Interlacing in charge-coupled imaging devices

Abstract

Solid-state imaging devices to be used in commercial broadcast TV or the Picturephone® system have to supply the video information in a 2:1 interlaced timing format. An efficient way to achieve such a readout from charge-coupled area imaging devices of the frame transfer type is described. The resolution cells of the device are elongated in the vertical dimension to extend across the distance corresponding to two scanning lines in the display. For the two fields forming a full frame the charge generated by the incident light is integrated alternately underneath different sets of electrodes. Experimental results obtained on a 64 × 106 element frame transfer array are presented and compared to theory. They show that in a three-phase structure, by alternately integrating the charge underneath electrodes number 1 and numbers 2+3 jointly, the vertical resolution can be improved by about a factor of 2. This results in a limiting resolution in the vertical direction of about 75 percent of that given by the spatial pitch of the transfer cells. The value 75 percent is characteristic of all raster scanned imaging devices and is a result of the line scanned display. The usefulness of this scheme for line imaging devices is also discussed but is dismissed as being inferior to a bilinear approach with separate interdigitated integration sites.