Phase noise measurements in dual-mode SC-cut crystal oscillators

This paper describes the phase-noise characteristics and the analysis model of an SC-cut dual-mode oscillator. The C mode phase-noise sideband levels of -124 dBc at 10 Hz and -154 dBc at 10 kHz have been demonstrated using a dual-mode oscillator that simultaneously excited the C and B mode of a 10-MHz, third overtone, SC-cut crystal resonator. Based on Leeson's model, a phase-noise analysis model for dual-mode oscillators has been proposed also. Actual phase-noise levels of the C mode in dual-mode oscillation corresponded well to results calculated from the proposed model.     

Broad tuning ultra low phase noise dielectric resonator oscillators using SiGe amplifier and ceramic-based resonators

This paper describes the design of very low noise, tunable, X-band dielectric resonator oscillators (DROs) demonstrating phase-noise performance of -135 dBc/Hz at 10 kHz offset. SiGe transistors are used for the oscillator sustaining amplifiers that offer a circulating power of 12 dBm and a gain of 5.4 dB per stage as well as a low flicker noise corner of 40 kHz. A variety of resonator configurations utilising BaTiO₃ resonators are presented demonstrating unloaded Qs from 10 000 to 22 000. These resonators are optimised and coupled to the amplifiers for minimum phase noise where Q_L/Q₀ = 1/2, and hence S₂₁ = -6 dB. To incorporate tuning with low additional phase noise, a phase shifter is also investigated. The theory for the low noise oscillator design is included; experimental results demonstrate close correlation with the theory.     

Reduction of quartz crystal oscillator flicker-of-frequency and white phase noise (floor) levels and acceleration sensitivity via use of multiple resonators

Through the use of N series-connected quartz crystal resonators in an oscillator circuit, a 10 log N reduction in both flicker-of-frequency noise and white phase-noise (floor) levels has been demonstrated. The reduction in flicker noise occurs as a result of the uncorrelated short-term frequency instability in each of the resonators, and the reduction in noise floor level is a simple result of the increase in net, allowable crystal drive level. This technique has been used in 40-, 80-, and 100-MHz AT-, BT-, and SC-cut crystal oscillators using low flicker-of-phase noise modular amplifier sustaining stages, and four series connected crystals. Total (four crystal) power dissipations of up to 30 mW have been utilized. State-of-the-art, flicker-of-frequency noise levels have been obtained with noise-floor levels (80 MHz) as low as -180 dBc/Hz. Four- to five-fold reduction in acceleration sensitivities has been determined     

Conversion of 1/f fluctuations in crystal resonator within an inter resonance gap

This paper presents general relationships for transformation coefficients of BAW or SAW crystal resonator amplitude and phase fluctuations through the 1/f flicker noises of its motional and static equivalent parameters within the resonator inter resonance gap. Approximate functions of phase and amplitude power spectral densities are found based on Leeson's oscillator open loop model and are given with detailed consideration of Butler and Colpitts modes of operation with the assumption of full and zero inter noise correlation. It is also substantiated that a low-noise frequency region of crystal resonator operation exists in which the fluctuation influence of its motional inductance and capacity tend to zero in oscillators. Five examples are given as an illustration of a good agreement of the measured data with the prediction curves, giving a possibility of resonator power phase and amplitude spectral densities valuation at an arbitrary offset frequency from the carrier through the 1/f flicker noises of resonator parameters. Emphasis is laid in conclusion on the possible way of parameter spectral densities definition.     

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     

Organic vapor sensors based on SAW resonator and organic films

The majority of investigations of SAW devices used as chemical sensors are based on delay line oscillators. However, SAW resonator oscillator offers some advantages over the SAW delay line oscillator for its higher stability. In the incipient stage of fabricating gas sensors based upon SAW resonator, taking detection of organic vapor as an example, the analysis method that combines the SAW theory with organic film technology has been adopted to give an intensive insight into the responses of two-port SAW resonator coated with LB-film and cast-film after exposure to organic vapors.     

The RF-powered surface wave sensor oscillator--a successful alternative to passive wireless sensing

A novel, passive wireless surface acoustic wave (SAW) sensor providing a highly coherent measurand proportional frequency, frequency modulated (FM) with identification (ID) data and immune to interference with multiple-path signals is described. The sensor is appropriate for bandwidth-limited applications requiring high-frequency accuracy. It comprises a low-power oscillator, stabilized with the sensing SAW resonator and powered by the rectified radio frequency (RF) power of the interrogating signal received by an antenna on the sensor part. A few hundred microwatts of direct current (DC) power are enough to power the sensor oscillator and ID modulation circuit and achieve stable operation at 1.0 and 2.49 GHz. Reliable sensor interrogation was achieved over a distance of 0.45 m from a SAW-based interrogation unit providing 50 mW of continuous RF power at 915 MHz. The -30 to -35 dBm of returned sensor power was enough to receive the sensor signal over a long distance and through several walls with a simple superheterodyne FM receiver converting the sensor signal to a low measurand proportional intermediate frequency and retrieving the ID data through FM detection. Different sensor implementations, including continuous and pulsed power versions and the possibility of transmitting data from several measurands with a single sensor, are discussed.     

