1. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems ECE.09.331 Spring 2008 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring08/ecomms/ Lecture 14a April 29, 2008

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

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

4. 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  + -

5. 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

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

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

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

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

10. 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');

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

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

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

14. 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

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