10_RF System Spec

8/6/2019 10_RF System Spec

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EEE 6374Radio Frequency Circuits andSystems

Notes#10 (RF System Specifications)Prof. Jenshan Lin

University of Florida

12/19/2010 2010 Jenshan Lin


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Channel

Propagating medium or electromagnetic path connectingtransmitter and receiver

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Building a transmitter

Large signal.Cannot interfere with other radio systems!

TX Tx output

Other radio

For transmitter design,a clean output spectrum is the key.

RX

Also need to meet output power requirement andget the efficiency as high as possible.

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Building a receiver

RX

Very weak signal at RX antenna.To process the signal at baseband, we need large signalwhile trying to maintain the best signal-to-noise ratio.

Channel

TX

Noise signal

going through RF receiver

For receiver design, S/N or S/(N+I)is the key.

Whats wrong here?

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SNR (Signal-to-noise ratio)

powernoise powersignalSNR N S

S

N Power ratio

SNR will be degraded due to Signal loss Noise increase Interference

Degradation is measured by Noise Figure (NF)

out

inSNRSNR

outputatSNRinputatSNR

NF

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An example of RF system

LO(Synthesizer,PLO, DRO)

BPF BPF

BPF BPFMixer

MixerLNA AGC

IF AMP

IFand/orBase-band

DriverHPA

Switch

Antenna

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Non-Ideal RF Componentnoisy and nonlinear

P in P out

P in (dBm)

P o u

t ( d B

m )

1dB

P 1dB

NF

Noise floor @ input = (kTB) dBm

Noise floor@ output= (GkTB) dBm +(NF) dB

P 1dB, in

P 1dB, out

Gaincompression

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k: Boltzmanns constant= 1.38x10 -23 J/K

T: absolute temperature

B: bandwidth


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3rd Order Intermodulation

fA fB 2fB - fA fB + fA2fA - fBfB - fA

Filter Bandwidth

2nd order2nd order

3rd order3rd order

nonlinear ampfA fB

?1st order

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IP3noisy and nonlinear

P in P out

P in (dBm)

P o u

t ( d B

m ) fA, fB

2fA-fB ,2fB-fA

IP3

3rd orderIntercept Point

NF

Input noise floor = kTB

Output noise floor

IIP3

OIP3

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Ideal Receiver

Assuming we have transceivers with perfectcomponents:Noiseless linear amplifiers (NF=0dB, IIP3=infinity).Noiseless linear mixers which generate the correctmixing product you want and has no image, no spurs.Perfect frequency source without phase noise or jitter.Lossless filters with infinite out-of-band rejection andextremely sharp roll-off.No power consumption.

Then, designing a system would be so easy!Unfortunately, none of the above is true.

Unrealistic wish list from system engineersThats why we need so many RFIC designers inthe world.

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System Specifications

Ideal receivers/transmitters do not exist.Now, you have built a non-ideal radio with non-ideal components, how do you know if it meetsthe specifications (specs)?Where did the specs come from?System specs came from standards documents.Documents were developed and published bystandards organizations.Examples:

ITU (International Telecommunication Union)ETSI (European Telecommunications StandardsInstitute)TIA (Telecommunications Industry Association) (US)

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System Specifications Example: GSM

Receiver sensitivity

* Published by ETSI

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System Specifications Example: GSM

Transmitter output spectrum

* Published by ETSI

30kHz RBW

100kHz RBW

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System Specifications Example: CDMA IS-95

Receiver sensitivity

* Published by TIA

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System Specifications Example: DECT

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Specifications: From system to component

System Component

Reference sensitivity level Rx NF

Reference interference level Rx LO phase noise

Receiver blocking characteristics Rx LO phase noise, Rx spur frommixerReceiver intermodulationcharacteristics Rx 3

rd order intermod

Receiver spurious emissions Rx radiated spur

Transmitter output power Power amplifier output

Output RF spectrum Modulator, Filter, PA

Spurious emissions Tx spur from mixer

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Receiver Spurious Emissions

Remember the FM radio demo?The FM receiver did cause interference!In GSM Standard (GSM0505), 5.4 defines the

receiver spurious emissions.

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Circuit ChallengesRx LNA NF(sensitivity), IP3(intermod)

Rx Mixer IP3(intermod), Spur(blocking)

Rx VCO Phase noise(blocking), jitter(timing)

Tx Modulator Noise floor(output spectrum), Signal balance(I&Q)

Tx Mixer Spur(spurious emission)

Tx AGC Gain control(output power level)

Tx PA Linearity(output spectrum), efficiencyDuplexer Insertion Loss(sensitivity), Rejection(spuriousemission)

TransceiverIntegration

Isolation/cross-talk, DC Power, OptimizedPartition.

