一种片外电容交叉充放电型振荡电路设计

An oscillator circuit with cross charge and discharge by off-chip capacitors

CMOS环形振荡器具有版图面积小、调谐范围大、电路简单便于集成等优点,广泛应用于各类电源系统及电子通信应用中。在常规的环形振荡电路基础上,设计了独立的充放电控制通路,实现了一种交叉充放电型环形振荡电路,并通过外接片外电容的方式,得到更低频率的振荡周期。基于0.18μm工艺,采用HSIM工具对电路进行功能仿真,经过后端物理实现后,版图面积为172μm×76μm,对电路进行提参后仿,结果表明:在3.3 V电压及25℃条件下,外接10 nF接地电容时,电路获得约1.2 ms的稳定振荡周期。在Vcc=2.7 V~5.5 V、T=-55℃~125℃条件下,时钟周期的最大偏移为5.83%。该电路已成功应用于某电源控制芯片中。

CMOS Ring Oscillator has many advantages such as small layout area, large frequency range and easy integration. It is widely used in the DC-DC buck converter and electronic communication systems. On the basis of the traditional ring oscillator circuit, an independent charge and discharge control path is designed to realize a cross charge and discharge ring oscillator circuit, and a lower frequency oscillation period is obtained by externally connecting an off-chip capacitor. Based on 0.18 μm process, the circuit has been simulated with HSIM tool. After the back-end physical implementation, the layout of the oscillation occupies an area of 172 μm×76 μm. Using tools to extract parasitic parameters from the layout and conduct post-simulation, the simulation results indicates that with externally connecting an off-chip capacitor, and the power supply voltage in 3.3 V and temperature in 25℃, the oscillator has a clock period of 1.2 ms. With the power supply voltage changes in 2.7 V~5.5 V and temperature changes in-55℃~125℃, the frequency deviation is 5.83%.The circuit has been successfully applied in a power management chip.