54 PERVASIVEcomputing Published by the IEEE CS and IEEE ComSoc ■ 1536-1268/06/$20.00 © 2006 IEEE

R F I D T E C H N O L O G Y

Self-Powered WirelessTemperature SensorsExploit RFID Technology

Emerging RFID technology lets usembed sensors into a very small chip,creating a wireless sensing device. So,we set out to develop such a single-chip versatile temperature sensor. We

also wanted to be able to transfer our design toan implantable temperature sensor for an animal

healthcare application withminimal structural modifica-tion (in compliance with theanimal identification standard,ISO 11785), so we chose arobust operating frequency—between 100 kHz to 150 kHz.In healthcare applications, thesensor generally requires asmaller temperature range (~35to 45oC) and higher accuracy

(~0.1oC) than in general applications.Here, we discuss the implementation of our sen-

sor. The fully integrated complementary metal-oxide semiconductor (CMOS) batteryless devicemeasures temperature and performs calibration tocompensate for the sensor’s inherent imperfections(see the “Related Work in Temperature Sensors”sidebar on page 56). An RF link using passiveRFID’s backscattering technique wirelessly trans-mits the data to a reading device while extractingpower from the same “airwave,” letting the deviceoperate anywhere and last almost forever. Theentire microchip, including the temperature sen-sor, consumes less than a few microamperes overa half a second, so the scanning device can capturedata from longer read distances. We hope it actsas a model for future low-power smart sensors.

A passive RFID solutionOur RFID chip has five parts: an analog front

end, a digital controller, a charge pump, an Eeprom, and the temperature sensor (see figure 1).

Analog front endAn external LC (inductor/capacitor) resonator

induces an AC voltage that generates DC volt-age through a fullwave rectifier and a systemclock through a clock extractor. An RF limiterguards the AC amplitude so that it doesn’texceed the breakdown operating voltage of thetransistors. A regulator then uses the generatedDC voltage to create a stable supply voltage forinternal circuits. When the chip enters the RFfield’s vicinity, the power-on-reset circuit givesa start-up signal to reset the digital controller toits initial state. To communicate with a readervia the RF link, the chip uses a load modulatorin a back-scattering manner to send data back.It uses a demodulator to detect an encoded com-mand signal sent from a reader.

Digital controllerThe controller comprises a state sequencer, bit-

rate generator, data encoder, and commanddecoder. The sequencer is a finite-state machinethat handles all main chip operations includingreading and programming memory, passing Eeprom data to the encoder, and timing the tem-perature sensor. The bit-rate generator gives ref-erence timing for the encoder to use in RF datatransmission. The data encoder appropriatelyencodes an NRZ (nonreturn to zero) data streamfrom the sequencer before sending it to the load

An embedded temperature sensor combined with passive RFID circuitryenables a single-chip solution for commercial smart sensors.

Karn Opasjumruskit, ThaweesakThanthipwan, Ohmmarin Sathusen,Pairote Sirinamarattana, PrachanartGadmanee, Eakkaphob Pootarapan,Naiyavud Wongkomet, ApinuntThanachayanont, and ManopThamsirianuntSilicon Craft Technology

modulator. The command decoder inter-prets demodulated data and tells thesequencer to jump to the state beinginstructed by the reader.

Charge pumpThe charge pump multiplies the recti-

fied voltage and converts it to the pro-gramming voltage (Vpp) used to modifydata in the Eeprom. The charge pumpalso incorporates a voltage regulator tocontrol the programming voltage at asuitable level during both erase and pro-gramming processes.

EepromThe Eeprom is nonvolatile; it stores

data even if the power supply is inter-rupted. Normally, it contains a set ofconfiguration data for the digital con-troller and a unique data ID to serve aprimary RFID function—identifying itsuniqueness. Our design includes anextended Eeprom section, where we canstore more useful data depending on thesoftware and applications. A small partof this extra memory stores process-dependent calibration parameters foreach temperature sensor unit.

Temperature sensorThe temperature sensor comprises

three major blocks—a digital-control cir-cuit, a proportional-to-absolute temper-ature (PTAT) current generator, and asigma-delta analog-to-digital converter(ADC). We designed the sensor to mea-sure industrial-grade temperatures from–40o to 120oC, with a maximum reso-lution of 8 bits.

The sigma-delta temperaturesensor

Our temperature sensor plays twomajor roles. First, it converts tempera-ture into a current using its PTAT cur-rent generator. Then, a data convertertransforms this current into digital infor-mation using the sigma-delta principle—so we call this the sigma-delta ADC.

