Research And Design Of Analog Front-End Circuit For Ultrasonic Echo Signal

In recent years,the number of cardiovascular diseases(CVD)has increased rapidly,and the aging process has intensified,which makes the CVD have shown a high incidence in recent years in China.In view of such a grim development situation,more effective and accurate diagnosis and treatment methods are urgently needed to deal with the frequent occurrence of CVD.Three-dimensional transesophageal echocardiography(TEE)uses ultrasound to image the heart for accurate diagnosis of CVD and guidance of interventional surgery.Compared with other imaging techniques,TEE has become an indispensable means in the diagnosis and treatment of cardiovascular diseases due to its low cost,non-invasive and ability to produce real-time images.TEE probes need a low-power ASIC that can be closely integrated with two-dimensional sensor arrays.The limitations of its area and power consumption pose a more severe challenge to the design of analog front-end(AFE)circuits.Based on 130nm BCD technology,this thesis designs a special echo signal front-end receiving circuit for TEE imaging system.An important function of ultrasonic echo signal receiving path is time gain compensation,which reduces the overall dynamic range of echo signal by compensating the propagation attenuation experienced by sound wave propagation in the body.the compensated signal is processed by an analog-to-digital converter(ADC).At present,discrete gain compensation is usually used in the analog AFE but only part of the propagation attenuation can be compensated,but not completely,so that the ADC still needs a large dynamic range to process the AFE output signal.This thesis introduces an AFE circuit with continuous variable gain with time and its application in three-dimensional TEE probe.The circuit provides continuous variable gain with linear-in-dB with time and compensates for continuous attenuation of echo signal with time.An AFE circuit for ultrasonic echo signal reception is designed,in which discrete gain is provided by low noise amplifier and continuous gain is provided by time gain compensation amplifier.Continuous gain is interpolated between discrete gain steps to achieve approximate continuous gain in a certain range,and the combination of the two achieves a continuous gain AFE circuit with continuously adjustable gain varying with time.It solves the problem that the traditional discrete gain compensation cannot be completely compensated,and avoids the problem of image artifacts caused by the instantaneous switching between a wide range of discrete gains.In this design,under the condition of 130nm BCD process and 1.5V power supply,the output voltage swing of1.8V is realized.The input-referred noise density is 8.3264n V/sqrt(Hz)at 5MHz frequency point,and integrate in the 2.5M-7.5MHz frequency band,the input-referred noise is 18.6μV.The AFE achieves a linear-in-dB gain error below±1.5 dB within a 0-36-dB gain range,the power consumption is 0.675m W/channel,and the AFE layout area is about 0.025mm~2.Under the condition of sinusoidal signal of input signal 4.96M and sampling frequency of 20M,the effective number of bits is 9.6,the spurious-free dynamic range is 62dB,and the signal-to-noise-distortion ratio is 59.7dB.All the indexes meet the design requirements.