RFIC Design and Testing for Wireless Communications

Transcription

1 RFIC Design and Tesing for Wireless Communicaions PragaTI (TI India Technical Universiy Course July 8,,, 008 Lecure 6: Basic Conceps Lineariy, noise figure, dynamic range By Vishwani D. grawal Fa Foser Dai 00 Broun Hall, uburn Universiy uburn, L , US

2 RFIC Design and Tesing for Wireless Communicaions Monday, July, 008 Topics 9:00 0:0 Inroducion Semiconducor hisory, RF characerisics :00 :0 Basic Conceps Lineariy, noise figure, dynamic range :00 :0 RF fron-end design LN, mixer :00 5:0 Frequency synhesizer design I (PLL Tuesday, July, 008 9:00 0:0 Frequency synhesizer design II (VCO :00 :0 RFIC design for wireless communicaions :00 :0 nalog and mixed signal esing Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008

3 Unis for Microwave and RFIC Design Peak-o peak volage: V pp Roo-mean-square volage: Power in Wa : Power in dbm : V Pwa R rms V rms V pp 8R V pp Pwa [ mw ] P dbm 0log0 mw On a 50Ohm load, 0dBmmWmV rms 6mV pp Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

4 Noise Figure In RF design, mos of he fron-end receiver blocks are characerized in erms of noise figure raher han inpu referred noise. Noise facor F is defined as F SNR SNR S S N N N o GN N in i i o ( oal o ( source o ( added ou Noise Figure, NF 0log 0F o o i N o( source N N N o( source N N o ( added o( source Noise figure measures how much he SNR degrades as he signal passes hrough a sysem. For a noiseless sysem, SNRin SNRou, namely, F, NF0dB, regardless of he gain. This is because boh he inpu signal and he inpu noise are amplified (or aenuaed by he same facor and no addiional noise is inroduced. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

5 Thermal Noise Thermal noise (Johnson noise due o random hermal moion of elecrons and is generaed by resisors, base and emier resisance r b,r E,and r c. of bipolar devices, and channel resisance of MOSFETs. Thermal noise is a whie noise wih Gaussian ampliude disribuion. Thermal noise floor: kt 0log 7dBm / Hz a 90 0 K mw R V n V n _ ktrδf _ V nb rb V ne Q _ re I n M I n kt g m Δf >/ for submirocn MOS Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 5

6 Sho Noise Sho noise (Schoky noise due o he paricle-like naure of charge carriers. Only he ime-average flow of elecrons and holes appears as consan curren. ny flucuaion in he number of charge carriers produces a random noise curren a ha insan. Sho noise is a Gaussian whie process associaed wih he ransfer of charge across an energy barrier (e.g., a p-n juncion. This random process is called sho noise and is expressed in amperes per roo herz. I n qiδf I n,b Q I n,c i bn i qi qi B cn C Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 6

7 Flicker noise Flicker noise (/f noise found in all acive devices. In bipolar ransisors, i is caused by raps associaed wih conaminaion and crysal defecs in he emier-base depleion layer. These raps capure and release carriers in a random fashion wih noise energy concenraed in low frequency. K depends on processing and may vary by order of magniude. I n K I a C f Δf, a 0. 5~ In MOSFETs, /f noise arises from random rapping of charge a he oxide-silicon inerfaces. Represened as a volage source in series wih he gae, he noise specral densiy is given by K V n WLCox f Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 7

8 Noise Power Specral Densiy -5 Noise Power (dbm/hz z Thermal and Sho Noise 0dB/Dec Toal Noise Flicker Noise Frequency (khz The /f corner frequency can be significanly higher for MOSFET Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 8

9 BJT Model wih Noise Sources b v b r b b C μ c ktr b i bf i bn r π C π gm v b e r o i cn qi B qi C e /f noise Base Sho Noise Collecor Sho Noise e a c b c b v rb r b b i cn r b b b i cn ktr b i bn qi B base sho noise e qiq C collecor sho noise kt r r b i bn qi B e qi C Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 9

