CMOS for Ultra Wideband and 60 GHz Communications

1
CMOS for Ultra Wideband and 60 GHz Communications
IEEE SCV Communications Society Lecture
Bob Brodersen Dept. of EECS Univ. of
Calif. Berkeley

• http//bwrc.eecs.berkeley.edu

2
FCC - Unlicensed Spectra
Ultra Wideband
UWB
U-NII
Millimeter
U-NII
ISM
UPCS
UPCS
ISM
U-NII
Wave Band
ISM
0
Frequency
902
928
960
1910
1930
2390
2400
2484
5150
5250
5350
5725
5825
5850
3100
59000
10600
64000
(MHz)
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?
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?
?
3
17 GHz of Unlicensed Bandwidth!
Mm Wave Band
UWB
UWB
UWB
10
20
30
40
50
60
0
GHz
Comm
Vehicular
Comm
ID

• The UWB bands have some use restrictions, but FCC
  requirements will allow a wide variety of new
  applications
• The 59-64 GHz band can transmit up to .5 Watt
  with little else constrained
• How can we use these new resources?

4
UWB and 60 GHz radios potentially extend the
range of application of radio technology
1 G
UWB
HDTV motion picture, Pt.-to-Pt. links
100 M
NTSC video rapid file transfer
10 M
Peak Data Rate (bps)
MPEG video PC file transfer
1 M
3G
Voice, Data
100 k
ZigBee
UWB
10 k
Carrier Frequency (GHz)
5
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 98-153, First Report and Order, Feb.
  2002

6
Signaling Approach
Sinusoidal, Narrowband
Frequency
Time
Impulse, Ultra-Wideband
Frequency
Time
7
FCC Emissions Limit for Indoor Systems
Allowed emissions from a PC
/MHz
8
Exploring a new regime of Shannons curve
Bits/sec/Hz
Usual goal
4
3
Energy Limited
2
Bandwidth Limited
1
-5db
Eb/N0
5 db
10 db
15 db
1/2
UWB
1/4
1/8
1/16
9
First Major Application Area

• High Speed, Inexpensive Short Range
  Communications (3.1-10.6 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 802.11a gt
  100 Mbits/sec for short range)

10
Sample waveforms
11
High Rate UWB Communications
1
0
Biphase signalling

• Basically pulsed rate data transmission sort of
  optical fiber without the fiber
• Key design problem, as in wireline transmission,
  is synchronization
• New design problems that do not exist in wireline
  
• Interference from other RF sources
• Multipath (delay spreads of 10s of ns at
  least)

12
High Data Rate UWB

• To Minimize Interference
• Break 7.5 GHz into smaller bands (gt 500MHz) and
  transmit in clear bands
• Filter out bands that are likely to have use
  (e.g. 5GHz wireless LAN bands)
• Directional antennas
• Multipath
• Equalizers (as used in SERDES), but much longer
  delay compensation digital?
• Directional antennas

13
Second Major Application Area

• Low Data Rate, Short Range Communications with
  Locationing (lt 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

14
Location Determination Using UWB

• Transmit short discrete pulses instead of
  modulating code onto carrier signal
• Pulses last 1-2 ns
• Resolution of inches

Time of flight

• UWB provides
• Indoor measurements
• Relative location
• Insensitivity to multipath
• Material penetration (0-1 GHz band)

15
Material penetration
(from Bob Scholtz)
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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
17
Interference From other Users
Everyone is an in-band interferer why isnt 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 (50W noise) per MHz over 1GHz is a
40mV pulse!
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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 ODonnell,
  Mike Chen, Stanley Wang

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Analog Circuits - Pulse Reception
Energy of Pulse is Contained in Small Time Window
Tsamp
Time
Twindow
Only Need Limited Amount of Fast Sampling
Use Parallel Sampling Blocks
Have Rest of Time in Cycle to Process Samples
Do Digital Correlation for Synchronization and
Detections
Minimum of Analog Blocks Run at Full Speed to
Reduce Power
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Chip Architecture
Transient
Parallel
Correlation, detection and
Capture
A/Ds
synchronization
A/D
Programmable
LNA
AGC
A/D
Correlators
.
A/D
.
.
.
.
.
.
Detector
ECC
Dout
.
.
AGC
Timing
Control
Synchronization
Encoder
Pulser
Oscillator
PLL
Crystal
Din

