Phase noise performance of microwave analog frequency dividers: application to the characterization of oscillators up to the millimeter-wave range

The phase noise performance of two different microwave analog frequency dividers is characterized and compared with the values obtained using simple theories of noise in injection-locked systems. The direct measurement of the divider noise with a low phase noise synthesizer is not accurate enough, and the residual noise technique is used. The noise levels observed using this technique, between -120 and -155 dBc/Hz at a 10 kHz offset frequency, demonstrate that this divider noise is much lower than the phase noise of most microwave free running oscillators, even if this noise is still high with respect to the residual noise of amplifiers realized with the same active devices. The down conversion of microwave sources up to 40 GHz, is proposed as an application example.     

A study of noise phenomena in microwave components using an advanced noise measurement system

A novel 9 GHz measurement system with thermal noise limited sensitivity has been developed for studying the fluctuations in passive microwave components. The noise floor of the measurement system is flat at offset frequencies above 1 kHz and equal to -193 dBc/Hz. The developed system is capable of measuring the noise in the quietest microwave components in real time. We discuss the results of phase and amplitude noise measurements in precision voltage controlled phase shifters and attenuators. The first reliable experimental evidences regarding the intrinsic flicker phase noise in microwave isolators are also presented.     

Noise properties of microwave signals synthesized with femtosecond lasers

We discuss various aspects of high resolution measurements of phase fluctuations at microwave frequencies. This includes methods to achieve thermal noise limited sensitivity, along with the improved immunity to oscillator amplitude noise. A few prototype measurement systems were developed to measure phase fluctuations of microwave signals extracted from the optical pulse trains generated by femtosecond lasers. This enabled first reliable measurements of the excess phase noise associated with optical-to-microwave frequency division. The spectral density of the excess phase noise was found to be -140 dBc/Hz at 100 Hz offset from the 10 GHz carrier which was almost 40 dB better than that of a high quality microwave synthesizer.     

Method of power recycling in CoAxial Mach-Zehnder interferometers for low noise measurements

We present the first experimental study of a new type of power recycling microwave interferometer designed for low noise measurements. This system enhances sensitivity to phase fluctuations in a device under test, independent of input power levels. The single sideband thermal white phase noise floor of the system has been lowered by 8 dB (reaching −185 dBc/Hz at 1 kHz offset frequency) at relatively low power levels (13 dBm).     

Residual phase noise measurements of VHF, UHF, and microwavecomponents

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted     

Microwave oscillators incorporating cryogenic sapphire dielectricresonators

Progress is reported on efforts to develop a commercially-viable high purity X-band signal source incorporating a cryogenic sapphire dielectric resonator. The resonator design is of the whispering gallery type to take advantage of the excellent electromagnetic field confinement offered by this geometry. Complications resulting from the high spurious mode density of this type of resonator have been eliminated by developing a very accurate and complete mode analysis program which fully incorporates the dielectric anisotropies of the sapphire ring. This program allows the design of a window in the frequency domain where no unwanted modes exist, with accurate placement of the desired mode at the center of this region. Preliminary evaluation of the phase noise properties of simple oscillators incorporating these resonators have been performed. For example, in a dual-oscillator comparison of two oscillators operating near 13 GHz phase noise values of L(f)=-55 dBc/Hz, -145 dBc/Hz and -161 dBc/Hz were obtained for offset frequencies of 1 Hz, 1 kHz and 10 kHz, respectively     

Advanced noise reduction techniques for ultra-low phase noise optical-to-microwave division with femtosecond fiber combs

We report what we believe to be the lowest phase noise optical-to-microwave frequency division using fiber-based femtosecond optical frequency combs: a residual phase noise of -120 dBc/Hz at 1 Hz offset from an 11.55 GHz carrier frequency. Furthermore, we report a detailed investigation into the fundamental noise sources which affect the division process itself. Two frequency combs with quasi-identical configurations are referenced to a common ultrastable cavity laser source. To identify each of the limiting effects, we implement an ultra-low noise carrier-suppression measurement system, which avoids the detection and amplification noise of more conventional techniques. This technique suppresses these unwanted sources of noise to very low levels. In the Fourier frequency range of ～200 Hz to 100 kHz, a feed-forward technique based on a voltage-controlled phase shifter delivers a further noise reduction of 10 dB. For lower Fourier frequencies, optical power stabilization is implemented to reduce the relative intensity noise which causes unwanted phase noise through power-to-phase conversion in the detector. We implement and compare two possible control schemes based on an acousto-optical modulator and comb pump current. We also present wideband measurements of the relative intensity noise of the fiber comb.     

