Variable ramp speed TV tuning system for rapid channel tuning

• US 4,374,437 A
• Filed: 12/29/1980
• Issued: 02/15/1983
• Est. Priority Date: 12/29/1980
• Status: Expired due to Fees

• Current Assignee: Zenith Radio Corporation (LG Corporation)
• Original Assignee: Zenith Radio Corporation (LG Corporation)
• Inventors: Falater, Scott L., Citta, Richard W.
• Primary Examiner(s): NG, JIN FAY
• Application Number:
  US06/220,619
• Time in Patent Office: 778 Days
• Field of Search: 455/164, 455/169, 455/182, 455/184-186, 358/193.1, 358/195.1
• US Class Current: 455/164.2
• CPC Class Codes: H03J 1/0041 for frequency synthesis with counters or frequency dividers
• CPC Class Codes: H03J 7/26 in which an automatic frequency control circuit is brought into action after the scanning action has been stopped

Abstract

Disclosed is a microcomputer-controlled frequency synthesis television tuning system utilizing variable tuning ramp speeds following channel selection. Channel tuning is expedited by means of three ramping speeds employed during the tuning process. The system initially ramps quickly toward the selected channel and then automatically and incrementally reduces tuning speed as the proper frequency is approached. Once the proper frequency has been reached, the variable ramp speed signal acquisition mode is terminated and an AFC mode is initiated. Large frequency changes are thus made possible over short periods to accomodate widely separated channels efficiently.

Claims

1. In a signal seeking television tuning system including tuning means for developing a local oscillator signal, channel selector means for providing signals representative of a selected VHF, UHF or CATV television channel to said tuning means, mixer means for combining said local oscillator signal with a received television signal in generating an intermediate frequency signal, automatic frequency control means coupled to said mixer means for detecting the video components of said intermediate frequency signal and for locking said tuning means to the carrier frequency of said received television signal, a system for providing a tuning voltage to said tuning means comprising:

frequency divider means coupled to said tuning means for generating a divided-down local oscillator signal;

variable, programmable counter means coupled to said frequency divider means for receiving and measuring the frequency of said divided-down local oscillator signal with a given frequency measuring resolution;

counter control means coupled to said programmable counter means for changing the frequency measuring resolution of said programmable counter, said counter control means including;

loading means for sequentially providing a plurality of control inputs to said programmable counter means with the counting interval of said counter means changed in response thereto, wherein each successive counting interval is of increasing duration; and

clock generator means for applying a clock pulse train to said counter means during each of said counting intervals, the duration of each of said counting intervals determining the frequency measuring resolution of said counter means, with the frequency measuring resolution of said counter means increasing with increasing counting interval duration;

programmable comparator means coupled to said counter means for comparing the divided-down local oscillator signal frequency with a predetermined frequency representing a selected channel and for generating a tuning voltage correction signal representing the difference between said frequencies; and

variable ramp voltage generating means coupled to said comparator means and to said tuning means for receiving said tuning voltage correction signal, developing a tuning voltage signal in response thereto, and providing said tuning voltage signal to said tuning means in ramping said divided-down local oscillator signal toward said predetermined frequency representing the selected television channel at a given ramping rate, the ramping rate of said ramp voltage generating means being successively decreased in a step-wise manner when the frequency difference between said local oscillator signal and said received television signal is within the frequency measuring resolution of said counter means in rapidly tuning said television receiver to said selected channel.

2. A system as in claim 1 wherein said counter control means provides three separate counting intervals and clock pulse trains to said counter means, with each successive counting interval of increasing duration and each successive frequency comparison in said comparator means having increasing frequency resolution in providing a three step ramping voltage to said ramp voltage generating means with each successive ramping rate of decreasing magnitude.

3. A system as in claim 2 further comprising timing delay means coupled to said loading means for decreasing counting interval duration when a UHF or CATV channel is selected thus increasing the ramping rate of said ramp voltage generating means over the UHF and CATV bands.

4. A system as in claim 3 wherein said loading means sequentially provides counting intervals of 2.458, 6.144 and 12.288 milliseconds to said counter means when a VHF channel is selected and sequentially provides counting intervals of 0.41, 1.024 and 2.048 milliseconds to said counter means when a UHF or CATV channel is selected resulting in frequency resolutions for the respective high, medium and low ramping speeds of 1 MHz, 333 KHz and 167 KHz over the VHF band and 6, 2 and 1 MHz over the UHF and CATV bands.

5. In a signal seeking television tuning system including tuning means for developing a local oscillator signal, channel selector means for providing signals representative of a selected VHF, UHF or CATV television channel to said tuning means, mixer means for combining said local oscillator signal with a received television signal in generating an intermediate frequency signal, automatic frequency control means coupled to said mixer means for detecting the video components of said intermediate frequency signal and for locking said tuning means to the carrier frequency of said received television signal, a system for providing a tuning voltage to said tuning means comprising:

frequency divider means coupled to said tuning means for generating a divided-down local oscillator signal;

variable, programmable counter means coupled to said frequency divider means for receiving and measuring the frequency of said divided-down local oscillator signal with a given frequency measuring resolution;

counter control means coupled to said programmable counter means for changing the frequency measuring resolution of said programmable counter means, said counter control means including;

loading means for sequentially providing a plurality of control inputs to said programmable counter means with the counting interval of said counter means changed in response thereto, wherein each successive counting interval is of increasing duration;

clock generator means for applying a clock pulse train to said counter means during each of said counting intervals, the duration of each of said counting intervals determining the frequency measuring resolution of said counter means, with the frequency measuring resolution of said counter means increasing with increasing counting interval duration; and

timing delay means coupled to said loading means for decreasing counting interval duration when a UHF or CATV channel is selected;

programmable comparator means coupled to said counter means for comparing the divided-down local oscillator signal frequency with a predetermined frequency representing a selected channel and for generating a tuning voltage correction signal representing the difference between said frequencies; and

variable ramp voltage generating means coupled to said comparator means and to said tuning means for receiving said tuning voltage correction signal, developing a tuning voltage signal in response thereto, and providing said tuning voltage signal to said tuning means in ramping said divided-down local oscillator signal toward said predetermined frequency representing the selected television channel at a given ramping rate, the ramping rate of said ramp voltage generating means being successively decreased in a step-wise manner when the frequency difference between said local oscillator signal and said received television signal is within the frequency measuring resolution of said counter means in rapidly tuning said television receiver to said selected channel with higher sequential ramping rates employed in tuning to a UHF or CATV channel and lower sequential ramping rates employed in tuning to a VHF channel.