Digital pixel clock generation circuit and method employing independent clock
View Patent ↗A digital pixel clock generation circuit receives image data and corresponding image presentation time information from at least one external image source. The digital pixel clock generation circuit includes an image presentation timing error determination circuit that produces desired pixel clock frequency control information, such as pixel output clock adjustment control information, based on a difference between an expected presentation time and an actual presentation image time information. A programmable digital waveform generation circuit is programmed based on the produced desired pixel clock frequency and has an input that is responsive to an independent clock source, that is independent from the clock source of the external image source. The programmable digital waveform generation circuit provides a digital representation of an independently generated desired pixel clock which is then output to a digital to analog converter (DAC).
1. A digital pixel clock generation circuit operative to receive timing information associated with image data from at least one external image source from which image presentation time information can be derived comprising:
an image presentation timing error determination circuit operative to produce desired pixel clock frequency control information based on a difference between expected presentation time, which is based on at least the received image presentation time information from the external image source, and presentation time information provided by a display controller that is operatively coupled to the digital display clock generation circuit;
a programmable digital waveform generation circuit that is programmed based on the produced desired pixel clock frequency control information, having an input responsive to an independent clock source and an output operative to provide a digital representation of an independently generated desired pixel clock; and
a digital to analog converter (DAC) having an input, operatively coupled to receive the digital representation of the independently generated desired pixel clock, and an output operative to provide an analog representation of the digital representation of the independently generated desired pixel clock for the digital display based on the independent clock source.
2. The digital pixel clock generation circuit of claim 1 further including a phase locked loop circuit (PLL) having an reference clock input operatively coupled to the output of the DAC, and an output that provides an independently generated desired pixel clock.
3. The digital pixel clock generation circuit of claim 2 farther including an analog filter operatively interposed between the DAC and the PLL to provide a filtered analog input signal for the PLL.
4. The digital pixel clock generation circuit of claim 1 including display timing control logic operatively responsive to the analog representation of the digital representation of the independently generated desired pixel clock and operative to produce the actual presentation time information.
5. A digital pixel clock generation circuit operative to receive image data and corresponding image presentation time information based on a first clock from at least one external image source comprising:
an image presentation timing error determination circuit operative to produce desired pixel clock frequency control information based on a difference between expected presentation time, which is based on at least the received image presentation time information from the external source, and actual presentation time information;
an independent clock source that is independent from the first clock;
a programmable digital waveform generation circuit that is programmed based on the produced desired pixel clock frequency, having an input responsive to the independent clock source and an output operative to provide a digital representation of an independently generated desired pixel clock;
a digital to analog converter having an input, operatively coupled to receive the digital representation of the independently generated desired pixel clock, and an output operative to provide an analog representation of the digital representation of the independently generated desired pixel clock for the digital display based on the independent clock source; and
a phase locked loop circuit (PLL) having an input operatively coupled to the output of the DAC, a phase reference input operatively coupled to receive control information and an output that provides an independently generated desired pixel clock with additional phase correction.
6. The digital pixel clock generation circuit of claim 5 farther including an analog filter operatively interposed between the DAC and the PLL to provide a filtered analog input signal for the PLL.
7. The digital pixel clock generation circuit of claim 6 including digital display timing control logic operatively responsive to the analog representation of the digital representation of the independently generated desired pixel clock and operative to produce the actual presentation time information.
8. A digital pixel clock generation circuit operative to receive image data and corresponding image presentation time information based on a first clock from a plurality of external image sources comprising:
an image presentation timing error determination circuit operative to produce a desired pixel clock frequency control information based on a difference between expected presentation time, which is based on at least the received image presentation time information from the external source, and actual presentation time information;
a digital display input signal multiplexing circuit operatively coupled to the image presentation timing error determination circuit, and operative to switch among a plurality of different received image data and corresponding image presentation time information as provided by the plurality of different image sources;
an independent clock source that is independent from the first clock;
a programmable digital waveform generation circuit that is programmed based on the produced desired pixel clock frequency control information, having an input responsive to the independent clock source and an output operative to provide a digital representation of an independently generated desired pixel clock;
a digital to analog converter having an input, operatively coupled to receive the digital representation of the independently generated desired pixel clock, and an output operative to provide an analog representation of the digital representation of the independently generated desired pixel clock for the digital display based on the independent clock source;
a phase locked loop circuit (PLL) having an input operatively coupled to the output of the DAC, a phase reference input operatively coupled to receive control information and an output that provides an independently generated desired pixel clock with additional phase correction; and
a video scaling circuit operatively responsive to the independently generated desired pixel clock to provide scaled image data for display on the digital display.
9. The digital pixel clock generation circuit of claim 8 further including an analog filter operatively interposed between the DAC and the PLL to provide a filtered analog input signal for the PLL.
10. The digital pixel clock generation circuit of claim 9 including digital display timing control logic operatively responsive to the analog representation of the digital representation of the independently generated desired pixel clock and operative to produce the actual presentation time information.
11. A method for generating a digital pixel clock in response to received image data and corresponding image presentation time information based on a first clock from at least one external image source comprising:
producing desired pixel clock frequency control information based on a difference between expected presentation time, which is based on at least the received image presentation time information from the external image source, and actual presentation time information;
programming a digital waveform generation circuit based on the produced desired pixel clock frequency control information to provide a digital representation of an independently generated desired pixel clock that is based on an independent clock source; and
providing an analog representation of the digital representation of the independently generated desired pixel clock for the digital display.
12. The method of claim 11 including filtering the analog representation of the digital representation of the independently generated desired pixel clock for the digital display.
13. The method of claim 12 including phase adjusting the filtered analog representation of the digital representation of the independently generated desired pixel clock for the digital display to provide an independently generated desired pixel clock with additional phase correction.