一种低温漂高电源抑制能力的振荡器设计

Design of oscillator with low⁃temperature drift and high power supply rejection ability

为了提升开关电源芯片中振荡器的温度特性和电源抑制能力,提出一种改进型拓扑结构的RC振荡器。该振荡器由电容充放电模块、偏置电流源模块、比较器模块以及寄存器模块组成。通过将电容的上下极板都接入电流源,并对电容下极板流过的电流进行采样,引入负反馈对充放电电流源进行动态调节,从而减小电容上极板电压通过沟道调制效应对充放电电流源的影响,增强充放电电流源的电源抑制能力。再配合偏置电流源模块中经过温度补偿的偏置电流,得到具有低温漂特性及高电源抑制能力的振荡频率。基于CSMC 0.18μm BCD工艺完成了电路设计,仿真实验结果表明,所设计的振荡器工作频率为411 kHz,电源电压为2.6~3.8 V时频率变化为0.119%,温度为-40~125℃时频率变化为3%。该振荡器具有较强的电源抑制能力,能很好地满足开关电源芯片中振荡器的设计要求。

In order to improve the temperature characteristics and power supply rejection ability of the oscillator in switching power supply chip,a RC oscillator with improved topology structure is proposed.The oscillator is composed of capacitor charge-discharge module,bias current source module,comparator module and register module.The upper and lower plates of the capacitor are connected to the current source,the current flowing through the lower plate of the capacitor is sampled and introduced to the negative feedback,and the charging and discharging current source is adjusted dynamically,thereby reducing the influence of channel modulation effect on the charging and discharging current source by the voltage of the upper plate of the capacitor,and enhancing the power suppression ability of the charging and discharging current source.The oscillation frequency with low temperature drift characteristic and high power suppression ability is obtained by combining with the temperature-compensated current in the bias current source module.The circuit is designed based on CSMC 0.18μm BCD process.The simulation results show that the operating frequency of the designed oscillator is 411 kHz,the frequency change is 0.119%,when the supply voltage is 2.6~3.8 V,and the frequency change is 3%when the temperature is-40~125℃.This oscillator has strong power suppression capability,and can well meet the design requirements of oscillators in switching power supply chips.