The measurement of close-to carrier phase modulation (PM) noise of state-of-the-art oscillators is always challenging. Quite often the residual noise of the phase detector used in these measurements is the source of difficulty. In particular at Fourier offset frequencies between 5 and 100 Hz, oscillator noise has a slope of f- -3 and may be lower than the mixer noise floor which follows a slope of f- -1. A conventional double balanced mixer (DBM) using 2N2222A transistors as the non-linear components of a diode ring is constructed for use as a phase detector. Residual single-sideband PM noise measurements at 5 MHz for this device have shown an extremely low flicker noise floor of L(10 Hz) = -165 dBc/Hz. The low noise floor of this mixer makes the device ideal for use as a detector for PM noise measurement systems. Implementing this mixer design in a dual-channel measurement system, a cross-correlated PM noise floor of better then L(10Hz) = -170 dBc/Hz is expected. These features set this DBM design apart from other mixers used for phase detection at 5 MHz.
Citation: Electronics Letters
Pub Type: Journals
Flicker noise, mixers, phase detector, phase noise