Xianhe Huang

The design and implementation of a 120-MHz pierce low-phase-noise crystal oscillator

The phase noise within the half-bandwidth of the loop is closely related to the loaded quality factor QL. The importance of loaded quality factor QL and the method of reducing phase noise on the basis of improving QL are analyzed in this paper. Formulation of QL is derived from analysis of the Pierce oscillator circuit, and calculated with commercial numerical analysis software. According to the results, we can draw a conclusion that QL is explicitly related to circuit pa rameters. Based on this conclusion, a design of the prototype 120-MHz crystal oscillator is presented and the experiments are carried out. The crystal resonator utilized is an SC-cut 5th-overtone crystal resonator with an unloaded quality fac tor Q0 of about 1.05 × 105. The circuit parameter values are adjusted to make QL reasonably higher, while maintaining an output amplitude of 2 to 3 dBm. The measurement results of near carrier frequency phase noise are -104 dBc/Hz at 10 Hz and -134 dBc/Hz at 100 Hz. Experimental results show that it is feasible to design a low-phase-noise crystal oscillator based on improving QL.

High-frequency overtone TCXO based on mixing of dual crystal oscillators

To implement a high-stability and high-frequency overtone temperature-compensated crystal oscillator (TCXO) conveniently, an improved design of the novel overtone TCXO is described in this paper. A 120-MHz TCXO based on mixing of dual crystal oscillators is implemented. It utilizes a 100-MHz AT-cut 5th-overtone crystal oscillator mixed with a 20-MHz AT-cut voltage-controlled crystal oscillator (VCXO). The 120-MHz mixed product is filtered to produce the output signal. The total frequency deviation of 20-MHz and 100-MHz crystal oscillators is compensated by adjusting the output frequency of the 20-MHz oscillator to produce the stable 120-MHz output frequency. In this work, verifying experimental results of the compensation are presented. The stability of the experimental 120-MHz overtone TCXO with microprocessor temperature compensation achieves plusmn2 times 10-7 over the temperature range from -30degC to +70degC. A phase noise level of -133 dBc/Hz at 1 kHz offset has been initially measured for the prototype TCXO. The experimental result demonstrates this approach can conveniently implement the high-frequency overtone temperature compensation with a relatively high stability, and it is available for a wider frequency range as well.

Precise derivation for the equivalent circuit parameters of a crystal resonator with series capacitor

An exact formula for the equivalent circuit of a crystal resonator in series with a capacitor is derived. Network analysis is used to obtain an exact formula for the equivalent circuit parameters without applying any approximations. The result is an expansion of that obtained by those who used assumptions regarding high frequency, high quality factor, high capacitance ratio, and so on. Hence, this formula can be used for instances of low quality factor or low capacitance ratio, and even for the actual inductor-capacitor network as long as these devices have the same equivalent circuits. The enhanced accuracy of the new formula extends itself to oscillator frequency calibration, temperature compensation, and electronic frequency control.

A Revisit To Phase Noise Model Of Leeson

Leesons is one of the most famous models for predicting the phase noise in feedback oscillator. But there are several limitations and drawbacks. Leeson equation involves some key parameters, and these parameters are often determined by the oscillator structure and the oscillator circuit itself. Then a directly application of the Leesons model without care would lead to erroneous results. Leesons also assumed that the amplifier gain is remained a constant versus the frequency close the carrier frequency, and the filter transfer function is considered symmetrical on both sides of the carrier frequency. For a state of the art crystal oscillator the flat noise floor should be about -180 dBc/Hz. The Leeson equation does not obviously describe these oscillators well, and the flat noise floor is about 15 dB lower than that would be expected from the Leeson model. In this paper, a detailed analysis is performed to enlighten the key parameters and try to make it valid for all oscillator circuits. It explicitly takes needed parameters into account for phase-noise calculation, especially for the detailed descriptions of the flicker corner frequency (fc) and the load Q-factor of oscillator circuits. In this paper, a phase flat noise floor model for oscillator is also described. This model allows us to specify that the flat noise floor is about -180 dBc/Hz. An example of the phase noise of the colpitts quartz oscillator is also simulated and discussed.

