Abstract: A CRT display system providing a raster pattern has digital means 30, 31, 32 to drive a DAC 34. In response, there are supplied analogue signals, on a line 37. There are also provided pulse generating means 90 controlled by the digital means, and integrating means comprising two integrators. Each integrator is connected individually to an X deflection plate 14 of the CRT, and comprises an amplifier and a feedback capacitor. One capacitor C2 is charged by negative-going pulses, and the other capacitor C2' is charged by positive-going pulses, until the pulses are removed, when the required ramps are applied to the deflection plates. Then a current flows through a transistor T7, and is controlled by the DAC output on the line 37. Hence, the waveforms applied to the deflection plates cause distortion of the raster pattern otherwise obtained, to be corrected, the DAC output representing a function comprising the inverse of the function representing the distortion.

Abstract: A circuit for converting a TV receiver to operate in accordance with the system associated with received signals, there being either F or F' scan lines in a field, with F<F', includes a counter driven by pulses each representative of one end of a raster scan line, and having M stages, with F and F'<M<2F and 2F'. There is also means to preload the counter selectively with a count of R or R', where (M-2R)=F and (M-2R')=F'. Wide window means detects when a field sync pulse is within a window including the (M-R)th and (M-R') stages, and, in response, the counter, initially, is preloaded with R'. Decision logic means then detects whether a field sync pulse occurs after the Kth stage, with K=M-[R+R']/2, when R' is continued to be preload; or occurs before the Kth stage, when R subsequently is preloaded; and the required TV receiver conversion is completed.