LED matrix driver ghost image prevention apparatus and method
LED drivers specially directed to LED matrix driver's ghost image prevention is disclosed. The LED driver receives an external input and decodes the input to produce a time multiplex timing on turning on an LED array. The LED driver inserts a dead time to the outputs and during this time the ghost image prevention circuit discharges the output stray capacitances to a predetermined level.
1. An apparatus for controlling voltage applied to terminals of a plurality of light emitting diodes (LEDs), to a predetermined voltage at a predetermined dead time interval, the apparatus comprising:
a multiplexing controller to generate predetermined dead time signals which serve as input signals to a plurality of voltage generators; and
said plurality of voltage generators to generate said predetermined voltage which is applied to anode and cathode terminals of said plurality of LEDs.
2. The apparatus according to claim 1 , wherein each of said plurality of voltage generators comprises:
a first transistor that connects a power supply to a first resistor;
said first resistor, having a first terminal electrically coupled to said first transistor and having a second terminal electrically coupled to said anode and cathode terminals of one of said plurality of LEDs;
a second resistor, having a first terminal electrically coupled to said anode and cathode terminals of one of said plurality of LEDs and having a second terminal electrically coupled to a second transistor; and
said second transistor that connects said second terminal of said second resistor to ground.
3. The apparatus according to claim 2 , wherein said first transistor is a PMOS transistor, having a gate terminal electrically coupled to said multiplexing controller, having a drain terminal electrically coupled to said first terminal of said first resistor, and having a source terminal electrically coupled to a path that leads to said power supply.
4. The apparatus according to claim 3 , wherein said second transistor is an NMOS transistor, having a source terminal electrically coupled to a path that leads to said ground, having a drain terminal electrically coupled to said second terminal of said second resistor and having a gate terminal electrically coupled to said multiplexing controller.
5. The apparatus according to claim 4 , wherein each of said plurality of voltage generators further comprise:
at least one pre-driver operative disposed between an output of said multiplexing controller and said gate terminal of each of said PMOS transistor and said NMOS transistor.
6. The apparatus according to claim 5 , wherein said pre-driver operative is an inverter.
7. The apparatus according to claim 5 , wherein said inverter is electrically coupled to said multiplexing controller for receiving one of said predetermined dead time signals during said predetermined dead time interval.
8. The apparatus according to claim 6 , wherein each of said plurality of voltage generators is identical.
9. The apparatus according to claim 6 , wherein said first resistor and said second resistor have a same resistance value.
10. The apparatus according to claim 9 , wherein each of said plurality of voltage generators is configured to generate said predetermined voltage during said predetermined dead time interval with said predetermined voltage being equal to half of a power supply voltage of said power supply.
11. The apparatus according to claim 1 , wherein said plurality of voltage generators generate said predetermined voltage during said predetermined dead time interval in correspondence with said predetermined dead time signals which are generated by and input from said multiplexing controller during said predetermined dead time interval.
12. The apparatus according to claim 11 , wherein each of said plurality of voltage generators is identical.
13. The apparatus according to claim 12 , wherein
said plurality of voltage generators is configured to apply a power supply voltage to said anode and cathode terminals of at least one of said plurality of LEDs during a first time interval, and configured to apply said predetermined voltage to said anode and cathode terminals of each of said plurality of LEDs during said predetermined dead time interval subsequent to said first time interval, and
said predetermined voltage is equal to half of the power supply voltage.
14. The apparatus according to claim 12 , wherein
said plurality of voltage generators is configured to apply a power supply voltage to said anode and cathode terminals of at least one of said plurality of LEDs during a first time interval, and configured to apply said predetermined voltage to said anode and cathode terminals of each of said plurality of LEDs during said predetermined dead time interval subsequent to said first time interval, and
said predetermined voltage is not enough to turn on said plurality of LEDs.