EE314 Stanford Lectures on RF

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EE314: CMOS RF Integrated Circuit Design Introduction to Wireless Communication systems Stanford University Hamid Rategh

Hamid Rategh

Stanford University

EE314 HO#1

1

Course Staff „

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Instructor: Dr. Hamid Rategh ‰ Email: [email protected] ‰ Office Hours: MW 2:15-3:15PM @ CIS-126; ‰ Phone: 725-8313 TA: Mehdi Jahanbakht and Deji Akinwande ‰ Email: [email protected] ‰ Office Hours @ Packard 106 „ „ „

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

Course Administrator: June Wang ‰ Email: [email protected] ‰ Office: CIS-203 ‰ Phone: 725-3706

Hamid Rategh

Stanford University

EE314 HO#1

2

TA announcements „ „

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Class URL is: http://eeclass.stanford.edu/ee314/ All students should register on class website to access handouts and to stay in touch with any announcements from the instructor or TA's The bulletin board on the class website will be supported by the TAs for exchange of information For 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.

Hamid Rategh

Stanford University

EE314 HO#1

3

Course snapshot „

Primary text ‰

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Recommended text: ‰

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“RF Microelectronics”, B. Razavi, Pearson Education, 1997

Grading ‰

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

Homework 30%, Project 30%, Final 40%

Prerequisite: EE214

Hamid Rategh

Stanford University

EE314 HO#1

4

Course Topics „ „

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Introduction to wireless communication systems ‰ Receiver architectures Review of passive networks ‰ Available passives in IC ‰ RLC networks and tune circuits ‰ Impedance transformation techniques ‰ Transmission lines Review of Distortion and circuit non-linearity ‰ IP3 ‰ 1dB compression point ‰ AM to PM distortion Noise ‰ Noise sources in passive and active circuits ‰ Classical noise theory

LNA design

Hamid Rategh

Stanford University

EE314 HO#1

5

Course Topics (Cont.) „

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Mixers ‰ frequency conversion techniques ‰ Passive and active mixers Oscillators ‰ Topologies (Ring, Colpitts, VCO, Quadrature, …) ‰ Phase noise Frequency synthesizers and Phase-locked loops (PLL) ‰ Integer-N ‰ Fractional-N Power Amplifiers ‰ Different classes of operation (A, B, C, D, …) ‰ Linearization techniques

Hamid Rategh

Stanford University

EE314 HO#1

6

Block diagram of a wireless transceiver Front-end Receiver Duplexer/

De-modulator

Base-band Signal Processing

LNA, Mixer, VCO, PLL,…

Switch

Front-end Transmitter

Modulator

PA, mixer,…

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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 antenna In 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 processor In this course we will be only looking at the front-end receiver and transmitter

Hamid Rategh

Stanford University

EE314 HO#1

7

Half-duplex systems Front-end Receiver

Switch

Front-end Transmitter

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

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Such as: Walki-talki, GSM

The antenna is switched between transmitter and receiver Typically antenna switches have 1-2dB insertion loss and provide about 40dB of isolation between the two ports

Hamid Rategh

Stanford University

EE314 HO#1

8

Full-duplex systems Duplexer

Front-end Receiver

Front-end Transmitter „

In a full duplex system the transceiver can transmit and receive simultaneously ‰

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How can we transmit and receive at the same time? ‰

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Such as: WLAN, CDMA, WCDMA Transmit at one frequency and receive at a different frequency

Duplexers are used to share the same antenna for transmit and receive. ‰ ‰

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

Hamid Rategh

Stanford University

EE314 HO#1

9

Multiple access „

From basic communication course: ‰

Different users (transmitters or receivers) share the same medium (i.e., air) by: „

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Hamid Rategh

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))

Stanford University

EE314 HO#1

10

Multiple channels and channel selection Undesired channel

60dB

B

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filter

f

In a typical wireless system, the frequency band is divided into smaller 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 stronger ‰ If 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 channel ‰ Such 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?

Hamid Rategh

Stanford University

EE314 HO#1

11

Heterodyne Receiver „

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

ωmix = ω RF ± ω LO „

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

ω IF = ω RF − ω LO „

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 frequency If 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

Hamid Rategh

Stanford University

EE314 HO#1

12

Image frequency in heterodyne receivers

ωLO „

Consider a superheterodyne receiver.

ω IF = ω RF − ω LO ⇒ ω RF = ω LO ± ω IF „

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”

ω RF − ωimage = 2ω IF „ „

Image reject filters are used to suppress the image frequency From 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?

Hamid Rategh

Stanford University

EE314 HO#1

13

Selection of IF frequency

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

Hamid Rategh

Stanford University

EE314 HO#1

14

Heterodyne receiver with dual IF IF1

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IF2

IF2 < IF1 Channel selection is done in two stages Therefore the requirements for each of the channel select and image reject filters is relaxed But now we need more filters. ‰

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

Hamid Rategh

Stanford University

EE314 HO#1

15

Homodyne (zero IF) receiver

ω RF = ω LO ⇒ ω IF = 0 ⇒ ωimage = ω RF „

In a homodyne receiver there is no image frequency ‰ ‰

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

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

Hamid Rategh

Stanford University

EE314 HO#1

16

Zero-IF receiver challenges

z

Susceptibility to flicker noise

Hamid Rategh

Stanford University

EE314 HO#1

17

Weaver image-reject receiver

vout = vin [cos(ω1t ) cos(ω2t ) − sin(ω1t ) sin(ω2t )] = vin cos[(ω1 + ω2 )t ] „ „ „

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If ω1+ ω2= ωRF then weaver receiver operates like a zero IF receiver and no image reject filter is needed Conversion to DC is done at the second stage where ω2
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