Digital circuit with band limiting characteristics for modem

摘要

The input digital signal is applied to a transition detector which causes an up/down counter to increment or decrement each time a transition is detected. The output of the counter is utilized to address a read only memory (ROM) which, in turn, generates binary words representing first and second integers. These binary words are used to control a programmable divider to generate an output having a frequency which moves between two values corresponding to the digital input. The rate at which the frequency changes between the two values is controlled by the ROM contents. In the implementation, the frequency changes with a raised cosine shape.