TDK Semiconductor Corporation 75T204-IP, 75T204-IL Datasheet
DESCRIPTION
75T204
5V Low-Power Subscriber
DTMF Receiver
April 2000
FEATURES
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-ofthe-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)
BLOCK DIAGRAM
ANALOG
PRE-PROCESSOR
60 Hz
PREEMP
REJECT
BAND
SPLIT
FILTERS
BS1 852
BS2
ZERO
CROSSING
DETECTORS
• 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
BANDPASS FILTERS
697
770
941
1209
AMPLITUDE
DETECTORS
TIMING
CIRCUITRY
1Mz
ATB
XEN
XIN
XOUT
1336
DATA STROBE
OUTPUT
DECODER
DV
DATA CLEAR
OUTPUT
REGISTER
DV
D1
D2
D4
D8
EN
1477
1633
÷ 8
CLOCK
GENERATOR
VP GND
CHIP CLOCKS
POWER REGULATOR
VOLTAGE
REF
75T204
5V Low-Power Subscriber
DTMF Receiver
DESCRIPTION (continued)
and to provide output timing and decoding. The
outputs interface directly to standard CMOS circuitry
and are three-state enabled to facilitate bus-oriented
architectures.
ANALOG IN
This pin accepts the analog input. It is internally
biased so that the input signal may be AC coupled.
The input may be DC coupled as long as it does not
exceed the positive supply. Proper input coupling is
illustrated in Figure 1.
The 75T204 is designed to accept sinusoidal input
wave forms but will operate satisfactorily with any
input that has the correct fundamental frequency
with harmonics less then -20 dB below the
fundamental.
CRYSTAL OSCILLATOR
The 75T204 contains an onboard inverter with
sufficient gain to provide oscillation when connected
to a low-cost television “colorburst” crystal. The
crystal oscillator is enabled by tying XEN high. The
crystal is connected between XIN and XOUT. A
1 Mz 10% resistor is also connected between these
pins. In this mode, ATB is a clock frequency output.
Other 75T204’s (or 75T202's) may use the same
frequency reference by tying their ATB pins to the
ATB of a crystal connected device. XIN and XEN of
the auxiliary devices must then be tied high and low
respectively. Ten devices may run off a single
crystal-connected 75T204 (or 75T202) as shown in
Figure 2.
OUTPUTS D1, D2, D4, D8 and EN
Outputs D1, D2, D4, D8 are CMOS push-pull when
enabled (EN high) and open circuited (high
impedance) when disabled by pulling EN low.
These digital outputs provide the hexadecimal code
corresponding to the detected digit. The digital
outputs become valid after a tone pair has been
detected (DV is high) and they are then cleared
when a valid pause is timed. The hexadecimal
codes are described in Table 1.
DV
DV signals a detection by going high after a valid
tone pair is sensed and decoded at the output pins
D1, D2, D4, and D8. DV remains high until a valid
pause occurs.
N/C PINS
These pins have no internal connection and may be
left floating.
Output Code
Digit D8 D4 D2 D1
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
0 1 0 1 0
* 1 0 1 1
# 1 1 0 0
A 1 1 0 1
B 1 1 1 0
C 1 1 1 1
D 0 0 0 0
TABLE 1: Output Codes
2
75T204
5V Low-Power Subscriber
DTMF Receiver
VIN < VP
Analog In
7
V
P
VIN > VP
0.01 µF
(On Chip)
10 pF
Analog In 10 pF
>100 kΩ
GND
FIGURE 1: Input Coupling
7
V
P
(On Chip)
GND
>100 kΩ
XIN
10
ATB
Up to 10 Devices
11
11
75T204
XIN Connected to VP
10
FIGURE 2: Crystal Connections
XOUT
9
VP
XEN
6
XEN
675T204
3
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