Circuit for combining the three color signals of a color television system to form two color difference signals and a luminance signal

Claim 1

A matrixing circuit for NTSC color television systems operative for receiving R, G and B color signals and deriving therefrom each of the requisite NTSC color difference signals -I and Q and also the NTSC luminance signal Y, the matrixing circuit comprising a voltage source having first and second source terminals; a first, a second and a third transistor each having a base, a collector and an emitter, the first, second and third transistors being respectively adapted to receive at their bases the R, G and B color signals, the collectors of the three transistors being all connected to the first source terminal; a first, a second and a third emitter resistor each having one terminal connected to the emitter of a respective one of the three transistors, the three other terminals of the emitter resistors being connected in common to a common junction; a constant current source connected between said common junction and said second source terminal, the conductivities of the three emitter resistors standing in the ratio k 1 : k 2 : k 3` , where k 1 , k 2 and k 3 are the coefficients in the NTSC luminance signal equation Y = k 1 R + k 2 G + k 3 B, so that an NTSC luminance signal Y develops at said common junction upon application of R, G and B color signals to the bases of the first, second and third transistors, respectively; and a first phase shift resistor connected between the emitters of the first and third transistors and a second phase shift resistor connected between the emitters of the second and third transistors, the first and second phase shift resistors having resistance values such as to cause the development of the NTSC color difference signals -I and Q at the collectors of the first and second transistors, respectively, upon applicaton of R, G and B color signals to the bases of the first, second and third transistors, respectively.