MEMS振蕩器石英晶體在射頻應用的挑戰(zhàn)

　　除了極少數(shù)例外，每個電子電路需要一個振蕩器，也被稱為時鐘，時鐘發(fā)生器，或定時電路。它的作用是為處理器、存儲器功能、通信端口、A/D和D/A轉(zhuǎn)換器（如有的話）等許多功能提供“心跳”。在非關鍵，低預算的情況下，如10美元的大眾市場電子溫度計，這個時鐘可以由一個簡單的電阻/電容（RC）振蕩器。然而，對于大多數(shù)更為關鍵的情況，振蕩器是基于石英晶體（圖1）。這是一個成熟的（80年以上）和高度有效的技術，它可以支持范圍廣泛的頻率從kHz到幾百兆赫，性能跨越相當不錯的優(yōu)秀，這取決于晶體切割，制造，包裝，和其他方面的考慮。

　　Figure 1： The venerable quartz crystal （but not the entire oscillator） is represented by a standard schematic symbol; b） the equivalent circuit starts with the simplified model shown， but can get much more complicated as operating frequency increases.

　　However， crystal advances have reached a plateau， while demands on the timing function’s performance， size， cost， and integration are increasing. To meet these needs， a new and disruptive approach is starting to encroach on quartz devices， based on silicon MEMS （microelectromechanical systems） technology which can provide quartz-level performance， and at a performance and cost level which is suitable for many applications. MEMS devices are already highly developed and used in high volume for sensing pressure， motion， and acceleration， and they are now being extended to a new role.