Characterization technique of optical whispering gallery mode resonators in the microwave frequency domain for optoelectronic oscillators

Optical Q factor measurements are performed on a whispering gallery mode (WGM) disk resonator using a microwave frequency domain approach instead of using an optical domain approach. An absence of hysteretic behavior and a better linearity are obtained when performing linewidth measurements by using a microwave modulation for scanning the resonances instead of the piezoelectric-based frequency tuning capability of the laser. The WGM resonator is then used to stabilize a microwave optoelectronic oscillator. The microwave output of this system generates a 12.48 GHz signal with -94 dBc/Hz phase noise at 10 kHz offset.     

A Test Set for the Accurate Measurement of Phase Noise on High-Quality Signal Sources

The test set described here is capable of measuring the spectral density of phase noise on carrier frequencies from 1 to 500 MHz, for offset frequencies from 20 Hz to 50 kHz. Measurements to 50 MHz are described. The test set has a residual single-sideband phase-noise-power-to-signal-power ratio of -142 dB/Hz at 20 Hz offset from the carrier, which decreases to a floor of -172 dB/Hz at offset frequencies greater than 5 kHz. The estimated calibration accuracy achievable is ±0.8 dB, exclusive of random reading errors due to the Gaussian distribution of the phase fluctuations being observed. The estimated 1 ? repeatability of a measurement is 0.7 dB (70 percent of the observations on a given test will fall within ±0.7 dB of the average value). This test set is capable of characterizing the phase-noise performance of existing atomic frequency standards, crystal oscillators, frequency synthesizers, and other high-quality sources more accurately than has previously been possible. The increased accuracy has been achieved by a system design that minimizes readout fluctuations, allows for the accurate measurement of correction factors used to reduce systematic errors, and minimizes the possibility of operator error and bias.     

Extremely low thermal noise floor, high power oscillators usingsurface transverse wave devices

This paper presents state-of-the-art results on 1-GHz surface transverse wave (STW) oscillators running at extremely high loop power levels. The high-Q single-mode STW resonators used in these designs have an insertion loss of 3.6 dB, an unloaded Q of 8000, a residual PM noise of -142 dBc/Hz at a 1-Hz carrier offset, and operate at an incident power of up to +31 dBm in the loop. Other low-Q STW resonators and coupled resonator filters (CRF), with insertion losses in the 5-9 dB range, can conveniently handle power levels in excess of two Watts. These devices were incorporated into voltage controlled oscillators (VCO's) running from a 9.6-V dc source and provide an RF output power of +23 dBm at an RF/dc efficiency of 28%. Their tuning range was 750 kHz and the PM noise floor was -180 dBc/Hz. The oscillators, stabilized with the high-Q devices and using specially designed AB-class power amplifiers, delivered an output power of +29 dBm and exhibited a PM noise floor of -184 dBc/Hz and a 1-Hz phase noise level of -17 dBc/Hz. The 1-Hz phase noise level was improved to -33 dBc/Hz using a commercially available loop amplifier. In this case, the output power was +22 dBm. In all cases studied, the loop amplifier was found to be the factor limiting the close-to-carrier oscillator phase noise performance     

An ultralow noise microwave oscillator based on a high-Q liquidnitrogen cooled sapphire resonator

