Tuning device for liquid crystal television

A tuning device for a liquid crystal television having a tuner for tuning according to a local oscillation frequency, a linear circuit for amplifying and detecting an intermediate frequency signal produced by the tuner, an A/D converter for converting a video signal detected by the linear circuit to a digital video signal, and a liquid crystal display unit for displaying video according to the digital video signal output from the A/D converter, comprising:

• a power source;
• a prescaler for dividing the local oscillation frequency of the tuner by a predetermined ratio when said power source is connected to the prescaler,
• a programmable counter for dividing further the frequency signal divided by said predetermined ratio by said prescaler to a selected value when said power source is connected to said couter,
• a phase comparator for comparing in phase the signal divided further by said counter with a reference frequency signal when said power source is connected to the phase comparator,
• a low pass filter for generating a tuning voltage for controlling the local oscillation frequency of said tuner in response to a comparison signal output from said comparator,
• mode deciding means for selecting one of a tuning mode and a receiving mode in response to operating conditions of the liquid crystal television, to output a decision signal,
• switching means for interrupting said power source at least to said prescaler when the receiving mode is determined by said mode deciding means, and
• holding means coupled to said mode deciding means for holding the tuning voltage of said tuner constant, including means for generating an AFT signal for drawing an S-curve characteristic with the intermediate frequency as a center, when in the receiving mode.