antenna array alalusi

1、a 60ghz antenna array front-end in cmos for gigabit-per-second indoor mobile applicationsbwrc lunch seminarsayf h. alalusimarch 21, 2003cmos for consumer 60ghz potential for very high integrationgetting any gain out of cmos circuits will be difficult. ft 60ghz, not ft 60 ghzinteresting design proble

2、m.year1 g757779818385878991933u2u1.5u1u0.8u0.6u9597990.5u0.35u0.25u3 g10 g30 g100 g0.18u010.13u03(hz)ft (speed)lmindetailed link budget calcsdbnpnenfgbpsrb26100 = extra eirp needed = antenna gain and/or xmit. powershift 802.11a to 60ghz, 1gbps: pt=14dbm, nf=5db, 64 qamthese optimistic numbers give:

3、= 39 db !more realistic: pt=10dbm, nf=10db, bpsk: = 26 db systemxmit. pow.(pt)bit rate (rb)modulationnf (typ)path loss (pl)802.11a(5ghz)60 mm+14 dbm54 mbps64 qameb/n0=19db5 db66 db 10m1gbps wlan(60 ghz)5 mm+10 dbm1000 mbpsbpskeb/n0=7db10 db88 db 10m224 rggpprttre.g., for 802.11a,at 10m need = -6db!p

4、resentation outline antenna array advantages and tradeoffs architecture exploration canonical array formulation antenna array: design space exploration,effects on standard rf blocks antenna weighting circuitsadaptive beamforming for high gain gain directivity beamwidth-1 antenna needs high gain in a

5、n arbitrary direction adaptive beamformer can adapt to achieve high gain in any direction, regardless of physical orientation added bonus: attenuate interfering signals from other directions requires digital control and computation for adaptation of weights.a0a1a2an-1x(t)n = number of antennasbeam p

6、attern controlled by antenna weights.adaptive beamforming advantage #1: directivity in any directiondirect all energy along chosen path only.preferentially receive energy from chosen path only.high gain in any direction, controlled electronically.can change nearly allchannel parameters.adaptive beam

7、forming advantage #2 subdivisionuse circuit level parallelism to achieve our performance goals. use n power amplifiers to get total transmit power use n low noise amplifiers to receive n copies of the signalthis is critical because of limited performance of cmos circuits due to: low voltage swing, o

8、peration close to ft, etc. limited performance at 60 ghzrelaxed spec.s for individual componentsarchitecture explorationdigitally weighted architectureoptimal capacity for all channel conditions: n data streamsvery high hardware complexity: n full transceiversvery high system power consumptions1(t)r

9、1(t)s2(t)s3(t)r2(t)r3(t)overlay of n independent beamsrf phase shifter architecture1 data stream, rf phase shifters only, digitally controlledachieves high antenna gain in an arbitrary directionlow hardware complexity: n rf phase shifterslow system power consumptions(t)a0a0a1a2r(t)a1a2canonical arra

10、y formulationantenna array patterns et = f(,i0) (a0+a1ejkdcos+a2ej2kdcos + ) = ef*af element factor (ef) is the field of a lone element. only array factor (af) can be controlled electronically, by changing the magnitude and phase of ai. for a beam to look at direction , set: progressive phase = ai+1

11、 - ai = -kd cos() |ai| = 1r1r221kd cosphase shift due tophysical separation.k=2/delement factorscommon array elements: dipole, patchother arrays: 2-dim. or even 3-dim. arrayselement is chosen to be “isotropic” over region of interestelement can be chosen for its properties in other dimensionsparalle

12、lcollinearafafexamples: 16-antenna arrayuniform array: mag.= 1, progressive phase = , uniform spacingwe only need phase shifters!phased: =-kd cos(60)d=12 dbisotropicradiatorsd=12 dbn = 16kd = broadside: = 0 antenna array: design space exploration, effects on standard rf blocksantenna elementsan effi

13、cient antenna needs to be /2 long in some linear dimension: /2 = 2.5mm in free spaceneed /2 lateral spacing between element origins best angular resolution without grating lobes.antenna unit cell is approx. 2.5mm x 2.5mm typ. laptop is 200mm x 300mm = 80 x 120 antennas - n = 9600! typ. pda is 70mm x

14、 110mm = 28 x 44 antennas - n = 1200! typ. pc card antenna is 20mm x 50mm = 8 x 20 antennas - n = 160!2.5mm2.5mmdipoleor patchunit cell can be tiled to form array.10 mm2.5mmnumber of antennasdirectivity = d0=umax/u0 afmax2 = nhalf power beamwidth(hpbw) 2*arccos(1-/nd)nulling of interferers reduces m

15、ain beam gain (a little).physical size of antenna array is not an issuecircuit complexity grows as nhpbwd0nd0hpbw46 db2689 db101210.8 db91612 db73215 db3.5(uniform array)array of power amplifiersat 60ghz, we are power limited, so let max. pa power = ptone factor of n in eirp from directivity of arra

16、y patternanother factor of n in eirp from combining power of n pas as we add antennas total gain is: pt * n2+6db eirp for each doubling of n, with constant individual pa power +24 db eirp for n = 16 antennas, compared to base system.constant individualtransmit poweroriginalpaarray of low noise ampli

17、fierseach added antenna receives another copy of the signal for free that is perfectly correlated, so: (s1 + s2)2 = s12 + 2s1s2 + s22 = 4s2 = n2*s2and another noise source, totally uncorrelated, so (n1 + n2)2 = n12 + 2n1n2 + n22 = 2n2 = n*e2n nf = (nf of lone lna)/n since cmos is performance limited

18、 here alsoalso effective voltage gain of n*(gain of one lna)a0a1antenna weighting circuitsrf phase shifters provides weighting of array coefficients at full rf. 3 major types: passive tuned: high-, low-, all-pass filter: ok, but require tunable elements on-chip, also have limited tuning range. switc

19、hed delay lines: provides phase shift through actual time delays. virtually guaranteed to work, but bulky in cmos. vector modulator: just need variable attenuators on the i and q signals (gives us full phase and magnitude control).x(t)90 x(t) * e(jt + )vector modulatorphase shifter accuracyprimary p

20、roblem is directivity: care about gain and direction of main beam.for n = 16, discretising to 3 levels ( +1, 0, -1) on each of i and q channels preserves main beam direction and angleangle error2-8321directivity error+/- vector modulatoronly need to select +,- or 0 for i and q.then add the 2 signals

21、 to get the desired phase shift.very easy if use differential signaling, but not necessary.+-sel+sel-vo+-sel0sel0vin(i or q)i&q generation at receiver must generate i&q before mixer, at full carrier freq. this is needed for the vector modulator there are 2 common ways of doing this: microwav

22、e, e.g. 90 degree hybrid (a.k.a. 3-db hybrid) lumped, e.g. +45/-45, using high-pass and low-pass filter sectionsiniqisolatediqinmicrowavelumpedtarget prototypeniqone cmoschip, 0.13um60 ghzeach block:pa, lna,phase shifterseach block:3 b. for phase1 b for tx/rx antennas need to be off-chip, in the package. (ltcc? pcb?) path length is not critical: array is adaptive and weights are relative.summary2 ways that an adaptive array increases eirp in any direc