基于DDS技术随钻测井仪发射电路研究

设计了一种随钻电磁波电阻率测井仪的发射电路。在电磁波测井仪中，频率源是关键的部件，其性能的好坏直接影响着系统的整体性能。锁相式频率合成器以较高的频率精度、分辨率及频谱纯度得到广泛应用，但是当需要窄频率步进时，环路带宽需要降低，致使锁定时间变长，不能满足要求。而DDS（直接数字频率合成）的出现恰好可以弥补这一缺陷，利用高精度、低功耗的DDS芯片AD9850组成频率为2MHz和400kHz数字电路作为随钻测井仪发射源，使对相位和幅度的控制和调试更方便快捷，并设计出具体的电路，通过实验验证了此方案的可行性。

RESEARCH ON LWD TRANSMIT CIRCUIT BASED ON DDS TECHNOLOGY

A new type of logging transmit circuit applied to measurement while drilling （MWD） based on DDS technology is presented.As for logging instrument，electromagnetic wave source is very important.Its performance affects the whole performance of the system directly.LWD （logging while drilling） signal waveform generation circuit，peripheral signal processing circuit，DDS module，DSP and AD9850 interfaces，software design flowchart etc are given.2MHz and 400kHz digital transmit circuits mainly composed of DDS AD9850 chip，which carries out the shift of the phase and the limit of the amplitude easily，are designed and debugged successfully.it is used to substitute for the conventional transmit circuit，so the alldigital transmit channel of phase shift is achieved.The experimental result shows that the logging transmit circuit for MWD is feasible.