EE194-EE290C28nmSoCforIoT
Ref:RFMicroelectronicsbyBehzadRazavi.SecondEdiFon
Terminology
f
In-Band Blocker Levels Out-of-Band Blocker Levels
Edge ofBand
DesiredChannel
-43 dBm
-70 dBm
-30 dBm
-23 dBm
0 dBm
RFFilteringFilteringrequirementsimpacttheRFdesignofthetransceiver.
BPF
TransmittedChannel
AdjacentChannel
BPF
PA
LNA
fDesiredChannel
AlternateChannel
AdjacentChannel
BPF
RFFiltering• Receivechainprecedingchannel-selecFonfilteringmustbesufficientlylinear.• ChannelselecFonfilteringisextremelydifficultattheRFfrequencies.
f
DesiredChannel
ReceiveBand
BPF
LNA
f
DesiredChannel
QBPF ≈foBW
=2450MHz/1MHz=2450
In-Bandinterferersaretypicallyremovedneartheendofthereceivechain.
RxArchitectureHeterodyneReceiver
RFInput
f
LO
IFOutput
Mixer
fRF ± fLO
ARF cos 2π fRFt +φRF( ) ALO cos 2π fLOt +φLO( )*
f
DesiredChannel
fRFfIF=RF-LO fRF+LO
ImageProblemHeterodyneReceivers
AIF cos 2π fIFt( ) = AIF cos 2π fRF − fLO( ) t{ }AIF cos 2π fIFt( ) = AIF cos 2π fLO − fRF( ) t{ }
f
DesiredChannel
fLOfRF fimage
fIF fIF
ffIF
ImageRejecFon
ffRF fimage
2fIF
Image Reject Filter
ImageRejecFon
ffRF fimage
2fIF
Image Reject Filter
ffIF
Channel Select Filter
ImageRejecFon
ffRFfimage
2fIF
Image Reject Filter
ffIF
Channel Select Filter
RxArchitectureHomodyneReceiver
BPF
LNA LPF
LPF
I
Q
cosωLOt
sinωLOt
Symmetricvs.AsymmetricSpectra
f0
ffLO
ffLO
xBB(t)
t
VCO
ffLO
Symmetricvs.AsymmetricSpectra
ffLO
f0OverlapofsignalsidebandsaWerdown-conversion
QuadratureDownconversion
LPF
LPF
I
Q
cosωLOt
sinωLOt
Twoversionsofthedownconvertedsignalthathaveaphasedifferenceof90o
CanreconstructtheoriginalinformaFon.
RxArchitectureDirect-conversionreceiver(Homodyne)
BPF
LNA LPF
LPF
I
Q
cosωLOt
sinωLOt• DCoffset• LOLeakage• 1/fnoise
LOLeakage
LNAPad
LOSubstrate
LNAPad
LO
DCOffsets
LNAPad
LO
VRF+kVLO
VIF+VDC
LNA
LO
A1
Vb
R1
C1
f0
BasebandSignal
HPF
DCOffsets
LNA
LO
A1
Vb
R1
C1
ffRF ffRF
LowFreq.DeviaFon LargeFreq.DeviaFon
f1 =1
2πR1C1<
Rs1000
• For802.11b@20Mb/s,f1=20KHz• Slowresponsetotransientinputs.
- LOfrequencyisswitchedtoanotherchannel,hencechangingtheLOleakage.- ThegainoftheLNAisswitched,thuschangingthereverseisolaFonoftheLNA.
RxArchitectureLow-IFReceiver
ffRF f0 If
Less1/fnoisepenaltyOn-chiphigh-passfilteringbecomesfeasible.
RxArchitectureRejectImagewithoutfiltering.Quadraturedownconversionasa90ophaseshiWer.
cosωLOt
sinωLOt
I
Q
VRF
ffRF fLO fImage
ffRF
fLO
fImage
-j/2
HartleyArchitecture
cosωLOt
sinωLOt
I
QVRF
LPF
LPF
90o
IF
RxArchitecture
x(t) = Asig cos ωsigt +φsig( )+ Aimage cos ωimaget +φimage( )
xI (t) =Asig2cos ωsig −ωLO( ) t +φsig⎡⎣ ⎤⎦+
Aimage2
cos ωimage −ωLO( ) t +φimage⎡⎣ ⎤⎦
xQ (t) = −Asig2sin ωsig −ωLO( ) t +φsig⎡⎣ ⎤⎦−
Aimage2
sin ωimage −ωLO( ) t +φimage⎡⎣ ⎤⎦
x(t) =Aimage2
sin ωLO −ωimage( ) t −φimage⎡⎣ ⎤⎦
RxArchitecture
x(t) = −Aimage2
cos ωLO −ωimage( ) t −φimage⎡⎣ ⎤⎦
x90 (t) = −Aimage2
cos ωimage −ωLO( ) t +φimage⎡⎣ ⎤⎦
RxArchitecturecosωLOt
sinωLOt
I
QVRF
LPF
LPF
90o
IF
ADC
ADC