DS8911

DS8911 DS8913 AM FM TV Sound Up-Conversion Frequency Synthesizer April 1990 DS8911 DS8913 AM FM TV Sound Up-Conversion Frequency Synthesizer General Description The DS8911 is a digital Phase-Locked Loop (PLL) frequency synthesizer intended for use as a Local Oscillator (LO) in electronically tuned radios The device is used in conjunction with a serial data controller a loop filter some varactor diodes and several passive elements to provide the local oscillator function for both AM and FM tuning The conventional superheterodyne AM receiver utilizes a low IF or down conversion tuning approach whereby the IF is chosen to be below the frequencies to be received The DS8911 PLL on the other hand utilizes an up-conversion technique in the AM mode whereby the first IF frequency is chosen to be well above the RF frequency range to be tuned This approach eliminates the need for tuned circuits in the AM frontend since the image half IF and other spurious responses occur far beyond the range of frequencies to be tuned Sufficient selectivity and second IF image protection is provided by a crystal filter at the output of the first mixer A significant cost savings can be realized utilizing this upconversion approach to tuning Removal of the AM tuned circuits eliminates the cost of expensive matched varactor diodes and reduces the amount of labor required for alignment down from 6 adjustments to 2 Additional cost savings are realized because up-conversion enables both the AM and FM bands ...