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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
A voltage-controlled oscillator (VCO) is an oscillator circuit in which the frequency of oscillation can be controlled by an externally applied voltage. VCOs are generally designed to operate over a wide frequency range, often with a frequency ratio of 100:1. One important feature that is often required for VCOs is a linear relationship between the oscillation frequency and the control voltage. Many VCOs have a maximum frequency of operation of around 1MHz, but there are some emitter-coupled VCOs that can operate up to 50MHz.
Smart Antenna System Architecture and Hardware Implementation
Published in Lal Chand Godara, Handbook of Antennas in Wireless Communications, 2018
In a typical frequency synthesizer circuit, the output of a voltage-control oscillator (VCO) is controlled in a phase-lock loop (PLL) so that its frequency remains locked to a multiple of the frequency of a known reference. The basic principle of the PLL frequency synthesizer is quite straightforward. In the feedback path of the loop, a signal whose frequency is a suitable submultiple of the VCO frequency is generated and compared with the reference signal via a phase comparator. If their frequencies are different, the error voltage from the phase comparator forces the VCO frequency to change in such a way that this frequency difference eventually is reduced to zero. The phase comparator may be a mixer, and the reference signal may be from a crystal oscillator. With this scheme, the output frequency is a multiple of the reference frequency, and the noise performance depends on the loop configuration, the phase detector technology, and the noise characteristics of the reference signal. In particular, the noise from the reference is multiplied in the output by the ratio of the VCO frequency over the reference frequency. This is important, because in a smart antenna a very low phase noise would be required. The most extensively used PLL synthesizer architecture is the single-loop PLL. Because these devices are simple, have low cost, and are easily implemented in integrated circuits, PLL frequency synthesizers are attractive. Description of the theory and design of PLL frequency synthesizers may be found in some of the references cited earlier.16–17
Frequency Synthesizer
Published in Kaixue Ma, Kiat Seng Yeo, Low-Power Wireless Communication Circuits and Systems, 2018
Nagarajan Mahalingam, Kaixue Ma, Kiat Seng Yeo
The phase noise is one of the important design parameters in the VCO as it directly affects the spectral purity of the frequency synthesizer. More works have been reported in literature to reduce the phase noise in the oscillator [6−11]. The relation between the phase noise generators and LC oscillator design parameters is given by [7] L(Δω)=10logKTReff(1+F)(ωoΔω)21Vrms2, $$ L(\Delta \omega ) = 10{\text{~log~}}\left[ {KTR_{{eff}} (1 + F)(\frac{{\omega _{o} }}{{\Delta \omega }})^{2} \frac{1}{{V_{{rms}}^{2} }}} \right], $$
Low-power fully monolithic MICS band receiver for 402-405 MHz implantable devices
Published in International Journal of Electronics, 2020
The tuning range of the VCO and its buffer, phase noise and power spectrum are measured by the R&S FSUP26 signal source analyzer as well as by the Agilent E4443A spectrum analyzer with phase noise measurement utility. The measurement tuning characteristics, shown in Figure 19, reveals that the measured frequency oscillation covers a frequency range from 368 to 442MHz (19%). Figure 19(a) shows the course tuning characteristics of the VCO at a fixed Vtune of 0.6 V. It is noted that the tuning curve of the VCO is closer to a straight line, where the transfer function between the frequency and the voltage of the VCO is very linear over more than 74 MHz. Figure 19(b) shows the measured tuning characteristics with a fine control voltage 0–1.2-V with a binary-weighted capacitor bank (in which the only one measured curve is shown at n is set to 1100) at a centre frequency of 403 MHz. Figure 20 shows the plot of the phase noise versus the offset frequency from the 403 MHz carrier. The oscillator shows a phase noise of −138 dBc/Hz at1MHz offset frequency from the carrier frequency, which is very comparable to the simulation results. Small variations in the phase noise and the carrier frequency are also caused due to process variations. Figure 21 shows the output spectrum at the 403MHz output frequency.
A wide-range 22-GHz LC-based CMOS voltage-controlled oscillator
Published in International Journal of Electronics, 2018
Karam Gharbieh, Mohammed Ranneh, Khaldoon Abugharbieh
The designed VCO has a frequency range of 10.75–22.43 GHz. It has a maximum KVCO of 175.7 MHz/V with a maximum variation of 1.78 over the complete frequency range and PVT. The design exhibits a phase noise of −111 dBc/Hz at 1 MHz offset from 10.75 GHz carrier frequency. It consumes 14.47 mW of power from a 1 V supply at typical process corner. Equation (9) presents a figure of merit, FOM, for the VCO. The FOM, similar to Cai et al., (2014), takes parameters into account like oscillation frequency, phase noise, supply voltage and tuning range. In Equation (9), is the phase noise, is the oscillation frequency and is the offset frequency. However, it should be noted that Equation (9) does not take into account the KVCO values and KVCO variations which are key parameters that are not often clearly reported in the literature. This VCO achieves a FOM 218 which is slightly lower than the VCO in Abdelfattah et al. (2013). While the transformer implementation provided a significantly wider tuning range, the phase noise has been adversely impacted.
Low-cost multifrequency electrical impedance-based system (MFEIBS) for clinical imaging: design and performance evaluation
Published in Journal of Medical Engineering & Technology, 2018
Gurmeet Singh, Sneh Anand, Brejesh Lall, Anurag Srivastava, Vaneet Singh
A sine wave of variable frequency is generated from VCO. The output of VCO is applied to the VCCS which generates a constant current. This current is applied to the current electrodes, and then the voltage developed on all the potential electrodes in neighbouring switching protocol (V1 to V13 in first projection as shown in Figure 3) is measured keeping both conducting and non-conducting in-homogeneities at different locations in the phantom area in the NaCl solution. The voltage data appear at electrodes that are applied to the input of the instrumentation amplifier which is then fed to the filter circuit. DSO (Tektronix Model no TBS 1072 B-EDU 70 MHz, IGs/s) captures the output of filter circuit. These acquired data are then fed to a PC using the serial port to electrical impedance reconstruction software for the reconstruction of images using surface potential.