Chapter 2 Basic Concept in RFIC Design

8/11/2019 Chapter 2 Basic Concept in RFIC Design

1/28

Basic Concepts in RF Design

From System requirements to

Rx/TX specifications


2/28

System Information


3/28

Objectives

Effects of nonlinearity (Harmonics. Gain

compression, desensitization andblocking, Inter-modulation)

Noise (definition, sources, NF) Cascaded stages (Nonlinearity, Noise)

How does this translate into the specs of

the individual blocks.


4/28

Nonlinearity_1

Definition of linear system

x1(t) y1(t), x2(t)y2(t)ax1(t)+bx2(t)ay1(t) + by2(t) for all values of a, b

Time-invariant system

x(t) y(t), then x(t-)y(t-)

A linear system can generate frequency components that do not exist in the input

signal if it is time variant

)T

n

(fVn

)(n

(f)V

)T

nf

n

(n(f).V(f)V

inout

inout

1

1

2/sin

()2/sin

=

=


5/28

Effects of nonlinearity Harmonics

RF Receiverx(t)=A cost t y(t)

Assume a nonlinear system

tA

tA

tAAA

ty

ttA

tA

tAty

tAtAtAty

tAtxsubstitute

txtxtxty

3cos4

2cos2

cos)4

3(

2)(

)3coscos3(4)2cos1(2cos)(

coscoscos)(

cos)(by

)()()()(

3

3

2

23

31

2

2

3

3

2

21

33

3

22

21

33

221

++++=

++++=

++=

=

++=

Harmonics

1. Differential configuration removes even harmonics

2. nth harmonic proportional to An

1, 2, 3, n


6/28

Gain CompressionDefinition of 1-dB compression

point

3

11

1

2

131

2

31

1

3

2

31

145.0

1log204320log

int1

4

3

,

0,

4

31

=

=

=

=


7/28

Desensitization and Blocking

Effect of system nonlinearity on the

capability of the receiver to extract the

weak signal from the strong interferers

(Blockers)

By checking the desired frequency 1

tAAty

AAfor

wheretAAAAty

11

2

231

21

31

2

213

3

1311

cos)2

3()(

0,cos)23

43()(

+=


8/28

Inter-modulationdefinition of IP3 point

Receiver

(nonlinear system)1 2 12

22-121-2

12 2

2

..

Receiver

(nonlinear system)1 2

Desired

channel

12

22-121-2

Desiredchannel

Two near-by

interferers


9/28


10/28

Inter-modulation-3

inIMoutIP

in

IP

IM

out

in

in

IM

out

AAAA

A

A

A

A

A

A

A

A

int,)2(3int,),(int,3

2

int,

2

3

)2(3int,

),(int,

int,2

3

int,1

)2(3int,

),(int,

log20)log20log20(2

1

log20

4

3

2121

21

21

21

21

+=

=

P/2

IIP3

OIP3Main Signal Power

3rd IM

Power

P

Pin


11/28

Cascaded Nonlinear Stages

Finding the System-level IIP3 Point

X(t) y1(t) y2(t)

........11

23,3

2

1

2

1

22,3

2

1

21,3

23

+++IPIPIPIP AAAA

1, 2, 3, n1, 2, 3, n

IIP3,1 IIP3,2

IIP3: Power quantity

AIP3: Voltage

quantity

The nonlinearity of stages away from the antenna is more critical than those located

directly after the antenna since the IP3 of each stage is scaled down by the total gain

preceding that stage


12/28

Thermal noise-associated with terminal resistances (G, D in MOSFET), and (B, E, C in BJT)

Vn2 = KTBR

Shot noise:

-Gaussian, associated with the transfer of Q across PN junction

-Dominant in BJT-modeled as a current source

In2 = 4KT (2/3gm)

Flicker noise

-Random trapping of charge at the oxide-silicon interface of MOSFETS

-voltage sourse in series with the gateVn

2=(K / WLCox)*(1/f) (FET)

Why is Noise important?

Sets dynamic range of a receiver (i.e. ratio of maximum to minimum power)

Determines sensitivity of receiver Determines required transmission power

Noise

Noise is defined as any random interference unrelated to the signal of interest.

Harmonic distortion and inter-modulation are deterministic processes

Noise: Physical sources of noise in active devices


13/28


14/28


15/28

Noise Figure

GNin=KTB Nout=G.F.KTB

L

NF=L

Lossy Circuits

Bandwidth:Be(K)Temperatur:T

ConstantBoltzmann:K

,..

.

KTBNoiseThermal

GNiFNo

Ni

No

So

Si

SNR

SNRFNF

out

in

=

=

===


16/28

Noise Figure of Cascaded Stages

FilterLNA

mixer

IF Amp.

G1,NF1 G2, NF2 G3, NF3 G4, NF4

n

ntot

GGGG

NF

GG

NF

G

NFNFNF

..

1.......

11

32121

2

1

21

++

+

+=

Friis Equation

For gain stages: noise is reduced by the gain factor

For lossy stages: noise is amplified as it propagates through the stage


17/28

Sensitivity

Min. detectable signal by the receiver according to a fixed S/N

determined by the BER

Sensitivity

BNF

SNRBNFdBmP

BLogKTBLog

SNRKTBNFP

SNRPNFPysensitivit

SNRP

P

SNR

SNR

NF

dB

dBoutdBin,

outin,

outinnoisein,

outinnoise

in

out

in

Log10dBm/Hz174F

systemtheofnoiseintegratedTotalfloorNoise

Log10dBm/Hz174)(

)(10174)(10

)..(

..

1

.

min,min

min,min

,min

,

+=

=

++=

+=

=

==

==


18/28

Spurious Free Dynamic Range

SFDR

1. Dynamic Range (DR): Ratio of the maximum input levelthat the circuit can tolerate to the minimum input level at

which the circuit provides reasonable signal quality.

2. Upper-end of the dynamic range (DR) depends on theintermodulation behavior

3. The lower end depends on sensitivity and NF


19/28

Spurious Free Dynamic Range

SFDR

min,3

min,3

min,max,

3

maxin,

inIM,

,,

3

,3

max,

min,max,min,max,

3

)FIIP(2

)(3

F2IIP

3

F2IIP

P

10logBNF-174F

FfloornoisePmax.The

2

3

2

2IIP

discussionIIP3From

floornoiseIM3wheretest,tone-twoainlevelinputmaximum

)log10174(

out

outinin

inIMininIMin

in

dBindB

in

outininin

SNRSFDR

SNRFPPSFDR

PPPP

PIIP

PP

P

NFSNRBPPPSFDR

=

++

==

+

=

++=

==

=

+=

+

=

=

+++==

12

21-2 22-1

PIM,in


20/28

Example: DECT

BER versus SNR in

demodulator


21/28


22/28


23/28

Transceiver Architecture

1. Super-heterodyne


24/28

Super-heterodyne_2


25/28

Homo-dyne (Direct Conversion)

Architecture_1


26/28

Direct Conversion Transceiver_2


27/28

Low-IF Transceiver_1


28/28

Low-IF Transceiver_2

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Chapter 2 Basic Concept in RFIC Design

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