To follow up the restenosis in arteries stented during an angioplasty is an important current clinical problem. A new approach to monitor the growth of neointimal tissue inside the stent is proposed on the basis of electrical impedance spectroscopy (EIS) sensors and the oscillation-based test (OBT) circuit technique. A mathematical model was developed to analytically describe the histological composition of the neointima, employing its conductivity and permittivity data. The bioimpedance model was validated against a finite element analysis (FEA) using COMSOL Multiphysics software. A satisfactory correlation between the analytical model and FEA simulation was achieved in most cases, detecting some deviations introduced by the thin “double layer” that separates the neointima and the blood. It is hereby shown how to apply conformal transformations to obtain bioimpedance electrical models for stack-layered tissues over coplanar electrodes. Particularly, this can be applied to characterize the neointima in real-time. This technique is either suitable as a main mechanism for restenosis follow-up or it can be combined with proposed intelligent stents for blood pressure measurements to auto-calibrate the sensibility loss caused by the adherence of the tissue on the micro-electro-mechanical sensors (MEMSs).

This paper describes the evaluation of an oscillation-based approach specially thought for testing a low-power analog system that monitors an implantable biomedical device (intelligent stent). Fault simulation analysis has been performed on the basic blocks of the CUT, and oscillation parameters (frequency and amplitude) have been measured at the output of the last system block, an oscillator. Taking advantage of fault reflection from the rest of the blocks, the proposed testing method will avoid the need of adding extra circuitry to convert the different partitions of the CUT into oscillators, reducing circuit complexity and possible performance degradation. The results obtained show that a good fault coverage figure for catastrophic faults can be achieved.

An analog circuit forming part of an intelligent-stent system is proposed with the aim of converting pressure-related capacitance measurements into a FM signal (around 800 MHz) to be analyzed outside of the patient body. Based on the information obtained from this signal, a reliable restenosis monitoring can be carried out. An energy-saver block controls the oscillator and reduces the power consumption of the whole circuit from 547.1 μW in active state to 152.1 μW in idle state, in order to comply with energy restriction imposed by inductive coupling powering. The design is implemented in TSMC 0.18 μm CMOS technology.

This paper discusses a compressed-ROM 600MSPS dual-branch Direct Digital Synthesizer (DDS) providing sinewaves of 80dBc. It supports positive chirp slopes up to 40MHz/s with ~1.3kHz/s resolution. The amplitude can be shaped with Gaussian envelopes of FWHM 2µs–2ms and SLRR >85dB. Any other envelope can be generated by pulsing programmable-step increment/decrements through dedicated LVDS inputs. The ASIC delivers two 14-bit 300MSPS LVDS buses to interface with an external DAC using a ping-pong arrangement. The output data is synchronous to a DDR clock coming from the DAC, which can pass through a programmable delay-line to adjust the loop phase. A demonstrator chip was manufactured in 0.18µm CMOS process.

Implantable biomedical devices generally comprise MEMS-type sensors used to acquire physiological signals, as well as CMOS electronics to perform powering, signal conditioning and data transmission. This work targets the modelling of capacitive MEMS pressure sensors, together with the development of a design tool, which provides an initial sensor approach based on a set of user-specified input constraints. This tool generates two output folders with all the files required to perform an electromechanical analysis of the sensor, as well as to create a layout cell ready to be included in a larger design. Several sensors, with and without injected defects, have been fabricated in PolyMUMPs technology, in order to compare their responses to the ones obtained from the sensor design program.