Frequency converter for a digital chrominance modulator

DETAILED DESCRIPTION It is an object of the present invention to provide a frequency converter circuit for converting color signals converted from Hi-Vision RGB signals into a carrier chrominance signal in accordance with the NTSC method.
According to the invention, the organization is as follows.
The present invention is provided with: a switching means into which the first and second color signal data and their sign-inverted color signal data are input respectively to first, second, third and fourth input terminals; a carrier chrominance signal generating circuit in which the above-mentioned color signal data are switched selectively in turn by means of a switching signal with a frequency four times as high as that of a color subcarrier; memory means in which the above first and second color signal data are temporarily stored; with a writing and reading of the above color signal data to and from the memory being performed using first and second clock signals, the latter of which is used as a switching signal for the above switching means.
Illustratively, two color signals sent in the field frequency of the Hi-Vision method fv(H) (=60.
00 Hz) are written to the memory means by a clock signal CK.
sub.
H with a frequency 4 fsc(H) which is four times higher than that of a color subcarrier signal, the color signals written in memory are read out through a clock signal CK.
sub.
N with a frequency 4 fsc(N) which is four times higher than that of a color subcarrier of the NTSC method to be input to the switching means.
In the switching means, the first and second color signals and their sign-inverted color signals are supplied respectively to the first, second, third and fourth input terminals, the supplied color signals are switched in turn by means of the clock signal CK.
sub.
N to be output as a carrier chrominance signal from the output terminal T5.
In this way, the switching means outputs a carrier chrominance signal following the NTSC method into which color signals converted into Hi-Vision RGB signals have been converted