MPEG video decoder having a high bandwidth memory

摘要

A decoder for a video signal encoded according to the MPEG-2 standard includes a single high-bandwidth memory and a digital phase-locked loop. This memory has a single memory port. The memory is used to hold 1) the input bit-stream, 2) first and second reference frames used for motion compensated processing, and 3) image data representing a field that is currently being decoded. The decoder includes circuitry which stores and fetches the bit-stream data, fetches the reference frame data, stores the image data for the field that is currently being decoded in block format and fetches this image data for conversion to raster-scan format. All of these memory access operations are time division multiplexed and use the single memory port. The digital phase locked loop (DPLL) counts pulses of a 27 MHz system clock signal, defined in the MPEG-2 standard, to generate a count value. The count value is compared to a succession of externally supplied system clock reference (SCR) values to generate a phase difference signal that is used to adjust the frequency of the signal produced by the DPLL. In addition, the DPLL is aligned in phase by substituting respective portions of the SCR value for the count value developed by the DPLL and for the accumulated phase value used by the DPLL. In one embodiment of the invention, flexible partitions are defined in the high-bandwidth memory. These partitions allow for a larger VBV buffer size when progressive scan signals are being received and displayed and allow for a larger display buffer when interlaced scan signals are being received and displayed.