| 摘要 |
<p>The basic dual channel pcm coder/decoder arrangement provides PCM/Analogue Codec facilities for use in speech transmission and comprises (a) a pair of transmit channel amplifiers and a pair of receive channel amplifiers controllable for mutually exclusive operation by channel switches and (b) a comparator together with segment-defining ladder networks and associated current steering switching (and compensated current sources). In the encode (A-D), the unit functions as a successive approximation encoder; the particular transmit amplifier creates a voltage condition across the resistors of the two ladder networks and this condition is balanced by the voltage generated by the current sources. A null is consequently produced at the comparator input to govern the PCM output. In the decode mode, both transmit amplifiers are switched "off" and the requisite receive amplifier is switched "on". The PCM signal is presented to the ladder network switches so that the ladder network produces analogue voltages at its resistors and this is applied to the operative receive amplifier.</p> |
