Berkeley Wireless Research Center CMOS for Ultra Wideband and 60 GHz Communications Bob Brodersen Dept. of EECS Univ. of Calif. Berkeley IEEE SCV Communications Society Lecture

Berkeley Wireless Research Center FCC - Unlicensed Spectra ISM (1986) UPCS (1994) U-NII (1997) Millimeter Wave (1998) Ultra Wideband (2002) Link Control Modulation Total Transmit Power Power Spectral Density Antenna Gain Out of Band Emission More Sharing U-NIIISMUPCS ISMU-NII ISM Millimeter Wave Band Frequency (MHz) Ultra Wideband 3100 UWB

Berkeley Wireless Research Center 17 GHz of Unlicensed Bandwidth! l The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications l The GHz band can transmit up to.5 Watt with little else constrained l How can we use these new resources? UWB Mm Wave Band GHz Comm Vehicular Comm ID

Berkeley Wireless Research Center UWB and 60 GHz radios potentially extend the range of application of radio technology Carrier Frequency (GHz) Peak Data Rate (bps) 1 G 100 M 10 M 1 M 100 k 10 k HDTV motion picture, Pt.-to-Pt. links NTSC video; rapid file transfer MPEG video; PC file transfer Voice, Data Cellular 3G b 60 GHz Pt.-to-Pt. 60 GHz WLAN Bluetooth a ZigBee UWB

Berkeley Wireless Research Center Lets start with UWB… According to the FCC: “Ultrawideband radio systems typically employ pulse modulation where extremely narrow (short) bursts of RF energy are modulated and emitted to convey information. … the emission bandwidths … often exceed one gigahertz. In some cases “impulse” transmitters are employed where the pulses do not modulate a carrier.” -- Federal Communications Commission, ET Docket , First Report and Order, Feb. 2002

Berkeley Wireless Research Center Signaling Approach Sinusoidal, Narrowband Frequency Time Frequency Impulse, Ultra-Wideband

Berkeley Wireless Research Center FCC Emissions Limit for Indoor Systems Allowed emissions from a PC /MHz

Berkeley Wireless Research Center Exploring a new regime of Shannon’s curve -5db 5 db 10 db 15 db /2 1/4 1/8 1/16 Bits/sec/Hz E b /N 0 Bandwidth Limited Energy Limited UWB Usual goal

Berkeley Wireless Research Center First Major Application Area High Speed, Inexpensive Short Range Communications ( GHz) »FCC limit of -41dBm/Mhz at 10 feet severely limits range –Even using all 7.5 GHz of bandwidth the maximum power that can be transmitted is equivalent to having -2dBm (.6 mW) from an isotropic radiator (EIRP) –For short range communications this may be OK – e.g. line of sight from 10 feet for connecting a camcorder to a set-top box, “wireless Firewire” »Advantage is that it should be less expensive and lower power than a WLAN solution (since a > 100 Mbits/sec for short range)

Berkeley Wireless Research Center Sample waveforms

Berkeley Wireless Research Center High Rate UWB Communications l Basically pulsed rate data transmission – sort of optical fiber without the fiber… l Key design problem, as in wireline transmission, is synchronization l New design problems that do not exist in wireline »Interference from other RF sources »Multipath (delay spreads of 10’s of ns – at least) “1” “0” Biphase signalling

Berkeley Wireless Research Center High Data Rate UWB l To Minimize Interference »Break 7.5 GHz into smaller bands (> 500MHz) and transmit in clear bands »Filter out bands that are likely to have use (e.g. 5GHz wireless LAN bands) »Directional antennas l Multipath »Equalizers (as used in SERDES), but much longer delay compensation – digital? »Directional antennas

Berkeley Wireless Research Center Second Major Application Area Low Data Rate, Short Range Communications with Locationing (< 960 MHz) »Round trip time for pulse provides range information – multiple range estimates provides location »Used for asset tracking – a sophisticated RFID tag that provides location »Can be used to track people (children, firemen in buildings) »Sensor networks

Berkeley Wireless Research Center Location Determination Using UWB l UWB provides »Indoor measurements »Relative location »Insensitivity to multipath »Material penetration (0-1 GHz band) Time of flight Transmit short discrete pulses instead of modulating code onto carrier signal –Pulses last ~1-2 ns –Resolution of inches

