Measured propagation loss for capacitive body-coupled communication (BCC) channel (1 MHz to 60 MHz) is limitedly available in the literature for distances longer than 50 cm. This is either because of experimental complexity to isolate the earth-ground or design complexity in realizing a reliable communication link to assess the performance limitations of capacitive BCC channel. Therefore, an alternate efficient full-wave electromagnetic (EM) simulation approach is presented to realistically analyze capacitive BCC, that is, the interaction of capacitive coupler, the human body, and the environment all together. The presented simulation approach is first evaluated for numerical/human body variation uncertainties and then validated with measurement results from literature, followed by the analysis of capacitive BCC channel for twenty different scenarios. The simulation results show that the vertical coupler configuration is less susceptible to physiological variations of underlying tissues compared to the horizontal coupler configuration. The propagation loss is less for arm positions when they are not touching the torso region irrespective of the communication distance. The propagation loss has also been explained for complex scenarios formed by the ground-plane and the material structures (metals or dielectrics) with the human body. The estimated propagation loss has been used to investigate the link-budget requirement for designing capacitive BCC system in CMOS sub-micron technologies.
This paper presents an analog receiver front-end design (AFE) for capacitive body-coupled digital baseband receiver. The most important theoretical aspects of human body electrical model in the perspective of capacitive body-coupled communication (BCC) have also been discussed and the constraints imposed by gain and input-referred noise on the receiver front-end are derived from digital communication theory. Three different AFE topologies have been designed in ST 40-nm CMOS technology node which is selected to enable easy integration in today's system-on-chip environments. Simulation results show that the best AFE topology consisting of a multi-stage AC-coupled preamplifier followed by a Schmitt trigger achieves 57.6 dB gain with an input referred noise PSD of 4.4 nV/ √ Hz at 6.8 mW.
Capacitive body coupled communication (BCC) channel has been modeled as a two-port complex path impedance matrix [Z] which varies as a function of ten different body positions over the frequency range of 1 MHz to 60 MHz. A systematic numerical simulation methodology has been used to estimate [Z] parameters. The estimated complex path impedance [Z] is a symmetric matrix showing BCC channel is a reciprocal network of passive components for given coupler configuration, body positions and frequency range. The estimated complex path impedance has been utilized to determine either input impedance Zin or output impedance Zout to conjugately match to Zs at transmitter or ZL at receiver, respectively for maximum power transfer. It has been found that the resistive matching below 1000 Ω and inductive matching between 0.5 μH to 5 μH on any side of the two ports can meet the conjugate matching requirements for maximum power transfer for the given body positions and frequency range.
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