Some Accuracy Considerations Applicable to the Automatic Measurement of Noise Using Schottky Barrier Detectors

Low-barrier Schottky diodes are attractive for use in automatic systems because their excellent speed of response allows measurements to be made very rapidly. In addition, with pulsed signals, measurements of the envelope are possible. Since noise measurements are required for many system and component evaluations, it is important to understand how power meters using diodes will perform when subjected to noisy signals. When operated over their entire useful dynamic range, diodes exhibit significant non-linearity. If noisy signals are measured out of the square-law region of operation the effects of the non-linearity must be taken into account. In this non-linear region the diode detector exhibits a different sensitivity to sinewave and broadband noise excitations. The useful dynamic range over which the accuracy of the noise measurement is maintained can be extended somewhat by correcting for this effect. However, at higher power levels it has been found that device dependent parasitics limit the accuracy with which diode detectors may be used for noise power measurements.