HYBRID DELTA MODULATORS FOR DIGITAL ENCODING AT LOW BIT RATES

A performance comparison study of four HDM systems is presented. The four systems studied are hybrid companding delta modulation (HCDM), hybrid constant factor incremental DM (HCFIDM), song hybrid companding DM (SHCDM) and modified SHCDM (MSHCDM). The study was done at low bit rates with three different input signals. According to our results, the MSHCDM always performs better while the HCDM systems may not always be good. Further, for low frequency input signals the dynamic range of SHCDM and HCFIDM is much wider than that of HCDM. In a noisy channel, the results for HCDM at a bit rate of 24 kbs s-1 indicate that the values of SNR at an error rate of 0.001 and 0.01 are, respectively, 15 dB and 6 dB, whereas in the case of HCFIDM and SHCDM they are 16 dB and 10 dB.