Performance of a direct-conversion receiver with ac coupling

This paper analyzes the performance of a direct-conversion receiver (DCR) with ac coupling when the received signal is a BPSK. Although a DCR with ac coupling is extremely attractive from an implementation perspective, it is employed almost exclusively with 'dc-free' modulation schemes such as binary frequency-shift keying (BFSK). More spectrally efficient modulation schemes, such as BPSK, are believed to suffer from significant performance loss because of the large signal bearing spectrum near dc. However, our analysis shows that by including an equalizer, the performance of a DCR with ac coupling when receiving BPSK signal is orders of magnitude better than previously reported. An equalizer is employed to mitigate the effects of intersymbol interference introduced by ac coupling. Compared to an ideal receiver, the SNR loss of a typical DCR with ac coupling and a linear equalizer is less than 2 dB for ac coupling corner frequencies as large as 30% of the symbol rate.