A/D, D/A Converter for PCM transmission system

DETAILED DESCRIPTION It is, therefore, an object of the present invention to provdide a codec which can be commonly adopted in transmission systems which use read/write clocks having a frequency different from one another.
Another object of the present invention is to provide a codec which can make the best use of an entire period of the sampling pulses during the a/d and d/a conversion.
A further object of the present invention is to provide a codec which can be constructed of very simple hardware.
According to the present invention a codec comprises an a/d and d/a conversion circuit, responding to frame pulses and internal operation clocks, for coding an analogue signal to a PCM digital signal and for decoding a PCM digital signal to an analogue signal, and a digital phase locked loop circuit for generating the internal operation clocks by dividing the frequency of applied external clocks by a value which is determined in accordance with a frequency ratio between the frame pulses and the external clocks.
Since the internal operation clocks are generated by dividing the frequency of applied external clocks by a value which is determined in accordance with a frequency ratio between the frame pulses and the external clocks, the codec according the present invention: can be commonly adopted in transmission systems which are use external clocks, in other words, read/write clocks, having respective frequencies which are different from one another; can make the best use of the entirety of a sampling period during a/d and d/a conversion; and can be constructed of simple hardware.
The aforementioned and other related objects and features of the present invention will be apparent from the following description of the present invention, with reference to the accompanying drawings, as well as from the appended claims.