Berkeley Wireless Research Center Material penetration (from Bob Scholtz)

Berkeley Wireless Research Center Avoiding Interfering With Other Users Co-existence through very low power transmission: Operate so that aggregate Interference from UWB Transmissions is “Undetectable” (or Has Minimal Impact) to Narrow-Band Receivers. What you can do with that for communications and locationing is a research question we are looking at… UWB Thermal (kT) Noise Floor

Berkeley Wireless Research Center Interference From other Users Everyone is an in-band interferer… why isn’t the UWB signal swamped? Energy in Pulse is Concentrated in Time If Equate Energies, Find Ratio of Amplitudes is: For a duty cycle of 1%, this implies a pulse amplitude 7x an equivalent power sinusoid. Ex: -77dBm (50  noise) per MHz over 1GHz is a 40mV pulse  Time Amplitude

Berkeley Wireless Research Center BWRC: UWB Transceiver Chip A single chip CMOS UWB transceiver at power levels of 1 mW/MHz for locationing and tracking applications »Flexible design for a wide range of data rates to investigate UWB transmission characteristics »For low rate applications, transmission at minimum possible signal level »Develop limits of locationing accuracy Being Implemented by PhD students Ian O ’ Donnell, Mike Chen, Stanley Wang

Berkeley Wireless Research Center Analog Circuits - Pulse Reception T samp T window Energy of Pulse is Contained in Small Time Window Only Need Limited Amount of Fast Sampling Have Rest of Time in Cycle to Process Samples Use Parallel Sampling Blocks Do Digital Correlation for Synchronization and Detections Minimum of Analog Blocks Run at Full Speed to Reduce Power Time

Berkeley Wireless Research Center Chip Architecture 1 GHz bandwidth (2 Gsample/sec A/D). LNA AGC A/D Transient Capture Parallel A/D’s Oscillator Crystal ECC Correlation, detection and synchronization Pulser Programmable Correlators PLL Detector Encoder Din Dout AGC Control Timing & Synchronization

Berkeley Wireless Research Center 1 Bit A/D is Adequate at Typical Interference Levels 1 GHz BW kTB Noise Floor 1-bit ADC Is Adequate (No AGC) NF Not Critical

Berkeley Wireless Research Center Specs for Baseband l Pulse Repetition Rate: 100MHz to 1 MHz l Maximum receivable Pulse ripple length (Nripple=Npulse+Nspread): < 64ns (128 samples) l Sampling rate: 2 GHz l PN spreading is ranging from 1 to 1024 chips

Berkeley Wireless Research Center RX: Digital Backend V[31:0] To Analog Data Out Acquisition: 128-Tap Matched Filter x 128 x 11 PN Phases Synchronization: Early/On-Time/Late PN Phases

Berkeley Wireless Research Center Receiving with Eb/No = -11db ChipsProb. of Miss lockProb. of False output dB e-31.3e dB PN sequence length requirement ( design max is 1024). (1) Acquisition mode, ~400 chips is enough for suppressing the acquisition error below 1e-3. Chips BER e-32e-5 (2) Data recovery mode, ~100 chips could achieve an uncoded bit error rate of 1e-3.

Berkeley Wireless Research Center MF/Correlator Area vs. Acquisition Time Area = 5.3 mm 2 Area ~ 55 mm 2

Berkeley Wireless Research Center Power Budget BlockDuty Cycle Power (Always On) Power (Per Period) Low Noise AmpT win /T rep 600  W60  W Variable Gain AmpT win /T rep 1.8mW 180  W Sample/Hold100% 1W1W1W1W A/D Converter100% 100  W Oscillator100% 100  W Sampling Clock Gen100% 400  W TX: Pulse Generation2ns/T rep 10mW 100  W Digital Logic100% 60  W Total Power Per Period: = 1001  W

Berkeley Wireless Research Center Status l Chip tape out by summer in.13 micron technology l Stay tuned at

Berkeley Wireless Research Center 17 GHz of Unlicensed Bandwidth! l The UWB bands have some use restrictions, but FCC requirements will allow a wide variety of new applications l The GHz band can transmit up to.5 Watt with little else constrained l How can we use these new resources? UWB Mm Wave Band GHz Comm Vehicular Comm ID

Berkeley Wireless Research Center 60 GHz Unlicensed Allocation (1998) Frequency GHz JapanEuropeU.S. Oxygen absorption band Prohibited Unlicensed Wireless LAN Test Radar Mobile ICBN Road Info. ISM UnlicensedPt.-to-Pt. Space and fixed & mobile apps Frequency GHz JapanEuropeU.S. Oxygen absorption band Prohibited Unlicensed Wireless LAN Test Radar Mobile ICBN Road Info. ISM UnlicensedPt.-to-Pt. Space and fixed & mobile apps.

