Wouter A. Serdijn

Full length article: Emerging applications of wavelets: A review

Although most of its popular applications have been in discrete-time signal processing for over two decades, wavelet transform theory offers a methodology to generate continuous-time compact support orthogonal filter banks through the design of discrete-time finite length filter banks with multiple time and frequency resolutions. In this paper, we first highlight inherently built-in approximation errors of discrete-time signal processing techniques employing wavelet transform framework. Then, we present an overview of emerging analog signal processing applications of wavelet transform along with its still active research topics in more matured discrete-time processing applications. It is shown that analog wavelet transform is successfully implemented in biomedical signal processing for design of low-power pacemakers and also in ultra-wideband (UWB) wireless communications. The engineering details of analog circuit implementation for these continuous-time wavelet transform applications are provided for further studies. We expect a flurry of new research and technology development activities in the coming years utilizing still promising and almost untapped analog wavelet transform and multiresolution signal representation techniques.

Co-Design of a CMOS Rectifier and Small Loop Antenna for Highly Sensitive RF Energy Harvesters

In this paper, a design method for the co-design and integration of a CMOS rectifier and small loop antenna is described. In order to improve the sensitivity, the antenna-rectifier interface is analyzed as it plays a crucial role in the co-design optimization. Subsequently, a 5-stage cross-connected differential rectifier with a 7-bit binary-weighted capacitor bank is designed and fabricated in standard 90 nm CMOS technology. The rectifier is brought at resonance with a high-Q loop antenna by means of a control loop that compensates for any variation at the antenna-rectifier interface and passively boosts the antenna voltage to enhance the sensitivity. A complementary MOS diode is proposed to improve the harvesters ability to store and hold energy over a long period of time during which there is insufficient power for rectification. The chip is ESD protected and integrated on a compact loop antenna. Measurements in an anechoic chamber at 868 MHz demonstrate a -27 dBm sensitivity for 1 V output across a capacitive load and 27 meter range for a 1.78 W RF source in an office corridor. The end-to-end power conversion efficiency equals 40% at -17 dBm.

Analysis of Power Consumption and Linearity in Capacitive Digital-to-Analog Converters Used in Successive Approximation ADCs

Successive-approximation analog-to-digital converters (SA-ADCs) are widely used in ultra-low-power applications. In this paper, the power consumption and the linearity of capacitive-array digital-to-analog converters (DACs) employed in SA-ADCs are analyzed. Specifically, closed-form formulas for the power consumption as well as the standard deviation of INL and DNL for three commonly-used radix-2 architectures including the effect of parasitic capacitances are presented and the structures are compared. The proposed analysis can be employed in choosing the best architecture and optimizing it in both hand calculations and computer-aided-design tools. Measurement results of previously published works as well as simulation results of a 10-bit 10 kS/s SA-ADC confirm the accuracy of the proposed equations. It will be shown that, in spite of what commonly is assumed, although the total capacitance and the power consumption of those architectures employing attenuating capacitors seem to be smaller than conventional binary-weighted structures, the linearity requirements impose much larger unit capacitance to the structure such that the entire power consumption is larger.

General current-mode analysis method for translinear filters

Log-domain or translinear filters are regarded as being a promising alternative in the area of low-voltage filter design. To date, most publications have reported on synthesis of translinear filters. Although synthesis is more powerful than analysis, it must go together with a generally applicable analysis method in the same domain. In this paper, a general current-mode analysis method is proposed. By using a current-mode approach, we stay close to the existing theory on static translinear circuits, which might be beneficial in developing a general, possibly more powerful synthesis method.

An RMS-DC converter based on the dynamic translinear principle

Translinear or log-domain filters are theoretically exact realisations of linear differential equations. However, the dynamical translinear principle can also be applied to the implementation of nonlinear differential equations. In this paper, an RMS-DC converter is proposed, comprising a direct implementation of the corresponding nonlinear differential equation by means of the dynamical translinear principle. Correct operation of the circuit was verified through measurements.

A low-voltage low-power fully-integratable automatic gain control for hearing instruments

A low-voltage low-power bipolar automatic gain control (A.G.C.) that works in the current domain and operates on a single 1.3-V battery is presented. In this A.G.C. a large time constant (50 ms) is realised on-chip. The A.G.C. consists of a gain cell, a comparator and a voltage follower. The active circuitry of the A.G.C. has been integrated in the DIMES01 process and the total circuit demonstrates operation down to 1 V with 4¿W power consumption.

Codesign of an impulse generator and miniaturized antennas for IR-UWB

The codesign of an impulse generator and miniaturized antennas for ultra-wideband impulse radio is described. The impulse generator, discussed by Bragga in 2004, is designed with differential outputs that are fed to the antenna, producing an optimum match of the generator to the antenna, an improved magnitude response, and reduced ringing of the radiated pulse. The impulse generator is preceded by a programmable pulse-position modulator and consists of a triangular pulse generator and a cascade of complex first-order systems, which, in turn, are made up of differential pairs employing partial positive feedback to approximate a Gaussian monocycle waveform. The complete pulse generator is fabricated in IBM 0.18-/spl mu/m Bi-CMOS IC technology. Measurements show the correct operation of the circuit for supply voltages of 1.8 V and a power consumption of 45 mW. The output pulse approximates the Gaussian monocycle having a pulse duration of about 375 ps. Proper modulation of the pulse in time is confirmed. A number of antennas with differentially fed baluns and input impedances of 100 /spl Omega/ have been designed. From measurements, it can be seen that ringing is considerably smaller as compared to conventionally fed antennas.

A PPM Gaussian monocycle transmitter for ultra-wideband communications

A Gaussian pulse generator incorporating a pulse position modulator for use in an impulse radio ultrawideband system is described. The pulse generator is preceded by a programmable pulse position modulator and comprises a cascade of complex first-order systems, which, in turn, are made up of differential pairs employing partial positive feedback. The resulting PPM Gaussian pulse generator is designed in IBM 0.18 /spl mu/m Bi-CMOS IC technology. Simulations predict the correct operation of the circuit for supply voltages of 1.8 V and a power consumption of 30 mW. The output monocycle indeed approximates a Gaussian monocycle, having a pulse duration of about 250 ps. Proper modulation of the pulse in time is confirmed.

Analog wavelet transform employing dynamic translinear circuits for cardiac signal characterization

An analog QRS complex detection circuit, for pacemaker applications, based on the Wavelet Transform (WT) is presented. The system detects the wavelet modulus maxima of the QRS complex. It consists of a wavelet transform filter, an absolute value circuit, a peak detector and a comparator. In order to achieve the low-power requirement in pacemakers, we propose a new method for implementing the WT in an analog way by means of the Dynamic Translinear (DTL) circuit technique. Simulations indicate a good performance of the WT and the QRS complex detection. The resulting circuit operates from a 2-V supply voltage, dissipates at most 55 nW per scale and can be fully integrated.

Application of the back gate in MOS weak inversion translinear circuits

Though the MOS transistor is a four-terminal device, it is most often used as a three-terminal device. Therefore, a large number of possible MOS circuits are overlooked. In this brief, the four-terminal point of view is elaborated with respect to MOS weak inversion translinear circuits, a class of circuits naturally very suitable for low-voltage and low-power applications. Some new circuits are described which sometimes are more suitable for low-voltage applications than bipolar translinear networks performing the same function. It is also shown that, using the back gate, translinear networks can be derived which cannot be realized with bipolar transistors. These network topologies increase the possibilities offered by translinear technology. As an example, measurement results of a low input-voltage current mirror and a sin(x)-circuit are shown.