5 MHz phase detector with low residual flicker

Abstract

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 higher than the noise of the source at Fourier offset frequencies between 5 and 100 Hz. A conventional double balanced mixer using 2N2222A transistors as the nonlinear components of a diode ring was constructed for use as a phase detector. Residual single-sideband PM noise measurements at 5 MHz for this device have shown a low flicker noise floor of L(10 Hz) ¼ 2163 dBc/Hz. When this mixer design is implemented in a dual-channel measurement system, a cross-correlated PM noise floor of better than L(10 Hz) ¼ 2170 dBc/Hz is expected.Introduction: The double balanced mixer (DBM) is the most widely used phase detector for high-resolution phase modulation (PM) noise detection at most carrier frequencies. Often, the measurement of PM noise is difficult owing to the high dynamic range that exists between the carrier and the modulated sidebands. In typical measurement systems, a phase detector is used to remove the carrier and downconvert noise sidebands to baseband. For offset frequencies close to the carrier, the residual flicker noise of the DBM is often the limiting factor of a phase noise measurement system. The most difficult range of offset frequencies to measure is between 5 and 100 Hz, where the oscillator noise has a slope of f 23 , while the measurement system noise floor follows f 21 . The 2N2222A bipolar junction transistor (BJT) has been successfully used in low-flicker PM noise circuits [1,2] and is chosen as the low noise nonlinear element in a custom-built DBM design. A pair of mixers using this design can be used to construct a cross-correlation PM measurement system to reduce the PM residual noise floor further.

Frequency synthesis from Cryogenic Sapphire Oscillator

“…The second low pass filter is used to remove the broadband noise due to thermal noise of the amplifier [18]- [20]. The built mixer is a well-proven double balanced mixer with a diode ring composed of four 2N2222A [21]. The transistors behave as diodes since the base is shorted to the collector.…”

Ultra-low-noise regenerative frequency divider for high-spectral-purity RF signal generation

“…This divider is designed with a custombuilt mixer [11,12], and we achieved L(10 Hz) equal to -163 dBc/Hz, when the divider operates at input frequencies of 40 MHz and lower.…”