射频功率测量技术

　　射频功率测量技术

　　随着今天一切无线化，射频功率测量正迅速成为必需品。本文着重介绍了许多用于精确测量rf信号电平的有用技术，以优化这些无线系统的性能。本文讨论了改变应用程序需求的最佳方法。

　　射频信号可以有多种形式，从单载波连续波（CW）到多载波、QAM（正交幅度调制），其中包含高波峰因数波形。测量这些广泛变化的信号的功率水平需要了解它们的特性以及所需的测量精度。如果信号是突发性的，如在TDD（时分双工）系统，就有时域测量中要考虑的因素更加复杂。无论如何，选择正确的检测器类型有助于简化设计任务。

　　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.