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.

Abstract: An amplifier circuit including a novel degeneration input stage that permits a low Noise Figure and superior linearity to be achieved in combination. The amplifier is suitable for use in fully integrated direct-conversion tuner circuits, and provides continuously variable gain functionality implemented by steering current away from an output load of the amplifier through differential transistor pairs located in the current signal paths of an input stage. Voltage headroom problems are avoided by placing the attenuation resistors of the degenerated input stage in the signal path, such that there is little or no DC voltage drop across the resistors. Further, this arrangement permits very accurate on-chip matching to an off-chip signal source. The distribution of IP3 values over the gain range of the amplifier, as well as gain and NF characteristics, are dependent on resistor ratios rather than absolute values. These amplifier characteristics are thus largely temperature and process independent.