Spread spectrum clock generator for reducing Electro-Magnetic Interference (EMI) noise in LCD driver IC

In this paper, we describe EMI noise reduction in LCD driver IC of which uses the spread spectrum clock generator. The proposed spread spectrum clock generator use pseudo random modulation technique for providing clock edge offset with coarsely and use fine selecting that make numerous time-offset in each coarse-offset signal. As a result of spread spectrum technique, the original clock edges which are used in LCD driver IC has been spread in time domain maximally about 3 n sec. Moreover the proposed SSCG has analog bias in delay circuit for the immunity of power supply variation. The LCD driver IC including proposed spread spectrum clock generator has been fabricated with one poly three metal 0.45 mum CMOS technology when the logic supply voltage varies from 2.3 V to 3.6 V and the driver supply voltage varies from 8 V to 13.5 V. The 6 pieces of test chips have been assembled to 17" LCD monitor, and have been under tested in anechoic chamber which has been surrounded with absorbers. As a test result, we achieved that the EMI noise levels of newly designed LCD driver IC have been reduced about 3 dBu at harmonic frequency of the system clock comparing with conventional one.