LED driver having non-linear compensation
A device driver which includes an input driver configured to produce a sequence of uncompensated drive signals along with compensation circuitry connected to receive the uncompensated drive signals and to produce corresponding compensated drive signals. The compensation circuitry is capable of storing two or less control points that define a single compensation curve such as a Bezier curve, with the compensation circuitry converting the uncompensated drive signals to the corresponding compensated drive signals utilizing the control points. An output driver is configured to drive a device such as one or more light emitting diodes to be connected to the output driver with the compensated drive signals.
1. A device driver circuit suitable for driving a device characterized by a non-linear response to drive signals, comprising:
driver input circuitry configured to produce uncompensated drive signals (x i ) associated with a device non-linear response curve;
compensation circuitry configured to receive the uncompensated drive signals (x i ), and to produce corresponding compensated drive signals (y o ) based on a parametric quadratic Bezier function B(t) with an associated compensated device drive curve, where B(t) is characterized by
a fixed start point and a fixed end point corresponding respectively to minimum and maximum values for (x i , y o ) on the compensated device drive curve, and
a pre-defined control point P 1 characterized by coordinates (x c , y c ), used to generate the compensated drive signals (y o ) according to B(t),
a parameter t with a range corresponding to a normalized value from 0 to 1;
the compensation circuitry including compensation arithmetic logic that instantiates a parameter function, and an output function,
the parameter-function arithmetic logic generates, in response to at least (x i ) and (x c ), a corresponding parameter t value on the compensated device drive curve, according to B(t), and
the output-function arithmetic logic generates, in response to at least the resulting parameter t value and (y c ), the corresponding compensated drive signal y o , according to B(t); and
driver output circuitry configured to drive the device based on the compensated drive signals (y o ).
2. The circuit of claim 1 wherein the parametric Bezier function is a cubic function with two control points P 1 and P 2 .
3. The circuit of claim 1 wherein the quadratic Bezier curve may be expressed as x i =2(1−t)tx c +t 2 and y o =2(1−t)ty c +t 2 .
4. The circuit of claim 3 ,
wherein the parametric-function arithmetic logic includes one multiply, one add, one square root, one subtract and one divide; and
wherein the output-function arithmetic logic includes two multiplies, one shift, and one add.
5. The circuit of claim 1 wherein the device is at least one light emitting diode (LED), wherein the uncompensated drive signals are forward currents for driving the at least one LED, and wherein the device non-linear response curve corresponds to human perceptual response to LED luminance.
6. The circuit of claim 1 wherein the uncompensated drive signal (x i ) and the compensated drive signal (y o ) are digital signals with substantially the same bit accuracy.
7. The circuit of claim 1 wherein the compensation circuitry stores the control point P1 coordinates (x c , y c ), and one or more constants k n derived from (x c , y c ).
8. The LED driver of claim 1 , wherein the uncompensated drive signals are forward currents for driving the at least one LED, and wherein the device non-linear response curve corresponds to human perceptual response to LED luminance.
9. An light emitting diode (LED) driver suitable for driving an LED characterized by a non-linear response to drive signals with compensation, said LED driver comprising:
driver input circuitry configured to produce uncompensated drive signals (x i ) associated with an LED non-linear response curve for at least one LED;
compensation circuitry configured to produce compensated drive signals for the at least one LED from the uncompensated drive signals (x i ), and to produce corresponding compensated drive signals (y o ) based on a parametric quadratic Bezier function B(t) with an associated compensated device drive curve, where B(t) is characterized by
a fixed start point and a fixed end point corresponding respectively to minimum and maximum values for (x i , y o ) on the compensated device drive curve, and
a pre-defined control point P 1 characterized by coordinates (x c , y c ), used to generate the compensated drive signals (y o ) according to B(t),
a parameter t with a range corresponding to a normalized value from 0 to 1;
the compensation circuitry including compensation arithmetic logic that instantiates a parameter function, and an output function,
the parameter-function arithmetic logic generates, in response to at least (x i ) and (x c ), a corresponding parameter t value on the compensated device drive curve, according to B(t), and
the output-function arithmetic logic generates, in response to at least the resulting parameter t value and (y c ), the corresponding compensated drive signal y o , according to B(t); and
driver output circuitry configured to drive the at least one LED with the compensated drive signal.
10. The LED driver of claim 9 wherein the parametric Bezier function is a cubic function with two control points P 1 and P 2 .
11. The LED driver of claim 10 wherein the uncompensated drive signal (x i ) and the compensated drive signal (y o ) are digital signals with substantially the same bit accuracy.
12. The LED driver of claim 9 wherein the quadratic Bezier curve may be expressed as x i =2(1−t)tx c +t 2 and y o =2(1−t)ty c +t 2 and wherein the compensating circuitry operates to calculate a value of parameter t for a given value of x i using x c .
13. The LED driver of claim 9 ,
wherein the parametric-function arithmetic logic includes one multiply, one add, one square root, one subtract and one divide; and
wherein the output-function arithmetic logic includes two multiplies, one shift, and one add.