Two liquid nitrogen-cooled sapphire loaded cavities (SLC's) operating at about 80 K have been successfully constructed, Both cavities were designed to operate on the whispering gallery (WG) E_{12, 1, δ} mode at a resonant frequency of 8.95 GHz. The first SLC was used as the frequency-determining element in a loop oscillator, while the second was used as a frequency discriminator to measure oscillator phase noise. The single sideband phase noise of a free running loop oscillator incorporating the first SLC was measured as -133 dBc/Hz at an offset frequency of 1 kHz, and was limited by the SLC Q-factor and the amplifier flicker phase noise. By using specially designed feedback electronics the oscillator phase noise was reduced to -156 dBc/Hz and -162 dBc/Hz at 1 and 10 kHz offset, respectively. This measurement was shown to be limited by the electronic flicker noise imposed by the phase detector in the feedback electronics, To our knowledge the phase noise and resonator Q-factor of 6×10⁷ represent the best results ever measured at liquid nitrogen temperatures or above     

HBAR-Based 3.6 GHz oscillator with low power consumption and low phase noise

We have designed and built 2 oscillators at 1.2 and 3.6 GHz based on high-overtone bulk acoustic resonators (HBARs) for application in chip-scale atomic clocks (CSACs). The measured phase noise of the 3.6 GHz oscillator is -67 dBc/Hz at 300 Hz offset and -100 dBc/Hz at 10 kHz offset. The Allan deviation of the free-running oscillator is 1.5 × 10^-9 at one second integration time and the power consumption is 3.2 mW. The low phase noise allows the oscillator to be locked to a CSAC physics package without significantly degrading the clock performance.     

Measurement of FM Noise Spectra of Low-Noise VHF Crystal Controlled Oscillators

The design and characterization of stable, low-noise crystal controlled VHF oscillators are described. Operating in the 60 MHz to 80 MHz frequency range, these oscillators have shown total rms frequency deviations of less than 4 parts per 1010 in a 5 kHz band. Noise characteristics have been determined from power spectra measurements, FM noise measurements, and phase noise measurements. The equivalent noise sideband power spectra corresponding to each method of measurement were calculated and compared to the spectra predicted by a very simple model of the oscillator circuit. Agreement within a few dB was found for the region within about 500 Hz of carrier frequency, but measured noise power was found to be considerably higher than predicted for higher baseband frequencies in the range from 800 Hz to 5 kHz. Measurement techniques and evaluation of data are presented.     

A novel phase noise measurement of phase modulation microwave photonic links

Abstract

Microwave photonic links can provide many advantages over traditional coaxial due to its low loss, small size, lightweight, large bandwidth and immunity to external interference. In this paper, a novel phase noise measurement system is built, since the input signal and the power supply noise can be effectively cancelled by a two-arm configuration without the phase locking. Using this approach, the phase noise performance of the 10-GHz phase modulation photonic link has been measured for the first time, evaluated the values of ?124 dBc/Hz at 1 kHz offset and ?132 dBc/Hz at 10 kHz offset is obtained. Theoretical analysis on the phase noise measurement system calibration is also discussed.     

High-Q thermoelectric-stabilized sapphire microwave resonators forlow-noise applications

Two low-noise high-Q sapphire-loaded cavity (SLC) resonators, with unloaded Q values of 2×10⁵ and very low densities of spurious modes, have been constructed. They were designed to operate at 0°C with a center frequency of 10.000000 GHz. The cavity was cooled with a thermoelectric (TE) Peltier element, and in practice achieved the required center frequency near 1°C. The resonator has a measured frequency-temperature coefficient of -0.7 MHz/K, and a Q factor which is measured to be proportional to T^-2.5. An upper limit to the SLC residual phase noise of ℒ (100) Hz=-147 dBc/Hz, ℒ (1 kHz)=-155 dBc/Hz, and ℒ (10) kHz=-160 dBc/Hz has been measured. Also, we have created a free-running loop oscillator based on one of the SLC resonators, and measured a phase noise of ℒ(f)~-10-30log [f] dBc/Hz between f=10 /Hz and 25 kHz, using the other as a discriminator     

Low voltage surface transverse wave oscillators for the next generation CMOS technology