10 CMOS Model wih Noise Sources C GD v o Inpu-referred noise v gs C GS g m v gs r o I nd V 8 n kt g m I nd kt g m 8 kt In Zin g m Gae resisance can be added o he noise model wih gae resisiviy ρ R GTE W ρ L Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 0

11 Linear vs. Nonlinear Sysems sysem is linear if for any inpus x( and x(, x( y(, x( y( and for all values of consans a and b, i saisfies ax(bx( ay(by( sysem is nonlinear if i does no saisfy he superposiion law. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

12 Effecs of Nonlineariy Harmonic Disorion Gain Compression Desensiizaion Inermodulaion For simpliciy, we limi our analysis o memoryless, ime invarian sysem. Thus, y( x( x ( x (... (. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

13 Effecs of Nonlineariy -- Harmonics If a single one signal is applied o a nonlinear sysem, he oupu generally exhibis fundamenal and harmonic frequencies wih respec o he inpu frequency. In Eq. (., if y cos cos cos ( frequencies wih respec o he inpu frequency. In Eq. (., if x( cos, hen y cos (cos cos ( cos cos cos cos ( cos cos cos ( Observaions:. even order harmonics resul from j wih even j and vanish if he sysem has odd symmery, i.e., differenial circuis. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page. For large, he nh harmonic grows approximaely in proporion o n.

14 Effecs of Nonlineariy -- Gain Compression y( ( cos cos cos (. Under small-signal assumpion, he sysem is normally linear and harmonics are negligible. Thus, dominaes small-signal gain. For large signal, nonlineariy becomes eviden. large-signal gain /. The gain varies when inpu level changes. If < 0, he oupu is a compressive or sauraing funcion of he inpu he gain is compressed when increases. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

15 Oupu of Bipolar Differenial Pair anh ( x x x x x K V V od id I F EE R C V anh V id T Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 5

16 Effecs of Nonlineariy db Compression Poin Oupu Volage (dbv db 0login db 0log db db db db V pp / 8 dbm 0log 50Ω mw db -db compression poin is defined as he inpu signal level ha causes small-signal signal gain o drop db. I s a measure of he maximum inpu range. -db compression poin occurs around -0 o -5 dbm (6. o 5.6mVpp in a 50-ΩΩ sysem in ypical frond-end d RF amplifiers. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 6

17 Effecs of Nonlineariy Desensiizaion (Blocking Desensiizaion -- small signal experiences a vanishingly small gain when coexiss wih a large signal, even if he small signal iself does no drive he sysem ino nonlinear range. pplying wo-one inpus x( cos cos o Eq.(., we have y( cos L For <<, i reduces o y, gain of desired signal cos L, ( Observaions: Weak signal ss gain decreases as a funcion of if < 0. For sufficienly large, he gain drops o zero he weak signal is blocked by he srong signal. (Why canno we see sars during day? Many RF receivers mus be able o wihsand blocking signals 60 o 70 db greaer han he waned signals. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 7

18 Effecs of Nonlineariy Inermodulaion Harmonic disorion is due o self-mixing of a single- one signal. I can be suppressed by low-pass filering i he higher order harmonics. However, here is anoher ype of nonlineariy -- inermodulaion (IM disorion, which is normally deermined by a wo one es. When wo signals wih differen frequencies applied o a nonlinear sysem, he oupu in general exhibis some componens ha are no harmonics of he inpu frequencies. This phenomenon arises from cross- mixing (muliplicaion of he wo signals. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 8

19 Effecs of Nonlineariy Inermodulaion ( DC Term y x ( ( cos cos ( s Order Terms ( cos ( nd Order [ ] cos cos cos ( Terms [ ] [ ] cos cos cos( cos( rd Order erms [ ] [ ] [ ] cos( cos( cos( cos( Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 9 [ ]

20 Inermodulaion Why do we care abou IM mosly? In wireless communicaion sysem such as cellular handses wih narrow-band operaing frequencies (i.e., a few ens of MHz, only he IM spurious signals (w - w and (w - w fall wihin he filer passband. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 0

