IL9270
PIN DESCRIPTIONS
NAME
PIN
DESCRIPTION
ESt
16
Early steering output. Presents a logic high immediately when the digital
algorithm detects a recognizable tone-pair (signal condition). Any momentary
loss of signal condition will cause ESt to return to a logic low.
GS
3
Gain Select. Gives access to output of front-end differential amplifier for
connection of feedback resistor.
IC
IN+
IN-
5,6
Internal Connection. Must be tied to GND.
1
Non-Inverting Input
Inverting Input
Clock Input
Connections to the front-end
differential amplifier.
2
7
C1
3.579545 MHz crystal connected between
these pins completes internal oscillator.
C2
8
Clock Output
Q1-Q4
11-14
3-state data outputs. When enabled by OE, provide the code corresponding to the
last valid tone-pair received.
StD
15
17
Delayed steering output. Presents a logic high when a received tone-pair has been
registered and the output latch updated; returns to logic low when the voltage on
St/GT falls below VTSt
.
St/GT
Steering input/guard time output (bi-directional). A voltage greater than VTSt
,
detected at St causes the device to register the detected tone-pair and update the
output latch. A voltage less than VTSt frees the device to accept a new tone-pair.
The GT output acts to reset the external steering time-constant; its state is a
function of ESt and the voltage on St.
OE
10
3-state output enable (input). Logic high enables the outputs Q1-Q4. Internal
pull-up.
VCC
18
4
Positive power supply, +5 V.
VREF
Reference voltage output, nominally VCC /2. May be used to bias the inputs at
mid-rail.
GND
9
Negative power supply, normally connected to 0 V.
FUNCTIONAL DESCRIPTION
The IL9270 monolithic DTMF receivers offer small size,
low power consumption and high performance. The
architecture consists of a bandsplit filter section, which
separates the high and low tones of a receiver pair,
followed by a digital counting section which verifies the
frequency and duration of the received tones before
passing the corresponding code to the output bus.
order for the low group. The band-widths of which
correspond to the bands enclosing the low-group and
high-group tones (see Figure 1). The filter section also
incorporates notches at 350 Hz and 440 Hz for
exceptional dial-tone rejection. Each filter output is
followed by a second order switched-capacitor section
which smooths the signals prior to limiting. Limiting is
performed by high-gain comparators which are provided
with hysteresis to prevent detection of unwanted low-
level signals and noise; the outputs of the comparators
provide full-rail logic swings at the frequencies of the
incoming tones.
Filter Section
Separation of the low-group and high-group tones is
achieved byapplying the dual-tone signal to the inputs of
two filters - a sixth order for the high group and an eight
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