基于电流补偿的低电源噪声PWM振荡器设计

Design of a low power noise PWM oscillator based on current compensation

基于CSMC0.18μm工艺,介绍了一种应用于LED驱动芯片内部的PWM振荡器电路。采用双低压线性稳压器(LDO)结构,针对传统PWM振荡器高频振荡时因内部时延造成输出占空比偏差严重的问题,通过电流双向补偿技术,在保持电路振荡频率不变的情况下,消除了内部时延对输出占空比的影响;利用高PSRR带隙基准为电路提供基准电压,抑制电源噪声。仿真结果表明,该振荡器输出频率为200Hz^20MHz,在固定频率下占空比可从10%~90%连续变化,电源电压抑制比为110dB。

Based on CSMC 0.18 μm process, the paper introduces a PWM oscillator circuit used in the LED driver chip. It adopts dual low dropout regulator （LDO） structure. To the problem that when the traditional PWM oscillator works in high frequency the output of duty cycle deviates seriously due to internal delay, it eliminates the influence to the duty cycle by the internal delay through the both-way compensated current technology under the condition of holding the oscillation frequency invariant. It uses high PSRR circuit to provide a reference voltage to suppress the power noise. Simulation results show that range of the oscillator output freqency is 200 Hz-20 MHz, under the fixed frequency the duty cycle can be change from 10% to 90%, and the power supply rejection ratio is 110 dB in low frequency band.