Patent ID: 7460138
Filing Date: 2008-12-02
Classification: G09G

Abstract:
1. A PWM signal generation circuit comprising: a change timing storage circuit that stores a pulse change timing of a grayscale clock pulse for generating a PWM signal, a first grayscale clock pulse generation circuit, a second grayscale clock pulse generation circuit, a selector, a timing counter, a calculation circuit, a grayscale counter, and a grayscale coincidence detection circuit, the change timing storage circuit including N (N is an integer greater than one) timing registers, each of the N timing registers storing m bits (m is an integer greater than one) of a predetermined change timing value, the timing counter updating and outputting a first count value in one of an increment direction and a decrement direction in synchronization with a clock signal, the first grayscale clock pulse generation circuit generating a grayscale pulse each time it is judged that the change timing value stored in each of the N timing registers coincides with the first count value, and outputting the grayscale pulse, which is sequentially generated, to the selector as a first grayscale clock pulse, the calculation circuit performing calculation processing of the first count value, and outputting a second count value that is updated in another direction differing from the one direction, the second grayscale clock pulse generation circuit generating a grayscale pulse each time it is judged that the change timing value stored in each of the N timing registers coincides with the second count value, and outputting the grayscale pulse, which is sequentially generated, to the selector as a second grayscale clock pulse, the selector alternately outputting the first or second grayscale clock pulse output from the first or second grayscale clock pulse generation circuit to the grayscale counter as the grayscale clock pulse in units of one horizontal scan period, the grayscale counter updating a grayscale count value in one of the increment direction and the decrement direction based on the grayscale clock pulse output from the selector, and the grayscale coincidence detection circuit comparing a relationship between grayscale data input to the grayscale coincidence detection circuit and the grayscale count value, and changing a voltage level of the PWM signal when the relationship between the grayscale data and the grayscale count value satisfies a predetermined relationship.