| 摘要 |
71041-14R A digital tuning system for use in radio frequency multisignal receiving systems, e.g., a CATV converter, utilizes a closed feedback loop digital arrangement for channel selection (local oscillator frequency control) and channel fine tuning. More particularly, the system includes an oscillator responsive to a variable control voltage for generating an oscillation having a frequency dependent on the magnitude of the control voltage. A sampler samples the actual output frequency of the oscillator for a predetermined interval of time and generates a first digital word representing the actual value of the frequency. A selected one of plurality of address words is generated in response to incoming channel information. Each address word represents a particular operating channel in a CATV system. A memory stores various second digital words, each of the second digital words representing any desired frequency of oscillation for the oscillator. One of the second digital words is retrieved from the memory in response to the address word, the particular location of the second digital word within the memory being identified by the address word representing a particular operating channel in the CATV system. The second digital word retrieved from the memory is stored and a comparator compares the values of the first digital word and the value of the stored second digital word. The control voltage of the oscillator is varied in response to a difference in value between the first digital word and the stored second digital word determined by the comparator. In this way, the actual frequency value is changed to the desired frequency value. |