The PTAT current generatorTo some extent, temperature governs

a semiconductor’s electrical properties.This principle led to the realization ofan electronic temperature sensor on asilicon chip. In 1965, Robert Widlar pro-posed a PTAT circuit, which produces a�vbe (the difference between two base-

emitter-junction voltages) that’s pro-portional to the temperature. The sin-gle-chip temperature sensor has evolvedever since.

Our temperature sensor circuitry isbased on Widlar’s concept. The PTATcurrent generator, directly representingthe temperature, delivers a PTAT currentand a reference current, keeping the lat-ter’s value constant over the temperaturerange of interest. The sigma-delta ADCthen processes both currents into the dig-ital data stream.

Digital controlThe digital controller handles the ana-

log-to-digital conversion after the com-mand decoder receives a temperature-reading command. The process involvesturning the PTAT and reference currentson and off, converting the bit-streamdata from the sigma-delta ADC, andsending the converted temperature valueback to the main digital circuit.

Sigma-delta ADCThe sigma-delta ADC consists of an

integrator and a clock comparator (seefigure 2a, which also shows the PTAT

JANUARY–MARCH 2006 PERVASIVEcomputing 55

(b)(a)

Temperature sensor

ElectricalErasable

ProgrammableROM

Temperaturesensor

Digitalcontrol

Eeprom

Chargepump Analog front end

Temperaturesensor

Datain

Dataout

Clock

Charge pump

Clock

Digital and memory

State sequencer

Command decoder

Data encoder

Bit-rate generator

Sigma deltaanalog-to-digital

converter

Digitalcontrol

Proportional-to-absolutetemperature current and

reference current generator

Analog front end

Regulator Demodulator

Rectifier and limiter Modulator

ClockPower-on-

reset circuit

External coiland capacitor

BitstreamIPTAT

IREF

950 μm

1,50

0 μm

Figure 1. The temperature sensor RFID chip: (a) a block diagram and (b) a photo showing each part’s actual location. The die areameasures approximately 1.4 mm2.

56 PERVASIVEcomputing www.computer.org/pervasive

R F I D T E C H N O L O G Y

current [IPTAT] and the reference current[IREF]). The converter’s operation tightlycorrelates with the clock signal. Figure2b displays the waveforms of signals,depicting the converter’s operation.

In each clock period, the integratorintegrates IPTAT to raise its output volt-age (VINT). At the end of each period, theclock comparator compares the integra-tor output (VINT) to the reference volt-age. The decision (bitstream) defines the“on” and “off” state of the switch S1 inthe next period. If the integrator outputis higher than the reference voltage, thedecision is “1” and S1 is closed, allow-ing IREF to flow. This current will reduceVINT until the comparator detects thatVINT is falling below the reference level.Then, the decision is “0” and the switch

S1 opens, so VINT increases again. Thisprocess repeats until the conversionphase ends. The total sum of the deci-sion result (that is, the number of timesthat “1” occurs in the decision result) isdirectly proportional to the PTAT cur-rent and proportional to the tempera-ture.

Our prototype sensors incorporated a16-bit ADC despite a requisite resolu-tion of only 8 bits. Given a fixed clockfrequency, the sigma-delta ADC needsmore time to convert bitstream data into16-bit resolution than into the 8-bitcounterpart. At a glance, the extendedtime seems like overkill, but it helps aver-age out several imperfections of the tem-perature sensor circuit, such as powersupply noise, thermal noise, and clock

jitter. In other words, noise and power-supply rejection requirements of the inte-grator and the comparator in the sigma-delta ADC are less stringent when usingthis overresolution technique. After theADC completes the conversion, the dig-ital control gets only the most significant8 bits from the overall 16 bits to repre-sent the averaged temperature data; itneglects the remaining 8 bits.

Acquiring the temperatureCommunication between the RFID

tag and reader is based on a simple pro-tocol. After initialization, a tag auto-matically sends its modulated serial IDrepeatedly until a companion reader orscanner interrupts the RF field with acommand. The tag then executes the

I n many applications, maintaining an appropriate temperature

level is essential. Rudimentary systems monitor temperatures

by employing copper wires as media, sending an analog or digital

signal between the sensors and host using data communication

protocols. This method, however, is inconvenient when accessibil-

ity is limited—such as in harsh environments or a living body. A

viable solution has been to use wireless communication between

temperature sensors and an RF interrogator or RFID reader based

on passive RFID technology. This technology eliminates an exter-

nal power supply from the RFID device, making it cheap and

maintenance free.

