All-Digital Galvanically-Coupled BCC Receiver Resilient to Frequency Misalignment

It is promising for wearable devices to go to a miniature size to alleviate the load of human body. One way to miniaturize the communication nodes on human body is to remove the bulky components such as antenna and crystal. Galvanically-coupled body channel communication (GC-BCC) has a great advantage over conventional wireless communications in reducing the size of wearable devices because it reuses the monitoring electrodes for signal transmission in place of antennas. To remove the crystal as well, the receiver must be immune to different types of frequency misalignments. This paper presents a GC-BCC receiver based on low power all-digital Gaussian frequency shift keying (GFSK) demodulation and clock-data recovery (CDR). A carrier tracking technique is proposed to detect and automatically adapt to the misalignment of carrier frequency. In addition, we also propose a circle-index CDR circuit to deal with the inaccuracy or drift of the clock frequency. The proposed circuit is implemented with 0.18 μm CMOS technology, and it operates at 200 kHz with a BFSK/GFSK modulation index of 1.0. Measured results show that the chip consumes 0.53 mA at a data rate of 100 kb/s. At a 10 cm body channel length, the GC-BCC receiver can tolerate a carrier misalignment up to ±12.5% and a clock error up to ±1.9%, while keeping the bit error rate (BER) below 0.1%.