Flicker noise of microwave power detectors

• Published in: 2009 IEEE International Frequency Control Symposium Joint with the 22nd European Frequency and Time forum pp. 40 - 43
• Main Authors: Grop, S., Rubiola, E.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.04.2009
• Subjects: 1f noise; Cryogenics; Detectors; Frequency measurement; Microwave filters; Microwave measurements; Noise measurement; Power measurement; Schottky diodes; Voltage
• ISBN: 1424435110; 9781424435111
• ISSN: 2327-1914
• DOI: 10.1109/FREQ.2009.5168138

A microwave power detector is a diode used in the quadratic region. In this region the resistance is proportional to voltage, and therefore the filtered output voltage is proportional to the mean square input voltage. Tunnel diodes and Schottky diodes are used in practice. Tunnel diodes are preferable because of their high gain, up to 1400 V/W, and of because of their suitability to cryogenic environment. Yet, they are easily damaged in case of to power overload. Schottky diodes work only at room temperature, with a gain of the order of 300 V/W. If overloaded, the Schottky detector turns into a peak-voltage detector, which is still useful to measure the power if the signal can be assumed to be sinusoidal. On the other hand, the overloaded detector cannot be used as a demodulator by exploiting the beat note between a pump carrier and a probe signal. Simple mathematics tells us that 1/f noise turns into a flat floor of the two-sample (Allan) deviation. Hence, the 1/f noise of power detectors is related to the power stability floor of the device, which is an important issue in a number of high-precision applications involving the measurement or stabilization of a RF/microwave power, the measurement of a beat note, and the Pound frequency- locking of an oscillator to a reference resonator. Nonetheless, the literature on this subject is totally absent.