Specifications: Circuit Design Issues

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Link Budget

Link Budget is a term used to determine thenecessary parameters for a successfultransmission of a signal from a transmitter to areceiver through space.

Includes TX PA output, gain and lossthroughout the system and the link, and theS/N level required at receiver for desired biterror rate (BER) of detection.

The most simple, basic system specificationsanalysis to begin with only gain, loss, noise(linear characteristics).

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Link Budget Analysis Example

http://www.ardentech.com/ Download trial version or Lite-version 21
http://www.ardentech.com/http://www.ardentech.com/


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EIPR and ERPEffective Isotropic Radiated Power, orEquivalent Isotropic Radiated Power

EIRP = (power delivered to the antenna) X (antenna gain)

in a given direction

ERP = Effective Radiated Power= (power delivered to the antenna) X

(relative antenna gain with respectto maximum directivity of half-wavelength dipole)

ERP (dB) = EIRP (dB) 2.15dB

Same EIRP

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Link Margin

Difference in dB between (E b /N 0) received and (E b /N 0) required

Bit energy Noise power spectral densityNoise power per Hertz (noise energy)

dBrequired,0

dBreceived,0

dB )()( N E

N E M bb

Varies from one system design to the other Depends on modulation and coding schemes.

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Bit Error Rate (BER)

000

,For PP x N E

E b

0 N

E b0

x

E P

0P

0.5

0

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BER BER

Eb /N 0 (dB)

OrthogonalModulation

M-PSK

M=2 k

M-aryM symbolson signal space

k=# of bits/symbol

e.g., FSK

BWBW

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Orthogonal Modulation vs. M-PSK

For orthogonal modulation, as k increases, biterror performance improves, with the trade-off of bandwidth.For M-PSK, as k increases, bit errorperformance degrades, but bandwidth is alsoreduced.Line (1): P B vs. E b /N 0 with k (BW) fixed

Line (2): P B vs. BW with E b /N 0 fixedLine (3): BW vs. E b /N 0 with P B fixed

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Channel Capacity (Sklar pp. 385-389)

Shannon-Hartley Capacity Theorem

C: bits/s, BW: HzTheoretically possible to transmit data over such achannel at any rate R, where RC, with an arbitrarilysmall error probability by using a sufficientlycomplicated coding scheme.

Shannon Limit (E b /N 0=-1.59dB)Below this limit, impossible to have error-freecommunication at any data rate.

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2log 1S

C BW N


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B

R

N

E

B N

T E

N

S bb

00

Hertzinbandwidth

ratebit1

bitperdurationtime

Hertzperpowernoise

bitperenergysignal

powernoise

powersignal

0

B

T R

T

N

E

N

S

b

Bit Energy to Noise Ratio and Signal to Noise Ratio

R

B

N

S

B N

T S

N

E b

/ 0

Energy

RFDigital baseband

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Sensitivity

B

R

N

E

N

S b

0

)log(10)log(10) / ( 0 B R N E SNR dBbdB

)log(10) / (dBm/Hz174)log(10dBm/Hz174

)log(10)(

)(ySensitivit

reqddB,0dB

reqddB,dB

reqddB,dBdBm/Hz

reqddB,dBdBmdBm

R N E NF SNR B NF

SNR B NF kT

SNR NF kTB

b

ySensitivit)()( requiredrequired0 N S

N

E b

At T = 290K, kT = -174dBm/Hz

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RF System Specifications

nonlinear system

P in P out

P in (dBm)

P o u

t ( d B m

) fA, fB

2fA-fB ,2fB-fA

IP3

1dBP 1dB

NF

Input noise floor = kTB

Output noise floor SNR required

Sensitivity

MDS = Minimum Discernible Signal30


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Dynamic Range (DR)

P in (dBm)

P o u

t ( d B m

)IP3

P 1dB

IM3 = MDSNF

MDSOutputnoise floor

SNR required

Sensitivity

3rd-order IM SFDR

Input noise floor

Usable DR

Max. IM3 allowed

There are many definitions for DR:

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OIP3: Output 3rd-order Intercept Point

IIP3: Input 3rd-order Intercept Point

IMD: Inter-Modulation DistortionIM3: 3rd-order Inter-Modulation product(dBm)

Summary of Acronyms

SFDR: Spurious Free Dynamic Range

NF: Noise Figure

SNR: Signal Noise Ratio

P1dB: 1dB compression Point(Remember to specify either input or output!)

10_RF System Spec

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