Display driver
An LC display driver including a gamma reference circuit to generate N gamma-compensated reference voltages based on at least one pre-defined gamma curve divided into M regions defined by M+1 breakpoint voltages, each generated by a range-region DAC coupled to a subset of voltage taps of a range resistor string (some subsets overlapping). An output circuit generates the N gamma-compensated reference voltages, and includes a reference resistor string with N reference voltage taps, and M+1 breakpoint locations to receive respective breakpoint voltages, the N reference voltage taps divided into M subsets corresponding to the M regions of the gamma curve, each of the M subsets of reference voltage taps forming a voltage divider. N output selector circuits output a corresponding one of the N gamma-compensated reference voltages based on a respective reference voltage tap and the associated voltage divider.
1. A circuit suitable for use in a system with an LCD (liquid crystal display), comprising:
an LCD display driver integrated circuit(IC),including multiple LCD source driver circuits and a gamma reference circuit;
each LCD source driver circuit to
convert video image data input to the LCD display driver integrated circuit into N analog gray-level gamma-adjusted source voltage signals, each based on a respective one of N gamma reference voltages, and
drive out the gamma-adjusted source voltage signals;
the gamma reference circuit to generate the N gamma reference voltages based on at least one pre-defined gamma curve that includes the N (0 to N−1) gamma reference voltages divided into M−1 regions defined by M breakpoint voltages corresponding to M−1 segments of the gamma curve, including
a gamma-breakpoint circuit, including
a range resistor string with a sequence of voltage taps;
M breakpoint digital-to-analog converters (DACs), designated DAC(1) to DAC(M),
each breakpoint DAC including inputs coupled to a respective subset of the voltage taps of the range resistor string, where at least some of the M subsets of voltage taps overlap, and
each breakpoint DAC to output a respective breakpoint voltage based on the respective subset of voltage taps, including
a breakpoint voltage BP(1) from breakpoint DAC(1) and a breakpoint voltage BP(M) from a breakpoint DAC (M), and
intermediate breakpoint voltages BP(2) to BP(M−1) from respectively breakpoint DAC(2) to DAC(M−1);
a gamma-reference output circuit to generate the N gamma reference voltages, including
a reference resistor string having a set of reference voltage taps, and
N reference multiplexers, designated MUX(0) to MUX(N−1) each to select from a subset of the reference voltage taps of the reference resistor string, and to generate at an output a respective one of the N gamma reference voltages,
the reference resistor string including a first end point provided by the breakpoint voltage BP(1) from DAC(1), and a second end point provided by the breakpoint voltage BP(M) from DAC(M),
M−2 selected reference multiplexers designated MUX(2) to MUX(M−1) each having its output coupled respectively to the intermediate breakpoint voltages BP(2) to BP(M−1) from DAC(2) to DAC(M−1).
2. The circuit of claim 1 , wherein N=64, M=4 and the M breakpoint voltages correspond to reference voltages N=0, 7, 24, 56, 63.
3. The circuit of claim 1 , wherein the gamma reference circuit to generate the N gamma reference voltages selectively for each of multiple pre-defined gamma curves, and, for each selected gamma curve,
the gamma-breakpoint circuit to generate respective M breakpoint voltages corresponding to M−1 segments for the selected gamma curve;
the gamma-reference output circuit to generate the N gamma reference voltages from the N reference multiplexers, including the M−2 selected reference multiplexers having respective outputs coupled respectively to the intermediate breakpoint voltages BP(2) to BP(M−1)from the gamma-breakpoint circuit.
4. The circuit of claim 3 ,
wherein gamma-breakpoint circuit includes polarity inversion circuitry to selectively invert a polarity of the voltages at respective endpoints of the range resistor string corresponding to positive and negative pre-defined gamma curves; and
wherein the multiple pre-defined gamma curves are for at least one of (a) red, green and blue, and (b) positive and negative inversion polarity.
5. The circuit of claim 1 , further comprising:
M buffer amplifiers coupled to respective breakpoint DACs, to output respective buffered breakpoint voltages BP(1) to BP(M).
6. The circuit of claim 1 , the gamma-breakpoint circuit further including
first and second inversion buffers coupled to the range resistor string respectively at first and second endpoints;
the first and second inversion buffers switched between high/low and low/high voltage outputs to invert a polarity of the voltages at the first and second endpoints.
7. The circuit of claim 1 , wherein spacings between the reference voltage taps of the reference resistor string are selectively non-uniform, to provide programmable nonlinearity for the pre-defined gamma curve.