A Practical Model of Quartz Crystal Microbalance in Actual Applications

A practical model of quartz crystal microbalance (QCM) is presented, which considers both the Gaussian distribution characteristic of mass sensitivity and the influence of electrodes on the mass sensitivity. The equivalent mass sensitivity of 5 MHz and 10 MHz AT-cut QCMs with different sized electrodes were calculated according to this practical model. The equivalent mass sensitivity of this practical model is different from the Sauerbrey’s mass sensitivity, and the error between them increases sharply as the electrode radius decreases. A series of experiments which plate rigid gold film onto QCMs were carried out and the experimental results proved this practical model is more valid and correct rather than the classical Sauerbrey equation. The practical model based on the equivalent mass sensitivity is convenient and accurate in actual measurements.

100-MHz Low-Phase-Noise Microprocessor Temperature-Compensated Crystal Oscillator

An AT-cut third-overtone 100-MHz quartz crystal resonator was used to achieve a 100-MHz low-phase-noise voltage-controlled crystal oscillator prototype. The unloaded quality factor of the used resonator is about 132 K, and the equivalent dynamic capacitance is about 1.2 fF. For the characteristic of the large equivalent dynamic capacitance of the resonator, the design method and the actual measured data of the low-phase-noise oscillator prototype are given. An explanation of why larger equivalent dynamic capacitance and higher voltage-control sensitivity can lead to bad phase noise in half-bandwidth is given. The STM32F103RCT6 MCU is used to read the real-time data of temperature sensor of the microprocessor temperature-compensated crystal oscillator (MTCXO) and the real-time control voltage loading on the MTCXO. Therefore, the real-time communication between a personal computer and an MTCXO is achieved. The control voltage

Design of a wide-tuning-range lithium tantalate low-phase-noise voltage-controlled oscillator

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Measuring microwave cavity response using atomic Rabi resonances

achieved in this way has already considered both the effect of the actual working condition of the MTCXO circuit and the effect of the MTCXO internal reference voltage that it is not accurate enough. After temperature compensation, the measured temperature performance of the 100-MHz low-phase-noise MTCXO are better than ±0.45 ppm/-30 °C -+50 ° C, and measured phase noise results are better than -157 dBc/Hz at 1 KHz and -170 dBc/Hz at 10 KHz.

Physical model of phase noise in feedback oscillator

In this brief, a lithium tantalate crystal with a low capacitance ratio and a wide tuning range is used to design a Butler common-base wide-tuning-range low-phase-noise oscillator considering a reasonable compromise between seeking high loaded quality factor and maintaining oscillator output power. The formulation of is derived from analysis of the Butler oscillator circuit and calculated with MATLAB. The unloaded quality factor of the crystal utilized in the design is about 1.24 K, and the frequency of the crystal is about 10.727 MHz. In the phase noise measurement experiments, of the Butler common-base oscillator is about 33% of , and the output power is about 11 dBm. The measured phase noise level without voltage control is 145 dBc/Hz at 1 kHz, and noise floor is better than 180 dBc/Hz. The tuning ability of the prototype oscillator is tested, and voltage control ability is also tested by increasing a low-voltage varactor BB155. After increasing a varactor capacitance, the measured phase noise at 1-kHz offset and noise floor are better than 142 and 180 dBc/Hz, respectively, when voltage-controlled slope are 86.6 and 19.2 ppm/V for a control voltage range of 2-10 V. Experimental results show that the Butler common-base oscillator with a wide tuning range can realize the characteristics of low phase noise based on the reasonable compromise between seeking high and maintaining output power.

The simulation and accomplishment of 80MHz low phase noise crystal oscillator

In this letter, an atom-based approach for measuring the microwave (MW) cavity response (including cavity frequency and Q-factor) is presented, which utilizes a MW magnetic field detection technique based on atomic Rabi resonances. We first identify the Rabi resonances on seven π transitions in Cs atoms and demonstrate their uses in continuously frequency-tunable field detectors. With the atom-based field detectors, we then indicate the possibility of reconstructing the MW cavity response by measuring the MW frequency-dependent Rabi frequency (i.e., MW field strength) inside the cavity. To demonstrate this approach, we measured the response curves of a 9.2-GHz cavity and a cavity resonating at 8.3 GHz and 9.7 GHz using π transitions and σ transitions, respectively. We compared the results measured by our approach with those measured by Vector Networker Analyzer and obtained good agreement. From such atom-based, SI-traceable measurements, the MW cavity response can be linked directly to the Rabi frequency,...