S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Electrical Electrical Communications SystemsCommunications Systems

ECE.09.331ECE.09.331 Spring 2008Spring 2008

Shreekanth MandayamECE Department

Rowan University

http://engineering.rowan.edu/~shreek/spring08/ecomms/

Lecture 14aLecture 14aApril 29, 2008April 29, 2008

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

PlanPlan

• Broadcast Transmitters and Receivers• AM Broadcast Transmitter• Class-C Amp Collector Modulator• TRF Receiver• Superheterodyne Receiver

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

ECOMMS: TopicsECOMMS: Topics

Probability

Inform ation

Entropy

Channel Capacity

Discrete

Pow er & Energy Signals

Continuous Fourier Transform

Discrete Fourier Transform

Baseband and Bandpass Signals

Com plex Envelope

Gaussian Noise & SNR

Random VariablesNoise Calculations

Continuous

Signals

AMSw itching M odulator

Envelop Detector

DSB-S CProduct M odulatorCoherent Detector

Costas Loop

SSBW eaver's MethodPhasing M ethod

Frequency M ethod

Frequency & Phase M odulationNarrowband/WidebandVCO & Slope Detector

PLL

Analog

Source EncodingHuffm an codes

Error-control EncodingHam m ing Codes

Sam plingPAM

QuantizationPCM

Line Encoding

Tim e Division M uxT1 (DS1) Standards

Packet Sw itchingEthernet

ISO 7-Layer Protocol

BasebandCODEC

ASKPSKFSK

BPSK

QPSK

M -ary PSK

QAM

BandpassM ODEM

DigitalDigital Com m Transceiver

Systems

Electrical Comm unication Systems

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

AM Broadcast TransmitterAM Broadcast Transmitter

Temp.StabilizedCrystal Oscillator

BufferAmplifier

Class-CModulatedPower Amp.Stage

Class-CModulatedPower Amp.Stage

ImpedanceMatchingNetwork

AudioAmplifier

ModulatorDriverAmplifier

Demodulator

AudioInput

+

-

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Amplifier ClassificationAmplifier Classification

ic

t

ic

t

ic

t

ic

t

Class A Class B

Class AB Class C

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

BJT Collector ModulatorBJT Collector Modulator

Circuit

Output Characteristics

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Circuit

OperationBJT Collector ModulatorBJT Collector Modulator

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

AM ReceiverAM Receiver

• Purpose• Demodulate received signal

• Requirements• Carrier frequency tuning • Filtering• Amplification

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Tuning CircuitsTuning CircuitsSeries Tuned Circuit

+

-

Vr

C

L

I

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Series Tuned CircuitSeries Tuned Circuitfunction [f,A]=resonance(f0,Q)%ECOMMS Spring 08 Class Demo%S. Mandayam, ECE Dept., Rowan University%To illustrate series resonance and Q-factorclose all;%defining frequency axisf=f0-f0/2:0.1:f0+f0/2;%calculating relative responsey=(f/f0)-(f0./f);A=20*log10(1./(1+(y*Q).^2).^0.5);plot(f-f0,A);grid on;xlabel('Shift from resonant frequency in Hz');ylabel('Relative Response in dB');title('Series Tuning Circuit');

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Tuning CircuitsTuning CircuitsParallel Tuned Circuit

+

-

Vr

C

L

I

Active Tuned Circuits?

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Tuned Radio Frequency (TRF) Tuned Radio Frequency (TRF) ReceiverReceiver

ActiveTuningCircuit

DetectorCircuit

LocalOscillator

BandpassFilter

BasebandAudio Amp

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

HeterodyningHeterodyning

Heterodyning(Upconversion/Downconversion)

SubsequentProcessing(common)

AllIncomingFrequencies

FixedIntermediateFrequency

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

Superheterodyne ReceiverSuperheterodyne Receiver

RFAmplifier

H1(f)Mixer

LocalOscillator

IFAmplifier

H2(f)Detector Audio

Amp

Commontuning

fRF

or fc

fLO

fIF fIFfm fm

Downconversion

fIF = |fRF - fLO|

Upconversion

fIF = fRF + fLO

S. Mandayam/ ECOMMS/ECE Dept./Rowan University

SummarySummary