7024203 ee314 stanford lectures on rf

Stanford University 1EE314 HO#1Hamid Rategh

EE314: CMOS RF Integrated Circuit Design

Introduction to Wireless Communication systems

Stanford UniversityHamid Rategh


Course Staff

Instructor: Dr. Hamid RateghEmail: [email protected] Hours: MW 2:15-3:15PM @ CIS-126; Phone: 725-8313

TA: Mehdi Jahanbakht and Deji AkinwandeEmail: [email protected] Hours @ Packard 106

Sunday 3:00 – 3:30 pm (for SCPD students only)Sunday 3:30 – 5:00 pmThursday 5:00 – 6:00 pm

Course Administrator: June WangEmail: [email protected]: CIS-203Phone: 725-3706


TA announcements

Class URL is: http://eeclass.stanford.edu/ee314/All students should register on class website to access handoutsand to stay in touch with any announcements from the instructor or TA's The bulletin board on the class website will be supported by theTAs for exchange of informationFor the SCPD OHs, (per encouragement from SCPD) we will be experimenting with instant message chatting (instead of phone calls) in an attempt to provide better TA OH support to more SCPD students. We will send instructions to the SCPD students in a few days.


Course snapshot

Primary text“The Design of CMOS RF Integrated Circuits”, T. Lee, Cambridge, 2004 (Second Edition)

Recommended text:“RF Microelectronics”, B. Razavi, Pearson Education, 1997

GradingHomework 30%, Project 30%, Final 40%

Prerequisite: EE214


Course Topics

Introduction to wireless communication systemsReceiver architectures

Review of passive networksAvailable passives in ICRLC networks and tune circuitsImpedance transformation techniquesTransmission lines

Review of Distortion and circuit non-linearityIP31dB compression pointAM to PM distortion

NoiseNoise sources in passive and active circuitsClassical noise theory

LNA design


Course Topics (Cont.)

Mixersfrequency conversion techniquesPassive and active mixers

OscillatorsTopologies (Ring, Colpitts, VCO, Quadrature, …)Phase noise

Frequency synthesizers and Phase-locked loops (PLL)Integer-NFractional-N

Power AmplifiersDifferent classes of operation (A, B, C, D, …)Linearization techniques


Block diagram of a wireless transceiver

In the transmit path, the base-band processor sends out the coded and compressed digital bits, which are then modulated and up-converted to the transmit frequency and finally amplified by the front-end module and transmitted via antennaIn the receive path the received signal from the antenna is amplified and down converted to either base-band or some other intermediate frequencies before it is processed with the base-band signal processorIn this course we will be only looking at the front-end receiver and transmitter

Duplexer/

Switch

Front-end Receiver

Front-end Transmitter

De-modulator

Modulator

Base-band Signal

Processing

LNA, Mixer, VCO, PLL,…

PA, mixer,…


Half-duplex systems

In a half-duplex system the transceiver either transmits or receives at any given time

Such as: Walki-talki, GSMThe antenna is switched between transmitter and receiverTypically antenna switches have 1-2dB insertion loss and provide about 40dB of isolation between the two ports

SwitchFront-end Receiver



Full-duplex systems

In a full duplex system the transceiver can transmit and receivesimultaneously

Such as: WLAN, CDMA, WCDMAHow can we transmit and receive at the same time?

Transmit at one frequency and receive at a different frequencyDuplexers are used to share the same antenna for transmit and receive.

The insertion loss of isolators is generally in the order of 1-2dBAbout 30-40dB isolation between the two ports

DuplexerFront-end Receiver



Multiple access

From basic communication course:Different users (transmitters or receivers) share the same medium (i.e., air) by:

Transmitting at different frequencies (i.e., frequency division multiple access (FDMA))Transmitting at different time slot (i.e., Time division multiple access (TDMA))Transmitting with a different code (i.e. code division multiple access (CDMA))


Multiple channels and channel selection

In a typical wireless system, the frequency band is divided intosmaller divisions called “channel”Consider a system with f=1.9GHz and B=1MHz

Assume we intend to use a filter at the carrier frequency to select the desired channel from the adjacent channel which is 60dB strongerIf we had to use a second order LC filter: the Q should be in excess of 107 to attenuate the adjacent channel 10dB below the desired channelSuch a high Q is very difficult (if not impossible) to achieve even with crystal/SAW filters at GHz frequencies.

How do we practically select the desired channel?

60dB filter

B f

Undesiredchannel


Heterodyne Receiver

A typical heterodyne receiver comprises of an optional front-end amplifier two filters and a mixer for frequency conversion.

If we select the IF to be the difference of the LO and RF frequencies then the receiver is called superheterodyn

LORFmix ωωω ±=

The main reason for frequency conversion is to make channel selection feasible with practical filters

The required Q of the filter is inversely proportional to the center frequencyIf fIF=10MHz and fRF=2GHz, then the required Q for the channel select filter will 2 orders of magnitude less when channel selection done at IF, instead of RF

LORFIF ωωω −=


Image frequency in heterodyne receivers

Consider a superheterodyne receiver.

Therefore there are two input frequencies which down-convert to the same IF frequency. One is the desired channel and the other is called “image frequency”

Image reject filters are used to suppress the image frequencyFrom channel selection discussion we learned that the lower the IF the lower the required Q of the filter. But is this also good for image rejection?

IFLORFLORFIF ωωωωωω ±=⇒−=

IFimageRF ωωω 2=−

ωLO


Selection of IF frequency

A large IF frequency makes image rejection simple and channel selection difficultA Low IF frequency makes image rejection simple and channels selection difficultIs there a way to break this relationship?


Heterodyne receiver with dual IF

IF2 < IF1Channel selection is done in two stagesTherefore the requirements for each of the channel select and image reject filters is relaxedBut now we need more filters.

Filters are generally off-chip components and are not desirable for fully integrated solutions

IF1 IF2


Homodyne (zero IF) receiver

In a homodyne receiver there is no image frequency

There is no need for image-reject filterChannel select filter is simply a low pass filter

Murphy says there is no free lunch! What is the catch?

RFimageIFLORF ωωωωω =⇒=⇒= 0


Zero-IF receiver challenges

Susceptibility to flicker noise


Weaver image-reject receiver

If ω1+ ω2= ωRF then weaver receiver operates like a zero IF receiver and no image reject filter is neededConversion to DC is done at the second stage where ω2<< ωRF and therefore LO and interferer leakage is less of an issueUnlike homodyne receiver the received signal is already amplified well above the flicker noise level before converted to DC and therefore flicker noise is also less of an issue in weaver receiverThe two filters are simple low pass filters to suppress ωRF+ ω1.Why do we need to that?

])cos[()]sin()sin()cos()[cos( 212121 tvttttvv ininout ωωωωωω +=−=


Reading material

Razavi: chapter 5

7024203 ee314 stanford lectures on rf

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