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

Abstract

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.

Keywords

• ring oscillator
• charge and discharge of capacitor
• power management chip
• clock