The design and performance of voltage controlled surface transverse wave oscillators (VCSTWO) in the lower gigahertz frequency range, operating on supply and tuning voltages in the 1.2 to 3.3 V range, and suitable for direct interfacing with the next generation CMOS circuits are presented. By applying the "boost" principle, as used in direct current (DC)-DC converters, to the design of the sustaining amplifier, the VCSTWO outputs are switched between 0 V and a positive peak value, exceeding the supply voltage Us, to provide safe CMOS-circuit switching while keeping the radio frequency (RF)/DC efficiency to a maximum for low DC power consumption. The investigated 1.0 and 2.5 GHz VCSTWO are varactor tuned feedback-loop oscillators stabilized with two-port surface transverse wave (STW) resonators. Each VCSTWO has a DC-coupled, high-impedance switched output to drive the CMOS circuit directly, and an additional sinusoidal 50 ohmz high-power reference output available for other low-noise system applications. Phase noise levels in the -103 to -115 dBc/Hz range at 1 kHz carrier offset are achieved with 1.0 GHz VCSTWO at a RF/DC efficiency in the 21 to 29% range. The 2.5 GHz prototypes demonstrate phase noise levels in the -97 to -102 dBc/Hz range at 1 kHz carrier offset, and efficiencies range between 8 and 15%.     

The Direct-Detection Noise-Measuring System and Its Threshold

This paper describes a typical direct-detection noise-measuring system, with particular attention given to the use of Schottky-barrier diodes as envelope detectors. The rise of threshold at low modulation frequencies encountered in these systems has been found to be mainly attributable to FM-to-AM conversion occurring in comparatively narrow-band detectors rather than to diode-flicker noise and thus is largely removable. A sensitivity improvement of 10-20 dB may result at low frequencies, yielding a noise-to-carrier ratio threshold range of about -150 to -155 dB/100 Hz at modulation frequencies from 100 Hz to 50 kHz for measurements of AM noise, and below 0.01 Hz/100 Hz for FM noise, of microwave oscillators at C band.     

Microwave bulk-acoustic-wave reflection-grating resonators

A technique for fabrication of bulk-acoustic-wave (BAW) resonators operating at fundamental frequencies between 1 and 10 GHz is presented. The resonators utilize a reflection grating made by optical holographic methods in iron-doped lithium niobate. Q factors of 30000 at 1 GHz have been demonstrated. Extension to Q of 10000 at 10 GHz appears feasible. Projected limitations to performance are discussed. The high Q at the high fundamental frequency directly results in low-phase noise. Phase-noise measurements of BAW resonator-stabilized oscillators operating at 1.14 GHz are presented. The single-sideband noise floor of <-140 dBc/Hz is shown to be in agreement with an analytical model. Projected improvements in the devices and circuits promise performance of <-160 dBc/Hz.     

On the flicker noise of ferrite circulators for ultra-stable oscillators

The flicker noise of the ferrite circulator is a critical element in ultra-stable microwave oscillators, in which the signal reflected from the input of the reference cavity is exploited to stabilize the frequency. This paper explains why the circulator noise must be measured in isolation mode, proposes a measurement scheme, and provides experimental results. The observed flicker spans from -162 to -170 dB[rad2]/Hz at 1 Hz off the 9.2 GHz carrier, and at +19 dBm of input power. In the same conditions, the instrument limit is below -180 dB[rad2]/Hz. Experiments also give information on the mechanical stability of the microwave assembly, which is in the range of 10(-11) m. The measurement method can be used as the phase detector of a corrected oscillator; and, in the field of solid-state physics, it can be used for the measurement of random fluctuations in magnetic materials.     

Frequency-Domain Measurement of the Frequency Stability of a Maser Oscillator

In this paper we present a direct measurement of the spectral density of both the fractional frequency fluctuations and the phase fluctuations for a rubidium (Rb) maser oscillator. A truncated polynomial is fitted to each independent set of data obtained over a Fourier frequency range between 0.1 Hz and 100 Hz. They are Sy(f) = 1.9 ×10-25f-2 + 3.4 × 10-27f2 and S? = 1.2 × 10-5f-4 + 1.9 × 10-7f0, respectively. A random walk of frequency noise is dominent for frequency below 2.8 Hz while a white phase noise is dominent for the higher frequency range. These results are used to predict time-domain measurements which are then compared to experimental values.