Development Of HV System Control Board In Multi-slice CT

High voltage system in Multi-Slice CT is a system that is used to control the generation of X-ray of CT. High voltage system control board(HVSCB) is one of the key components of the high voltage system. The research is done under the support of National Digital Medical Imaging Equipment and Engineer Technology Research Center in order to study the control process of high voltage system and to master the intellectual property of the high-frequency high-voltage generator, as well as to achieve a more rapid temperature control of X-ray tubes and reduce the cost of the equipment.This paper presents a HVSCB with an FPGA based processing core, focusing on its interface technology and realizing its main control unit and interface controllers. From hardware and circuit aspect, firstly, three differential SPI communication based interface is been build, the realization of the SPI interface circuit also includes two levels of electrical isolation design based on the transient suppression and photo-electric-electro-optical conversion. Designed and realized a single-mode fiber interface circuit which convert signals from LVTTL to TTL, and then to ECL voltage level.Secondly,the series DAC interface with12precision chip, can make an conversion from digital parameter to analog parameter and then to analog signal. Thirdly,the serial ADC interface realize a circuit which change the analog feedback signal into analog parameter and then into an digital parameter with12bit accuracy. Finally, this paper achieve the necessary services module for TTS module that is an external RTC module with battary and RAM.From the software of FPGA based processor aspect, first of all, three serial SPI module interface controllers with build-in series CRC encoder-decoder has been realized,in which the two spi receive controllers can deal with both4group of12bis data and5group of12bits data, decoding the spi data and changing data from series to parallel, while the send controller change5group of12bits data from parallel to series and encoding them into spi signal. Second, the design of controller for DAC and ADC interface is state machine based, they can produce signal that meet specific timing requirements of the specific chips to initial circuits and to drive data for writing or reading,in order to finish8channels of converting and sampling. Then analyzed TTS function and the RTC chip control timing, realized a kind of RTC controller by using state machine. The RTC controller has functions like basic time seting and reading, as well as writeing or reading its RAM. Finally, a main process controller is accomplished, which is state machine based and contain some data processing logics, including multiplier, CLA and comparators,etc.All of the interfaces control modules work rightly, SPI interfaces can receive concurrent data within15μs as soon as possible the receiving start, SPI sent need21μs, a full adc scan requires the minimum30μs, but for the main control processer, the read of adc feedback data just need120ns. A full cycle work of RTC is about120μs long. An effective whole module control period’s is less than50μs,but the maximum time is about128μs. MA range from0-300mA and voltage value range from0to140KV.Through In-system test, all of the control sequence fit the design requirement accurately.