| 摘要 |
<p>A frequency synthesizer has two cascaded phase-locked loops (48,50), each of which receives an input signal and a feedback signal and generates an output signal. The output of the first phase-locked loop (48) is supplied as input to the second phase-locked loop (50). The output of the second phase-locked loop is supplied as feedback to both the first and second phase-locked loops. The output frequency of the second phase-locked loop is selected by means of programmable frequency dividers (28,30,38,40) inserted in the input and feedback lines of the first phase-locked loop. Such a frequency synthesizer may be used in a television receiver that converts a high-definition television signal (HDTV signal) to a standard television signal for display on a standard size television screen. <IMAGE></p> |
