Second derivative memory-saving all channel digital tuning system

Abstract

A tuning system for a television receiver includes fine tune memories and tuning information memories, the latter having reference channel nominal tuning information for each of the various frequency bands, first increment tuning information for each frequency band and second increment tuning information for each channel. The first increment information represents the initial slope of the tuning characteristic and the second increment information represents the slope of the slope of the tuning characteristic for each channel. Accumulator means add the reference channel and first and second increment informations to derive nominal tuning information for any selected channel. Control logic including counters and latches control the operation of the accumulator means and memories. The accumulator means and fine tune counters are interrogated by counter-driven comparators which develop pulse-width modulated signals corresponding to the tuning information therein. A tuning voltage generator develops the final tuning voltage from the pulse-width modulated signals. Increment tuning information representative of the slope of the tuning characteristic at each channel is derived and used to equalize any auxiliary tuning source. The reference channel information is combined with appropriate numbers of first tuning increments and second tuning increments for deriving nominal tuning information for the selected channel.