A complementary metal-oxide semiconductor temperature sen-

sor is a strong candidate for passive RFID because it consumes little

power, letting us easily integrate it into a passive RFID system.

Using a CMOS process, we can also incorporate signal-interfacing

circuitries (for example, a current-to-voltage converter, an analog-

to-digital converter, and so on) within a single chip to minimize the

system’s power consumption, cost, and size. This renders a very

small, self-contained temperature-sensing system that can commu-

nicate with other reading and logging devices via the RF signal. The

chip might require only an external LC (inductor/capacitor)

resonator.

Existing sensors such as TempSens1 and TELID (Telemetry ID,

http://microsensys.de/unten-sensor.htm) can measure tempera-

ture from –40 to 85oC at 1oC accuracy, operating at 13.56 MHz.

However, to function as temperature loggers—sensing and mem-

orizing temperature at specified intervals—they require external

power sources. In healthcare applications, the sensor generally

requires a smaller temperature range (~35 to 45oC) and higher

accuracy (~0.1oC) than in general applications. For example, a

read-only RFID sensor, Bio-Thermo,2 was designed for an animal

healthcare application. It comes in an implantable glass-tube form

and uses a 134.2 kHz carrier frequency and protocol that conforms

to an animal identification standard (ISO 11785). However, it

doesn’t provide a memory space to store user data.

In general RFID development, more has been focused on RFID

application-specific integrated circuits using ultra high frequency

bands (900 MHz and higher).3,4 However, such circuits are usually

designed for general temperature measurement, not for a specific

application. Also, although UHF RFID offers lower production costs

and longer read ranges, it suffers heavily from electromagnetic-field

absorption near metal or water or in humid environments.5

REFERENCES

1. “New Low-Cost Temperature Sensor,” RFID J., July 2002; www.rfidjournal.com/article/view/28/1/1.

2. S.J. Miller-Smith, “New Chip Can Read Your Pet’s Temperature,” Dar-win Veterinary Center, www.darwinvets.plus.com/topical/biothermo.htm.

3. F. Kocer, P.M. Walsh, and M.P. Flynn, “Wireless, Remotely PoweredTelemetry in 0.25 �m CMOS,” Radio Frequency Integrated CircuitsSymp., IEEE Press, 2004, pp. 339–342.

4. N. Cho et al., “A 8-�W, 0.3 mm2 RF-Powered Transponder with Temper-ature Sensor for Wireless Environmental Monitoring,” Proc. Int’l Symp.Circuits and Systems (ISCAS 2005), IEEE Press, 2005, pp. 4763–4766.

5. K. Finkenzeller, RFID Handbook, 2nd ed., John Wiley & Sons, 2003.

Related Work in Temperature Sensors

command and sends the requested data(see the “Usage Model” sidebar).

To probe for a target’s temperature, acompanion reader or scanner sends acommand to the RFID tag using a 100percent amplitude shift keying (ASK) oron-off-keying modulation (see figure 3).In the tag, the demodulator detects theRF envelope and converts this envelopesignal into digital data. The commanddecoder then decodes this data to deter-mine the command type. If it’s not a

“read temperature” command, the dig-ital circuit performs only a basic RFIDoperation, such as reading from or writ-ing to the tag’s memory. In this mode,

the temperature sensor is inactive or inthe “power down” mode.

If the sensor unit receives a “read tem-perature” command, it converts the tem-

JANUARY–MARCH 2006 PERVASIVEcomputing 57

W arehouses, cold-storage facilities, and produce distributors can have miniatur-

ized RFID tags attached inside styrofoam packaging, on a tray that holds the

food, or in a freezing chamber. To read the tag’s temperature, the RFID reader beams

the RF field to power up an RFID chip, simultaneously sending a command to activate

the microchip and wirelessly collecting the data from it. A single operation can read

both the manufacturer lot’s ID and the goods’ temperature—anytime, anywhere—to

ensure that each lot has been treated and maintained at the proper temperature.

Usage Model

(b)(a)

ClockClockClock

comparatorTime

Reference level

Integrator

Bitstream(to digital)

S1

BitstreamIPTAT

IREF

VINT

VINT

∫

Figure 2. The sigma-delta converter: (a) a block diagram and (b) signals at each converter node.

