面向CMUT换能器的微弱信号检测电路设计与分析

Design and analysis of weak signal detection circuit for CMUT transducer

针对电容式微机械超声换能器(CMUT)在声-电转换过程中产生的微弱电信号检测难的问题,提出了两种微弱信号检测电路,基于电荷检测原理的电荷放大电路和基于电流检测原理的跨阻放大电路。首先对两种电路结构的瞬态及交流小信号特性进行仿真分析并进行电路性能测试,然后两种电路分别与CMUT换能器连接,进行超声波信号检测试验。测试结果表明:电荷放大电路具有高增益特性,其放大倍数为1×10^(11)倍,其信噪比为20.57 dB;跨阻放大电路通过反馈电阻将CMUT换能器输出的微弱电流信号转换和放大为电压信号,放大倍数为560倍,信噪比为38.05 dB。跨阻放大电路利用反馈电容引入极点的方式,增加了电路的稳定性。经过理论、仿真以及实际测试对比,跨阻放大电路更加适合CMUT换能器微弱信号的检测与放大。

Aiming at the problem that it is difficult to detect the weak electrical signal generated in the process of acoustic electrical conversion of capacitive micromachined ultrasonic transducer(CMUT),two kinds of weak signal detection circuits are proposed,one is charge amplification circuit based on charge detection principle,and the other is trans resistance amplification circuit based on current detection principle.First,the transient and AC small signal characteristics of the two circuits are simulated and tested,and then the two circuits are connected with CMUT transducer respectively for ultrasonic signal detection test.The test results show that the circuit has high gain characteristics,and the amplification factor is 1×10^(11).The signal-to-noise ratio is 20.57 dB.The transimpedance amplifier converts and amplifies the weak current signal from CMUT transducer into voltage signal through feedback resistance.The amplification factor is 560 and the signal-to-noise ratio is 38.05 dB.The transimpedance amplifier uses the feedback capacitor to introduce poles,which increases the stability of the circuit.Through the comparison of theory,simulation and actual test,the trans impedance amplifier circuit is more suitable for the detection and amplification of CMUT transducer weak signal.