Research And Design Of Calibrated High Precision On-chip RC Relaxation Oscillator

With the rapid development of portable consumer electronic devices,the on-chip clock source is one of the important modules.The RC relaxation oscillator has significant advantages such as low cost,low power consumption,and simple circuit topology.However,the frequency of the traditional RC relaxation oscillator varies greatly with the manufacturing process,power supply voltage and ambient temperature,which cannot meet the requirements of the chip for high precision and high stability of the clock signal.At the same time,all the indicators of the traditional RC relaxation oscillator cannot be well balanced.In this thesis,an on-chip RC relaxation oscillator architecture with high calibration accuracy is proposed to comprehensively improve the performance indicators of the on-chip RC relaxation oscillator.The main work is as follows :In this thesis,the voltage-mode RC oscillator based on the average voltage negative feedback structure is used as the core circuit of the oscillator to ensure that the target frequency is achieved while taking into account the power consumption.The integrator is used to form a voltage feedback loop to eliminate the delay caused by the comparator offset voltage and improve the frequency stability.The single-point calibration circuit based on digital Trimming technology is used to calibrate the output frequency of the oscillator by trimming the charging current of the zero temperature coefficient,which solves the problem that the output frequency of the oscillator fluctuates with the manufacturing process and ensures the absolute accuracy.At the same time,the method of trimming current greatly reduces the area of the layout and saves the cost.The on-chip low dropout linear regulator circuit with Miller compensation is used to supply power to the oscillator core circuit and the current source circuit,which solves the problem that the output frequency of the oscillator fluctuates with the voltage of the power supply,and ensures the low frequency voltage coefficient.The bandgap reference circuit with voltage summation mode is combined with the temperature compensation current source module based on gain boosting technology to provide a zero temperature coefficient charging current for the core circuit of the oscillator,which solves the problem that the output frequency of the oscillator fluctuates with the ambient temperature and ensures the low temperature coefficient of the frequency.At the same time,the startup time of the output frequency of the oscillator is greatly reduced by using the startup circuit controlled by the internal signal to separate the bandgap reference from the degenerate point.The design is taped out in SMIC 180 nm process,and the overall schematic design and layout design of the circuit are completed.The final layout area is 248μm × 216μm.The post-simulation results show that the target frequency of the oscillator is 2MHz,and the typical frequency accuracy is 0.18%.The duty cycle range is 49.45%-50.26%;the voltage coefficient of the output frequency is 0.33%@1.98-3.63V;the temperature coefficient of the output frequency is 0.89% @-40～125℃.The startup time is 17.65μs and the average power consumption is 199.45μW.Therefore,the high-precision RC relaxation oscillator designed in this thesis can output high-precision and high-stability clock signals,and each target is excellent.