Frequency drift

About: Frequency drift is a research topic. Over the lifetime, 5054 publications have been published within this topic receiving 56191 citations. The topic is also known as: chirp rate.

Apparatus for controlling the receive and transmit frequency of a transceiver

Abstract: Apparatus for maintaining a transmit radio signal frequency in a predetermined frequency relationship with a received radio signal. A common voltage controlled frequency source serves as an Lo signal generator for both the receiver and transmitter. A reference frequency oscillator is phase compared with a receive IF signal to derive a control voltage for the voltage controlled frequency source. The resulting phase lock loop provides transmit signal frequency control with respect to a received signal.

A Third-Order MAF Based QT1-PLL That is Robust Against Harmonically Distorted Grid Voltage With Frequency Deviation

Abstract: The quasi-type-l phase-locked loop (QT1-PLL) is a grid synchronization technique that has become very popular in recent years thanks to its attractive performance such as easy implementation, fast dynamic response, and good accuracy in steady-state operation. However, it is still vulnerable to operation under harmonically distorted grid voltages with frequency drift. This paper proposes a novel QT1-PLL based synchronization algorithm that makes an appropriate combination of two filters’ types: an in-loop third-order moving average filter (MAF) with a reduced window width, and a simplified second-order fast delayed signal cancellation (FDSC) based prefiltering stage. The proposed PLL is named third-order MAF based QT1-PLL (TQT1-PLL). Though both TQT1-PLL's filters do not need any adaptive algorithm, it is able to reject non-triplen odd-harmonics and the fundamental frequency negative sequence (FFNS) even under grid frequency drift. Its correct operation is confirmed through numerical simulations and real-time implementation on a digital signal processor (DSP). Moreover, the obtained results confirm its ability to reduce the ripple in the estimated frequency and phase under distorted grid voltages and off-nominal frequency operation. Authors show also through an analytical development that the topology of the proposed TQT1-PLL can be extended to enable the rejection of the DC-offset.

The modulational method of quartz crystal oscillator frequency stabilization

Abstract: A new trend in self-contained (without the use of quantum discriminators) frequency stabilization of an oven controlled crystal oscillator (OCXO) and frequency standard is proposed and discussed. The method developing the trend is called a modulational method and is based on the use of the reference properties of crystal resonator natural bulk vibrations (double-frequency and multi-frequency oscillators are not used in this case). The concept is based on dynamic modulation characteristics of an oscillator, and basic relationships are found for their calculation. The construction principles of the frequency control systems are formulated substantiating mathematically the essence of the method. Basic ratios of modulating signals are determined, the solution of which shows only a slight influence of the modulation signal on the Allan variance and spectral density of an OCXO. The results of the method's practical use are considered. Their subject is the OCXO with the oven system adapted to the ambient temperature and crystal frequency standard with aging rate compensation.

Method and apparatus for reducing the start time of a VCXO

Abstract: A voltage controlled oscillator, such as a VCXO (Voltage Controlled Crystal Oscillator), for generating a desired reference frequency in a wireless terminal with a reduced start-up time is described herein. According to the present invention, the VCXO comprises an oscillator that generates the desired reference frequency based on a variable voltage applied to the oscillator by a voltage controller. In addition, the VCXO includes a start-up controller that applies a bias voltage to an oscillator input node to reduce a capacitance associated with the oscillator, and therefore, to reduce the start-up time without negatively impacting the DC current consumption or the tuning range of the VCXO.

Swept frequency domain relectometry enhancement

Abstract: An improved swept frequency domain reflectometry instrument has an input/output terminal coupled to one end of a cable. A radio frequency at the input/output terminal is converted to an intermediate frequency using a swept local frequency. The radio frequency is derived from the swept local frequency and a variable offset frequency. A controller controls the variable offset frequency, monitoring the amplitude of the intermediate frequency. A period counter counts the intermediate frequency at a first maximum response of the intermediate frequency and further counts the offset frequency at a second maximum response of the intermediate frequency. The location of a discontinuity in the cable is calculated from the counted frequencies.