New generation speech CODEC for digital telephone switching
Shaojun Wei · Journal of Tsinghua University(Science and Technology) · 1999
In order to decrease cost and improve performance of Digial Telephone Switching, a four channel CODEC device based on DSP was designed. In this device, oversampled analog to digital converting technique and digital signal processing technique were used. Due to these techniques, it is possible to take the advantages of digital VLSI technique, implement multi channel speech CODEC in a single chip, and make the cost of switching low. Meanwhile, programmable digital filters were used, the performance of the system can be improved just by adjusting the coefficients of the filters by software according to different line characteristics. This device was fabricated in a 0.5μm CMOS process with double poly and 3 layers metal, and integrated on a die size of 25mm 2. Measurements show that all the necessary CCITT's recommendations are fullfilled.