A 20 pJ/b (10 μW) Digital Receiver based on a new Modulation (SAS) for Retinal Prosthesis Application F. Goodarzy and E. Skafidas NICTA & Department of Electrical and Electronic Engineering University of Melbourne, Parkville, Victoria 3010 Melbourne, Australia f.goodarzy@pgrad.unimelb.edu.au Abstract— Low power consumption and small size transceivers are critical for biomedical instruments and devices specially those that are implanted. In this paper a novel modulation scheme called saturated analog signal (SAS) has been developed that can reduce the power consumption and area of the receiver. The new CMOS receiver is implemented in 65nm technology and operates in the MICS band (402-405 MHz), while consumes 10 μW from a 1 V power supply to deliver 500 Kb/s of data and occupies an area of just 0.6 mm 2 . This is equivalent to an energy consumption of 20 pJ/b and the design is capable of being fully integrated on single chip solutions for retinal prosthesis and embedded neural applications. Keywords- ultra low power; digital modulation; medical implant; fully integrate; SAS; low-noise amplifier I. INTRODUCTION Batteries have finite stored energy. Implanted biomedical devices require ultra-low power consumption to permit them to operate for extended periods and to also minimize adverse histological changes to tissue due to heating caused by the device. This is especially true for retinal prosthesis, where size of the device and the battery needs to be small in order to fit within the eye and changing the battery is not desirable as it requires surgery. Although energy harvesting techniques are desirable and usually implemented, these techniques are not very efficient, and low power receivers and design remain critical [1-5]. Wires penetrating through the human skin can act as a conduit for bacteria and antigens, increasing the risk of infections and disease. Wireless transmission is commonly used in biomedical devices as it eliminates the need for wires. Wireless transceivers can consume a large portion of the power budget, which necessitates the low power consumption design [2, 5, 6]. In order to build energy efficient devices architecture and modulation techniques need to be considered. Traditionally transceiver designs are based on modulating the digital data with a high frequency carrier that is then transmitted over the air. The received signal is then down-converted and demodulated at the receiver [6]. Usually these architectures require analog digital converters (ADC), for advance modulation techniques, or high precision phase locked loops (PLL), for simpler frequency shift keying (FSK) modulations. These components can consume significant power. Some of the commonly used modulation schemes and implementations are shown and compared in table I. There the high relative power consumption per bit transferred is evident, making them unsuitable for retinal prosthesis applications. In this paper a new digital receiver and novel modulation scheme is described. The receiver architecture and implementation are designed to reduce energy consumption and area. The new receiver operates in MICS band (402 MHz - 405 MHz with 10 equally spaced channels) and consumes less than 10 microwatts, from a 1 V supply, while occupying 0.6 mm 2 . The receiver is implemented on an IBM 65 nm. The receiver requires no external components making it an ideal candidate for retinal prosthesis applications. TABLE I. RECENT DIGITAL RECEIVER PUBLISHED WORKS Ref. Modulation Power Area Energy/bit Data Rate [7] GFSK 23.94 (mW) 4 (mm 2 ) 23.94 (nJ/b) 1000 (Kb/s) [8] AM 52 (μW) 0.1 (mm 2 ) 520 (pJ/b) 100 (Kb/s) [9] OOK 350 (μW) 0.5 (mm 2 ) 8.75 (nJ/b) 40 (Kb/s) [10] UWB 2.6 (mW) 17.2 (mm 2 ) 2.6 (nJ/b) 1000 (Kb/s) The paper is organized as follows: The second section describes the new architecture and modulation scheme while the electronic circuits are explained in the third section. The fourth section illustrates the results, and then the summary of the results are discussed in the fifth. Finally, some directions for future work are also presented. II. SATURATED ANALOG SIGNAL (SAS) MODULATION TECHNIQUE Digital design has long been utilized for low power consumption as well as small size designs [2, 5, 6, 11]. In digital design, an important consideration for radio frequency (RF) receiver systems, that significantly impacts all the aspects of the system, from data rates and efficiency to power consumption and even area, is the digital modulation technique used This work was sponsored by National Information and Communications Technology Australia (NICTA)