Circuit for superimposing text on an image

Abstract

A superimposing circuit includes an N-bit transmission gate for transmitting N-bit RGB data in a pixel unit in response to a blanking signal; a signal synthesizer for generating R, G and B signals, by separating each component of R, G and B from the N-1 least significant bits of the N-bit RGB data output from the transmission gate; an RGB matrix for receiving the R, G and B signals and generating a luminance signal, first and second color difference signals; a luminance signal amplifier for amplifying the luminance signal; a pair of modulators for modulating the first and second color difference signals, respectively; a first mixer for synthesizing the modulated color difference signal and generating a carrier color signal; a second mixer for synthesizing the carrier color signal, the amplified luminance signal and a complex synchronizing signal and generating a complex image signal; an attenuator for attenuating an external image signal; an image signal selector for selectively outputting the attenuated external image signal or the complex image signal according to the most significant bit value of the N-bit RGB data; and an output amplifier for amplifying the selected image signal. Therefore, the internal and external image signals can be superimposed at high speed in a pixel unit.