Design and experimental investigation of charge amplifiers for ultrasonic transducers

Amplifiers are used in all types of electrical circuits to boost signal and there is a huge variety in designs used for different applications. For ultrasonic applications our group has previously used commercial available transimpedance amplifiers that converts a current to a voltage, but these amplifiers have a linear response over its frequency range. To preserve as much information as possible for lower frequencies a flat frequency response is preferable. The main goal of this thesis were to design an amplifier that has a reasonable flat frequency response within the desired frequency range, from 1 to 20 MHz, while also having an acceptable amplification. To achieve this we have taken a brief look at opamps and amplifier design in a very general way, and the theory behind amplifier design. We have then used this theory to design two charge amplifiers we believe will work satisfactory with an ultrasonic transducer.We have simulated these amplifier circuits with a SPICE program, built them and then tested them experimentally. Our single stage amplifier gave us lower amplification then the current amplifier, but we are still inside the acceptable amplification range. The charge amplifier has a frequency response that matches the original signal much more closely then the current amplifier and our amplifier is less expose to high frequency noise.