• 1 GHz bandwidth (2 Gsample/sec A/D)

21
1 Bit A/D is Adequate at Typical Interference
Levels

• 1 GHz BW
• RX _at_ kTB Noise Floor
• 1-bit ADC Is Adequate
• (No AGC)
• NF Not Critical

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Specs for Baseband

• Pulse Repetition Rate 100MHz to 1 MHz
• Maximum receivable Pulse ripple length
  (NrippleNpulseNspread) lt 64ns (128 samples)
• Sampling rate 2 GHz
• PN spreading is ranging from 1 to 1024 chips

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RX Digital Backend

• Acquisition 128-Tap Matched Filter x 128 x 11
  PN Phases
• Synchronization Early/On-Time/Late PN Phases

24
Receiving with Eb/No -11db
PN sequence length requirement ( design max is
1024). (1) Acquisition mode, 400 chips is
enough for suppressing the acquisition error
below 1e-3.
(2) Data recovery mode, 100 chips could achieve
an uncoded bit error rate of 1e-3.
 
25
MF/Correlator Area vs. Acquisition Time
Area 55 mm2
Area 5.3 mm2
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Power Budget
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Status

• Chip tape out by summer in .13 micron technology
• Stay tuned at http//bwrc.eecs.berkeley.edu/Resear
  ch/UWB/

28
17 GHz of Unlicensed Bandwidth!
Mm Wave Band
UWB
UWB
UWB
10
20
30
40
50
60
0
GHz
Comm
Vehicular
Comm
ID

• The UWB bands have some use restrictions, but FCC
  requirements will allow a wide variety of new
  applications
• The 59-64 GHz band can transmit up to .5 Watt
  with little else constrained
• How can we use these new resources?

29
60 GHz Unlicensed Allocation (1998)
Oxygen absorption band
Oxygen absorption band
Prohibited
Space and fixed mobile apps.
Prohibited
Space and fixed mobile apps.
Wireless LAN
Wireless LAN
Japan Europe U.S.
Japan Europe U.S.
Radar
Radar
Test
Test
Unlicensed Pt.-to-Pt.
Unlicensed Pt.-to-Pt.
Wireless LAN
Wireless LAN
Mobile ICBN
Mobile ICBN
Road Info.
Road Info.
Unlicensed
Unlicensed
ISM
ISM
56 57 58 59 60 61 62 63
64 65 66
56 57 58 59 60 61 62 63
64 65 66
Frequency GHz
Frequency GHz
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Exploiting the Unlicensed 60 GHz Band

• 5 GHz of unlicensed and pretty much unregulated
  bandwidth is available
• Requires
• New approaches for design of CMOS integrated
  circuits (distributed, transmission line based)
• New system architectures

31
Application Scenarios
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Why Isnt 60 GHz in Widespread Use?

• Oxygen absorbs RF energy at 60 GHz
• The technology to process signals at 60 GHz is
  very expensive
• 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.

33
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

34
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?

35
CMOS modeling at microwave frequencies
Maximum unilateral gain
Current gain

• fmax is the important number to look at

36
Need to Model CMOS at Microwave Frequencies
37
And we find that CMOS can do it!

• If the device is designed correctly and enough
  current is used, with .13 micron fmax can easily
  surpass 60 GHz
• Phillips reported 150 GHz fmax in .18 micron
  technology

38
However, New Kinds of CMOS Circuits are Needed

• Since the device dimensions are on the order of
  the wavelength, distributed structures can be
  used
• Distributed techniques allow for extremely
  wideband linear-phase amplification approaching
  fmax
• This a new circuit style for CMOS

39
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

40
Overcome the Small Antenna Problem by Using
Multiple Antenna Beamformers
Single Channel Transceiver

• Wavelength is 5mm, so in a few square inches a
  large antenna array can be implemented
• Antenna gain provides increased energy to
  receiver without extra noise and power
• Multiple antenna implementation may actually
  reduce analog requirements

41
New Design Strategies Traditional Radio vs.
Microwave CMOS

• Operate device far away from fT to enhance
  gain (cell phones at 1-2 GHz, fT 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 fT
• Integrated front-end (antenna/filter)
• Many structures electrically large distributed

42
60 GHz Radio Frequency Planning
Use 5 GHz as an IF frequency
43
The open question

• 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

44
Conclusions

• 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
• 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!