuit according to claim 9 , wherein an input end of the light-emitting unit is connected with a source electrode of the fourth PMOS transistor and a drain electrode of the light-emitting control transistor.
11 . The pixel circuit according to claim 1 , further comprising: a G point initialization unit, configured to adjust a voltage of a G point;
wherein the G point initialization unit is connected with the first end of the first energy storage unit.
12 . The pixel circuit according to claim 11 , wherein the G point initialization unit comprises: a sixth PMOS transistor;
wherein a gate electrode of the sixth PMOS transistor is input with an initialization control signal, a source electrode of the sixth PMOS transistor is input with an initialization signal, and a drain electrode of the sixth PMOS transistor is connected with the first end of the first energy storage unit.
13 . A method for driving the pixel circuit according to claim 1 , comprising in sequence: an initialization stage; a self-discharge stage; a writing stage; and a light-emitting stage;
wherein at the self-discharge stage, a working time of the compensation unit is adjusted to complete an adjustment of a threshold voltage of the light-emitting control transistor.
14 . The method for driving the pixel circuit according to claim 13 , comprising:
starting the initialization stage: turning on the driving unit and the data writing unit;
ending the initialization stage: turning off the data writing unit and the driving unit;
starting the self-discharge stage: turning on the compensation unit, turning off the compensation unit and turning on a reset unit after t 1 time period, and turning off the reset unit after t 2 time period, wherein the self-discharge stage lasts for t time period, and t=t 1 +t 2 ;
at the writing stage, turning on the data writing unit;
at the light-emitting stage, turning off the data writing unit, and turning on the driving unit.
15 . The method for driving the pixel circuit according to claim 14 , wherein:
when
a
=
b
,
then
t
1
=
0
,
t
2
=
t
;
when
a
=
b
/
(
1
-
b
)
2
,
then
t
1
=
t
,
t
2
=
0
;
wherein b=C 2 /(C 1 +C 2 ), a is an substrate bias coefficient, C 1 is a first capacitance value, and C 2 is a second capacitance value.
16 . The method for driving the pixel circuit according to claim 15 , wherein at the initialization stage, the first PMOS transistor, the second PMOS transistor, and the light-emitting control transistor are all turned on, the data signal is Vofs, and the G point is initialized.
17 . The method for driving the pixel circuit according to claim 16 , wherein:
when a is between b and b/(1−b) 2 , then t 1 =t*f[b, b/(1−b) 2 ];
wherein the function f is adjusted according to an operation of a panel; and
the function f is a linear function, a quadratic function or an exponential function.
18 . The method for driving the pixel circuit according to claim 17 , wherein during the t 1 time period:
the fourth PMOS transistor is turned on, a source voltage of the light-emitting control transistor is reduced, a gate voltage of the light-emitting control transistor is increased;
due to a substrate bias effect, the threshold voltage of the light-emitting control transistor is increased until a difference between the source voltage and gate voltage is equal to the threshold voltage of the light-emitting control transistor, and the light-emitting control transistor is turned off.
19 . The method for driving the pixel circuit according to claim 17 , wherein, during the t 1 time period:
❘
"\[LeftBracketingBar]"
V
TH_EF
❘
"\[RightBracketingBar]"
=
a
*
(
VDD
-
Vs
)
+
❘
"\[LeftBracketingBar]"
V
TH
❘
"\[RightBracketingBar]"
=
Vs
-
Vg
;
(
VDD
-
V
s
)
*
C
2
+
[
(
VDD
-
Vofs
)
-
(
Vs
-
Vg
)
]
*
C
1
=
(
Vg
-
Vofs
)
*
C
1
*
C
2
/
(
C
1
+
C
2
)
;
wherein, V TH_EF is an equivalent threshold voltage of the light-emitting control transistor, V TH is the threshold voltage of the light-emitting control transistor, and Vofs is an initialization voltage;
Vs
1
=
{
[
a
-
(
1
+
x
)
2
]
VDD
+
Vofs
+
❘
"\[LeftBracketingBar]"
V
TH
❘
"\[RightBracketingBar]"
}
/
[
1
+
a
-
(
1
+
x
)
2
]
;
Vg
1
=
{
(
1
+
a
)
Vofs
-
(
VDD
-
❘
"\[LeftBracketingBar]"
V
TH
❘
"\[RightBracketingBar]"
)
(
1
+
x
)
2
}
/
[
1
+
a
-
(
1
+
x
)
2
]
;
wherein a is an substrate bias coefficient, x=C 2 /C 1 , Vs 1 is a source voltage of the light-emitting control transistor, Vg 1 is a gate voltage of the light-emitting control transistor.
20 . The method for driving the pixel circuit according to claim 19 , wherein, during the t 1 time period, a threshold voltage compensation of the light-emitting control transistor is calculated as follows:
(
VDD
-
Vs
1
)
*
C
2
+
[
(
VDD
-
Vofs
)
-
(
Vs
1
-
Vg
1
)
]
*
C
1
=
(
Vg
1
-
Vofs
)
*
C
1
*
C
2
/
(
C
1
+
C
2
)
=
Q
;
wherein Q is the threshold voltage compensation of the light-emitting control transistor, during the t 1 time period, ΔVs 1 is a change amount of the source voltage of the light-emitting control transistor, and ΔVg 1 is a change amount of the gate voltage of the light-emitting control transistor:
Δ
Vg
1
=
Vg
1
-
Vofs
=
Q
*
(
C
1
+
C
2
)
/
(
C
1
*
C
2
)
;
Δ
Vs
1
=
Vs
1
-
VDD
=
Q
*
C
1
/
C
2
*
(
C
1
+
C
2
)
;
Δ
Vs
1
/
Δ
Vg
1
=
(
1
-
b
)
2
;
wherein a current through the light-emitting control transistor is calculated as follows:
I =β*( Vs 1 −Vg 1 −|V TH_EF |) 2 ; wherein, β is a constant.