A simple interface circuit for digital readout of lossy capacitive sensors

Direct Interface Circuits (DICs) allow straightforward digital reading from a range of sensors. Their architecture consists of a few passive components that help a digital processor (DP) perform a series of charge and discharge processes that provide time measurements to determine the sensor's resistive, capacitive, or inductive magnitudes. This article presents a new DIC that only requires two resistors for the digital readout of a group of sensors with a wide range of applications, namely lossy capacitive sensors. The DP does not need any analog element in its architecture, and the arithmetic operations involved are simple additions and multiplications. Apart from its simplicity, the new circuit brings significant improvements compared to other DICs proposed in the literature for the same type of sensors. Thus, the systematic errors in the capacitance estimates are only 0.30% for a wider range (100 pF − 95.92 nF), and the measurement time is 34% shorter.Funding for open access charge: Universidad de Málaga / CBU

Capacitive impedance measurement : dual-frequency approach.

The most widely used technique for measuring capacitive impedances (or complex electrical permittivity) is to apply a frequency signal to the sensor and measure the amplitude and phase of the output signal. The technique, although efficient, involves high-speed circuits for phase measurement, especially when the medium under test has high conductivity. This paper presents a sensor to measure complex electrical permittivity based on an alternative approach to amplitude and phase measurement: The application of two distinct frequencies using a current-to-voltage converter circuit based in a transimpedance amplifier, and an 8-bit microcontroller. Since there is no need for phase measurement and the applied frequency is lower compared to the standard method, the circuit presents less complexity and cost than the traditional technique. The main advance presented in this work is the use of mathematical modeling of the frequency response of the circuit to make it possible for measuring the dielectric constant using a lower frequency than the higher cut-off frequency of the system, even when the medium under test has high conductivity (tested up to 1220 ?S/cm). The proposed system caused a maximum error of 0.6% for the measurement of electrical conductivity and 2% for the relative dielectric constant, considering measurement ranges from 0 to 1220 ?S/cm and from 1 to 80, respectively

Design and implementation of a multi-modal sensor with on-chip security

With the advancement of technology, wearable devices for fitness tracking, patient monitoring, diagnosis, and disease prevention are finding ways to be woven into modern world reality. CMOS sensors are known to be compact, with low power consumption, making them an inseparable part of wireless medical applications and Internet of Things (IoT). Digital/semi-digital output, by the translation of transmitting data into the frequency domain, takes advantages of both the analog and digital world. However, one of the most critical measures of communication, security, is ignored and not considered for fabrication of an integrated chip. With the advancement of Moore\u27s law and the possibility of having a higher number of transistors and more complex circuits, the feasibility of having on-chip security measures is drawing more attention. One of the fundamental means of secure communication is real-time encryption. Encryption/ciphering occurs when we encode a signal or data, and prevents unauthorized parties from reading or understanding this information. Encryption is the process of transmitting sensitive data securely and with privacy. This measure of security is essential since in biomedical devices, the attacker/hacker can endanger users of IoT or wearable sensors (e.g. attacks at implanted biosensors can cause fatal harm to the user). This work develops 1) A low power and compact multi-modal sensor that can measure temperature and impedance with a quasi-digital output and 2) a low power on-chip signal cipher for real-time data transfer