The CD22859 is a CMOS dual-tone multifrequency (DTMF) tone generator for use in dual-tone telephone dialing systems. The device can easily be interfaced to a standard push-button telephone keyboard to provide enabling operation directly with the telephone lines.

The CD22859 generates standard DTMF sinusoidal dialing tones from an on-chip reference crystal oscillator. The reference oscillator uses an inexpensive 3.579545MHz color TV crystal to create highly stable and accurate tones. The sinusoidal tones are digitally synthesized by a stair-step approximation.

Features

• Mute Drivers On-Chip

• Device Power can Either be Regulated DC or Telephone Loop Current

• Use of an Inexpensive 3.579545MHz TV Crystal Provides High Accuracy and Stability for all Frequencies

Applications

• For Use In Dual-tone Telephone Dialing Systems