此篇研究提出適用於二維陣列之 CMOS MEMS 製程技術所製
作的微電容式超音波傳感器之峰值感測電路（Peak Detection Circuit），
在傳感器接收到超音波並轉換為電壓訊號後放大並取樣峰值，循序輸
出後可由軟體二維光聲成像。相較於傳統三維成像具有快速、適用小
規模像素面積與高度晶片整合性的特性。

在傳統三維光聲成像的量測環境中，晶片上每一像素收到物體被
雷射激發後的超音波類比訊號，類比波型包含了超音波發射源的軸向、
側向、縱向資訊，但須藉由多個像素收到的超音波訊號及發射時間來
運算出發射源的位置，在建立三維模型的掃描時間與後續成像複雜度
較高；若使用峰值保持器將類比波型轉換為輸出峰值，則可以利用此
單純之二維數值表反向運算物體模型，複雜度較低且快速成像。

實驗成功的證明了在輸入頻率為 1 MHz 至 10 MHz ，振幅為
100 mVpp 至 800 mVpp 的弦波及方波，峰值感測電路可以正確的輸
出峰值，誤差值在± 20% 之內；當輸入振幅在 200 mVpp ~ 600 mVpp
範圍中，誤差值更可以改善至 ± 15%。

若峰值感測電路採用更先進之製程將可提升電路性能與減少峰值
誤差，將可提升影像解析度，於醫療將有更大應用。

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.

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