| 摘要 |
<p>A limited-position television tuning system includes a read-only memory (ROM) dedicated to VHF channel coarse tuning information. UHF coarse tuning information and VHF/UHF fine tuning information are contained in an electrically alterable ROM (EAROM). Equalization information for equalizing both fine tuning information and automatic frequency control (AFC) information for VHF is contained in another ROM. The memories are addressed by a vieweroperated switch. Information is read out as pulse-width modulated (PWM) signals by counter-interrogated comparators. A hybrid scaling circuit includes a pair of operational amplifiers (Op Amps) and three transistors, with each PWM signal being applied to a separate transistor. The fine tune transistor, along with the receiver AFC signal, drives the first Op Amp which, in turn, supplies operating potential to the equalization transistor, the output of which is coupled to the input of the second Op Amp. The output of the coarse tuning information transistor also drives an input of the second Op Amp, the output of which is used to develop the tuning voltage.</p> |
