| 摘要 |
<p>The present invention, generally speaking, provides a method and apparatus for accurately measuring a communications signal. In accordance with one aspect of the invention, DC offset effects and nonlinearities attributable to a communications amplifier (703) are made spectrally separable from DC offset effects and nonlinearities attributable to the measurement apparatus. Spectral reparability may be accomplished, for example, by adding an offset frequency to a local oscillator use by a downconverter of the measurement apparatus. As a result, the signal of interest is moved away from baseband (zero frequency) to the offset frequency. Similarly, other nonlinearities in the video amplifier (725) (such as third order distortion) manifest themselves mostly at harmonics of the offset frequency. Hence spectral separability between the power amplifier characteristics and these nonlinear impairments of the measurement system is achieved. At the offset frequency, the signal of interest may be represented by a single signal component (e.g., the in-phase component I) instead of requiring an I/Q representation. The measurement apparatus may therefore be dramatically simplified, and errors stemming from undesired interaction of I and Q signal processing chains may be avoided. In accordance with another aspect of the invention, the effects of noise are mitigated through different averaging methods.</p> |
