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Smart Antenna System Architecture and Hardware Implementation
Published in Lal Chand Godara, Handbook of Antennas in Wireless Communications, 2018
As mentioned previously, in a cellular mobile system, two or more signals from adjacent channels may be picked up by the antenna and amplified by the LNA before being applied to the mixer RF port. The nonlinear characteristics of these devices may result in a large number of radio components called intermodulation products, the frequencies of which are combinations of harmonics of the input signals. In most practical cases, however, the third-order intermodulation product is more likely to fall within the desired signal frequency band, and affects the receiver performance unless a special measure is used to suppress it. One obvious method is to ensure that the intermodulation product stays below the noise floor by operating the devices within the linear range of the input–output curve. However, the problem is complicated by the fact that most receivers are required to operate over a wide range of signal strengths. Thus, if strong signals are present at their input, these devices may operate in the nonlinear part of their input–output curves, and third intermodulation products may grow quickly with increase in input signal strength.
Amplifiers and The Audio Signal
Published in Douglas Self, Audio Power Amplifier Design, 2013
Intermodulation distortion occurs when signals containing two or more different frequencies pass through a non-linear system. Harmonics that are integer multiples of the fundamental frequencies are generated as in harmonic distortion, but, in addition, intermodulation between any pair of frequency component creates new components at the sum and difference frequencies of that pair, and at multiples of those sum and difference frequencies. Thus, if the input signal is composed of two sine waves at f1 and f2, harmonics will be generated at 2fl, 3f1, 4f1, etc., and at 2f2, 3f2, 4f2, and so on. In addition, inharmonic components are generated at f1+f2, f1 -f2, 2fi+f2, and so on. The number of frequencies generated is already large, and increases significantly if three or four signals with non-commensurate frequencies are present in the input. Very soon the total power in the inharmonic sum-and-difference frequencies completely dominates the output and gives the unpleasant muddled and crunchy sound associated with the distortion of music. Orchestral music can easily be composed of a hundred or more signals from individual instruments, so the sensation of intermodulation distortion is often not unlike the addition of white noise.
Satellite orbital parameters and outline satellite communication principles
Published in L. Tetley, D. Calcutt, Understanding GMDSS, 2012
When using FM and frequency division multiple access (FDMA), the transponder cannot be operated at maximum output power because of non-linearity of the output power device—usually a travelling-wave tube amplifier (TWTA), at high values of output power. Backoff is usually employed, usually between 3 to 7 dB at the output of the device, to keep intermodulation products down to a level that is acceptable. For a system with many channels, the backoff will need to increase as the number of multiple accesses increases. Intermodulation is caused by the non-linearity of the transponder output device when operating with a multiplicity of signals. The generation of a large number of intermodulation products under these conditions can cause some interference within the transponder passband. The effect may be minor but it does cause an overall increase in noise levels which would reduce the C/N value of the required signal at the earth station.
Dependence of Lateral Straggle Parameter on DC, RF/Analog, and Linearity Performance in SOI FinFET
Published in IETE Journal of Research, 2021
Rajesh Saha, Brinda Bhowmick, Srimanta Baishya
IIP3 defines the extrapolated input power at which fundamental and third-order harmonic powers are equal. Likewise, IMD3 represents the extrapolated intermodulation distortion power at which fundamental and third-order harmonic intermodulation power are equal. IIP3 and IMD3 are expressed as follows [34]: where Rs = 50 ohm for RF application. Higher the value of IIP3 implies the better the linearity characteristics. It is seen from (8) that IIP3 is directly and inversely proportional to gm and gm3, respectively. Lower value of σ gives lesser value of gm3, which in turn increases the value of IIP3, and accordingly, linearity also improves as shown in Figure 17(a). The impact of σ on IMD3 is shown in Figure 17(b) and lower the value of IMD3 better is the linearity characteristics. Putting the expression of VIP3 in (9), it is realized that the IMD3 is independent of gm3. The increase in IMD3 with σ is due to an increase in gm (Figure 9). It is also visualized that lower value of IMD3 is obtained at σ = 0 nm compared to σ = 5 nm and this improvement in linearity is due to better short channel characteristics at lower value of σ.
Demonstration of Temperature-Dependent Analysis of GAA – β-(AlGa)2O3/Ga2O3 High Electron Mobility Transistor
Published in IETE Journal of Research, 2022
Ravi Ranjan, Nitesh Kashyap, Ashish Raman
This section describes the linear performance of the reported GAA β-AGO/GO HEMT device at different temperature ranges to examine the characteristics of the device. For high frequency and power devices, linearity parameters play a key role. The nonlinearity of a device degrades the performance of high-frequency devices. Intermodulation products of second- and third-order results generate nonlinearity of the device and can cause IM distortion.