Pulse width correction for LED display driver
The LED display system comprises an array of LEDs and a driver circuit that employs a scrambled PWM generator. The scrambled PWM generator is configured to generate a plurality of PWM pulses. The PWM pulses are distributed into a corresponding number of refresh segments. The driver circuit is configured so that one or more of PWM pulses are extendable by a certain offset value so that the pulse width in the corresponding refresh segments is wide enough for the LED to emit light.
1. An LED display system, comprising:
an array of LEDs arranged in rows and columns, each LED having an anode and a cathode; and
a driver circuit that drives the array of LEDs, wherein the driver circuit comprises a scrambled PWM generator,
wherein the scrambled PWM generator is configured to generate a plurality of PWM pulses, and the width of at least one of the plurality of PWM pulses is extendable by an offset value,
wherein the offset value equals N GCLK cycles, wherein N=C*V f *f GCLK /I,
whereby I represents an LED driving current, C represents an LED and PCB loading, V f represents an LED forward voltage, and f GCLK represents an GCLK frequency.
2. The LED display system according to claim 1 , wherein the driver circuit comprises a register that is configured to store the offset value.
3. The LED display system according to claim 1 , wherein the LED array comprises a plurality of common anode nodes, wherein each of the plurality common anode nodes is operably connected with anodes of LEDs of a same color in a corresponding column.
4. The LED display system according to claim 3 , wherein each of the common anode nodes is operably connected with a power source.
5. The LED display system according to claim 1 , wherein the LED array comprises a plurality of common cathode nodes wherein each of the plurality common cathode nodes is operably connected with cathodes of LEDs of a same color in a corresponding row.
6. The LED display system according to claim 5 , wherein each of the common cathode nodes is operably connected with a power source.
7. The LED display system according to claim 1 , wherein the LEDs are RGB LEDs or single color LEDs.
8. A method for operating an LED display, comprising the steps of:
connecting an array of LEDs to a driver circuit, wherein the driver circuit comprises a scrambled PWM generator, wherein the scrambled PWM generator is configured to generate a plurality of PWM pulses; and
extending a width of each of the plurality of PWM pulses by an offset value,
wherein the offset value equals N GCLK cycles, wherein N=C*V f *f GCLK /I,
whereby I represents an LED driving current, C represents an LED and PCB loading, V f represents an LED forward voltage and f GCLK represents an GCLK frequency, whereby the pulse width with offset substantially matches a rise time (T r ) of a LED in the LED array.
9. The method for operating an LED display according to claim 8 , further comprises the steps of determining the offset value; and loading the offset value into a register in the driver circuit.
10. The method for operating an LED display according to claim 8 , wherein the LEDs in the LED array are arranged into rows and columns, wherein the LEDs are RGB LEDs or single color LEDs.
11. The method for operating an LED display according to claim 10 , wherein the LED array comprises a plurality of common cathode nodes wherein each of the plurality common cathode nodes is operably connected with cathodes of LEDs of a same color in a corresponding row.
12. The method for operating an LED display according to claim 11 , further comprising connecting a power source to a common cathode node of the LED array.
13. The method for operating an LED display according to claim 10 , wherein the LED array comprises a plurality of common anode nodes wherein each of the plurality common anode nodes is operably connected with anodes of LEDs of a same color in a corresponding column.
14. The method for operating an LED display according to claim 13 , further comprising connecting a power source to a common anode node of the LED array.
15. A method for operating an LED display, comprising:
connecting an array of LEDs to a driver circuit, wherein the driver circuit comprises a scrambled PWM generator, wherein the scrambled PWM generator is configured to generate a plurality of PWM pulses;
extending a width of each of the plurality of PWM pulses by an offset value;
determining the offset value; and loading the offset value into a register in the driver circuit,
wherein the step of determining the offset value comprises the steps of:
loading a test value to the register so that the width of each of the plurality of PWM pulses is extended by the test value;
measuring a performance characteristic of the LED display in response to the test value;
repeating the loading step and the measuring step; and
assigning the test value to the offset value when the test value results in a performance characteristics that satisfies a pre-determined criteria.
16. The method of claim 15 , wherein the performance characteristics is a brightness, a visual refresh rate, or a resolution of the LED display.