MEMS振蕩器石英晶體在射頻應(yīng)用的挑戰(zhàn)

　　除了極少數(shù)例外，每個(gè)電子電路需要一個(gè)振蕩器，也被稱為時(shí)鐘，時(shí)鐘發(fā)生器，或定時(shí)電路。它的作用是為處理器、存儲(chǔ)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(guān)鍵，低預(yù)算的情況下，如10美元的大眾市場(chǎng)電子溫度計(jì)，這個(gè)時(shí)鐘可以由一個(gè)簡(jiǎn)單的電阻/電容（RC）振蕩器。然而，對(duì)于大多數(shù)更為關(guān)鍵的情況，振蕩器是基于石英晶體（圖1）。這是一個(gè)成熟的（80年以上）和高度有效的技術(shù)，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(dāng)不錯(cuò)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.