Glaucoma is an eye disease, which is the third leading cause of blindness globally [Thy95]. Like many other eye diseases, intraocular eye pressure is one of the most informative symptoms that can lead to successful treatment [Asr00]. Continuous wireless monitoring of intraocular eye pressure is highly desirable from a clinical perspective.
The Figure shows the self-powered implantable system and its location inside the eye. It
senses the pressure using its integrated sensors, stores them in its local
memory, and transmits all the data to the external readout system through a
wireless link on a ~weekly basis. The main two challenges are RF data
transmission without an external antenna and sleep mode power leakage
reduction. The latter can be addressed using novel circuit techniques to bring
down the sleep mode current [Seo08]. RF transmission through lossy body tissue
using an integrated circuit with its inherent low-quality factor requires
specific system design for these specific constraints of the system. Since body
tissue becomes unacceptably lossy above 2GHz [Poo07], the system should operate
below this maximum frequency. The first thing to be determined is the physics
of transmission. Capacitive coupling, antennas, and inductive coupling are the
three options. Capacitive coupling tends to be inefficient due to poor
dielectric properties of body tissues [Pet87]. Antennas are very difficult to miniaturize
unless high-GHz frequencies are used. However, our recent work [Atif07A-07E]
has shown that miniaturized on-chip antennas can be realized at low-GHz
frequencies and can be completely integrated with RF circuits for short-range
A number of practical design and characterization challenges have been highlighted in [Atif07E], which indicates that there is still much to be done for efficient realization of such antennas at feasible frequencies. Inductive coupling achieves its highest efficiency at low-GHz frequencies [Odr09]. At these ranges, integrated inductors show the highest quality factor and inductance possible. Our work [Atif07C and 07D] has furthered the inductive coupling concept by optimizing the resonant tank inductor of the VCO to act as an antenna as well. This enabled the system to communicate for a range of up to 2m, unlike the traditional inductive coupling ranges of few mms from non-optimized chip inductors. Moreover, the circuits and routing were realized inside the antenna geometry to optimize miniaturization, which is critical for this application
References:[Asr00] S. Asrani, R. Zeimer, J. Wilensky, D. Gieser, S. Vitale, K. Lindenmuth, “Large diurnal
fluctuations in intraocular pressure are an independent risk factor in patients with glaucoma,” J. of
Glaucoma., Vol. 9, No. 2, pp. 134-142, 2000.
[Atif07A] A. Shamim, M. Arsalan, L. Roy, K. N. Salama, “Co-design of On-chip Antennas and Circuits for a UNII Band Monolithic Transceiver ”, IEEE APS, Toronto, Canada, submitted to, Jan 2010.
[Atif07B] M. Arsalan, A. Shamim, L. Roy, M. Shams, “A Fully Differential Monolithic LNA with On-chip Antenna for a Short Range Wireless Receiver,” IEEE Microwave Wireless and Components Letter, vol. 19, no. 10, pp. 674-676, Oct 2009.
[Atif07C] A. Shamim, M. Arsalan, L. Roy, G.Tarr., “Wireless Dosimeter: System on Chip (SoC) versus System in Package (SiP) for Biomedical and Space Applications,” IEEE Transactions on Circuits & Systems II, vol.55, no.7, pp.643-647, Jul 2008.
[Atif07D] P. Popplewell, A. Shamim, et.al., “A 5.2-GHz, BFSK Transceiver using Injection-Locking and an On-Chip Antenna,” IEEE Journal of Solid State Circuits, vol.43, no.4, pp.981-990, Apr 2008.
[Atif07E] A. Shamim, K. N. Salama, E. Ezzeldin, S. Sedky, “On-Chip Antenna: Practical Design and Characterization Considerations”, ANTEM/AMEREM, Ottawa, Canada, submitted to, Jan 2010.
[Beh07] Nader Behdad, Dan Shi, Wonbin Hong, Kamal Sarabandi and Michael P. Flynn, “A 0.3mm2 Miniaturized X-Band On-Chip Slot Antenna in 0.13μm CMOS,” IEEE RFIC Sym., 2007.
[Lin08] Yu-Shiang Lin, Dennis Sylvester and David Blaauw, “Near-Field Communication using Phase-Locking and Pulse Signaling for Millimeter-Scale Systems,” Custom Intengrated Circuits Conference , 2008.
[Man08] S. Mandal R. Sarpeshkar, “Power-Efficient Impedance-Modulation Wireless Data Links for Biomedical Implants,” IEEE Transactions on Biomedical Circuits and Systems A, Vol. 2, No. 4, pp. 301-311, 2008.
[Odr09] S. O’Driscoll, ASY. Poon, TH. Meng, “A mm-Sized Implantable Power Receiver with Adaptive Link Compensation,” ISSCC 2009.
[Pet87] R. Pething, “Dielectric Properties of Body Tissue”, Clin. Phys. Physiol. Meas., Vol 8, pp 5-12, 1987
[Poo07] ASY.. Poon, S. O’Driscoll, and TH. Meng, “Optimal Operating Frequency in Wireless Power Transmission for Implantable Devices,” International Conference of the IEEE EMBS, Aug 2007.
[Seo08] Mingoo Seok, Scott Hanson, Yu-Shiang Lin, Zhiyoong Foo, Daeyeon Kim, Yoonmyung Lee, Nurrachman Liu, Dennis Sylvester, David Blaauw, “The Phoenix Processor: A 30pW Platform for Sensor Applications”, VLSI Sym., 2008
[Thy95] B. Thylefors, A. D. Négrel, R. Pararajasegaram, K. Y. Dadzie, “Global data on blindness,” Bull World Health Organ, Vol. 73, pp. 115-121, 1995.