Tag's ID

Poweron reset

Eeprom read +modulator

Demodulate andcommand decode

Turn on temperaturesensor

Data encode and modulate(ASK Manchester, RF/64)

Measurement time ≈ 0.51s

1 off

off1 1 0 0 0 0 01 1

Frame data

Framesynchron-

izer

Framesynchron-

izer8-bit temperature

dataTemperature

sensor enableoperation code

Reader's RF field

Tag's RF field

Figure 3. The RFID reader generates the RF field that powers the RFID tag. After initialization, the reader sends a command toinvoke the temperature-sensing operation.

58 PERVASIVEcomputing www.computer.org/pervasive

R F I D T E C H N O L O G Y

perature into 16-bit output data, repre-senting a value between –60º and 135ºC.However, the actual sensing range is nar-rower owing to the sigma-delta ADC’sinherent inaccuracy. The temperaturesensor can precisely sense the tempera-ture from –40º to 120ºC.

During the temperature measurementand data conversion phase, the RF fieldisn’t modulated to avoid the power sup-ply fluctuation that could deterioratethe sigma-delta ADC’s accuracy. Themeasurement time lasts for 216 clockperiods or approximately 0.51 secondat 125kHz. After the conversion com-pletes, the temperature sensor turns off,and the converted 16-bit data is storedin a temporary register. Finally, themain digital circuit serially reads theeight most significant bits of stored dataand encodes them using ManchesterRF/64 (the bit rate is 1/64 of the RF fre-quency) encoding.

The modulator sends the encodedtemperature data through the RF linkwith ASK modulation (see figure 3). Amodulated data frame consists of aframe synchronizer and the encodeddata. The synchronizer pattern defines abeginning for each frame so that thereader can mark the data package’s start.The 8-bit temperature data repeats four

times in each frame, mimicking a 32-bitdata read from a block of the Eepromorganized in 32 bits � 32 blocks. Themodulated data frame repeats until thechip receives a new command. Throughpostprocessing firmware or a supportedsoftware application, users can read thetemperature measurement after theRFID reader decodes the received data.

Errors and calibrationAll temperature sensors more or less

inherit nonlinear properties, which cancause errors in the output data in termsof the offset and gain. We approximatedthese errors using the data from the fab-rication foundry, such as device model-ing and parameter matching. The circuitsimulation showed that the worst-caseoutput error was ±10oC; the main causeof error was transistor mismatches.

To ensure accuracy, designers shouldfirst calibrate each sensor using one ofseveral possible schemes. Analog cali-bration techniques usually relate toadjusting the primitive values of theselected circuit components or parame-ters—for example, bias current, resis-tance, capacitance, or even transistor size.The designer must routinely tune thesecombinations until he or she obtains thecorrect measurement. A more convenient

method is to eliminate the errors usingcalculations performed in the digitaldomain, or digital calibration.

For our initial study, we used a one-point digital calibration method becauseit’s simple yet well understood. Thismethod can cancel an offset error at thereference point used for calibration butcan’t eliminate a gain error and nonlin-earity error.1 So, reading the temperaturenear the calibration point produces lesserror than reading it from further awaypoints.

In our experiment, we left calibration-related duties to the reader unit; theRFID tag just kept calibration data in theEeprom. First, we put the RFID tag intoa well-controlled temperature chamberset to a fixed reference temperature—weused 40ºC as the calibrating point. Thereader obtains the temperature datafrom the tag and compares it to a refer-ence value to determine if an erroroccurred. Then, the reader writes the off-set correction data back to the RFIDtag’s Eeprom block allotted to keep thecalibration value. In practice, the readermust acquire from the RFID tag bothtemperature data and the calibrationvalue and simultaneously perform sub-traction to compensate the offset anddisplay the final temperature.

1

Operationcommand code Frame

synchronizerFrame

synchronizer8-bit data RF/64, Manchester(4 slots)

0

(a) (b)

Figure 4. The captured waveforms at a tag’s antenna: (a) The read temperature command interrupts normal data modulation, andthe temperature sensor is later turned on. (b) At the end of the sensor’s operation, a tag transmits framed data repeatedly.

JANUARY–MARCH 2006 PERVASIVEcomputing 59

Because we’re not limited to the sin-gle-point technique, we can extend thiscalibration method to compensate for ahigher order of errors. For example, ifwe use two-point calibration, which cancalibrate both the offset and the gainerrors, the two calibration parameterscan help determine the measured tem-perature. The reader or scanner canwrite both calibration attributes intoeach microchip’s memory. When per-forming a measurement, the reader thencomputes the measured result on thebasis of these two-point calibrated val-ues, for potentially better accuracy.

