Study And Design Of High Linearity And Fully Integrated Transmit Front End Circuit For Micromachined Ultrasonic Transducer

At present,the medical ultrasound imaging system is developing in the direction of high precision and miniaturization.The front end integrated circuits for micromachined ultrasonic transducers(MUT)can be integrated with MUT to form a micromachined active sensors,which has broad application prospects in the field of medical ultrasound,especially in high precision ultrasound imaging such as eyeball,blood vessels,and cardiac angiography with the advantages of small size and wide bandwidth.The research of front-end integrated circuits for MUT has also become a trend in microelectronics,biomedical Emerging hotspots in interdisciplinary fields such as engineering.The research on front end integrated circuits for MUT has also become an emerging research hotspots in the fields of microelectronics and biomedical engineering and Interdisciplinary engineering Scientific Field.For the application of advanced high-precision ultrasound imaging algorithms,it is necessary to transmit specific analog ultrasound signals that require digital-to-analog conversion(DAC),such as continuous frequency modulation.However,the MUT front-end switching power amplifier that can only transmit a single pulse is difficult to meet the demand,and additional circuits are needed to provide off-chip high voltage bias for capacitive MUT,increasing the system complexity.The high linearity fully integrated transmitter front end circuit proposed in this thesis integrates high order Gm-C filtering unit,high-gain driver unit and positive and negative DC boost unit.High order filtering to suppresses high frequency harmonic components in the DAC output signal;driver unit drives MUT by integrating linear differential structure of matching network;DC booster unit provides high voltage offset to capacitive MUT in the form of positive and negative voltage.The schematic diagram and layout of the transmitter front end circuits are designed based on CSMC 0.18μm BCD process.The main research work and innovation points of this thesis are as follows:(1)The fourth-order Gm-C bandpass filter unit is designed by cascading biquad structure.In the design of the core transconductance amplifier,an active inductance zero-pole compensation structure is designed,which has less static power dissipation and higher output impedance under the same bandwidth.The source negative feedback and cross-coupled differential pair structure are designed to improve the linearity.The filter out of band decade rejection rate is 86 d B,the GBW of the transconductance amplifier is 15.6MHz,the static power consumption is 82μW,and the linear range can reach 1.6V.(2)The high-gain driver unit is designed with a linear fully differential structure,which can effectively suppress even harmonic distortion.An impedance matching network is proposed to match with the MUT and and the inductance in the network is realized by the equivalent inductance of the output stage source,which achieves on-chip integration and does not require large-scale off-chip inductance.When driving a load of 100 p F in parallel with1kΩ,the operating frequency of the power amplifier unit is up to 10.3MHz,the maximum output voltage swing is up to 24 V,the average power consumption is 5.24 m W,and the second harmonic distortion is-66 d B.(3)The positive and negative DC boost unit provides an on-chip high voltage bias to the MUT by combining a positive voltage charge pump and a negative voltage charge pump,which can improve the circuit tolerance,adjustment range and MUT array element isolation.The auxiliary boost circuit is designed to reduce the parasitic capacitance and the on-resistance of the switching transistor,which can improve the output efficiency and driving ability.When powered by a single power supply,the output voltage drop of the charge pump can rerach 90 V,and the output efficiency could reach 77%.