Research On A High Performance TCD

Transcranial Doppler (TCD) is a non-invasive device for measuring blood flow velocities by low frequency ultrasound waves. For practical use, the operation of the device is very difficult because of the high attenuation from the skulls. Sensitivity is one of the key capabilities of TCD.It is the optimization of the circuit to improve the sensitivity of the system that is the main work of this paper. In order to improve the transmit efficiency, the transmit amplifier is redesigned so that its power is matched with the transducer. Low noise amplifier (LNA), determining the system's sensitivity and noise figure (NF), is redesigned by adjusting its DC level and the parameters of the components. In order to reduce NF, two transistors are placed in parallel and the LNA is matched with the Ultrasound Transducer in impedance. A simple delayed canceller is designed and applied to remove the stationary echo which is 100 times bigger than the flow echo. At last a digital method of the Doppler audio is realized. The IP core of Xilinx FPGA is used to replace the analog module to make the Hilbert Transform. It is more convenient for doctor to store and analyze the patient's audio record. The performances of the device have been improved by these works.