Generally, when sensors are in servicefor a long time, reading accuracy deteri-orates owing to errors introduced by thedevice’s inherent long-term drift. Userscan recalibrate our temperature sensorsanytime by rewriting the new calibrationvalues into the Eeprom via the RF link.

ExperimentsUsing chip characterization data, we

determined that RFID tags consume, onaverage, 2�A for read operations and10�A to measure temperatures. Wedesigned a companion handheld readerwith a 60 mm-diameter antenna coil (60turns of winding) to perform a tempera-ture-reading experiment. Figure 4 showswaveforms at the tag’s antenna when itreceives a “read temperature” command.

The average AC current through thereader’s antenna is approximately 100mA. The reader can communicate witha ring-shaped tag (with a 365-turn, 27mm-diameter antenna coil inside) at amaximum distance of 10 cm when bothantenna planes are perfectly parallel. We

can refer to the field strength required atthis distance to activate the tags as theleast-minimum field strength, or approx-imately 2.4 A/m2. An RFID system readrange depends on many factors, such asantenna area (for both the reader andtag), the antenna’s quality factor, or thenumber of antenna turns. When weexperimented with a larger square readerantenna (80 � 100 mm), the read rangeimproved considerably—to a distancegreater than 25 cm.

To evaluate chip performance, we putour RFID tag in a clear plastic packageand dipped it in a beaker of water(which helps stabilize the temperature).We compared our tag’s temperaturedata to a temperature read from a com-mercially available digital mulimeterwith an optional thermocouple (0.1ºCresolution). We placed the sealed ther-mocouple next to our RFID tag in tem-perature-controlled water. Figure 5

shows the measurement results. Beforecalibration, chip-to-chip errors were aswide as 100C. After a single calibrationat 40ºC, the error became less than2.5ºC in a measurement range between0 to 100ºC. This indicates that we needto perform two-point calibration forbetter accuracy.

Figure 6 shows an RFID reader read-ing the temperature data from an RFIDtag in an ice cube. This shows that ourmicrochip can operate and communicatein ice- or water-filled packages or foodcontainers, in cold storage, or inside ananimal’s body, where RF field absorp-tion is highly likely.

We haven’t yet tested oursensor’s full temperaturerange but hope to do so inthe near future. We intend

to perform a detailed chip characteriza-

Themicrochip

The RFID Tag

The reader

(a) (b)

Figure 6. Our microchip can operate inice-filled packages: (a) our chip in an icecube and (b) the reader measuring thetemperature at the freezing point.

0

(a)0

121086420

–2–4

10 20 30 40 50 60 70 80 90 100

Erro

r bef

ore

calib

ratio

n (°

C)(b)

2.52.01.51.00.5

0–0.5–1.0–1.5–2.0

10 20 30

Temperature (°C)

Microchip 1 Microchip 2 Microchip 3 Microchip 4

40 50 60 70 80 90 100

Erro

r afte

r cal

ibra

tion

(°C)

Temperature (°C)

Figure 5. Error plots for four prototypemicrochips (a) before calibration and (b)after calibration, with one-point digitalcalibration at 40�C.

tion with a temperature chamber, andwe anticipate accuracy better than 1ºCusing two-point calibration. However,to obtain an accuracy of 0.1ºC, we’llneed to pay more attention to the ana-log portion of the overall temperaturesensor unit.

We plan to improve microchip cali-

bration by transferring all calibrationsteps, which the reader currently per-forms externally, to the on-chip digitalcontrol circuit. Figure 7 demonstrates ourproposed autocalibration process. First,the microchip receives a start commandand a reference temperature from thereader. Then, it compares the measured

temperature with the reference value, cal-culates errors, and programs them intothe Eeprom. During the read-tempera-ture command, the digital control circuitloads the calibration data from the Eep-rom and performs the arithmetic com-putation to compensate for sensor inac-curacies before modulating the correctedtemperature back to the reader. So, thereader doesn’t need to perform data post-processing, which incurs delays associ-ated with the normal read/write dataexchange through the RF field.

