Power-Efficient Impedance-Modulation Wireless Data Links for Biomedical Implants

Abstract

We analyze the performance of wireless data telemetry links for implanted biomedical systems. An experimental realization of a bidirectional half-duplex link that uses near-field inductive coupling between the implanted system and an external transceiver is described. Our system minimizes power consumption in the implanted system by using impedance modulation to transmit high-bandwidth information in the uplink direction, i.e., from the implanted to the external system. We measured a data rate of 2.8 Mbps at a bit error rate (BER) of <10(-6) (we could not measure error rates below 10(-6) ) and a data rate of 4.0 Mbps at a BER of 10(-3). Experimental results also demonstrate data transfer rates up to 300 kbps in the opposite, i.e., downlink direction. We also perform a theoretical analysis of the bit error rate performance. An important effect regarding the asymmetry of rising and falling edges that is inherent to impedance modulation is predicted by theory and confirmed by experiment. The link dissipates 2.5 mW in the external system and only 100 muW in the implanted system, making it among the most power-efficient inductive data links reported. Our link is compatible with FCC regulations on radiated emissions.

A Low-Power 32-Channel Digitally Programmable Neural Recording Integrated Circuit

“…All 32 amplifiers were configured with a spike-recording setting, with a gain of 60 dB, and a nominal front-end amplifier's bias current of 2.08 A. The power consumption of the 32-channel neural-recording TABLE V COMPARISON TO OTHER STATE-OF-THE-ART NEURAL RECORDING SYSTEMS chip for this experiment was 325 W. The power consumption of the internal unit of the impedance-modulation wireless data telemetry system was approximately 100 W, while the receiver unit's power consumption was approximately 3.0 mW for a 2.5 Mbps data rate [26]. Fig.…”

“…Our wireless neural-recording system consisted of a recording unit and a receiver unit. For wireless data transmission, we used the impedance-modulation data-telemetry system described in [26], which transmits data using an inductive-coupling scheme at a carrier frequency of 25 MHz. The 32-channel neural recording chip (in a QFP80 package) was integrated onto the recording unit on a custom PCB with dimensions of 8.5 cm 9.5 cm.…”

Power Amplifiers for Electronic Bio-Implants

“…There are several methods used to generate data carrier frequencies for implantable devices. Many systems involve the generation of data carrier signals on the external side of the system, leaving only the data recovery, modulation and transmission to the implantable circuitry (Mandal andSarpeshkar, 2008, Zhou et al, 2006). Ziaie et al presented a dual band implantable neuromuscular stimulator, the 2MHz data clock of which is recovered from 2MHz power supply (Ziaie et al, 1997), while Wise et al operated at 4MHz (Wise et al, 2004) as did Sauer et al's (Sauer et al, 2005).…”

“…Since it usually involves switching one part of the load on and off, the frequency of transmission is varied with each bit, making this scheme very similar to FSK. A number of medical devices make use of this scheme , Mandal and Sarpeshkar, 2008, Wang et al, 2005. Shifting a carrier frequency's phase occurs to achieve PSK.…”

A Shared Channel Design for the Power and Signal Transfers of Electric-field Coupled Power Transfer Systems

“…A signal channel whose frequency is closed to the power transfer frequency using two auxiliary coils has been prsented [16], [17]. A power and signal transfer method was proposed for mini equipment with an operating frequency greater than 1MHz and a 12mW transfer power [18], [19]. Additionally, a high-speed and accurate controller is used to modulate a signal for avoiding noise due to the current switching in an inverter, which aids in the simultaneous transfer of power and signals [20].…”