In a copending U.S. patent application Ser. No. 526,700 entitled, "Progressive Scan Television Display System Employing Interpolation in the Luminance Channel" filed concurrently herewith in the name of D. H. Pritchard, a progressive scan television system is described. According to the Pritchard application, in the case of NTSC, 525 lines of the display are displayed in 1/60th of a second wherein alternate "real"0 and "interpolated" lines are successively displayed at some multiple (i.e., two-times) standard horizontal rate. During the next 1/60th of a second another 525 lines are displayed to complete a total frame time in 1/30th of a second, however, these second 525 lines are related to the first 525 lines such that in successive fields "interpolated" and "real" lines are displayed on top of each other. This progressive scan format results in the elimination of artifacts of "interline flicker" and "line break-up with motion" that exists in conventional two-to-one interlaced displays such as the NTSC system. The subjective effect of progressive scan is a flicker free, " smooth" or "quiet", picture presentation that is more pleasing to the viewer. The Pritchard application applies as well to other interlaced systems such as the 525/25 PAL system.
To perform progressive scanning as described in the aforementioned Pritchard application a speed-up processor is used for providing two horizontal lines of video during the time period of one horizontal line of incoming broadcast video signal. This speed-up processing requires that a line of video be written into memory in real time at a rate sufficient to sample the incoming video, i.e., at more than the Nyquist rate, and be readout of memory at some multiple of the input sample rate (generally, two-times). Such processing requires extremely high speed memories which are capable of operating at high sampling speeds, for example, 28 MHz for NTSC signals sampled at four-times color subcarrier. It is desirable to provide inexpensive speed-up processors which are capable of operating at these speeds without the use of memory elements which operate at extremely high speeds.