A single chip /spl Delta/-/spl Sigma/ ADC with a built-in variable gain stage and DAC with a charge integrating subconverter for a 5 V 9600-b/s modem

A 12-b, 19.2-ksamples/s /spl Delta/-/spl Sigma/ A/D and D/A converter for a 9600-b/s facsimile modem analog front end is described. In the proposed /spl Delta/-/spl Sigma/ ADC, the reference voltage is varied to adjust the signal gain, thus, eliminating the need of a variable gain amplifier. The /spl Delta/-/spl Sigma/ DAC uses a 4-b charge integrating subconverter which is insensitive to process variations. >