1. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Electrical Communications Systems 0909.331.01 Spring 2005 Shreekanth Mandayam ECE Department Rowan University http://engineering.rowan.edu/~shreek/spring05/ecomms/ Lecture 12a April 26, 2005

2. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityPlan Broadcast Transmitters and Receivers AM Broadcast Transmitter Class-C Amp Collector Modulator TRF Receiver Superheterodyne Receiver Performance of Comm. Systems corrupted by Noise Performance Measures: Digital and Analog Thermal (Johnson) Noise Amplitude: Recall Random Variables: lab1.ppt Power Spectral Density Autocorrelation function Wiener-Khintchine Theorem

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 00 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 University Performance of Communications Systems Corrupted by Noise Digital Bit Error Rate (BER) Analog Output SNR

16. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityNoise A random, unwanted fluctuation in signal amplitude Thermal (Johnson) Noise Amplitude vs. time: Gaussian PDF Model See Lab1 Pre-lab Lecture: lab1.pptlab1.ppt We also want to know how much noise power there is per Hz – why?

17. S. Mandayam/ ECOMMS/ECE Dept./Rowan UniversityWhy? f |W(f)| Baseband 0 f |W(f)| Bandpass 0 fcfc -f c f |W(f)| Bandpass 0 f IF -f IF 1. Modulation 2. Demodulation 3. Demodulation

18. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Power Spectral Density (PSD) Normalized power of a waveform in the frequency domain Used for measuring signal/noise power loss/transfer in communications system blocks

19. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Autocorrelation Function Measure of similarity of a waveform observed at times  seconds apart how rapidly a random waveform fluctuates with time 0 Rx()Rx()  (time delay) Slowly fluctuating signal rapidly fluctuating signal R w (  ) P w (f) F Wiener-Khintchine Theorem Matlab Demo: autocorr.m

20. S. Mandayam/ ECOMMS/ECE Dept./Rowan University Thermal (Johnson) Noise 00.511.522.53 x 10 12 0 0.5 1 1.5 2 x 10 -21 PSD of thermal noise frequency, Hz PSD, W/Hz Matlab script: psd_noise.m

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