| 摘要 |
A telephone system uses above voice-band ASK control and supervisory signals which are appended to digitally encoded voice by forcing the least significant bits to a selected level for transmission to the receiving end. At the receiving end, the ASK is regenerated by a circuit including special filter and a pulse generator. To eliminate audible noise resulting from the filter action, the ASK signal or the pulses from the pulse generator is shifted in phase by about 90 degrees before application to a filter. The result is significantly reduced noise.
|
