Baseband circuits RF circuits I vo= R(O cos(o t+0(o i Modulated signal out adulation Circuit may e(t) Phase modulator FIGURE 69. 1 Generalized transmitter using the AM-PM generation technique Thus gl] performs a mapping operation on m(t). The particular relationship that is chosen for g(r)in terms of m(r) defines the type of modulation used. In Table 69.1, examples of the mapping function g( m) are given for the following types of modulation AM: amplitude modulation DSB-SC: double-sideband suppressed-carrier modulation FM: frequency modulation SB-AM-SC: single-sideband AM suppressed-carrier modulation SSB-PM: single-sideband PM SSB-FM: single-sideband FM SSB-EV: single-sideband envelope-detectable modulation SSB-SQ: single-sideband square-law-detectable modulation QM: quadrature modulation Modulation In Table 69. 1, a generalized approach may be taken to obtain universal transmitter models that may be reduced to those used for a particular modulation type. We also see that there are equivalent models which correspond to different circuit configurations, yet they may be used to produce the same type of modulated signal at their outputs. It is up to communication engineers to select an implementation method that will optimize perfor mance, yet retain low cost based on the state of the art in circuit development There are two canonical forms for the generalized transmitter. Figure 69. 1 is an AM-PM type circuit as described in Eq (69.2). In this figure, the baseband signal processing circuit generates R(o) and e(r) from m(o). The R and e functions of the modulating signal m(t) as given in Table 69. 1 for the particular modulation type desired. Figure 69.2 illustrates the second canonical form for the generalized transmitter. This uses in-phase and quadrature-phase(IQ)processing. Similarly, the formulas relating x(n) and yr) are shown in Table 69.1, and the baseband signal processing may be implemented by using either analog hardware or digital hardware with software. The remainder of the canonical form utilizes radio frequency(RF)circuits as indicated Any type of signal modulation(AM, FM, SSB, QPSK, etc )may be generated by using either of these two canonical forms. Both of these forms conveniently separate baseband processing from RF processing Superheterodyne Technique Most receivers employ the superheterodyne receiving technique(see Fig 69.3). This technique consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency(IF)band, and then extracting the information(or modulation) by using the appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM, AM, satellite, and radar signals. c 2000 by CRC Press LLC© 2000 by CRC Press LLC Thus g[·] performs a mapping operation on m(t). The particular relationship that is chosen for g(t) in terms of m(t) defines the type of modulation used. In Table 69.1, examples of the mapping function g(m) are given for the following types of modulation: • AM: amplitude modulation • DSB-SC: double-sideband suppressed-carrier modulation • PM: phase modulation • FM: frequency modulation • SSB-AM-SC: single-sideband AM suppressed-carrier modulation • SSB-PM: single-sideband PM • SSB-FM: single-sideband FM • SSB-EV: single-sideband envelope-detectable modulation • SSB-SQ: single-sideband square-law-detectable modulation • QM: quadrature modulation Modulation In Table 69.1, a generalized approach may be taken to obtain universal transmitter models that may be reduced to those used for a particular modulation type. We also see that there are equivalent models which correspond to different circuit configurations, yet they may be used to produce the same type of modulated signal at their outputs. It is up to communication engineers to select an implementation method that will optimize perfor￾mance, yet retain low cost based on the state of the art in circuit development. There are two canonical forms for the generalized transmitter. Figure 69.1 is an AM-PM type circuit as described in Eq.(69.2). In this figure, the baseband signal processing circuit generates R(t) and q(t) from m(t). The R and q are functions of the modulating signal m(t) as given in Table 69.1 for the particular modulation type desired. Figure 69.2 illustrates the second canonical form for the generalized transmitter. This uses in-phase and quadrature-phase (IQ) processing. Similarly, the formulas relating x(t) and y(t) are shown in Table 69.1, and the baseband signal processing may be implemented by using either analog hardware or digital hardware with software. The remainder of the canonical form utilizes radio frequency (RF) circuits as indicated. Any type of signal modulation (AM, FM, SSB, QPSK, etc.) may be generated by using either of these two canonical forms. Both of these forms conveniently separate baseband processing from RF processing. Superheterodyne Technique Most receivers employ the superheterodyne receiving technique (see Fig. 69.3). This technique consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency (IF) band, and then extracting the information (or modulation) by using the appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM, AM, satellite, and radar signals. FIGURE 69.1 Generalized transmitter using the AM-PM generation technique