The Circuit Design Of Multi-Frequency Electromagnetic Well Logging Based On DDS

In recent years with the development of the digital integrated circuits and the microelectronics technology, direct digital frequency synthesis (DDS) as the third generation of frequency synthesis has been a rapid development.DDS has many advantages, such as: fast frequency conversion, high frequency stability, high phase resolution, low noise, the continuous phase, high integration, an arbitrary waveform output capability and digital modulation capabilities. So DDS is considered as a standard reference clock source or source, which is widely used in radar, navigation, instrumentation and other equipments.The article describe the design of stepped-frequency signal source of multi-frequency electromagnetic wave logging circuit based on DDS. Multi-frequency electromagnetic well logging, also known as dielectric logging which compute the dielectric constant of formation resistivity by means of measuring the propagation of electromagnetic waves generated in the formation amplitude attenuation and phase shift and then to determine the formation of reservoir parameters. High accuracy, high stability signal sources play a crucial role on the accuracy of logging.The main content of the article is introduce the source part of multi-frequency electromagnetic logging circuit based on DDS.The second is designing the phase detection and phase detection of the receive circuit and the data acquisition system.After learning the theory of multi-frequency electromagnetic wave logging and the basic theory of DDS circuits, the stepped-frequency signal source using AD9954 as the core has been introduced. At the same time, a theoretical analysis was used for DDS spurious features and designd the low-pass elliptic function filter which was used in the signal source. The gain and phase detection circuit and data acquisiition system were designed to detect and convert two receive signals.In the whole system, C8051F020 as a whole controller to realize the data acquisition, storage and communicate with PC, at the same time verify the detection of AD8302 and the validity of data acquisition ,finally complete the software and hardware design and debug.