75T202

DESCRIPTION w The 75T202 and 75T203 are complete Dual-tone Multifrequency (DTMF) receivers detecting a selectable group of 12 or 16 standard digits. No front-end pre-filtering is needed. The only externally required components are an inexpensive 3.58 MHz television “colorburs” crystal (for frequency reference) and a bias resistor. Extremely high system density is made possible by using the clock output of a crystal-connected 75T202 or 75T203 receiver to drive the time bases of additional receivers. Both are monolithic integrated circuits fabricated with low-power, complementary symmetry MOS (CMOS) processing. They require only a single low tolerance voltage supply and are packaged in a standard 18-pin plastic DIP. w at .D w h S a t e e 4U m o .c 75T202/203 5V Low-Power DTMF Receiver February 1998 FEATURES Central office quality NO front-end band-splitting filters required Single, low-tolerance, 5-volt supply Detects either 12 or 16 standard DTMF digits Uses inexpensive 3.579545 MHz crystal for reference Excellent speech immunity Output in either 4-bit hexadecimal code or binary coded 2-of-8 18-pin DIP package for high system density Synchronous or handshake interface Three-state outputs Early detect output (75T203 only) (continued) BLOCK DIAGRAM PRE-PROCESSOR ANALOG 60 Hz REJECT PREEMP BAND SPLIT FILTERS BS1 ZERO CROSSING DETECTORS ATB XEN XIN 1Mz XOUT w w ÷8 .D w BS2 t a S a 697 770 852 941 1209 1336 1477 1633 CHIP CLOCKS e h t ...