The Design Of The Voltage Controlled Temperature Compensated Crystal Oscillator With A Single Varactor

As one of the seven international units,the measurement accuracy of time frequency has always been the focus of research.The paper elaborates on the history of the development of quartz oscillators,which are widely used as frequency sources.This paper also presents the existing problems of the current voltage controlled temperature compensated crystal oscillator by consulting a large number of related products.Because of the controlled voltage and temperature compensated voltage work on different varactors,they are prone to interfere with each other.Because controled voltage and temperature compensated voltage work on different varactors,they are prone to interfere with each other.And capacitance cannot be simply superimposed,resulting in a complex formula of frequency calculation.In addition,there is the Trim effect that the temperature frequency curve rotation and stability decline.In order to make up for the above deficiencies and to obtain applications in the high-end market,a low-cost single capacitor diode voltage controlled temperature compensated crystal oscillator has been researched and designed.The research and design work mainly includes the following aspects:The main method is to consider the controlled voltage and temperature compensated voltage as a whole,and output the appropriate varactor diode control voltage according to the set frequency and the current temperature so that the output frequency is the same as the setting.The key to achieving this goal is to obtain accurate initial data and process the data correctly.Starting from the principle of oscillation,the thesis analyzes the NE555/LC capacitor three-point oscillation circuit and gives the phase condition of oscillation balance.Then according to the theory,the oscillation frequency of the equivalent circuit of the quartz crystal resonator in series with a capacitor is calculated.Combined with its commonly used oscillator circuit,the clock structure of the MCU is selected to design a voltage controlled temperature compensated crystal oscillator with the inverter oscillator structure and a single varactor diode,then the simulation verification is carried out.Then the paper completes the design of the hardware circuit based on the selected oscillator structure and determined the specific selection of each device,including: oscillator circuit,main control chip,DAC and so on.After completing the hardware circuit,we test each function to ensure that it meets the design requirements.We use the designed circuit board for the temperature chamber experiment to achieve the initial data collection.Interpolated and fitted the data and then extracted the data to reproduce the Trim effect.The surface fitting obtains a cubic function of the control voltage V with respect to the current temperature T and the set output frequency F.The surface compensation experiment shows that when the oscillator's setting frequency is changed in the range of the whole pulling frequency,the output frequency offset is basically within ±1ppm when the temperature range is-30?-70?.It has a high temperature frequency stability.The experimental data of the circuit proves the design theoretical correctness and the feasibility of the voltage controlled temperature compensated crystal oscillator with a single varactor,and it can overcome the trim effect.In addition,the design has achieved a result of two well-designed samples and one published paper.