Method and apparatus for filter selection from a frequency synthesizer data

Abstract

Modern portable communications units, and in particular cellular telephones, can contain several frequency bands for receiving and several frequency bands for transmitting signals. Typically these units contain a baseband unit and a frequency synthesizer unit, which may be embodied as VLSI integrated circuits. The baseband unit commonly contains the user interfaces and control signals for controlling other portions of the circuitry. The second unit is sometimes called a frequency synthesizer unit. The second unit is dedicated to producing frequencies that are used by the communications system to create RF signals for broadcast and also to take RF signals and extract the modulated signal from them for decoding. As personal communications units have begun using an increasing number of bands it is often necessary to configure different filters to receive or broadcast the different bands. Typically, the baseband Integrated Circuit or separate circuitry does this filter configuration management. The data for filter switching, however, can be decoded from the data that is communicated across the serial bus to the frequency synthesizer integrated circuit. By allowing the frequency synthesizer Integrated Circuit to control the filtering as well as the frequency synthesizer functions, integrated circuit pins can be eliminated from the baseband integrated circuit. In addition, timing and latency problems involved with commanding the frequency change over a serial bus and switching filters directly are eliminated.