This paper proposes two novel and compact low-power tunable AC amplifiers with ultra-low high-pass corner frequency. The circuits are based on alternative AC capacitively coupled feedback topologies using novel implementations leading to better performance in terms of area, power and noise efficiency. This is accomplished by a combination of actively boosting the resistive value of a pseudo-resistor (allowing more than two decades of tuning) and an optimization of the active devices required. Measurement results from a fabricated prototype using a$0.18~\mu \text{m}$technology are provided to demonstrate the technique. The proposed amplifiers can provide tunable high-pass corner frequencies ranging from 31 mHz to 7 Hz, with power consumption as low as$0.425~\mu \text{W}$, CMRR of 84 dB, 0.1 mm2 area, 39.7 dB gain, and integrated IRN of$2.42~\mu \text{V}_{\mathrm {rms}}$.

Vibrato constitutes one of the most interesting features of singing voice. It has been the topic of interest of many researchers in different knowledge areas such as acoustics, physiology, and psychoacoustics. In spite of this, some basic aspects related to vibrato production still remain unclear, such as the origin of its most relevant acoustical features, (frequency and amplitude variations of the partials) or the relevance of recently identified physiological effects, such as pitch synchronous variations of the voice organ. In this paper, a novel interactive vibrato production model will be proposed in order to accomplish a realistic voice production description, in such a way that the source-tract interaction will be included in the prediction model. This will allow us to identify, from the acoustical signal, additional effects typical of vocal vibrato, such as slight pitch synchronous variations of the vocal tract response, as well as to analyze the relationship between the acoustical features of vibrato and the voice production elements

Pulse width modulation (PWM) and sigma delta modulation (SDM) have been used in several high linearity, high accuracy power delivery applications such as DC-DC power converters, audio and RF power amplifiers as well as in data converters. In this paper, we present a particular class of carrier frequency modulated PWM (CFMPWM), which spreads the tonal content of regular PWM uniformly in frequency and reduces the baseband noise with respect to SDM by up to 15 dB. The new modulation scheme preserves at the same time the high efficiency properties of PWM. An approximate method to estimate the spectrum of CFMPWM signals with both deterministic and random modulation is also presented. Simulation results and experimental data are reported to analyze the spectral spreading properties of the proposed CFMPWM scheme.

A 1.5-V square-root domain (SRD) first-order filter possessing multiple operating points is presented. The basic building blocks of the filter are based on MOS translinear loops and dynamic level shifter techniques, allowing low voltage operation and an extended dynamic range. However the dynamic level shifters introduce positive feedback inducing three operating points to the filter through a negative differential resistance. A detailed analysis of such performance employing a bi-port analysis is offered. Simulation and measurement results are provided in order to demonstrate the analysis and circuits proposed.

A novel technique is proposed to achieve highly linear programmable voltage-to-current (V-I) converters over a rail-to-rail input range. It employs two passive resistors with one of their terminals tied to a very low impedance node to achieve an almost distortionless V-I conversion for rail-to-rail input signals. The resistor currents are conveyed to the output via programmable floating-gate MOS current mirrors that work in moderate inversion, thus achieving transconductance tuning in a wide range while preserving linearity in the rail-to-rail input range. Initial charge of the floating gates is removed during fabrication. An implementation fabricated in a 0.5-/spl mu/m CMOS technology using a dual supply of /spl plusmn/1.5 V achieves a THD of -60 dB over a wide transconductance tuning range with differential input swings equal to the total supply voltage. The area and power consumption are 0.1 mm/sup 2/ and 2.6 mW.

A new implementation of a resistorless and capacitorless scheme for continuous time highly linear weighted additions is presented. It is based on a circuit denoted "flipped folded voltage follower". Simulation and experimental results from a test chip prototype in 0.5mum technology validate the proposed circuit

Inverse filtering provides a noninvasive method to extract the voice source, and thus get insight into voice quality. Although this technique is widely used in speech analysis, this is not the case in singing voice, where its use has been even questioned by some authors. In this paper, a comparative study of some representative inverse filtering techniques will be presented in order to identify their main limitations in singing voice analysis. After a rough classification of the inverse filtering techniques, three representative procedures will be selected in order to cover all kind of approaches, and then evaluated taking into account two relevant features: their fundamental frequency limitation, and their sensitivity to the source-tract interaction. To make this comparative study possible, an interactive source-filter model we propose will be used such that the source-tract interaction can be controlled. In this way, the above-mentioned effects will be evaluated based on a simulation analysis, with a realistic singing production model. Natural singing voice results will be also reported to validate the simulations. This study will allow concluding that the main limiting aspect of inverse filtering in singing voice analysis is the fundamental frequency limitation, whereas the source-tract interaction represents a less relevant issue

