A 200-MHz IFBICMOS signal component separator for linear LINC transmitters

The linear amplification with nonlinear components (LINC) transmitter is an architecture that provides linear amplification using nonlinear but power efficient amplifiers. The signal component separator (SCS) is a crucial signal processing function of LINC. It forms two constant-amplitude phase-modulated signal components from the input signal. Due to the nonlinear signal processing involved, digital signal processing (DSP) implementation of the SCS at baseband has so far been assumed to be the best choice although it suffers from matching, bandwidth and power consumption problems. In this paper a new SCS architecture based on analog integrated circuit techniques is presented to avoid the disadvantages in a DSP-based realization. A 200-MHz IF SCS chip using the proposed architecture was designed and fabricated in a 0.8 mu m BiCMOS process. An experimental LINC transmitter was built with the SCS chip,nonlinear amplifiers and a power combiner. Test results showed that spurious levels around -50 dBc could be obtained with a pi/4-shifted DQPSK modulated North American Digital Cellular (NADC) signal. This implies a high degree of linearity in the implemented LINC transmitter.