Furthermore, embedding the RFIDwith other sensory circuitries—such as ahumidity sensor, pressure gauge, or evenchemical detector—will enable the dawnof new age in measurement. Togetherwith an anticollision protocol (not sup-ported in our current prototype), theseubiquitous sensors will use the powerprovided by a single RFID reader to con-vert many physical quantities from mul-tiple tags into figures that many controland monitoring applications can under-stand. This emerging technology, dubbedsensor RFIDs, will supersede traditionalsensor-wired equipment and let us mea-sure environment parameters morefreely�wirelessly and without physicalor visual contact.

REFERENCES1. G.v.d. Horn and J.L. Huijsing, An Inte-

grated Smart Sensor: Design and Calibra-tion, Kluwer Academic, 1998

2. K. Finkenzeller, RFID Handbook, 2nd ed.,John Wiley & Sons, 2003.

For more information on this or any other comput-ing topic, please visit our Digital Library at www.computer.org/publications/dlib.

60 PERVASIVEcomputing www.computer.org/pervasive

R F I D T E C H N O L O G Y

Receive starttemperature command

Calibration/temperature reading

Receive a command

Receive starttemperature command

Calibration Temperature reading

Receive exacttemperature

Chips measuretemperature

Chips measuretemperature

Load error fromEeprom

Compare with exacttemperature (from reader)

Calculate exacttemperature

Write error to EepromSend exact temperature

to reader

ID modulation

Power on reset

End

Figure 7. The next-generation microchipwill perform the calibration algorithmitself. The calibration reader will sendonly the reference value to a tag, and thetag will do the rest.

JANUARY–MARCH 2006 PERVASIVEcomputing 61

the AUTHORS

Karn Opasjumruskit is amember of the researchstaff at Silicon Craft Technol-ogy. His research interestsinclude high-frequency andultra high-frequency RFIDtags and biosensors. He re-ceived his MEng in electrical

engineering from Chulalongkorn University.Contact him at 196/103 Mu 1 Soi Kosumruam-jai, Chaengwattana Rd., Donmueang, Bangkok10210, Thailand; karn@sic.co.th.

Thaweesak Thanthipwanis a member of the researchstaff at Silicon Craft Technol-ogy. His research interestsinclude low-frequency RFIDtags, microelectromechani-cal sensors, and sigma-deltaanalog-to-digital conversion.

He received his MEng in electrical engineeringfrom Chulalongkorn University; Contact him atthaweesak@sic.co.th.

Ohmmarin Sathusen is amember of the research staffat Silicon Craft Technology.His research focuses on sili-con-based sensors. He re-ceived his MEng in electricalengineering from Chula-longkorn University. Contact

him at ohmmarin@sic.co.th.

Pairote Sirinamarattanais a member of the researchstaff at Silicon Craft Tech-nology. His research inter-ests include video filters,sensor-processing units,and long-range RFID read-ers. He received his MEng in

electrical engineering from Chulalongkorn Uni-versity. Contact him at pairote@sic.co.th.

Prachanart Gadmanee isa member of the researchstaff at Silicon Craft Tech-nology. His research inter-ests include computer-aided-design-generatedlayout techniques, routingoptimization, and physical-

device characterization. He received his MEngin electrical engineering from Kasetsart Univer-sity. Contact him at prachanart@sic.co.th.

Eakkaphob Pootarapan isa member of the researchstaff at Silicon Craft Tech-nology. His research inter-ests include anticollisionalgorithms, digital-circuitoptimization, and encryp-tion techniques. He received

his BEng in electrical engineering from KingMongkut’s Institute of Technology Ladkrabang.Contact him at eakkaphob@sic.co.th.

Naiyavud Wongkomet is aproject director at SiliconCraft Technology. His re-search interests include elec-trostatic micropositioners,pipelined and sigma-deltaanalog-to-digital conversion,and antialiasing filters. He

received his PhD in integrated-circuit designfrom the University of California, Berkeley. Con-tact him at naiyavud@sic.co.th.

Apinunt Thanachayanontis a project director at SiliconCraft Technology. His researchinterests include complemen-tary metal-oxide semiconduc-tor RF bandpass filters, active-inductor circuits, translinearphase-locked loops and direct

digital synthesizers. He received his PhD in elec-trical and electronics engineering from theImperial College of Science, Technology andMedicine. Contact him at apinunt@sic.co.th.

Manop Thamsirianunt is adirector of product develop-ment at Silicon Craft Technol-ogy. His research interestsinclude wireline transceivers,phase-locked loops and volt-age-controlled oscillator andgigabit I/O. He received his

MEng in electrical engineering from Carleton Uni-versity. Contact him at manop@sic.co.th.