The SM8223A is a FSK (Frequency shift keying) decoder and DTMF (Dual tone multi-frequency) receiver IC. It is fabricated using a CMOS process and features a power-down function for low power dissipation operation. The FSK decoder and DTMF receiver have the same performance characteristics as dedicated ICs that perform the same functions, with the added benefit of an FSK decoder/DTMF receiver auto-select function1 using the telephone tip/ring input signal. It also features a ring (call signal) signal detection circuit, making for easy construction of low power dissipation, high-performance analog telephone-related applications.