A 5.2 GHz BFSK Receiver with On-Chip Antenna for Self-Powered RFID Tags and Medical Sensors Peter H. R. Popplewell, Victor Karam, Atif Shamim, John Rogers, and Calvin Plett Department of Electronics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada, K1S 5B6 Email: [email protected]Abstract— A completely inte grate d rec eive r desi gn suita ble for shor t range wirele ss appli catio ns is pre sente d. The circuit re pr ese nts one hal f of an SoC solution that mak es use of an on-chip antenna, and consumes 5.5 mW while receiving. A thin film ultr acapac ito r and a sol ar ce ll can be stacked on top ofthe chip to supply powe r to the radio ; yie ldi ng a completely integrat ed soluti on. The re ce iv er make s us e of a PLL to initially lock an RF VCO which is then allowed to be injection- lock ed to an incomi ng FM si gnal. An integrat ed ante nna prov ides adequate gain give n the short range radio ’s intended applications. The solution has a communication range of 1.75 m which can be increased at the expense of the bit-rate, increased power consumption in the receiver, or by using off-chip antennas. Index T erms - Injection Locked Oscillator, Integrated Antenna, Medical Sensor Readout, RFID, Self Powered Circuit. I. I NTRODUCTION The increasing adoption of RFID technologies by merchant corporations has fuelled much research into new, more power ef fici ent, siz e ef fici ent , and ult ima tel y mor e cost ef fici ent methods of radio communication. Applications for RFID tags include asset tracking and merchandize scanning where a low communication range is acceptable, but the cost of a particular solution directly dictates its success. A completely integrated and self -po wered SoC solution is small and cost effective, precluding the need for off-chip components such as passives, a battery, and an antenna which increase the system size and cost considerably. Surp risi ngly , the requ irements for an RF dev ice that can communicate the data from medical sensors can best be met by a device that is similar to an RFID tag, although the cost of the solution may be somewhat less important. In the treatment ofcancer patients by means of radiation, dosimeters are used to measure the dose of radiation experienced at different locations on the bod y . Cur ren t gen era ti on dos imeters are wir ed and can be bot h cumber some and det riment al to the tre atment process as the metal in the wire can block the radiation. As such, a short range radio for transmitting the output data from the sensor would be beneficial. Unfortunately, most wireless devices require batteries which typically contain elements ofhigh atomic mass number and would scatter radiation. Thus, having a self-powered solution with no battery is critical for this application. The rec ei ve r pre sented in this pap er rep res ent s one hal fof a completely integrated SoC solution which is fabricated in a 0.13 µm CMOS pro cess on a sta ndard, lo w res istiv- ity sil ico n sub str ate. The sol uti on mak es use of an on- chi p antenna, and can be powered by an ultracapacitor and solar cell which are fabricated on top of the chip. If the receiver is always on and searching for an incoming signal (allowing a transmitter to transmit efficiently), it consumes 5.5 mW ofpower . Con vers ely , if the recei ver is communic atin g with a transmitter that is always on then the receiver can be enabled only intermittently , dropping its average power consumption considerably. II. ON-C HI P ANTENNA DESIGN The use of an on-chip antenna allows for a very compact and cost effi cien t shor t range communic ation solu tion . Pre vious studies, [1], [2], have demonstrated successful use of inductive integrated antennas, but these antennas typically rely on high resistivity substrates. Here we use an inductive design which is fabricated on the same low resistance silicon substrate as the receiver’s circuits. The antenna is a rectangular single turn loop with an outer diameter of 825 µm by 675 µm, a metal width of 100 µm, a feeding gap of 100 µm, and having room for the active circuitry of the receiver to be placed in the center. A square loop is typically not the best choice for an on-chip inductor because it has sharp 90 o bends which increase the series resistance of the structure and therefore decrease the Q when compared to an octagonal geometry, yet the sharp bends in the square loop tend to increase the radiation resistance and consequently the gain of the antenna. The peak gain of the antenna was measured in an anechoic chamber to be -22 dBi. The measured input impedance of the antenna is Zin = 9.6 + j 58.0 Ω at 5.2 GHz, corresponding to an inductance of 1.8 nH with a Q of 6. III. RECEIVER DESIGN A. Overall Topology The receiver topology is based on a traditional 3 rd order PLL with a static divide ratio and a second order on-chip loop filter. Unique to the design is that the loop can be opened and closed to allow the VCO to be injection-locked by the incoming FM signal, while the divider, phase-frequency detector (PFD), and a second charge pump (CP) work together to demodulate the baseband signal. The basic topology is shown in Fig. 1. The rece i ver loop is init ia ll y cl os ed to se t the ce nt er fr equ enc y of the osci lla tor to 5.2 GHz, which is 64 ti mes the 81.25 MHz reference. The loop is then opened, and the oscillator is injection-locked to the incoming FM modulated signal being broadcast by the transmitter. The on-chip antenna 1-4244-0530-0/1-4244-0531-9/07/$20.00 2007 IEEE 2007 IEEE Radio Frequency Integrated Circuits Symposium 669 Authorized licensed use limited to: Michigan State University. Download ed on August 13,2010 at 21:29:24 UTC from IEEE Xplore. Restrictions apply.
