射頻功率測量技術

　　隨著今天一切無線化，射頻功率測量正迅速成為必需品。本文著重介紹了許多用于精確測量rf信號電平的有用技術，以優(yōu)化這些無線系統(tǒng)的性能。本文討論了改變應用程序需求的最佳方法。

　　射頻信號可以有多種形式，從單載波連續(xù)波（CW）到多載波、QAM（正交幅度調(diào)制），其中包含高波峰因數(shù)波形。測量這些廣泛變化的信號的功率水平需要了解它們的特性以及所需的測量精度。如果信號是突發(fā)性的，如在TDD（時分雙工）系統(tǒng)，就有時域測量中要考慮的因素更加復雜。無論如何，選擇正確的檢測器類型有助于簡化設計任務。

　　Measuring RF power using peak detection

　　Take the simplest case of a CW waveform measurement. Even if the amplitude can vary， as long as the signal is within a prescribed time interval during which the amplitude is relatively constant， accurate measurement can be made with a peak level detector， such as the LTC5532 from Linear Technology. This device is built with a very fast Schottky detector with on-chip temperature compensation and a 2 MHz bandwidth output buffer. The internal Schottky circuit peak-detects the incoming RF signal and performs a peak-hold filtering， producing a DC output voltage that is proportional to the RF input peak level.

　　The LTC5532 is a very low power device that runs on 500 μA supply current in active mode. Yet its internal Schottky circuit is capable of detecting 7 GHz RF signals. A version of the part， the LTC5532EDC in a 6-lead， 2 mm x 2 mm plastic DFN package， offers low parasitics and can support operation to 12 GHz and higher.