Berkeley Wireless Research Center Exploiting the Unlicensed 60 GHz Band l 5 GHz of unlicensed and pretty much unregulated bandwidth is available l Requires »New approaches for design of CMOS integrated circuits (distributed, transmission line based) »New system architectures

Berkeley Wireless Research Center Application Scenarios

Berkeley Wireless Research Center Why Isn’t 60 GHz in Widespread Use? l Oxygen absorbs RF energy at 60 GHz l The technology to process signals at 60 GHz is very expensive l The signal radiated is attenuated by the small antenna size – i.e. the power transmitted at 60 Ghz from a quarter wave dipole is 20 dB less than at 5GHz.

Berkeley Wireless Research Center Oxygen attenuation The oxygen attenuation is about 15 dB/km, so for most of the applications this is not a significant component of loss For long range outdoor links, worst case rain conditions are actually a bigger issue

Berkeley Wireless Research Center The technology to process signals at 60 GHz is very expensive Yes, it has been expensive, but can we can do it in standard CMOS?

Berkeley Wireless Research Center CMOS modeling at microwave frequencies f max is the important number to look at Maximum unilateral gain Current gain

Berkeley Wireless Research Center Need to Model CMOS at Microwave Frequencies

Berkeley Wireless Research Center And we find that CMOS can do it! l If the device is designed correctly and enough current is used, with.13 micron f max can easily surpass 60 GHz l Phillips reported 150 GHz f max in.18 micron technology

Berkeley Wireless Research Center However, New Kinds of CMOS Circuits are Needed l Since the device dimensions are on the order of the wavelength, distributed structures can be used l Distributed techniques allow for extremely wideband linear-phase amplification approaching f max l This a new circuit style for CMOS

Berkeley Wireless Research Center 60 GHz Microwave CMOS Oscillators 0.13  standard CMOS process Use coplanar waveguide inductors and capacitors Calibration structures on same chip Siemanns presented circuit in.18 micron at ISSCC 2002

Berkeley Wireless Research Center Overcome the Small Antenna Problem by Using Multiple Antenna Beamformers l Wavelength is 5mm, so in a few square inches a large antenna array can be implemented l Antenna gain provides increased energy to receiver without extra noise and power l Multiple antenna implementation may actually reduce analog requirements a1a1 b1b1 a0a0 b0b0 a2a2 b2b2 PA Single Channel Transceiver

Berkeley Wireless Research Center New Design Strategies: Traditional Radio vs. Microwave CMOS  Operate device far away from f T to enhance gain(cell phones at 1-2 GHz, f T ~ 50 GHz)  Many off-chip front-end components (filters, switches, matching networks, antenna)  Clear separation between lumped circuits on- chip and limited consideration of distributed effects off-chip (package and board)  Operate close or beyond f T  Integrated front-end (antenna/filter)  Many structures electrically large & distributed

Berkeley Wireless Research Center 60 GHz Radio Frequency Planning Use 5 GHz as an IF frequency

Berkeley Wireless Research Center The open question… l What is the best way to use 5 GHz of bandwidth to implement a high datarate link? »Extremely inefficient modulation but at a very high rate? (say 2 GHz of bandwidth for 1 Gigabit/sec) – requires analog processing »Or use an efficient modulation, so lower bandwidth. e.g. OFDM – but needs digital processing and a fast A/D

Berkeley Wireless Research Center Conclusions l UWB radios provide a new way to utilize the spectrum and there is a wide variety of unique applications of this technology However, it takes a completely new kind of radio design… l At the present state of technology CMOS is able to exploit the unlicensed 60 GHz band However, it will take a new design and modeling methodology… There is 17 GHz of bandwidth ready to be used for those willing to try something new!