S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE Spring 2008 Shreekanth Mandayam ECE Department Rowan University Lecture 14a April 29, 2008

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Broadcast Transmitters and Receivers AM Broadcast Transmitter Class-C Amp Collector Modulator TRF Receiver Superheterodyne Receiver

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

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Broadcast Transmitter Temp. Stabilized Crystal Oscillator Buffer Amplifier Class-C Modulated Power Amp. Stage Class-C Modulated Power Amp. Stage Impedance Matching Network Audio Amplifier Modulator Driver Amplifier Demodulator Audio Input  + -

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Amplifier Classification icic tt  icic tt icic tt icic tt Class A Class B Class AB Class C

S. Mandayam/ ECOMMS/ECE Dept./Rowan University BJT Collector Modulator Circuit Output Characteristics

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Circuit Operation BJT Collector Modulator

S. Mandayam/ ECOMMS/ECE Dept./Rowan University AM Receiver Purpose Demodulate received signal Requirements Carrier frequency tuning Filtering Amplification

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Tuning Circuits Series Tuned Circuit + - V r C L I

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Series Tuned Circuit function [f,A]=resonance(f0,Q) %ECOMMS Spring 08 Class Demo %S. Mandayam, ECE Dept., Rowan University %To illustrate series resonance and Q-factor close all; %defining frequency axis f=f0-f0/2:0.1:f0+f0/2; %calculating relative response y=(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 Circuits Parallel Tuned Circuit + - V r C L I Active Tuned Circuits?

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Tuned Radio Frequency (TRF) Receiver Active Tuning Circuit Detector Circuit Local Oscillator Bandpass Filter Baseband Audio Amp

S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityHeterodyning Heterodyning (Upconversion/ Downconversion) Subsequent Processing (common) All Incoming Frequencies Fixed Intermediate Frequency

S. Mandayam/ ECOMMS/ECE Dept./Rowan University Superheterodyne Receiver RF Amplifier H 1 (f) Mixer Local Oscillator IF Amplifier H 2 (f) Detector Audio Amp Common tuning f RF or f c f LO f IF fmfm fmfm Downconversion f IF = |f RF - f LO | Upconversion f IF = f RF + f LO

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