21 Inermodulaion -- Third Order Inercep Poin (IP Two-one es: and is sufficienly small so ha higherorder nonlinear erms are negligible and he gain is relaively consan and equal o. s increases, he fundamenals increases in proporion o, whereas IM producs increases in proporion o ³. x( y( 9 cos cos >> IIP and OIP IIP 9 cos 9 cos db dB IP / [ cos cos ] [ cos( cos( ] ] [ cos cos ] [ cos( cos( ] [ cos( cos( ] Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

22 Inermodulaion IP vs. IP 0 IP Fundamenal 0 ND Order IM Produc: IP IP rd Order IM Produc RD Order IM Produc IP Freq IIP nd Order IM Produc Δ P Freq Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

23 Calculae IIP wihou Exrapolaion Δ P P Freq 0login P/ ΔP[ db] IIP [ dbm] Pin[ dbm] Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

24 Relaionship Beween -db Compression and IP -db compression poin wih single one applied: IP db 0. 5 IP db db -db compression poin wih wo ones applied: IP 5.5. db db 0. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page

25 Deermine IIP and -db Compression Poin from Measuremen n amplifier operaes a GHz wih a gain of 0dB. Two-one es wih equal power applied a he inpu, one is a.0 GHz. he oupu, four ones are observed a.99,.0,.0, and.0ghz. The power levels of he ones are -70,-0,-0, and -70dBm. Deermine he IIP and -db compression poin for his amplifier. Soluion:.99 and.0 GHz are he IP ones. IIP P db dBm ( P G [ P P ] 0 0 [ 0 70] 5dBm OIP 0log( P 0log ΔP[ db] IIP [ dbm] Pin[ dbm] 0login P/ IIP Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 5

26 Inermodulaion of Cascade Nonlinear Sages y y ( x( x ( β y ( β y ( x ( β y L x( y ( y ( (... (... IP, IP, IP, Lineariy is more imporan for back-end sages. IP β IP, IP, IP, K Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 6

27 Noise Figure of Cascade Sages NF o NF ( NF NF m NF... G p G pg p G pg p... G p( m NF o oal equivalen Noise Figure NF m Noise Figure of m h sage G pm vailable power gain of m h sage Noise figure is more imporan for fron-end sages. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 7

28 Sensiiviy Sensiiviy -- defined as he minimum signal level ha he sysem can deec wih accepable SNR. NF SNR SNR in OUT P sig SNR / P RS OUT The overall signal power is disribued across he channel bandwidh, B, inegraing over he bandwidh o obain oal mean square power P sig, o P RS NF SNR OUT B P in, min PRS NF SNRmin 0log dbm dbm / Hz db db B where P RS is he source resisance noise power. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 8

29 Maximum Inpu Power OIP P 0log( 0login P/ 0log IIP P IIP P P in in P P in in P P ou P IM, ou P P IM, in in IM, in PIIP PIM, in where P IM,ou denoes oupu-referred power of IM producs, P ou P in G, P IM,OUT P IM,in G. The inpu level for which he IM producs become equal o he noise floor F is hus given by P in PIIP F PIIP 7dBm 0log NF B Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 9

30 Dynamic Range Dynamic Range (DR -- defined as he raio of he maximum o minimum inpu levels ha he circui provides a reasonable signal qualiy. Spurious-Free Dynamic Range (SFDR -- deermine he upper end of dynamic range on he inermodulaion behavior and he lower end on sensiiviy. The upper end of he dynamic range is defined ed as he maximum inpu power in a wo one es for which he rd IM producs do no exceed he noise floor F-7dBmNF0logB. The SFDR is hus given by SFDR P in,max P in, mim PIIP F ( F SNR min ( P IIP F SNR min Example: NF9dB, P IIP -5dBm, B00kHz, SNR min db SFDR(-5-(-7950/.5-5.7dB. Basic Conceps Lineariy, noise figure, dynamic range, FDI, 008 Page 0