Chapter 4 Bandpass signaling Principles and Circuits
1 Chapter 4 Bandpass Signaling Principles and Circuits
Introduction (chapter objectives Complex envelopes and modulated e signals Spectra of bandpass signals .. Nonlinear distortion .. Communication circuits(mixers, phase locked loops, frequency synthesizers, and detectors) e. Transmitters and receivers Software radios
2 Introduction (chapter objectives) • Complex envelopes and modulated signals • Spectra of bandpass signals • Nonlinear distortion • Communication circuits(mixers, phaselocked loops, frequency synthesizers, and detectors) • Transmitters and receivers • Software radios
Introduction(main goals) Mastering how to represent complex envelope of bandpass waveform. . The principle of bandpass filtering and linear distortion Bandpass sampling theorem Nolinear distortion Detector circuits Knowing PLL, DDC, general principle of Transceiver, concept of software radios
3 Introduction(main goals) • Mastering how to represent complex envelope of bandpass waveform. • The principle of bandpass filtering and linear distortion • Bandpass sampling theorem • Nolinear distortion • Detector circuits • Knowing PLL, DDC, general principle of Transceiver, concept of software radios
Introduction The bandpass communication signal is obtained by modulating a baseband analog or digital signal onto a carrier. Complex envelope can represent any type of bandpass signal
4 Introduction • The bandpass communication signal is obtained by modulating a baseband analog or digital signal onto a carrier. • Complex envelope can represent any type of bandpass signal
4.1 Complex Envelope Representation of Bandpass Waveforms general representation for bandpass igital and analog signals Representation for modulated signal Representation for bandpass noise
5 4.1 Complex Envelope Representation of Bandpass Waveforms • general representation for bandpass digital and analog signals • Representation for modulated signal • Representation for bandpass noise
4.1 Complex Envelope Representation of Bandpass Waveforms Definition1: baseband waveform having a spectral magnitude that is nonzero for frequencies in the vicinity of the origin (,e,f0) and negligible elsewhere For example: the information source signal; audio signal in communication systeme
6 4.1 Complex Envelope Representation of Bandpass Waveforms • Definition1： baseband waveform having a spectral magnitude that is nonzero for frequencies in the vicinity of the origin (i,e,..f=0) and negligible elsewhere. • For example: the information source signal; audio signal in communication system
4.1 Complex Envelope Representation of Bandpass Waveforms Definition2: bandpass waveform e having a spectral magnitude that is nonzero for frequencies in some band concentrated about at frequency f= t f, where f>>0. The spectral magnitude is negligible eleswhere. fs is called the → carrier frequency
7 4.1 Complex Envelope Representation of Bandpass Waveforms • Definition2： bandpass waveform having a spectral magnitude that is nonzero for frequencies in some band concentrated about at frequency ƒ= ± ƒc ,where ƒc >>0. The spectral magnitude is negligible eleswhere . ƒc is called the carrier frequency
4.1 Complex Envelope Representation of Bandpass Waveforms Definition3: Modulation the process of imparting the source information onto a bandpass signal with a carrier frequency by the introduction of amplitude or phase perturbations or both. This bandpass signal is called the modulated signal s(t), and the baseband source signal is called the modulating signal m(t)
8 4.1 Complex Envelope Representation of Bandpass Waveforms • Definition3: Modulation the process of imparting the source information onto a bandpass signal with a carrier frequency by the introduction of amplitude or phase perturbations or both. • This bandpass signal is called the modulated signal s(t), and the baseband source signal is called the modulating signal m(t)
4.1 Complex Envelope Representation of Bandpass Waveforms The definition of modulation indicates e that modulation may be visualized as a mapping operation that maps the source information m(t) onto the bandpass signal, s(t), the bandpass signal will be transmitted over the channel
9 4.1 Complex Envelope Representation of Bandpass Waveforms • The definition of modulation indicates that modulation may be visualized as a mapping operation that maps the source information m(t) onto the bandpass signal, s(t), the bandpass signal will be transmitted over the channel
4.1 Complex Envelope Representation of Bandpass Waveforms Informatio n input N Signal 1g(t).Carrier 's(t Transmissi ntl Carrier g(). Signal pondi mr Processing circuits Non mediuml (channel) circuits processing Transmitter Receiver Fig 4-1 communication system As the modulated signal passes through the channel, noise corrupts it; e. the result is a bandpass signal-plus-noise waveform that is available at the receiver input, r(t). The receiver has the job of trying to recover the information that was sent from the source 10
10 4.1 Complex Envelope Representation of Bandpass Waveforms • Fig.4-1 communication system Informatio n input m(t) Signal processing g(t) Carrier circuits s(t) Transmissi on medium (channel) r(t) ( ) ~ Carrier g t circuits Signal processing (( ) ~ m t Transmitter Receiver • As the modulated signal passes through the channel, noise corrupts it; • the result is a bandpass signal-plus-noise waveform that is available at the receiver input, r(t). • The receiver has the job of trying to recover the information that was sent from the source