Image signal processing apparatus producing a narrowed pulse width modulated signal using an asymmetrically centered triangle reference waveform

An image signal processing apparatus comprising:

• a pulse-width modulating circuit for comparing an image signal and a triangle-shaped wave signal to output a pulse-width modulated signal therefrom based on the result of its comparison, said image signal varying between a first d.c. level and a second d.c. level exceeding said first d.c. level, said triangle-shaped wave signal varying between a third d.c. level, which is less than said first d.c. level, and said second d.c. level;
• a delay circuit for delaying said pulse-width modulated signal for a predetermined period of time;
• and
• an AND circuit having a first input terminal to which a pulse-width modulated signal outputted from said pulse-width modulating circuit is inputted, and a second input terminal, such that said image signal varies asymmetrically with respect to a baseline of said triangle-shaped wave signal to which a time-delayed pulse-width modulated signal outputted from said delay circuit is inputted, said AND circuit being adapted to output a narrow pulse-width modulated signal having the pulse width narrower than that of said pulse-width modulated signal,
• wherein said pulse-width modulating circuit comprises an image signal output device for outputting an image signal therefrom in synchronism with a pixel synchronizing signal, a triangle-shaped wave signal generator for outputting a triangle-shaped wave signal therefrom in synchronism with said pixel synchronizing signal, and a comparator for comparing said image signal and said triangle-shaped wave signal so as to output a pulse-width modulated signal therefrom based on the result of its comparison.

An apparatus for producing pulse-width modulated signals from digital image data and a synchronizing signal, said apparatus comprising:

• triangular-shaped wave signal generator means for receiving the synchronizing signal and for producing a triangular-shaped wave signal having a voltage level which varies between an upper voltage level and a lower voltage level;
• image signal generator means for receiving the synchronizing signal and the digital image data and for producing an analog image signal having a voltage level which varies between the upper voltage level of said triangular-shaped wave signal and an intermediate voltage level, the intermediate voltage level being between the upper voltage level and the lower voltage level, and the intermediate level being offset from the lower voltage level by an offset amount, wherein said image signal varies asymmetrically with respect to a baseline of said triangular-shaped wave signal;
• and
• comparison means for comparing the analog image signal and the triangular-shaped wave signal to produce the pulse-width modulated signals.