MEMS振荡器石英晶体在射频应用的挑战

　　MEMS振荡器石英晶体在射频应用的挑战

　　除了极少数例外，每个电子电路需要一个振荡器，也被称为时钟，时钟发生器，或定时电路。它的作用是为处理器、存储器功能、通信端口、A/D和D/A转换器（如有的话）等许多功能提供“心跳”。在非关键，低预算的情况下，如10美元的大众市场电子温度计，这个时钟可以由一个简单的电阻/电容（RC）振荡器。然而，对于大多数更为关键的情况，振荡器是基于石英晶体（图1）。这是一个成熟的（80年以上）和高度有效的技术，它可以支持范围广泛的频率从kHz到几百兆赫，性能跨越相当不错的优秀，这取决于晶体切割，制造，包装，和其他方面的考虑。

　　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.