A 3μm-CMOS Analogue Audio Circuit for Mobile Telephone Application

An analogue IC for mobile telephone application (Handset IC) is presented. The circuit performs the analogue functions required for the speech channels (low noise microphone amplifier, earphone driver for 130 nF load, sidetone buffer, transmit line driver, speaker line drivers, variable gain-loss stage) and DTMF generation. A buzzer driver has also been integrated for general purpose system signalling. A watchdog circuit supervises the correct functioning of the microprocessor. Common time-continuous and switch-capacitor techniques have been used to minimize the number of external components. The above functions have been implemented in a manner that fulfills the standards NMT DOC.900-3 incl. addendum, NMT DOC.450-3, BABT/SITS/84/13/Aincl. addendums, and EIAIS-19-A. The circuit has been integrated in a standard 3μm-CMOS double-poly single-metal process and requires 26.4 mm2.