Alberto Yúfera

A tissue impedance measurement chip for myocardial ischemia detection

In this paper, the design of a specific integrated circuit for the measurement of tissue impedances is presented. The circuit will be part of a multi-micro-sensor system intended to be used in cardiac surgery for sensing biomedical parameters in living bodies. Myocardium tissue impedance is one of these parameters which allows ischemia detection. The designed chip will be used in a four-electrode based setup where the effect of electrode interfaces are cancelled by design. The chip includes a circuit to generate the stimulus signals (sinusoidal current) and the circuitry to measure the magnitude and phase of the tissue impedance. Several integrated circuits have been designed, fabricated and tested, in a 0.8-/spl mu/m CMOS process, working at 3 V of power supply. Some of them including building blocks, and other with the whole measurement system. Experimental tests have shown the circuit feasibility giving expected results for both in-vitro and in-vivo test conditions.

A 1.25-V micropower Gm-C filter based on FGMOS transistors operating in weak inversion

This paper presents a novel linearized transconductor architecture working at 1.25 V in a 0.8-/spl mu/m CMOS technology with very low power consumption. The special features of the floating-gate MOS (FGMOS) transistor are combined in weak and strong inversion leading to a simplified topology with fewer stacked transistors and a very low noise floor. The design methodology is thoroughly explained, together with the advantages and disadvantages of working with the FGMOS transistor. Furthermore, second-order effects arising from nonideal behavior of the device are analyzed and limits for the performance are established. Experimental results from a second-order low-pass/bandpass filter that was implemented using the transconductor show a tunability of over one and a half decades in the audio range, a dynamic range of over 62 dB, and a maximum power consumption of 2.5 /spl mu/W. These results demonstrate the suitability of the FGMOS transistor for implementing analog continuous-time filters, while at the same time pushing down the voltage limits of process technologies and simplifying the circuit topologies to obtain significant power savings.

A 1-V micropower log-domain integrator based on FGMOS transistors operating in weak inversion

This paper describes the implementation of a low-power floating-gate MOS (FGMOS)-based log-domain integrator that reduces the minimum required voltage supply and the risk of instabilities. The performance of the block is illustrated with the experimental results of a second-order low-pass/bandpass filter working in the audio range with a 1-V voltage supply and a maximum power consumption of 2 /spl mu/W. The experimental results show that the FGMOS transistor is a powerful device that enables the design of low-voltage-supply low-power-consumption filters which have very simple topologies.

Design of a CMOS closed-loop system with applications to bio-impedance measurements

This paper proposes a method for impedance measurements based on a closed-loop implementation of CMOS circuits. The proposed system has been conceived for alternate current excited systems, performing simultaneously driving and measuring functions, thanks to feedback. The system delivers magnitude and phase signals independently, which can be optimized separately, and can be applied to any kind of load (resistive and capacitive). Design specifications for CMOS circuit blocks and trade-offs for system accuracy and loop stability have been derived. Electrical simulation results obtained for several loads agree with the theory, enabling the proposed method to any impedance measurement problem, in special, to bio-setups including electrodes.

Programmable switched-current wave analog filters

This paper presents a methodology to realize programmable switched-current filters. A universal wave filter structure is built based on a low-pass (LP) to band-pass (BP) frequency transformation in the z-domain that allows obtaining different filtering functions from a single low-pass reference filter without altering the global circuit topology. Two different parameters, modified by changing the gain of current mirrors, independently control the filter bandwidth and center frequency. A 2.88-mm/sup 2/ IC prototype has been fabricated in a 1.6-/spl mu/m CMOS digital technology that is capable of implementing three LPs (and their three complementary HPs) and nine BPs (and their nine complementary BR) Chebyschev filters. The realization of the 24 filtering functions requires less than 15% of additional area than that required to implement only one BP function. The chip operates from a 5-V supply, dissipates 0.83 mW/pole, and met the expected performance levels for all filter functions. >

An integrated circuit for tissue impedance measure

In this paper, the design of as integrated circuit (IC) for the measurement of tissue impedance is presented. The chip is intended to be used in monitoring biomedical parameters in living bodies. Tissue impedance is one of these parameters which allows ischemia monitoring. The designed IC is used in a four-electrode based set-up in order to minimize the effect of electrode-electrolyte interface impedance. A needle shaped probe which contains the four electrodes for the impedance measurement and ICs required for excitation and measurement purpose have been designed, fabricated and tested in-vivo. The IC has been fabricated in a 0.8 /spl mu/m CMOS process, working at 3 V of power supply. Test results have shown the circuit feasibility.

A method for bioimpedance measure with four- and two-electrode sensor systems

This paper presents an alternative method to measure impedances based on constant amplitude voltage excitation. The method makes use of feedback principle to adapt the measure conditions to load under test, being easily applied to bioimpedance measure with electrode sensors. The method has been tested for several frequencies and loads, employing four and two electrode setups. Results from electrical simulations, using CMOS circuits, fulfil the expected performance. This technique can be extended to wide frequency and load ranges, being an excellent option for impedance spectroscopy and EIT applications.

Studying the effects of mismatching and clock-feedthrough in switched-current filters using behavioral simulation

Mismatching and clock-feedthrough are sources of error in Switched-Current (SI) circuits producing DC offset, gain errors, and harmonic distortion, which cause deviations in SI filter responses in both the passband and the stopband. This paper develops formulas including these effects in the input-output description of filter building blocks to make possible not only a faster prediction of the filter performance levels but also to analyze tradeoffs at the early design stages. The block input-output descriptions have been derived taking into account the real physical realization of these blocks together with simple error models. Using these behavioral input-output descriptions, we have studied the extent of these effects in the performance of two different SI filter realizations of passive LC ladder structures: one using integrators to simulate the signal flow graph (SFG) of the ladder and another based on the use of wave active filter (WAF) structures. Monte Carlo simulations of a filter example are presented and analyzed.

Programmable low-voltage continuous-time filter for audio applications

The implementation of a continuous-time filter (CTF) useful for audio frequency applications is presented in this paper. The filter functions can be programmed and tuned with two independent control variables. The filter here proposed has been designed to work at 1.5 V of power supply and at a maximum of 0.5 /spl mu/A/OTA for the worst case current consumption. Electrical simulations of a Tow-Thomas biquad (TTB) show the possibility of obtaining low-pass and band-pass filter functions over the 10 Hz-40 kHz frequency range by changing a control current over four decades.

Switched-current wave analog filters

A novel approach to the realization of switched-current (SI) filters is presented. This approach relies on wave filter functions, which the authors have proved to be particularly suitable for switched-current implementations owing to the simplicity of SI realization for summation, scaling, and time delay operations. Filter design using this concept requires a limited library of modular building blocks (adaptors and delay elements). The total size, power consumption, and dynamic range of these building blocks can be made nearly independent of the filter function coefficient values, which enables the practical realization of wave SI filters over a wide range of bandwidths.<<ETX>>