Analogue multiplexing using a digital technique

A digital technique of multiplexing analogue signals is described whereby improved isolation between channels and negligible equivalent-channel `on? resistance is achieved. It is also suggested that the proposed method may find application in analogue?digital conversion     

Effective measurements using digital signal analysis

In order to be effective, measurements must be unambiguous and quantitative, which is only possible when such measurements yield numerical values that can attach to a given aspect of the system being measured in only one way and have only one interpretation. This article discusses the use of correlation, transfer, and coherence functions in obtaining such measurements.     

A low-power direct digital synthesizer using a self-adjustingphase-interpolation technique

A complete direct digital synthesizer (DDS) using a self-adjusting phase-interpolation technique is fabricated using 0.35-μm CMOS process technology. A self-adjusting delay generator reduces the periodic jitter in the most significant bit (MSB) of the accumulator in this DDS. To improve the spectral performance, a method of spurious signal reduction that uses offset current sources (OCSs) is newly adopted in the delay generator. Test results confirm that the delay generator produces highly accurate delay timing without the need to adjust circuit constants. The measured spurious free dynamic range (SFDR) is 62 dBc for a dc to 10-MHz output and the power consumption of the complete DDS is 39.2 mW at a 100-MHz clock rate     

Design of a selective digital filter using the decimation technique

The implementation of an Intermediate Frequency (IF) filter in Digital Audio-VIsual Council (DAVIC) compliant modems is a particularly complex task. In previous works, we compared the performance of different designs (analog and digital) for the radio-frequency stage in a modem application. These designs have been evaluated for a particular case defined in the DAVIC recommendation. The design limits that were pointed out are mainly due, in the digital approach, to the high frequencies at which the IF stage must operate, and to the variation of the sampling frequency.

In this paper, we propose a digital implementation of the IF filter based on the decimation technique. The evaluation of the performance has been performed using the PTOLEMY software from the Berkeley University.     

Fast-acquisition PLL using fully digital natural-frequency-switching technique

A new phase-backed loop (PLL) with a simple architecture that overcomes the trade-off problem between acquisition time and phase noise was fabricated in a 0.2 mum CMOS process. One-fifth of the acquisition time of the integer-JV is achieved by switching only the division ratio with the optimised damping factor to control the natural frequency.     

A deterministic digital calibration technique for pipelined ADCs using a non-nested algorithm

Analog Integrated Circuits and Signal Processing - This paper proposes a novel deterministic technique to digitally calibrate 1.5-bits/stage and 1-bit/stage pipelined as well as algorithmic...     

A new technique for RF measurements using superconductors

The quantization of magnetic flux in a superconducting circuit can serve for the measurement of electrical quantities in the same way that we use the wavelength of light to measure length. We report a demonstration of this function in the measurement of attenuation ratio at a frequency of 30 MHz.     

Improving time-domain measurements with a network analyzer using arobust rational interpolation technique

A method to efficiently and accurately compute a time-domain waveform from a network-analyzer frequency-domain measurement is presented in this paper. The method is based on a robust interpolation technique to construct a pole-residue representation of the response of the device-under-test. First, the rational function is expressed in terms of Chebyshev polynomials, instead of the usual power series, to accurately determine the poles of the network over a wide frequency range. The properties of a passive system are then utilized to efficiently calculate the residues. The resulting pole-residue model is analytically transformed to obtain the time-domain response in any time window, beyond the limitations of the discrete Fourier transform (DFT) technique. Unlike the DFT technique, the method does not require a large number of equally spaced harmonically related frequency points. The parametric model can also be used to economically store large measurement data. The proposed procedure is computationally inexpensive and less sensitive to numerical instability. To illustrate the validity of the method, examples of frequency- and time-domain measurements of a Beatty structure and simulation data of a low-pass Butterworth filter are given     

Out-of-band emissions of digital transmissions using Kahn EER technique

The Kahn envelope elimination and restoration (EER) technique allows for linear RF power amplification by combining nonlinear, but efficient, RF and AF power amplifiers (PAs). In order to use the EER technique for digital signals, a coordinate transform from the original Cartesian in-phase and quadrature mode into a polar mode has to take place, yielding an envelope (or amplitude) and a PM RF signal. This coordinate transform is extremely nonlinear and thereby broadens the spectra of the original signals. In the final PA stage, both signals are recombined. However, since this recombination process is imperfect, out-of-band (OOB) emissions come up, also known as adjacent channel power or spectral regrowth. In this paper, the impact of the broadening of the amplitude and phase signals on OOB emissions is investigated with respect to imperfect restoration due to signal delays and limited bandwidth of the amplitude path. It is shown that the amount of OOB emissions can significantly be reduced if the modulation scheme shows a "hole" at the origin in its vector diagram.     

CW gain measurements in small-bore argon-ion laser discharges using a novel modulation technique

A technique for small-signal gain measurements for CW laser systems is described. The method is applied to the measurement of multimode small-signal gain coefficients of small-bore argon-ion laser transitions.     

Quadrature direct digital frequency synthesis using fine-grain angle rotation technique

An area- and power-efficient quadrature direct digital frequency synthesis technique called fine-grain angle rotation is presented. To reduce the large bitwidth requirement of the angle rotation, multiple start points are introduced and the angle rotation is applied to the remaining small angle. A prototype chip occupies 0.16 mm/sup 2/ in 0.25 /spl mu/m 1P5M CMOS technology and consumes 90 mW at 400 MHz clock frequency, which is a significantly improved performance compared to previous state-of-the-art chips.     

