Wireless digital system for information transmission between deep inside and outside the body using capacitive coupling: Measurement of communication characteristics under electromagnetic noise environment

Recently, many medical electronic devices have been developed that can be implanted deep inside the body. The devices are designed to transmit information collected from deep inside the body for receiving antennas outside the body. Therefore, we proposed a wireless digital information transmission system that transmits datum from deep inside the body to the outside using capacitive coupling. Inverting amplifier and low-pass filter (LPF) circuit in the receiving circuit are necessary for shaping distorted waveform before transferring it to the peripheral interface controller. To determine the optimum transmit filter constant (e.g., cutoff frequency and amplification rate), communication accuracy is measured using a prototype digital information transmission and receiving circuit and simulated human body. The optimum setting value of the cutoff frequency and the amplification rate were determined to be 17 kHz and 20 times, respectively. However, the communication accuracy reduced by approximately 40% when electromagnetic noise voltage (1.8 V, 50–100 kHz) was added to the receiving wave. To overcome this problem, a common-mode choke coil was inserted in front end of the receiving circuit. Thereby, communication accuracy was improved to approximately 98.7%.