avoid slope overload, the input signal, V must not receiving end, each incoming positive or negative pulse causes the change by more than one quantum step (A) in the sampling interval, output voltage from a similar integrator to rise and fall by one 1/fs, i.e. as in Equation 19.63. If is given by Equation 19.64 then quantum step, thereby reproducing the input signal of the sending Equation 19.65 is obtained, its maximum value being given by Equation 19.66 SO that V must satisfy Equation 19.67. Pulse Comparator generator Transmission Baseband input Baseband output Integrator Integrator Figure 19.24 Basic delta modulation system 19/20 Digital modulation (19.63) vantages by adapting the step size under changing signal conditions (Steele, 1975; Peebles, 1976; Taub and Schilling, 1986). In a basic DM system, a rapidly changing input signal results in a long sequence of 1's or 0's being transmitted. In continuously (19.64) variable slope delta modulation (CVSDM), the rate of change of the integrator output is increased if there is a sequence of several 1's or (19.65) O's. Thus, the CVSDM coder can follow a rapidly changing signal more accurately (Taub and Schilling, 1976). (19.66) 19.6.3 Delta sigma modulation Because slope overload causes the dynamic range to decrease with (19.67) frequency, simple DM is unsuitable for baseband signals having a flat frequency spectrum. This disadvantage can be overcome by preceding the delta modulator by an integrator to reduce the high Thus, DM has a dynamic range which is large at low frequencies, frequency energy of its input signal, as shown in Figure 19.25(a). but which decreases with frequency. This is satisfactory for speech, This is known as delta sigma modulation (DSM), (Steele, 1975; since speech signals contain little energy at high frequencies. Peebles, 1976). In order to obtain a flat overall gain/frequency In DM, the output voltage increases and decreases in increments response, a corresponding differentiator can be added at the output of one quantum step; it cannot rema