The Design Of High-order Temperature Compensated Crystal Oscillator

With the continuous development and progress of the electronics industry,more and more electronic products are appearing in every corner of our lives,and their functions are becoming more and more abundant.With the gradual improvement of product functions,people have turned their attention to the performance of products.The performance of a product is closely related to many factors,but for electronic products,the frequency source is critical to product performance.The current crystal oscillator is the most important frequency generation device,but one of its problems is that its frequency is affected by temperature,therefore,if it is applied to a large temperature change environment,it may cause a large error,In order to obtain better temperature characteristics for the crystal oscillator output frequency,the temperature and frequency characteristics of the crystal oscillator are studied in this paper,and the design circuit is studied to improve the frequency temperature characteristics.The main work of this paper is as follows:By analyzing and modeling the crystal,the temperature and frequency characteristics of different cut crystals are compared.The temperature characteristics of the AT-cut and SC-cut crystals are mainly analyzed.Based on the basic characteristics of both crystals,the AT-cut crystal is finally selected to implement the oscillator Circuit design.By comparing various ways to increase the frequency characteristics of the crystal temperature and the compensation method,the temperature compensation is finally selected by using analog temperature compensation.The principle of crystal oscillation was analyzed by means of negative resistance analysis and a high-precision crystal oscillator with high-order temperature compensation was designed using a multiplier structure.An innovative adjustable bandgap reference circuit structure is proposed,which can still achieve higher accuracy when the current gain of the transistor is small,and the on-chip temperature acquisition and protection functions are realized;a crystal-based application is designed.The zero-temperature current generation circuit enables the crystal to maintain relatively stable power consumption in a large temperature change application environment and ensures the consistency of the circuit work.An oscillator structure based on a common-mode feedback adjustment method is proposed to reduce the chip area.At the same time,the stability of the output frequency is ensured;an analog multiplier temperature compensation structure based on a common-mode feedback structure is adopted,and a more accurate compensation voltage is obtained.This article is based on the 0.35?m BCD process to draw the temperature-compensated crystal oscillator each module and the overall layout,and in the Cadence integrated environment to complete the circuit of the various modules and the overall circuit after the simulation analysis,the simulation results show that the power supply voltage is 3.3V ~ 5V When the output frequency is set to 13.56 MHz,this circuit structure can achieve a frequency accuracy of ±2.5ppm in the temperature range from-40°C to 80°C.