| 摘要 |
In a channel selecting apparatus for a television receiver having a tuner with a voltage-controlled variable reactance device as its tuning element; digital codes representing or identifying respective channels are stored at respective addresses in a memory, and a digital-to-analog converter provides an analog control voltage for the variable reactance device in correspondence to each digital code selectively read out of the memory in a channel selecting mode of the apparatus. Further, in a programming mode of the apparatus, the changing digitally coded counts of a counter which is counting sweep pulses are applied to the digital-to-analog converter for similarly controlling the variable reactance device and selected counts of the counter, for example, those which result in the appearance on the receiver screen of pictures or test patterns broadcast by selected television stations or channels, are written at selected addresses in the memory as the channel identifying digital codes. Preferably, the digital-to-analog converter is constituted by a pulse-width modulator which produces a chain of pulses at a constant repetition rate with the widths of such pulses being varied in dependence on the absence of coincidence between a circulating digital code and the digitally coded count from the counter as established either by read out of a channel identifying digital code from the memory or by counting of the sweep pulses, and the output of the modulator is passed through a low-pass filter to provide the analog control voltage in dependence on the modulated pulse width. |
