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 (/spl mu/C) for a full-duplex 2400-b/s modem is discussed. The /spl mu/C 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.