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Discrete signals
Published in J. Dunlop, D. G. Smith, Telecommunications Engineering, 2017
The dynamic range of delta modulation may be increased by a form of companding. In the case of the delta modulator the slope of the voltage across the integrating capacitor is varied with input signal amplitude. This gives rise to continuously variable slope delta modulation (CVSDM). Essentially the output of the delta modulator is monitored and when several successive pulses have the value ‘1’ or ‘0’ (indicating that slope overload is occurring) the amplitude of the charging voltage V is increased thereby increasing the slope of the integrator output. When the output returns to 010101 overload is removed and the step size may be progressively reduced. The analysis of several forms of CVSDM is covered in Steele.6
An efficient two-digit adaptive delta modulation for Laplacian source coding
Published in International Journal of Electronics, 2019
Zoran Peric, Bojan Denic, Vladimir Despotovic
Slope overload distortion problem can be addressed using Adaptive Delta Modulation (ADM) (Jayant & Noll, 1984; Sayood, 2005), where the step size adaptation is performed according to changes in the input signal. An example of ADM is the Constant Factor Delta Modulation (CFDM), where one- or two-bit memory is introduced to estimate the step size at each sampling instant (Sayood, 2005). In Continuously Variable Slope Delta Modulation (CVSDM) the step size of the approximated signal is progressively increased or decreased, in case the same state has been observed three times in a row. Various multi-bit and multi-digit DM systems were proposed for variable step size estimation (Denic, Peric, & Despotovic, 2017; Prosalentis & Tombras, 2007; Tombras, 1990a, 1990b). The adaptive 2-digit system has been discussed in Tombras (1990a), that uses both ‘memory’ and ‘look ahead’ step size estimation and generates output codeword consisting of a binary and a ternary digit. The implementation of 2-digit ADM has been presented in Tombras (1990b), while a proper line coding format for a 2-digit ADM is provided in Tombras (1992). The modification of such system has been proposed in Prosalentis and Tombras (2007) that eliminates the need for a ternary digit and produces 2-bit output codeword. The ADM algorithm with three-level quantization designed for variable length code-words has been studied in Denic et al. (2017), where the adaptation is framewise. The algorithms based on Sigma Delta Modulation (SDM) have also received significant attention (Aldajani & Sayed, 2001; Frick, Dadouche, & Berviller, 2016; Prosalentis & Tombras, 2008, 2009; Zhang & Shi, 2018; Zierhofer, 2000). Basically, the SDM system is characterized by an integrator added in front of the ordinary DM, followed by a differentiator in front of the DM demodulator.