8. An LCD display system, comprising:
an LCD (liquid crystal display);
an LCD display driver including,
multiple LCD source driver circuits, and
a gamma reference circuit;
each LCD source driver circuit to
convert video image data input to the LCD display driver into N analog gray-level gamma-adjusted source voltage signals output to the LCD, each based on a respective one of N gamma reference voltages, and
drive out the gamma-adjusted source voltage signals to the LCD;
the gamma reference circuit to generate the N gamma reference voltages based on at least one pre-defined gamma curve that includes the N (0 to N−1) gamma reference voltages divided into M−1 regions defined by M breakpoint voltages corresponding to M−1 segments of the gamma curve, including
a gamma-breakpoint circuit, including
a range resistor string with a sequence of voltage taps;
M breakpoint digital-to-analog converters (DACs), designated DAC(1) to DAC(M), wherein
each breakpoint DAC including inputs coupled to a respective subset of the voltage taps of the range resistor string, where at least some of the M subsets of voltage taps overlap, and
each breakpoint DAC to output a respective breakpoint voltage based on the respective subset of voltage taps, including
a breakpoint voltage BP(1) from breakpoint DAC(1) and a breakpoint voltage BP(M) from a breakpoint DAC (M), and
intermediate breakpoint voltages BP(2) to BP(M−1) from respectively breakpoint DAC(2) to DAC(M−1); and
a gamma-reference output circuit to generate the N gamma reference voltages, including
a reference resistor string having a set of reference voltage taps, and
N reference multiplexers, designated MUX(0) to MUX(N−1) each to select from a subset of the reference voltage taps of the reference resistor string, and to generate at an output a respective one of the N gamma reference voltages,
the reference resistor string including a first end point provided by the breakpoint voltage BP(1) from DAC(1), and a second end point provided by the breakpoint voltage BP(M) from DAC(M),
M−2selected reference multiplexers designated MUX(2) to MUX(M−1) each having its output coupled respectively to the intermediate breakpoint voltages BP(2) to BP(M−1) from DAC(2) to DAC(M−1).
9. The system of claim 8 , wherein N=64, M=4 and the M breakpoint voltages correspond to reference voltages N=0, 7, 24, 56, 63.
10. The system of claim 8 , wherein the gamma reference circuit to generate the N gamma reference voltages selectively for each of multiple pre-defined gamma curves, and, for each selected gamma curve,
the gamma-breakpoint circuit to generate respective M breakpoint voltages corresponding to M−1 segments for the selected gamma curve;
the gamma-reference output circuit to generate the N gamma reference voltages from the N reference multiplexers, including the M−2 selected reference multiplexers having respective outputs coupled respectively to the intermediate breakpoint voltages BP(2) to BP(M−1) from the gamma-breakpoint circuit.
11. The system of claim 10 ,
wherein gamma-breakpoint circuit includes polarity inversion circuitry to selectively invert the polarity of the voltages at respective endpoints of the range resistor string corresponding to positive and negative pre-defined gamma curves; and
wherein the multiple pre-defined gamma curves are for at least one of (a) red, green and blue, and (b) positive and negative inversion polarity.
12. The system of claim 8 further comprising:
M buffer amplifiers coupled to respective breakpoint DACs, to output respective buffered breakpoint voltages BP(1) to BP(M).
13. The system of claim 8 , the gamma-breakpoint circuit further including
first and second inversion buffers coupled to the range resistor string respectively at first and second endpoints;
the first and second inversion buffers switched between high/low and low/high voltage outputs to invert a polarity of the voltages at the first and second endpoints.
14. The system of claim 8 , wherein spacings between the reference voltage taps of the reference resistor string are selectively non-uniform, to provide programmable nonlinearity for the pre-defined gamma curve.
15. A method for use in a system with an LCD (liquid crystal display), comprising:
converting video image data into N analog gray-level gamma-adjusted source voltage signals for input to the LCD, each based on a respective one of N gamma reference voltages, and
generating the N gamma reference voltages based on at least one pre-defined gamma curve that includes the N (0 to N−1) gamma reference voltages divided into M−1 regions defined by M breakpoint voltages corresponding to M−1 segments of the gamma curve, including generating the M breakpoint voltages designated BP(1) to BP(M) using M respective range decoders with inputs coupled to a respective subset of voltage taps of a range resistor string, where at least some of the M subsets of voltage taps overlap;
generating the N gamma reference voltages using N reference multiplexers, each to select from a respective subset of reference voltage taps of a reference resistor string,
the reference resistor string including a first end point provided by the breakpoint voltage BP(1), and a second end point provided by the breakpoint voltage BP(M),
the N reference multiplexers including M−2 selected reference multiplexers with outputs respectively couple to intermediate breakpoint voltages BP(2) to BP(M−1).
16. The method of claim 15 , wherein N=64, M=4 and the M breakpoint voltages correspond to reference voltages N=0, 7, 24, 56, 63.
17. The method of claim 15 , wherein N gamma reference voltages are selectively generated for each of multiple pre-defined gamma curves.
18. The method of claim 15 , further comprising:
selectively inverting a polarity of the voltages at respective endpoints of the range resistor string corresponding to positive and negative pre-defined gamma curves.
19. The method of claim 18 , wherein multiple pre-defined gamma curves are generated for at least one of (a) red, green and blue, and (b) positive and negative inversion polarity.
20. The method of claim 15 , wherein spacings between the reference voltage taps of the reference resistor string are selectively non-uniform, to provide programmable nonlinearity for the pre-defined gamma curve.