FET noise-parameter determination using a novel technique based on50-Ω noise-figure measurements

A novel method for measuring the four noise parameters of a field-effect transistor (FET) is presented. It is based on the determination of its intrinsic noise matrix elements [C₁₁^INT, C₂₂^INT, Re(C₁₂ ^INT), Im(C₁₂^INT)] by fitting the measured device noise figure for a matched source reflection coefficient (F₅₀) at a number of frequency points, thus, a tuner is not required. In contrast to previous works, no restrictive assumptions are made on the intrinsic noise sources. The receiver full-noise calibration is easily performed by using a set of coaxial and on-wafer standards that are commonly available in a microwave laboratory, thus, an expensive broad-band tuner is not required for calibration either. On-wafer experimental verification up to 26 GHz is presented and a comparison with other F₅₀-based and tuner-based methods is given. As an application, the dependence of the FET intrinsic noise sources as a function of the bias drain-current and gate-length is obtained     

A novel digital predistorter technique using an adaptive neuro-fuzzy inference system

This letter presents a novel digital predistorter technique using an adaptive neuro-fuzzy inference system (ANFIS). The proposed approach employs real-time input and output signals of a nonlinear power amplifier as inputs to the ANFIS, so as to approximate the inverse functions of the power amplifier. The antecedent and consequent parameters of the FIS constructed by the ANFIS are tuned using backpropagation and least squares algorithms. Simulation shows that this novel technique has improved the linearity of a WCDMA signal by a further 4 dBc compared to a conventional look-up table (secant) approach. Moreover, this proposed technique is capable of adapting to instantaneous variation in the power amplifier response through time, which is a topic often omitted by researchers in this area.     

A simple and robust digital current control technique of a PMsynchronous motor using time delay control approach

A simple and robust digital current control technique of a permanent magnet (PM) synchronous motor using a time delay control approach is presented. Among the various current control schemes for a voltage source inverter-fed PM synchronous motor drive, the predictive control is known to give a superior performance. This control technique, however, requires the full knowledge of machine parameters and operating conditions, and gives an unsatisfactory response under the parameter mismatch between the motor and controller. To overcome such a limitation, the disturbances caused by the parameter variations are estimated by using a time delay control approach and used for the computation of the reference voltages by a simple feedforward control. Thus, the steady-state control performance can be significantly improved in an extremely simple manner, while retaining the good characteristics of the predictive control such as the good transient response and stable inverter operation. The proposed control scheme is implemented on a PM synchronous motor using the software of DSP TMS320C30 and the effectiveness is verified through the comparative simulations and experiments     

Far-field accuracy investigation using modulated scattering technique for fast near-field measurements

Near field measurement techniques in conjunction with near-field to far-field transformation algorithms are widely used today. Two of the most important concerns are, firstly, the degree of accuracy achieved, and secondly, the measurement duration. Although high degrees of accuracy can be obtained, the time required to scan completely the near field of an antenna using the classical near-field measurement techniques is rather long. The modulated scattering technique would offer a means to reduce this time by a factor of 10 to 100 while maintaining a reasonable degree of accuracy. Using this technique, however, one introduces further sources of inaccuracy such as the mutual coupling between the elements of the array used to probe the test antenna, and the further limitation of the available measurement dynamic range. In this paper, these two sources of inaccuracy inherent in this technique or other techniques which use a similar set-up, are explored. Multiple reflections between the test antenna and the probe array are ignored. A parabolic reflector is chosen as the test antenna, and an array of dipoles is chosen as the probe antenna in the numerical simulation.     

Birefringence measurements of single-mode fibers using the polarization shuttle pulse technique

A novel and practical polarization shuttle pulse (PSP) technique has been developed to measure the intrinsic birefringence in short lengths of nominally circular-core low-birefringence single-mode fibers. By adding a linear polarizer, a Soleil-Babinet compensator, and a linear analyzer to the conventional shuttle-pulse arrangement, the length dependence of the phase delay (and hence the birefringence) can be measured nondestructively. An order-of-magnitude improvement in measurement repeatability over the conventional cut-back method has been achieved.     

Single-mode-fibre cutoff measurements using offset splice technique: excess loss effects

The effect of excess loss mechanisms on the measurement of the LP11 mode cutoff wavelength using the offset splice technique is investigated. We show that the measured cutoff wavelength will shift towards shorter wavelengths only if excess attenuation is present in both the emitting and receiving fibres. The shift is not observed if the excess loss is only present in one of the two fibres.     

Gain measurements on GaAs-based quantum cascade lasers using atwo-section cavity technique

A two-section cavity device has been used to measure gain spectra and waveguide losses of a GaAs-based quantum cascade laser. The device operates at 8.9 μm and optical confinement is obtained by means of Al-free cladding layers. We investigated the gain characteristics in a spectral window of ~60 meV and up to 200 K. For current densities ranging from 1 to 8 kA/cm², we report a constant gain coefficient of 13 cm/kA at 4 K and 6 cm/kA at 200 K. At low temperatures and for current densities above 8 kA/cm², we observe gain saturation which we attribute to a reduced electron injection in the active region caused by space charge effects. We report a value of 22 cm ^-1 for the waveguide losses in good agreement with previous measurements     

Improved digital/analogue conversion technique using currentsplitting in lateral bipolar transistors

Describes the use of multiple collector lateral bipolar transistors as precision current splitting elements suitable for use in high resolution monolithic D/A convertor design. Multiple collector structures result in better overall linearity and smaller chip area than previously suggested techniques. A six-bit convertor implemented on a linear bipolar semicustom array is used to demonstrate the advantages of this technique