Q-sensitivities and omega-0-sensitivities in positive gain second-order RC active filters

An active filter configuration with a general three-terminal second-order RC feedback network and a positive voltage gain is considered. The sensitivities of the Q factor and resonant frequency with respect to the voltage gain are calculated, and a relationship between lower bounds on them is formulated

Simple quadrature oscillator for BIST

A simple quadrature oscillator for the built-in self-test (BIST) of integrated analogue filters is proposed. A new hardware-efficient approach for amplitude control is described, the main assets being: (i) the technique requires little hardware, which makes it very useful for BIST; (ii) the oscillation amplitude is well defined, and (iii) the distortion-level introduced by the amplitude control loop is under the control of the designer

Method for electric field and potential calculations in Hall plates

Electrostatic field problems occurring in Hall plates are difficult to solve, mainly because of a non-standard boundary condition defining an oblique angle of the electric field w.r.t. an isolating boundary. A new approach for solving Hall-related field problems is presented. Compared to prior approaches, the technique leads more easily to closed-form expressions for the electric field, and allows obtaining voltage-related Hall characteristics in numerically well conditioned forms

Improved DAC driving scheme for OFDM applications

Presented is a 'Redundant Signed Digit' driving scheme for binary weighted D/A conversion. This scheme retains the simplicity of conventional binary weighted D/A conversion, but has greatly improved robustness with regard to parasitic effects, especially when processing signals with a high crest factor. Such signals occur in communication systems that use, e.g. orthogonal frequency-division multiplexing (OFDM). In this case an improvement of 9 dB in Missing Tone Power Ratio performance was measured on a prototype 250 MSample/s circuit implemented in 0.18 mu m CMOS

Adressing static and dynamic errors in bandpass unit element multibit DAC's

This paper describes a general model for static as well as dynamic errors in multibit unit element DAC's. Apart from the static mismatch there are two other error terms arising from switching imperfections. Based on the model, some bandpass mismatch shaping techniques are presented. These address both the static mismatch as well as the switching imperfections. The techniques can significantly improve the in band noise

A closed-loop digitally controlled MEMS gyroscope with unconstrained Sigma-Delta force-feedback

In this paper, we describe the system architecture and prototype measurements of a MEMS gyroscope system with a resolution of 0.025 degrees/s/root Hz. The architecture makes extensive use of control loops, which are mostly in the digital domain. For the primary mode both the amplitude and the resonance frequency are tracked and controlled. The secondary mode readout is based on unconstrained Sigma Delta force-feedback, which does not require a compensation filter in the loop and thus allows more beneficial quantization noise shaping than prior designs of the same order. Due to the force-feedback, the gyroscope has ample dynamic range to correct the quadrature error in the digital domain. The largely digital setup also gives a lot of flexibility in characterization and testing, where system identification techniques have been used to characterize the sensors. This way, a parasitic direct electrical coupling between actuation and readout of the mass-spring systems was estimated and corrected in the digital domain. Special care is also given to the capacitive readout circuit, which operates in continuous time

A describing function study of saturated quantization and its application to the stability analysis of multi-bit sigma delta modulators

Just as their single-bit counterparts, multi-bit sigma delta modulators exhibit nonlinear behavior due to the presence of the quantizer in the loop. In the multi-bit case this is caused by the fact that any quantizer has a limited output range and hence gives an implicit saturation effect. Due to this, any multi-bit modulator is prone to modulator overloading. Unfortunately, until now, designers had to rely on extensive time-domain simulations to predict the overloading level, because there is no adequate analytical theory to model this effect. In this work, we have developed such an analytical theory based on multiple input describing function analysis. This way, we obtained expressions for the signal gain, the noise gain and the variance of the quantization noise. Here, both the case of DC as well as sinusoidal signals was considered. These results were used for the stability analysis of multi-bit Sigma Delta modulators, which allows to predict the overloading level. Code implementing the proposed expressions is available for download at http://cas1.elis.ugent. be/cas/en/download

Calibration of DAC mismatch errors in sigma delta ADCs based on a sine-wave measurement

We present an offline calibration procedure to correct the nonlinearity due element mismatch in the digital-to-analog converter (DAC) of a multibit Sigma Delta-modulation A/D converter. The calibration uses a single measurement on a sinusoidal input signal, from which the DAC errors can be estimated. The main quality of the calibration method is that it can be implemented completely in the digital domain (or in software) and does not intervene in any way in the analog modulator circuit. This way, the technique is a powerful tool for verifying and debugging designs. Due to the simplicity of the method, it may be also a viable approach for factory calibration

Folded-cascode amplifier with efficient feedforward gain-boosting

An efficient implementation of a two-stage feedforward amplifier is proposed. The new amplifier topology boosts the DC gain of a folded-cascode amplifier by adding a gain path, which makes use of the 'free' transconductance of the folding current sources. Only a single differential pair is used to convert the input voltage to a current. A current splitter extracts the parts needed for feedforward and for the first gain stage. This turns out to be favourable in terms of noise when compared with more traditional feedforward amplifiers

A dual-mass capacitive-readout accelerometer operated near pull-in

A mechanical two-mass configuration and a readout circuit for a single-axis capacitive-readout accelerometer with ΣΔ force-feedback is presented. The system reduces electrical and quantisation input-referred noise through the use of negative springs, reduced gaps in the readout capacitors and maximised readout voltage. A theoretical analysis and simulation results are discussed