Analog baseband processor for CDMA/FM portable cellular telephones

62The analog baseband processor is designed for use in dual-mode CDMA/FM cellular telephones, and contains both receive (RX) and transmit (TX) circuitry. The challenge presented by this circuit is to maintain low noise and precise filter characteristics in a high-gain, high-offset system and to recover a small input signal (1mVrms) in the presence of a large jammer (800mVpp). The primary function of the RX circuitry is the down-conversion of IF (intermediate frequency) to analog baseband followed by conversion to digital signals. TX circuits convert digital data into analog baseband signals that are then up-converted to IF. Both CDMA and FM analog processing are done by the circuit. A corresponding digital processor completes the CDMA and FM processing tasks.