An analog front end for a two-chip 2400-bit/s voice-band modem

A complete two-chip solution comprised of an analog front end (AFE) and a general-purpose microcontroller (μC) for a full-duplex 2400-b/s modem is discussed. The μC performs all the necessary digital signal processing algorithms for modem signals along with providing software for modem control and the widely used AT command set. The AFE chip incorporates a ROM-based transmitter, 51 orders of filtering for channel selection, an automatic pain control circuit, and many other complex analog signal processing functions employing 65 op-amps on a 53000-mil/SUP 2/ die area with 150-mW power in a CMOS process. Design details on some of the functional blocks of the AFE are presented.