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Advanced Instrumentation for High-Resolution Capacitance and Impedance Measurements
Published in Jian V. Li, Giorgio Ferrari, Capacitance Spectroscopy of Semiconductors, 2018
Giorgio Ferrari, Marco Carminati
To maintain a high accuracy independent of frequency, wide bandwidth impedance analyzers use a down-conversion, amplification, up-conversion topology [30, 31]. An example of such architecture is shown in Fig. 6.8. The sinusoidal signal at the measurement frequency fs coming from the DUT is demodulated by the multipliers M1 operated at the same frequency fs. Therefore, the DC value at the output of the multipliers is proportional to the amplitude of the input signal at the frequency fs. The in-phase and quadrature components are separately demodulated to preserve the information of the phase of the input signal, similarly to a lock-in amplifier. The input signal translated at zero frequency is successively amplified by the stages A that provide an amplification independent of the measurement frequency fs. The following low-pass filters (LPF) prevent the propagation of the 2fs component and other unwantedharmonics given by the multipliers M1. Finally, the signals are up-converted by M2 and added together to obtain an output signal with the same frequency and phase of the input signal and a gain factor irrespective of the measurement frequency fs.
Cognitive Radio Spectrum-Sharing Technology
Published in Krzysztof Iniewski, Wireless Technologies, 2017
Danijela Cabric, Robert W. Brodersen
If pulses are processed as real signals, the perfect estimation of an impulse phase is not possible. Commonly, the phase is extracted from the analytic signal composed of the in-phase and quadrature components. In narrowband receiver, the analytic signal is obtained via mixing with sine and cosine at the intermediate frequency (IF) stage of the receiver. In case of wideband, it can be obtained by performing a Hilbert transform on the received real signal after A/D conversion. Note that this approach effectively does not require I and Q mixers; thus, only one A/D converter is sufficient. The Hilbert transformers can be implemented in digital domain as an finite impulse response (FIR) or fast Fourier transform (FFT). The real and imaginary parts of the analytic signal are orthogonal, and the phase information can be studied on the Euler plane. A coordinate rotation digital computer (CORDIC) block can be used to calculate the phase and magnitude of the complex signal, which are used for impulse detection. For antipodal signaling the constellation plot allows threshold-based detection, similar to binary phase shift keying (BPSK) detection [8].
Continuous-Time Circuits
Published in Tertulien Ndjountche, CMOS Analog Integrated Circuits, 2017
Homodyne architectures [6] for receivers and transmitters, as illustrated in Figures 7.4 and 7.5, respectively, have the advantage of eliminating many off-chip components in the signal paths. They are sometimes referred to as direct-conversion or zero-IF receivers and transmitters. Here, the conversion from the radio frequency to the baseband frequency, and vice versa, is achieved using only one mixer stage. The word “homo” implies “same;” this is equivalent to having an identical frequency for the signal of interest and local oscillator signal. Even though the IF frequency is zero, the mirrored image of the desired signal will be superimposed on the down-converted signal, which is generated by the mixer. The image problem is solved by performing the frequency conversion in quadrature. The amplitude and phase of the desired signal can readily be determined from the in-phase and quadrature components. In homodyne architectures, the channel select filtering at baseband is simply performed by lowpass filters, suitable to monolithic IC integration. Hence, the requirements associated with different communication standards can be met using programmable filters and high-dynamic range data converters. Overall, this approach is excellent at saving cost, die area, and power consumption. However, the effects of dc offset, device flicker noise, even-order harmonics, and local-oscillator leakage can critically limit the accuracy of the signal detection.
Adaptive Quadrature Spatial Modulation
Published in IETE Technical Review, 2020
S. Oladoyinbo, N. Pillay, H. Xu
In [6], the Alamouti space-time block code is investigated for QSM to further improve the diversity gain by subdividing the information into two groups. The information is conveyed with the indices of the antennas corresponding to the group, coupled with two complex modulated symbols. These two complex symbols are decomposed into their in-phase and quadrature components and independently transmitted through their corresponding active transmit antennas. This still requires two-time slots to send out two symbols. Therefore, the data rate remains the same. However, the reliability of the link has improved due to the transmission of redundant copies of data. The CC of the system at the receiver increases exponentially with the size of the constellation, which makes the implementation not only difficult but expensive.
Design and development of FPGA-based real-time RF cavity simulator using LabVIEW
Published in International Journal of Electronics Letters, 2020
Sweta Khare, Nitesh Tiwari, Pritam Singh Bagduwal, Mahendra Lad
X(n) and y(n) are sampled input and output, respectively. ak and bk are filter coefficients. From the z-domain, transfer function filter structure was formed. The filter structure for implementation of RF cavity is shown in Figure 3. In the electrical model of RF cavity input and output, both are complex numbers. The real and imaginary parts of both input and output are in-phase and quadrature components, respectively. Filter coefficients are also complex numbers. So complex multiplication and complex addition are required.
A computational investigation and smooth-shaped defect synthesis for eddy current testing problems using the subregion finite element method
Published in Research in Nondestructive Evaluation, 2019
Mohammad R. Rawashdeh, Anders Rosell, Lalita Udpa, S. Ratnajeevan H. Hoole, Yiming Deng
The excitation coil that contains the AC input voltage will be the source for the first part of the magnetic flux density at the predetermined measuring points BCoil (T), while the eddy current will contribute the second part as BEddy Current (T). We are dealing with a 2D problem, so we will choose By as the normal value that we are planning to measure using the TMR sensor at these measuring points. The TMR sensor is placed on a scanner that positions the sensor over the surface of the tested sample where it will read the values of the normal magnetic flux densities By (T). The TMR sensor will output a voltage Vy (V) directly proportional to the value of By (T). It is necessary to note that we are planning to have values of By within the linear region of the sensor, so we will have proportional output voltages. If the values of By are high, there is a risk of saturating the sensor. This will be a limitation for the coil size. The voltages Vy (V) are small related to input values, so we need to amplify these values. To do that, we will use an instrument amplifier with a gain Gm. The output of the amplifier then will be Vmy = GmVy (V). This amplified signal will be then input to a lock-in amplifier to measure phasor parameters for Vmy (V). We use the same input waveform as a reference to measure the in-phase and quadrature components of the output signal. There may be a small phase shift in the output voltages due to the existence of the low pass filter in the lock-in amplifier. The output voltages of the lock-in amplifier are related to the magnetic flux density values. This relation is linear, and the resulted signal will be a scaled version for By. We will study two experimental cases to validate the subregion FEM.