應用於微定位器之電流電荷感測電路探討

Abstract

微定位器(Micropositioner)屬於微機電系統的範疇，它提供高精確度、高頻寬下的驅動以及較低的成本，因此可以廣泛應用於磁性和光學性的儲存設備。當微定位器的移動元件以一固定頻率來回運動時，上下兩側的感應電容大小因為移動元件與上下兩端電極平板的距離改變而變化，故產生正比於上下兩感應電容間不匹配量的電荷，而單位時間內的電荷的改變即為電流。分別把電荷、電流輸入其適當對應的運算放大器，經過運算放大器的處理而產生輸出信號，此輸出信號就是微定位器中運動元件移動的速度或位移的函數，因此藉由量測此輸出信號即可得到微定位器的速度或是位移；之後可進一步利用噪訊比的關係，得到微定位器其最小可偵測到的位移或是速度大小。

Micropositioner, which provides the advantages such as high precision, the driving capability on wide-frequency bandwidth and the lower costs, belongs to Micro-electromechanical Systems (MEMS). Therefore it is widely used in the magnetic or optical storage device. The values of the two capacitors change because the distance between the moving element from upper and lower electrodes are changing respectively while the moving element is vibrating in a fixed frequency. There is a net charge proportional to the mismatch between the two sensing capacitor. Differentiating the charge yields current. Input charge and current into the corresponding op-amp respectively, and by the processing of op-amp, there is an output signal which is function of velocity or displacement of the micropositioner. Measuring the output signal then we can get the velocity or displacement of the micropositioner. Furthermore by the signal to noise ratio, we can get the magnitude of minimum detecting displacement, or call it resolution.