In this paper, we analyze some methodological and practical grounds affecting a correct estimation of the instantaneous amplitude (IA) and instantaneous frequency (IF) of the partials of vocal vibrato signals. This particular class of acoustical signals can be described as a set of harmonics, or partials, whose amplitude and frequency vary with time following a particular pattern. The interest in the correct measurement of these two magnitudes stems from the fact that they are widely used to extract more information about the production mechanisms of this vocal effect, and even the singing voice. Focusing on the estimation of these magnitudes from the signal processing point of view, the estimation of the IA and the IF of a partial represents a practical example for the more general problem of the AM-FM decomposition of a bandpass signal, which has received considerable attention by the Time-Frequency community. With this in mind, this work will investigate the most appropriate AM-FM decomposition of the partials, and how it is affected by the reverberation present in recordings. A mathematical description of the effect of reverberation on the measurement will be given. It will be shown that the measurement of the IA and the IF of the partials will be corrupted by reverberation regardless of the employed estimation method

We investigate the relationship between the instantaneous amplitude (IA) and the instantaneous frequency (IF) of vibrato signals in the singing voice. It is shown that this relationship is of great value in obtaining information about the vocal tract model. However, to make this analysis possible, it is necessary to cope with two basic limitations: reverberation in recordings, which shows up as multiharmonicity in each partial, and the phase effect of vocal tract formants which distort the instantaneous frequency of some partials.

Trabajo presentado al 8th European Conference on Speech Communication and Technology (EUROSPEECH 2003 - INTERSPEECH 2003), Ginebra (Suiza), 1-4 de septiembre de 2003

Trabajo presentado al 8th European Conference on Speech Communication and Technology (EUROSPEECH 2003 - INTERSPEECH 2003), Ginebra (Suiza), 1-4 de septiembre de 2004

In this paper the methods for estimating the parameters of two closely spaced tones in frequency are presented. They are iterative procedures posed as an optimization problem. Both first and second order methods in combination with the corresponding tone estimation techniques are treated in order to circumvent the problem of interharmonic interference. It is shown that the convergence can be achieved for the frequency separation less then a bin within the limited number of iterations.

A current-mode companding biquad based on the quasi-quadratic MOST large-signal characteristics in strong inversion is presented. It is derived from an externally equivalent Gm-C biquad by a simple component-to-component substitution. The nonlinear blocks required are based on simple MOS TL loops, leading to a very regular structure. Measurement results from a 2.4-/spl mu/m CMOS IC implementation are presented.

A CMOS current-mode Square-Root Domain oscillator is designed by applying a synthesis method that allows to obtain it from an externally equivalent Gm-C oscillator by a simple component-to-component substitution. A second-order MOS Translinear Loop constitutes the basis for all the nonlinear blocks required, leading to a very regular structure. Measurement results from a 2.4-/spl mu/m CMOS IC implementation confirm a good tunability and low THD.

This paper describes a novel variable frequency MOSFET-C oscillator that features a precise amplitude control, exhibiting at the same time a very low distortion. It can be useful as a stand alone VCO, and also as master oscillator in frequency tuning loops for an slave filter using the same topology. The oscillator has been integrated and tested on a 0.5 /spl mu/m CMOS technology, giving satisfactory results. Experimental results are given.

In this paper we summarise the necessary properties that a nullor conceived to be a universal active device, must have. This approach lead us to propose a practical implementation of a nullor, consisting of a four terminal, fully floating transconductor with high gain. These design conditions are validated with some unconventional applications.>

This paper illustrate the use of a new class of amplifiers known as 'current feedback amplifiers' as the active devices in sinusoidal oscillators. From theoretical analysis, supported by experiments, it is concluded that they offer improved performance, with respect to their opamp based counterparts in terms of frequency accuracy, dynamic range, distortion level and frequency span. At the same time they seem to be more flexible for the inclusion of automatic gain control schemes.>