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8/8/2019 A 5.2 GHz BFSK Receiver With on-Chip Antenna for Self-Powered RFID Tags and Medical Sensors
Peter H. R. Popplewell, Victor Karam, Atif Shamim, John Rogers, and Calvin Plett
Department of Electronics, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada, K1S 5B6Email: [email protected]
Abstract— A completely integrated receiver design suitablefor short range wireless applications is presented. The circuitrepresents one half of an SoC solution that makes use of anon-chip antenna, and consumes 5.5 mW while receiving. A thinfilm ultracapacitor and a solar cell can be stacked on top of the chip to supply power to the radio; yielding a completelyintegrated solution. The receiver makes use of a PLL toinitially lock an RF VCO which is then allowed to be injection-locked to an incoming FM signal. An integrated antennaprovides adequate gain given the short range radio’s intendedapplications. The solution has a communication range of 1.75 m
which can be increased at the expense of the bit-rate, increasedpower consumption in the receiver, or by using off-chip antennas.
direction of current flow through the loop filter depends on the
phase difference at the PFD inputs. If the transition happens
when the phase difference is 0 radians (or multiples of 2π),
indicated by point A (or point D), then there is no delay before
the CP begins reversing current. If, however, the transition
happens when the phase difference is slightly lower than 2π(point C), then the phase difference would begin decreasing,
passing through point B and onto point A where the CP finally
begins reversing the current. The worst case delay until the
current reverses occurs when the phase difference is slightly
lower than 2π at the time of a bit change, and the length of thedelay is inversely related to the beat frequency between F REF and F DIV . The period of this beat frequency is also the time
between cycle slips. Here we have used a reference frequency
of 81.25 MHz in the receiver, a bit-rate of only 1 kb/s, and a
∆f = 500 kHz. These settings were chosen such that the
maximum delay between a bit change (and corresponding
frequency change) at the input to the PFD in the receiver and
the resulting bit change at the output of the receiver’s CP is
≈ 12 % of the bit length. The beat period at the input of the
PFD is given by
T BEAT =1
∆f /N =
1
500 kHz/64= 128 µs (3)
Increasing ∆f would clearly decrease this wait time, but as (1)
suggests, this would require greater received power to keep the
receiving VCO injection-locked. Recalling (2) we see that P Rcan be increased with a decrease in range, or increased antenna
gain. Thus there are many trade-offs that can be made.
A microphotograph of the receiver is shown in Fig. 8.
V I . ULTRACAPACITORS AS A POWER SOURCE
Developments in the design and manufacturing of ultra-
capacitors have made it possible to meet the power supply
requirements of small integrated circuits without using a
can give up to 1 F/cm2 [6], [7], which is ample charge storageto power the circuits discussed in this paper. A complete
transceiver chip measuring 2 mm by 2 mm, of which the
integrated antenna and the circuitry occupy one quarter, allows
for three 1 mm by 1 mm ultracapacitors to be manufactured
on top of the remaining three quadrants of the chip without
covering up the antenna which would decrease its gain. This
results in a 30 mF capacitance which is capable of ≈ 4.2 µAhr
or ≈ 5 mA for three one second bursts between chargings.
Standard integrated capacitors are fabricated in the regular
Fig. 8. Receiver test chip microphotograph.
CMOS process below the ultracapacitors and serve as local
charge storage devices because they can deliver charge quicker
than the ultracapacitors which recharge them. Finally, a solar
cell can be manufactured on top of the ultracapacitors to trickle
charge the ultracapacitors using ambient light.
VII. CONCLUSION
A completely integrated 5.2 GHz BFSK receiver with an
on-chip antenna has been presented. If the receiver is always
on, the measured power consumption is 5.5 mW, enabling
the corresponding transmitter to power up only intermittently
and to save power. The communication range is 1.75 m when
one transceiver uses an on-chip antenna to communicate withanother transceiver using a patch antenna. The receiver uses a
PLL to pre-tune a VCO, and the loop is then opened to allow
the VCO to be injection-locked to the incoming FM signal.
The remaining loop components serve to demodulate the
signal. The architecture is well suited for use in inexpensive
RFID tags, and wireless radiation sensors where solutions with
no battery (that would scatter radiation) are desirable.
REFERENCES
[1] R. N. Simons, D. G. Hall and F. A. Miranda, “RF telemetry system for animplantable bio-MEMS sensor,” in IEEE MTT-S International MicrowaveSymposium Digest , June, 2004, pp. 1433–1436.
[2] R. N. Simons, D. G. Hall and F. A. Miranda, “Spiral chip implantable
radiator and printed loop external receptor for RF telemetry in bio-sensorsystems,” in Proceedings of the IEEE Radio and Wireless Conference,September, 2004, pp. 203–206.
[3] R. Adler, “A study of locking phenomena in oscillators,” Proceedings of the IRE , vol. 34, pp. 351–358, June, 1946.
[4] B. Razavi, “A study of injection locking in oscillators,” IEEE Journal of Solid State Circuits, vol. 39, no. 9, pp. 1415–1424, September, 2004.
[5] H. T. Friis, “A note on a simple transmission formula,” in Proceedingsof the IRE , May, 1946, pp. 254–256.
[6] A. Burke, “Ultracapacitors: why, how, and where is the technology,” Journal of Power Sources, vol. 91, pp. 37–50, 2000.
[7] R. Kotz and M. Carlen, “Principles and applications of electrochemicalcapacitors,” Electrochimica, vol. 45, pp. 2483–2498, 2000.
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