Abstract
The research focuses on the study of a peak detection circuit which is used in a two-dimensional (2-D) capacitive ultrasonic sensor array implemented in a standard CMOS process. Ultrasonic waves produced by the photoacoustic effect are received by the sensing pixels, followed by signal amplification, peak detection, and collection of all the detected values to produce a 2-D photoacoustic image. Compared to 3-D imaging, the required time for image production is significantly reduced. The CMOS MEMS technology allows convenient signal processing to enhance scalability of the array and sensor miniaturization to increase image resolution. In the traditional 3-D Photoacoustic Imaging (PAI), every sensing pixel receives the ultrasound from the object illuminated by laser. The produced waveform contains the axial, lateral, and depth information of the object. We have to obtain many waveforms from other pixels so as to identify the position of emitter origin, where the complexity is higher than 2-D imaging. 2-D imaging is less complicated and faster because it depends on the peak-value detection of the sensed waveforms. In the experiment we successfully detect and hold the peak values by using input signals with frequencies from 1 MHz to 10 MHz and amplitudes from 100 mVpp to 800 mVpp. The errors are within ±20%. The errors reduce to less than ±15% when input voltage is from 200 mVpp to 600 mVpp. The peak detection circuit design can benefit from the use of a more advanced CMOS process to enhance the circuit speed and reduce the detection error; in other words, a better image resolution can therefore be achieved.