Chapter 7. Analog Communication System PowerPoint Presentation

Chapter 7. Analog Communication System PowerPoint Presentation

2017-04-05 58K 58 0 0


Husheng Li. The University of Tennessee. Superheterodyne. Receiver. Four tasks of the receiver:. Demodulation. Carrier frequency tuning. Filtering. Amplification of signal. In theory, all of the foregoing requirements could be met with a high-gain tunable . ID: 534126

Embed code:

Download this presentation

DownloadNote - The PPT/PDF document "Chapter 7. Analog Communication System" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.

Presentations text content in Chapter 7. Analog Communication System


Chapter 7. Analog Communication System

Husheng Li

The University of Tennessee


Superheterodyne Receiver

Four tasks of the receiver:


Carrier frequency tuning


Amplification of signal

In theory, all of the foregoing requirements could be met with a high-gain tunable


amplifier. In practice, it is hard to achieve both selective and




Superhet Principle

In the superhet principle, there are two distinct amplification and filtering sections prior to demodulation: RF section and IF section.


Parameters of AM and FM


Illustration of Spectrum


Direct Conversion Receivers

Direct conversion receivers (DC) are a class of tuned-RF (TRF) receivers that consist of an RF amplifier followed by a product detector and suitable message amplification.


Image Signal Rejection

The DC’s chief drawback is that it does not reject the image signal that is present in the opposite sideband and is thus more susceptible to noise and interference.



Deadline: Nov. 18th, 2013


Double Conversion Receiver

A double-conversion receiver takes the superhet principle one step further by including two frequency converters an two IF sections. The second IF is always fixed-tuned, while the first IF and second LO may be fixed or tunable.


Receiver Specification

Receiver sensitivity is the minimum input voltage necessary to produce a specified signal-to-noise radio (SNR) at the output of the IF section. A good-quality shortwave radio typically has sensitivity of 1 uV for a 40dB SNR.Dynamic range (DR) is Selectivity specifies a receiver’s capability to discriminate against adjacent channel signals.The noise figure indicates how much the receiver degrades the input signal’s S/N.Image Rejection is


Scanning Spectrum Analyzers

If the LO in a superhet is replaced by a VCO, then the predetection portion acts like a votlage-tunable bandpass amplifier with center frequency f0=f_LO +/- f_IF


Operation of Spectrum Analyzer

The number of resolvable spectral lines equalsThe IF output produced by a single line takes the form of a bandpass pulse with time duration A rapid sweep rate may exceed the IF pulse response. Hence, we haveHence, the accurate resolution (small B) calls for a slow rate and long observation time.



The basic multiplexing techniques include FDM, TDM and CDM. The multiple access techniques include FDMA, TDMA and CDMA, and OFDM.




Crosstalk in FDM

The major practical problem of FDM is crosstalk, the unwanted coupling of one message into another.

Intelligible crosstalk arises primarily because of nonlinearities in the system which cause one message signal to appear as modulation on another subcarrier.

The crosstalk may also come from imperfect spectral separation by the filter bank.


Example: FDMA Satellite System


Quadrature-Carrier Multiplexing

Quadrature-carrier multiplexing, also known as quadrature amplitude modulation (QAM), utilizes carrier phase shifting and synchronous detection to permit two DSB signals to occupy the same frequency band.




Synchronization Markers

Markers are needed for time synchronization


Crosstalk and Guard Times

The filter design in TDM should be avoid inter-channel crosstalk.A guard time is needed to avoid the crosstalk in TDM.The crosstalk reduction factor is


Crosstalk in PPM

The avoidance of crosstalk in PPM requires


Comparison of TDM and FDM

TDM is readily implemented with high-density VLSI circuitry where digital switches are extremely economical.

TDM is invulnerable to the usual causes of crosstalk in FDM.

TDM may or may not be advantageous when the transmission medium is subject to fading.

Most systems are hybrids of FDMA and TDMA.



GSM is a hybrid of TDMA and FDMA



Deadline: Nov. 25th, 2013


Phase Locked Loops

A PLL uses phase comparator


Phase Dynamics in PLL

The instantaneous angle in PLL is given by


Dynamics in PPL

The dynamics of the phase error are described in the nonlinear differential equation:where the loop gain is defined asThe steady state is given by



A necessary condition for the stead-state solution is given byWhen the error is very close to zero, we have the following approximation:


PLL Pilot Filter

We can use the following circuit to generate a sinusoid synchronized with the pilot:


Synchronous Detection

When there is no pilot (e.g., in DSB), we can use the following Costas-PLL to lock the phase:


Frequency-offset Loop

We can use the following PLL to realize the synthesize the sum of two frequencies:


Frequency Multiplication

We can us the following PLL and frequency divider to realize the multiplication of a frequency with an integer:


Adjustable Local Oscillator

We can use the following circuits to obtain 100kHz and 1.6MHz and adjustable LO that covers 9.90—9.99 MHz.



Use the following figure to explain the purpose of phase locked loop and its operation procedure:


Linearized PLL

The frequency domain model of PLL can be obtained by linearizing the PLL:


FM Detection

When the input is FM signal, the PLL can be approximated by a first-order lowpass filter:The output is given by


Software Project

Topic: Analyze the spectrum of AM and FM signals.Software: MatlabTasks:1. Consider triangle series shown in the right figure. Consider carrier frequency 200Hz. Choose the modulation indices by yourself.2. Sample the modulated signal. Plot the time domain curves of the AM and FM modulated signals. Determine the sampling rate by yourself.3. Read the introduction to discrete Fourier transform (DFT) in Matlab ( and the function fft ( Use function fft in Matlab to obtain the spectrum of the modulated signal. Compare the spectrum of AM and FM.5. Change the parameters such as modulation index and draw conclusions on the impact of these parameters.







About DocSlides
DocSlides allows users to easily upload and share presentations, PDF documents, and images.Share your documents with the world , watch,share and upload any time you want. How can you benefit from using DocSlides? DocSlides consists documents from individuals and organizations on topics ranging from technology and business to travel, health, and education. Find and search for what interests you, and learn from people and more. You can also download DocSlides to read or reference later.