Phase-noise reduction in surface wave oscillators by using nonlinear sustaining amplifiers

Nonlinear sustaining amplifier operation has been investigated and applied to high-power negative resistance oscillators (NRO), using single-port surface transverse wave (STW) resonators, and single-transistor sustaining amplifiers for feedback-loop STW oscillators (FLSO) stabilized with two-port STW devices. In all cases, self-limiting, silicon (Si)-bipolar sustaining amplifiers that operate in the highly nonlinear AB-, B-, or C-class modes are implemented. Phase-noise reduction is based on the assumption that a sustaining amplifier, operating in one of these modes, uses current limiting and remains cut off over a significant portion of the wave period. Therefore, it does not generate 1/f noise over the cut-off portion of the radio frequency (RF) cycle, and this reduces the close-in oscillator phase noise significantly. The proposed method has been found to provide phase-noise levels in the -111 to -119 dBc/Hz range at 1 KHz carrier offset in 915 MHz C-class power NRO and FLSO generating up to 23 dBm of RF-power at RF versus dc (RF/dc) efficiencies exceeding 40%. C-class amplifier design techniques are used for adequate matching and high RF/dc efficiency.     

Overtone Oscillator for SAW Gas Detectors

A design of an overtone oscillator a with surface-acoustic-wave (SAW) resonator is described in this paper. The circuit works stably on the frequency 4.710 GHz (29th harmonic of loaded resonator) at about the -2 dBm level. In the construction, distributed-constant circuits have been applied. Commercially available SAW sensors usually work within the range of frequency from a few dozen to a few hundred megahertz. On the other hand, it is a well-known fact that the mass sensitivity of such devices is directly proportional to the square of its operating frequency, and SAW sensors for organic vapors, for instance, are usually mass sensitive. For this reason, an increase in the SAW sensors' operating frequency seems to be useful. The circuit described in this paper shows the possibility of a dramatic rise in SAW operating frequency by exerting its operation through a specific high overtone (harmonic frequency) of the SAW resonator. The overtone frequency in such a solution then plays the role of basic mode. The oscillator proposed in this paper seems to be a good tool for chemisensitive-SAW-coating investigation     

Reduced transposed flicker noise in microwave oscillators using gaas-based feedforward amplifiers

Transposed flicker noise reduction and removal is demonstrated in 7.6 GHz microwave oscillators for offsets greater than 10 kHz. This is achieved by using a GaAs-based feedforward power amplifier as the oscillation-sustaining stage and incorporating a limiter and resonator elsewhere in the loop. 20 dB noise suppression is demonstrated at 12.5 kHz offset when the error correcting amplifier is switched on. Three oscillator pairs have been built. A transmission line feedback oscillator with a Qo of 180 and two sapphire-based, dielectric resonator oscillators (DROs) with a Qo of 44,500. The difference between the two DROs is a change in the limiter threshold power level of 10 dB. The phase noise rolls-off at (1/f)(2) for offsets greater than 10 kHz for the transmission line oscillator and is set by the thermal noise to within 0-1 dB of the theoretical minimum. The noise performance of the DROs is within 6-12 dB of the theory. Possible reasons for this discrepancy are presented.     

Prototype of a microwave generator with a high-temperature superconductor disk resonator in a feedback circuit with a low phase-noise level

Phase noise of a prototype of microwave generator with a disk resonator based on high-temperature superconductor (HTSC) Y₁Ba₂Cu₃O_{7 ? δ} films in the feedback circuit has been measured for the first time. The disk resonator was cooled to a temperature of 77 K, while the other generator components remained at room temperature. The generator carrier frequency was 7.5 GHz. Phase noises have been measured for different offsets from the carrier frequency. For example, the minimum measured phase-noise level was found to be 136.2 dB/Hz for a 10-kHz offset from the carrier frequency. It is shown that the results obtained correspond to the classical Leeson formula with flicker noise neglected. Thus, a disk resonator based on Y₁Ba₂Cu₃O_{7 ? δ} films does not introduce additional noise (in comparison with the amplifier noise) at small offsets and, correspondingly, is promising for microwave generators with extremely low phase noise. The possibility of further decrease in the phase-noise level by increasing the Q factor of the HTSC disk resonator and optimizing its housing design is discussed.     

