Development Of Oven Controlled Crystal Oscillator Synchronous Control Device Based On Adaptive PID

Synchronization is a key part of digital systems, and precision synchronization technology is needed in many fields, such as communications synchronization, television synchronization, power grids synchronization, computer networks synchronization, space satellite synchronization and so on. Synchronous measurement and control is also important in geophysical measurement field. In Electromagnetic method detecting, precision synchronization between the transmitter and receiver, not only improves the accuracy of phase measurement, but also obtains a very weak signal of the secondary field from strong electromagnetic interference noise by multiple synchronous superposition.With the polarized development of electromagnetic method ,which is form deep and array measurement to shallow surface measurement, as well as the increasing complexity of measure environment, conventional synchronous measurement technology( wire connections, radio communications, clock timing, GPS timing ) has been difficult to meet the needs of high-precision detection. In the case of this situation, development of Oven Controlled Crystal Oscillator(OCXO)synchronous control device based on adaptive PID is presented, which have overcome the impact of the many factors, and achieved a high-precision synchronous clock signal output .Oven Controlled Crystal Oscillator(OCXO)synchronous control device based on adaptive PID is composed by two key components: base system and calibrated system. Because actual operating frequencies between OCXO exist more or less the total deviation, a phase shift is brought in between crystal generated second clock signals, so crystal generated second clock signal of calibrated system is corrected by the precise base system crystal generated clock signal which is used as the standard in synchronous control device. Thus, synchronization control device needs to complete frequency calibration process and phase calibration process in order to achieve synchronous signal output.In the frequency calibration process, frequency offset between both system crystal oscillators is measured by the measuring frequency offset module of FPGA. Because there is a frequency offset drift between crystal oscillators of systems and strict mathematical model about the existing frequency drift has not yet formed, it's not accurate enough that DSP provides DAC control data just by a certain amount of frequency offset. According to the previous records of historical data, DSP regulates the DAC control data based on self-adaptive PID control method to, so as to achieve calibrating frequency control voltage purposes. But there are still error correction algorithms, in order to compensate this deviation, manual fine-tuning function is added to adjust DAC control data by key press.In the phase calibration process, because of crystal oscillator generated clock signals which come from high frequency pulse division, resetting the counters of dividers, counters are to start from scratch. In this way, eliminating the stable phase difference between crystal oscillators generated clock signals. Finally the synchronization between the clock signals is realized.In order to get better synchronization between the clock signal adjustment, a number of auxiliary modules have been designed in this thesis: It's convenient to observe of the phase shift conditions between clock signals by designing the measuring phase difference module in FPGA; The initial phase difference adjustment module is designed, in order to increase the duration of clock signals within the synchronization accuracy scope. In order to facilitate real-time observation of changes in trend and in direction crystal clock frequency deviation and phase deviation between the signals as well as the DAC control data, the display module is designed to display parameters. Isolated module is designed in order to avoid impacts between base system and calibrated system; For different measurement and control system requirements the difference frequencies synchronous signals, in FPGA, we have designed a series of frequency dividers, and the dividers can switch by button press to achieve synchronization signal frequency settings.In order to test the performance of synchronous control device, a button fine-tune test, synchronous signal output frequencies test, the test of initial phase difference modulation between synchronous signals, as well as the duration of clock signals within the synchronization accuracy scope. Experiments shows: OCXO control device can provides synchronization signals continuously and synchronization accuracy stays better than 1μs within 30 minutes. Button fine-tune, button switch synchronization signal frequencies and the initial phase difference regulation functions are realized. At the same time, OCXO control device has good stability and practicality, thus it's applied in distributed measurement and control systems. This method is a more comprehensive, more cutting-edge research methods in similar Departments, and has good prospects for development.Finally, this thesis gives the full text of the summary of the work and the analysis of problems, in order to put forward amendments suggestions in the algorithm and hardware design for further improvement.