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Communication Systems

source transmitter channel receiver sinks(t) r(t)

Digital source: finite or countable set of messages

Analog source: produces messages that vary in a continuum way

A digital communication system transmits and receives messages from a digital source.

An analog communication system transmits and receives messages from an analog source.

Example communication systems• Prehistoric: animal comm.; analog• 4-5K years ago: written language; digital• 1834: Gauss-Weber telegraph; digital• 1876: Bell telephone; analog• 1894: wireless radio; analog• 1918: Armstrong superheterodyne receiver;

analog• 1920: Carson applies sampling in

communications• 1926: Baird-Jenkins television; analog

Example communication systems• 1933: Armstrong invents FM; analog• 1935: Watson-Watt radar; analog• 1947: Bell Lab invents transistors• 1948: Shannon published information theory• 1958: Kilby-Noyce built integrated circuits• 1963: Bell touch-tone phone; digital• 1972: Motorola cellular phone; analog• 1980: Bell fiber-optic communication; analog• 1989: GPS• 1990’s: Internet and the digital comm era

Where things are and where they are heading

Future office

Today’s office

Office(opt)

USB2.0

Office(core)

10/100/1000Ethernet

802.11x USB HUB

Monitor2-4Gbps

GCdatabase

Backbone

2D1DLPS

GPS

Layered Geolocation Networks

PROGRAM

Smart Home Networks

Small Unit Operations Environment for Situation Awareness Systems (SUO-SAS)

Intra-tech handoff

Inter-techhandoff

Non-Homogeneous Wireless Networks

AM RadioAM Radio

A. Input acquired from OSCILLATOR (1000 KHZ) B. A 2nd signal from transducer is mixed with 1000 CW to produce an

Amplitude Modulated (AM) signal or Carrier Transmission.

OSCILLATOR1000 KHZ CW

TRANSDUCER{Microphone}

POWER AMPLIFIER

Now Back to old, existing

Modulatoror

Mixer

Television

Cam

Mic FM modulation

Processing & AM Mod

Stereo audio

Video part

Oscillatorand PLL

Quadrature modulation

A lot of filtering

Video part

Phase locked loop

TV receiver

Optical Transceiver Architecture

TIA Postamp

LDD

Photodetector

Laser Diode

Clk out

Data out

Data in

ClockAndData

Recovery

RECEIVER

TRANSMITTER

BERT

Optical Fiber

Optical Fiber

PRBS

OpticalChannel

OEDevices

Transceiver Test

AGC Postamplifier• Automatic gain control maintains gain stages in their

linear region to reduce jitter• Excess gain can be dynamically traded for additional

bandwidth and better phase response• Different gain control for each VGA stage to reduce

noise

DC OffsetCancellation

VIN VOUT

AGC

VGA VGA VGAInputStage

DC OffsetCancellation

VIN VOUT

AGC

VGA VGA VGAInputStage

Laser Diode Driver• Cherry-Hooper limiting preamplifier• Transconductance amplifier output stage

VIP VIN

VDD VDD

LWIREBOND

VIP VIN

VDD VDD

LWIREBOND

Interleaved PRBS Architecture

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D1

D1

Q

QXOR

LATCH

D0

D0

D1

D1

Q

QXOR

LATCH

D0

D0

CLK

CLK

D1

D1

Q

Q

MUX

D0

D0

SEL

PRBS OUT

RRESET

RRESET

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D

D Q

Q

LATCH

CLK

D1

D1

Q

QXOR

LATCH

D0

D0

D1

D1

Q

QXOR

LATCH

D0

D0

CLK

CLK

D1

D1

Q

Q

MUX

D0

D0

SEL

PRBS OUT

RRESET

RRESET

• The shift register operates at only half the data rate

Generic Wireless Phone Block Diagram

Keys/Buttons

Digital Logic

and

AudioProcessing

Tx / RxSwitch

Synthesizer

Rx Amp / Filter

PA

Transmit and Receive RF

Buffer

IF / Frequency Generation

A/D

D/A

DSP /Micro-

processor

Audio CODEC

Mic

Earpiece

PA Control

Audio Amp

Power Mgmt/Audio/Control

Power Amp

Memory

DisplayDriver

Tx Vcc

LogicVcc

Regulator

Rx Vcc

EL Driver

Baseband Signal Processing

State-of-the-Art 2.5G Phone Architecture

State-of-the-Art 3G Smart Phone Architecture

Functional block diagram

DIG

ITA

LFI

LTE

R

Superheterodyne Receiver

+ Best overall performance+ Usually lowest power+ Flexible frequency plan+ Avoid DC problems

- Expensive, large- many discrete, external components- Image problemDifficult for multi-mode (need multiple IF filters

PGA

PGA

LNA

RFSAW ADC

ADC

DIG

ITA

LFI

LTER

I

Q

RFPLL

sin cos

270 kS/s

925-960MHz

925 - 960MHz

Direct Conversion Receiver

1/f noise here can end up in channel

+ Eliminate IF SAW, IF PLL and image filtering+ Integration+ Avoids image problem

- Quadrature RF down conversion required- DC problem- Typically requires offset or 2x LO to avoid coupling

ADC

ADC

PGA

PGA

LNA

RFPLL

DIG

ITA

LFI

LTE

R

100 kHz

I

Q

sin cos

RFSAW

sin cos

270 kS/s

925-960MHz

925.1 - 960.1MHz

Low IF receiver

- Quadrature RF down conversion required- Require higher performance ADC- Additional mixerSlower RF PLL settling

+ Eliminate IF SAW, IF PLL and image filtering

+ Integration

+ Relaxes image rejection requirements

+ avoids DC problems

CMOS transceiver architecture

ADC

ADC

PGA

PGA

LNA

LNA

LNA

Si4200

IFPLL

RFPLL

Si4134T

GSM

DCS

PCS

GSM

DCSPCS

DCXO

0 / 90

AN

TEN

NA

SW

ITC

H

φDET

BA

SEB

AN

D

DAC

DAC

PGA

PGACH

AN

NEL

FILT

ER

100 kHz

Si4201

I

Q

I

Q

PA

PA

AFC

CLK

Our Focus is on VLSI Circuit Design

Cell phone example

Audio interface

Basebandconversion RF

AntennaAnalog and mixed-signal

technology

Application in other communication systems

Major components• Antenna and interface• RF input filter• Low noise amplifier• Mixer• Oscillator• Phase-locked loop• Frequency synthesizer• ADC/DAC• Power amplifier

Performance Concerns• DC offset• Image rejection• Quadrature requirements• Noise and noise figure• Phase noise and Jitter • Distortion

– Compression– Desensitization– Cross modulation– Intermodulation– IP2, IP3– Harmonic distortion (THD, SFDR,…)

• Bit error rate• Data rate (bandwidth)