1/f noise in etched groove surface acoustic wave (SAW) resonators

Measurements of 1/f (or flicker) frequency fluctuations in SAW resonators fabricated with etched groove reflectors on single crystal quartz have shown that the observed noise levels vary inversely with device size. These measurements were made on sixteen 450 MHz resonators of four different sizes. The 1/f noise levels were also evaluated on twenty-eight other SAW resonators ranging in frequency from 401 to 915 MHz. This additional data provides valuable information on the dependence of the flicker noise levels on resonator frequency. A model based an localized, independent velocity fluctuations in the quartz is proposed which correctly fits the observed size and frequency dependence of the measured 1/f noise levels. This model suggests that the velocity fluctuations originate in small regions (much less than ~5 mum in diameter) randomly distributed throughout the quartz with an average separation of about 5 mum between independent (incoherent) sources. The magnitude of the localized fractional velocity fluctuations, Deltav/v, averaged over a 5 micron cube is on the order of 1x10 (-9).     

Linear frequency tuning of SAW resonators

Frequency tuning in SAW (surface acoustic wave) resonator-stabilized oscillators is normally accomplished via utilization of a voltage-controlled phase shifter. The design of abrupt junction varactor diode-inductor networks which employ impedance transformation techniques to obtain linear frequency tuning of two-port SAW resonators is reported. The approach is similar to that previously developed for linear tuning of bulk wave, quartz crystal resonators. This technique uses varactor diode parallel inductance to provide a linear reactance versus voltage network, which is effectively connected in series with the resonator motional impedance in order to tune the effective resonator center frequency. Typical tuning ranges are significantly larger than those achievable using the phase shifter approach, and are on the order of 400 ppm for the 320-MHz resonator used.     

Frequency stability of high-overtone bulk-acoustic resonators

The results of phase noise measurement for high-overtone bulk-acoustic resonators (HBARs) for use in high-performance oscillators, operating at 640 MHz with insertion losses of 10-15 dB and unmatched Qs greater than 110 K are reported. Noise measurements made on these resonators with input drive levels of 16 dBm have shown self-noise levels of S(y)(f=100 Hz)=8.0x10(-26) for 1/f noise which represents state-of-the-art for a UHF resonator.     

声表面波谐振器型振荡器的研制

本文介绍了金属条射栅双端对声表面波谐振器型的原理和结构特点，给出了一种采用声表面波谐振器稳频的低噪声，高稳定性的振荡器电路设计方案。对影响振荡器频率稳定度的因素进行了分析讨论，并探讨改善声表面波振荡器频率稳定性的方法。该声表面波谐振器的中心频率为１２０ＭＨｚ，无载Ｑｖ，大于２０，０００，插入损耗小于６．０ｄＢ，经测试，秒级频率稳定度为１０＾－１０数量级，在自由室温下的日平均波动为１０＾－６／ｄ数量     

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.     

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     

Gigahertz range resonant devices for oscillator applications using shear horizontal acoustic waves

It is shown that surface transverse wave (STW) resonant devices are not only very well suited for stable oscillator applications but have some unique features offering greater design flexibility than their surface acoustic wave (SAW) counterparts. Various designs for single- and multimode resonators and resonator filters are presented, and their properties in respect to applications in stable fundamental-mode fixed-frequency and voltage-controlled oscillators in the range of 750 MHz to 2 GHz are discussed. Characteristics of SAW and STW two-port metal strip resonators using identical designs are compared. Data from frequency trimming on STW resonators, using heavy ion bombardment, are presented.     

Mode selection in a multimode SAW oscillator using FM chirp mixing signal injection

Mode-selection control of a multimode surface-acoustic-wave (SAW) oscillator has been obtained using SAW linear FM chirp signal injection. The prototype 60-100-MHz SAW oscillator design employed a single-phase unidirectional transducer (SPUDT) low-loss comb filter in the feedback loop, with minimum insertion loss of approximately 3.7 dB. Mode selection was achieved using an injection signal derived from the mixed output of two 27.5-52.5-MHz up- and down-chirp SAW filters. Mode switching times of less, similar2 mus were obtained. The device could be useful as a local oscillator on frequency-agile radars, where hopping is required over a moderate number of frequencies.     

Applications of amorphous magnetic-layers in surface-acoustic-wave devices

This paper reviews the theory and potential applications of magnetically variable delay lines and oscillators which employ a magnetostrictive film on a piezoelectric surface-acoustic-wave (SAW) substrate. Cases analyzed in detail indicate that the delay change arises mainly from a rotation of the magnetic moment from the films' easy axes toward the applied field direction; thus the interaction is essentially nondispersive. Use of amorphous metallic-glass overlays is particularly attractive because their high magnetostriction and low magnetic anisotropy makes a relatively large delay variation possible with a small change in bias field. Since the SAW velocity can be changed only bysim .1% or less with present film technology, applications are restricted to those where only a small frequency or delay adjustment is required. Two prototype examples are considered in detail--a variable delay line for steering an adaptive array antenna and a tunable resonator oscillator capable of tracking high speed Doppler targets. In both of these examples, the magnetic film/SAW substrate geometry is seen to be an attractive alternative to competitive approaches.