Electronic devices with low refresh rate display pixels
A display may have an array of organic light-emitting diode display pixels operating at a low refresh rate. Each display pixel may have six thin-film transistors and one capacitor. One of the six transistors may serve as the drive transistor and may be compensated using the remaining five transistors and the capacitor. One or more on-bias stress operations may be applied before threshold voltage sampling to mitigate first frame dimming. Multiple anode reset and on-bias stress operations may be inserted during vertical blanking periods to reduce flicker and maintain balance and may also be inserted between successive data refreshes to improve first frame performance. Two different emission signals controlling each pixel may be toggled together using a pulse width modulation scheme to help provide darker black levels.
1. A display pixel comprising:
a light-emitting diode;
a drive transistor coupled in series with the light-emitting diode;
an emission transistor coupled in series between the drive transistor and the light-emitting diode; and
a switching transistor configured to reset an anode of the light-emitting diode, wherein the switching transistor is activated multiple times during a vertical blanking period.
2. The display pixel of claim 1 , further comprising:
an initialization transistor coupled between an initialization line and a gate terminal of the drive transistor.
3. The display pixel of claim 2 , wherein the initialization transistor comprises a semiconducting-oxide transistor and wherein the drive transistor comprises a silicon transistor.
4. The display pixel of claim 2 , wherein the initialization transistor comprises an n-type semiconducting-oxide transistor and wherein the drive transistor comprises a p-type silicon transistor.
5. The display pixel of claim 1 , further comprising
a semiconducting-oxide transistor coupled between a gate terminal and a source-drain terminal of the drive transistor, wherein the drive transistor comprises a silicon transistor.
6. The display pixel of claim 1 , further comprising:
a capacitor having a first terminal coupled to a positive power supply line and having a second terminal coupled to the anode of the light-emitting diode.
7. The display pixel of claim 6 , further comprising:
an additional emission transistor coupled in series between the positive power supply line and the drive transistor.
8. The display pixel of claim 7 , wherein at least one of the emission transistor and the additional emission transistor is activated during the vertical blanking period.
9. The display pixel of claim 7 , wherein during at least a portion of the vertical blanking period, the emission transistor and the additional emission transistor are simultaneously activated.
10. The display pixel of claim 1 , wherein the switching transistor is configured to load a data signal into the display pixel.
11. A method of operating a display having a plurality of pixels each with a light-emitting diode, the method comprising:
during a first period, outputting a first frame;
during a second period, outputting a second frame different than the first frame; and
during a transition period between the first period and the second period, performing multiple anode reset operations for resetting an anode of the light-emitting diode to a reset voltage in at least some of the pixels in the display.
12. The method of claim 11 , wherein each pixel in the plurality of pixels further comprises:
a drive transistor; and
a switching transistor coupled to the drive transistor, wherein the switching transistor is activated during the multiple anode reset operations.
13. The method of claim 12 , wherein each pixel in the plurality of pixels further comprises:
an initialization transistor coupled to a gate terminal of the drive transistor.
14. The method of claim 13 , wherein the initialization transistor is also coupled to the anode of the light-emitting diode.
15. The method of claim 13 , wherein the drive transistor comprises a first silicon transistor and wherein the switching transistor comprises a second switching transistor.
16. The method of claim 13 , wherein the drive transistor comprises a silicon transistor and wherein the initialization transistor comprises a semiconducting-oxide transistor.
17. The method of claim 13 , wherein the switching transistor comprises a silicon transistor and wherein the initialization transistor comprises a semiconducting-oxide transistor.
18. The method of claim 13 , wherein the switching transistor is coupled between the anode of the light-emitting diode and a first voltage line, and wherein the initialization transistor is coupled between the gate terminal of the drive transistor and a second voltage line different than the first voltage line.
19. The method of claim 11 , further comprising:
during the transition period between the first period and the second period, performing multiple data refresh operations for loading data into at least some of the pixels in the display.
20. The method of claim 19 , wherein:
during the transition period, the data refresh operations are performed at a first frequency; and
during the transition period, the anode reset operations are performed at a second frequency different than the first frequency.