| In the operation of the automatic scanning platform for ultrasonic testing, the output signal of the air-coupled ultrasonic transducer is small, and there is interference from motor noise and external noise. Therefore, the noise requirements for the detection system are high. In order to detect and extract weak signals effectively, this paper designs an amplification circuit with anti-interference, ultra-low noise, high gain, and continuously adjustable gain. The amplifier circuit consists of a first stage ultra-low noise preamplifier circuit and a two-stage cascaded circuit composed of low noise, variable gain amplifiers. This circuit design adopts a preamplifier with very low input noise, high input impedance, and high common mode suppression ratio. Based on the noise coefficient of the circuit, a suitable feedback circuit is designed to achieve optimal noise matching. The last two-stage circuit can achieve continuous adjustable gain of 0dB-80dB. The measurement result indicates that the overall gain of this circuit is continuously adjustable between 20dB and 100dB and can detect weak signals of air-coupled ultrasonic transducer and can be widely used in weak signal detection. |
