A 2.75mW wideband correlation-based transceiver for body-coupled communication

Abstract

Electronic devices in contact or in close proximity to the human body can use its conductive properties to establish body coupled communication (BCC) between each other. This human centric communication paradigm can be used for wireless body-area networks to reduce the impact of interference on/from RF systems, to avoid the fading effect that the body has on radio systems and to enable power efficient, high data-rate wireless links.BCC, without skin contact, can be realized via two electrode RX/TX devices capacitively coupled to the human body (Fig. 11.5.1); TX generates a variable electric field while RX senses the variable potential of the body with respect to the environment. The signal transfer along the body has high-pass characteristics with a corner frequency determined by the input impedance of the RX device. A signal attenuation of less than 70dB has been measured between devices placed at various positions on the human body (Fig. 11.5.1,[1,2]). Concerning interference, the body-channel is especially affected by interference below 1MHz while for higher frequencies the observed interference level is below -75dBm (Fig. 11.5.1). However, in the FM band the body starts acting as an antenna and this level may rise to -30dBm [4]. The BCC implementation in [3] used wideband digital TX signals and was very low-power but a cognitive FSK approach [4] was preferred to it due to the afore-mentioned high levels of FM interference above 50MHz.Here, as in [3], we couple a wideband digital signal to the human body but instead of a 50Ω input resistance for the RX we use high resistance so that the RX can effectively sense the 1 to 30MHz band, thus avoiding the FM band. Moreover, for further interference suppression, we designed a novel correlation-based RX that attenuates any signal that is poorly correlated to the expected one.The transceiver architecture is shown in Fig. 11.5.2. Figure 11.5.3 shows functional and measured waveforms. The TX performs Manchester encoding on the digital data-stream so that at least one voltage transition occurs per bit. The RX input stage is a clamped low-noise amplifier (LNA). For each bit-period the electrodes are shorted for a short time (20% duty cycle) and the DC level of the amplifier is restored. For the rest of the period the input resistance is very high and the input signal is amplified. This approach suppresses low frequency interference while the fast voltage transitions from the TX are amplified when they occur during the RX period. The bandwidth of the LNA is limited to 30MHz so that high frequency interference is attenuated. The interference is further suppressed by correlating the output of the LNA with a one-bit data template with transitions in the middle of the RX period (Fig. 11.5.3). For this purpose, the received signal is multiplied by -1 in the first half of the period and by +1 in the second half and the result integrated. The computed data correlation is maximal for digital-like transitions occurring in the middle of the RX period, while any other signal is str...

A Novel Intrabody Communication Transceiver for Biomedical Applications

“…While a distinctive feature of IBC is to design efficient hardware transceivers, the hardware complexity of units including size, power, and cost must be minimized [66].…”

Variation-Aware System Design Simulation Methodology for Capacitive BCC Transceivers

“…That is why efforts have been made to make low noise receivers for capacitive BCC channel, e.g., [22][23][24][25]. But it is not clearly known that for how many body positions and for which coupler configuration/sizes, communication distances, environmental conditions, etc., the results have been reported, which are important limiting factors in determining the overall propagation loss.…”

“…2.1. It is however not known, whether the earth grounded lab instruments were connected during the actual testing of BCC transceivers designed in [22], [23], [24], [25]. The propagation loss for capacitive BCC channel not only increases with communication distance between transmitting and receiving electrodes but it is also affected by specific body positions and the coupler configurations (i.e.…”

“…The low noise front end amplifier constitutes one of the most important building blocks in most of the capacitive BCC communication architectures which have been demonstrated so far in CMOS technologies, e.g., [22], [56], [57], [23], [24], [78], [79], [25], [80], [81] and [82]. It is important to define the right specifications at the system level when designing low noise front end amplifier for capacitive BCC channel because its design influences the entire receiver chain.…”

A 0.24nJ/b wireless body-area-network transceiver with scalable double-FSK modulation

“…There are 3 PHY schemes discussed in the IEEE 802.15.6 Task Group for WBAN standardization [1]: ultra-wide-band (UWB) PHY, narrow-band (NB) PHY, and body channel communication (BCC) PHY. The BCC, which uses the human body as a communication channel based on the near-field coupling mechanism, has advantages over UWB and NB in energy efficiency because it provides low pathloss without the body shadowing effect in low-frequency bands below 150MHz [2][3][4]. However, the previous body channel transceivers (BCTs) were not optimized for WBAN because only phenomenological circuit models were used for the body channel analysis [5] and were unable to satisfy requirements such as energy efficiency, scalability of QoS, interference mitigation, and coexistence at once.…”