75T204 Datasheet, PDF (1/9 Pages) List of Unclassifed Manufacturers – 5V Low-Power Subscriber DTMF Receiver

DESCRIPTION
The 75T204 is a complete Dual-Tone Multifrequency
(DTMF) receiver that detects 16 standard digits. No
front-end pre-filtering is needed. The only external
components required are an inexpensive 3.58-MHz
television “colorburst” crystal for frequency reference
and a bias resistor. An Alternate Time Base (ATB)
is provided to permit operation of up to 10 75T204's
from a single crystal. The 75T204 employs state-of-
the-art "switched-capacitor" filter technology,
resulting in approximately 40 poles of filtering, and
digital circuitry on the same CMOS chip. The analog
input signal is pre-processed by 60-Hz reject and
band split filters and then zero-cross detected to
provide AGC. Eight bandpass filters detect the
individual tones. Digital processing is used to
measure the tone and pause durations
(continued)
75T204
5V Low-Power Subscriber
DTMF Receiver
FEATURES
April 2000
• Intended for applications with less
requirements than the 75T202/75T203
• 14-pin plastic DIP or 16-pin SO package for
high system density
• NO front-end band-splitting filters required
• Single low-tolerance 5-volt supply
• Detects all 16 standard DTMF digits.
• Uses an inexpensive 3.579545-MHz crystal
• Excellent speech immunity
• Output in 4-bit hexadecimal code
• Three-state outputs for microprocessor
interface
BLOCK DIAGRAM
ANALOG
PRE-PROCESSOR
60 Hz
REJECT
PREEMP
BAND
SPLIT
FILTERS
BS1
BS2
ZERO
CROSSING
DETECTORS
BANDPASS FILTERS
697
770
852
941
1209
AMPLITUDE
DETECTORS
TIMING
CIRCUITRY
ATB
XEN
XIN
1Mz
XOUT
1336
1477
1633
÷8
CLOCK
GENERATOR
CHIP CLOCKS
DV
DV
DATA STROBE
D1
D2
OUTPUT
DECODER
OUTPUT
REGISTER
D4
POWER REGULATOR
VP
GND
VOLTAGE
REF
D8
DATA CLEAR
EN