China
Africa
Explore chapters and articles related to this topic
Oscillator Circuits
Published in Mike Golio, Commercial Wireless Circuits and Components Handbook, 2018
The accuracy of the fundamental frequency of an oscillator is usually specified in ppm or parts per million. So a 2.488 GHz oscillator which is accurate to ±10 ppm will have an output frequency within ±24.88 kHz of 2.488 GHz at the stated temperature, supply voltage, and load impedance. Ambient temperature changes also change the oscillator frequency. The perturbation in a oscillator frequency from temperature is often given in MHz/degree C or ppm/degree C. Manufacturers use several techniques to compensate for temperature changes, such as using an oven to keep the oscillator at a constant temperature such as 70° C, building in a small amount of tuning that is either adjusted digitally or directly from a temperature sensor, and finally resonators can be built with temperature compensating capacitors or cavities [2]. Oscillator components also change with time, which causes a frequency drift due to aging. Aging is usually specified in ppm/year or some other time frame.
Bulk Acoustic Wave Gyroscopes
Published in Vikas Choudhary, Krzysztof Iniewski, MEMS, 2017
The temperature-induced frequency drift of a similar prototype was measured using a temperature-controlled chamber. As shown in Figure 5.13a, the measured frequency drifts for both drive and sense modes have a linear trend with a slope of −26 ppm/°C over the temperature range −5°C to 55°C. The frequency drift is mainly due to the temperature dependence of Young’s modulus of silicon, resulting in both degenerate modes tracking each other with the same slope. This implies the stability of the frequency separation between the modes over a temperature range 60°C. Also, the Qs of both modes were characterized over the same temperature range both in 1 mTorr and in 2 Torr vacuum pressure and are shown in Figure 5.13. The Qs were dropped ~4% over the 60°C temperature range. This indicates that the Qs in BAW modes are not mainly limited by the TED mechanism in contrast with low-frequency gyros [3,30], resulting in performance stability over temperature.
Radio frequency receivers
Published in Geoff Lewis, Communications Technology Handbook, 2013
In order to maximise the selectivity and S/N ratio, and minimise the effects of interference, the superhet concept is often extended to two or three conversion stages. The first stage of frequency conversion normally produces a fixed value of IF, while the second and subsequent conversion stages may be tuneable over the band of interest. At the first stage of conversion two possibilities exist, either the sum or difference frequency of the mixing products can be selected to provide up-converting or down-converting systems and both are in use. Up-conversion improves the rejection of the first image frequency but produces a higher value first IF. High gain in this stage, therefore has to be sacrificed in the interests of amplifier stability. The effects of frequency drift, caused by a change of temperature, can be largely overcome by combining both up- and down-conversion in the same receiver, if the oscillator frequencies are all controlled from the same basic crystal oscillator. Where frequency synthesis is employed for the local oscillator, the use of a high local oscillator frequency improves the system design by reducing the octave range of this circuit. This then allows the up-conversion receiver to provide a better dynamic range.
Angular symmetrical components-based anti-islanding method for solar photovoltaic-integrated microgrid
Published in Automatika, 2023
V. Arivumani, Sujatha Balaraman
Besides, the AIM are performed depending on the comparison of the frequency with the setting of the threshold value. These approaches execute their operation via Active Frequency Drift [13], Sandia Frequency Drift [14], Sandia Voltage Shift [15], Slip mode frequency shift [16], Reactive Power variation [17] and Voltage Positive Feedback [18]. The NDZ in this approach is little contrasted to the passive anti-islanding techniques. Nevertheless, it reduces the quality of the power because of the variation in the supply via initiating the disturbances. Besides, the Hybrid Anti-Islanding method (HAIM) combines the operation of Passive Anti-islanding and Active Anti-Islanding methods. Voltage Unbalance/Total Harmonic Distortion and Positive Feedback [19], and Average Rate of Change of Voltage and Real Power Shift [20] are the finest hybrid islanding detection approaches. However, the implementation is very multifaceted and recognition time is hugely contrasted to other techniques.
Transmission of Images on High-Temperature Nuclear-Grade Metallic Pipe with Ultrasonic Elastic Waves
Published in Nuclear Technology, 2021
A. Heifetz, D. Shribak, X. Huang, B. Wang, J. Saniie, R. Ponciroli, E. R. Koehl, S. Bakhtiari, R. B. Vilim
Communication protocols typically involve frequency modulation (FM) or amplitude modulation (AM) coding. Ultrasonic transducers have a typical bandwidth of 10% of central frequency. However, our studies and prior results on guided elastic wave ultrasonic communications reported in the literature have shown that using AM is more reliable than FM coding. The reason is that transducer frequency response can drift with temperature. Instead of continuous amplitude roll-off from the center frequency, the ultrasonic transducer frequency response usually consists of a comb of narrowband spikes of decreasing amplitude.22 Thus, frequency drift could result in a complete loss of transmission. The commonly used AM in ultrasonic communications is OOK, in which information is encoded in the envelope of the modulating signal of the high-frequency carrier wave. To increase the reliability of transmission, the carrier frequency could be chirped.
Progress of optomechanical micro/nano sensors: a review
Published in International Journal of Optomechatronics, 2021
Xinmiao Liu, Weixin Liu, Zhihao Ren, Yiming Ma, Bowei Dong, Guangya Zhou, Chengkuo Lee
The inherent nonlinearity, harnessed in the optomechanical radiation-pressure interaction, namely, as the radiation-pressure increase, the conservative force is not proportionally increased, can be used to explore synchronization effects. Based on this, enhanced scalability is possible for future applications involving arrays of injection-locked precision sensors. In 2017, Bekker et al. firstly demonstrated a radiation-pressure-driven optomechanical system actuated and locked by an integrated electrical interface.[72] The injection signal is employed to suppress the drift in the optomechanical oscillation frequency and reduce the phase noise by over 55 dBc/Hz at 2 Hz offset. The left of Figure 6(c) shows the micrograph of this silica microtoroid optomechanical cavity. The cavity is electrostatically probed by circular electrodes and optically probed by a tapered fiber. The right-top figure shows the comparison of power spectra of unlocked and locked oscillations. We can find that the oscillations are indeed locked and that the frequency drift is eliminated. The right-bottom figure shows plots of phase noise of different driving voltages, from which we can find that a significant suppression of phase noise when the oscillator is locked.