Impact of spectral shaping location on the performance of communication transceivers

In this paper, the impact of the filtering location in a communication transceiver is investigated. In a classic architecture, the spectral shaping is done in base band, i.e., before signal amplification. This approach may increase significantly the peak-to-average of the signal. This in turn means that the power amplifier has to be operated at a higher back-off thus increasing its size and reducing its DC-RF efficiency. The use of analog filtering after amplification can circumvent these limitations. However, given the limited control on the analog filter, system linearity will be affected. In this paper, we study and compare the performance of both architectures with digital and analog filters. It is found that an optimized digital filter at the receiver allows obtaining excellent linearity with analog, post-amplifier, filter at the transmitter.