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Integrated telephone answering machine
End-to-end signalling
Fax Machines
-40擄C to +85擄C
signal and requires external software guard time to
validate the DTMF digit. The ZL490x1, with preset
internal guard times, uses a delay steering (DStD)
logic output to indicate the detection of a valid DTMF
digit. The 4-bit DTMF binary digit can be clocked out
synchronously at the serial data (SD) output. The SD
pin is multiplexed with call progress detector output. In
the presence of supervisory tones, the call progress
Description
The ZL490xx is a family of high performance DTMF
receivers which decode all 16 tone pairs into a 4-bit
binary code. These devices incorporate an AGC for
wide dynamic range and are suitable for end-to-end
signalling. The ZL490x0 provides an early steering
(ESt) logic output to indicate the detection of a DTMF
PWDN
VDD
VSS
1
Voltage
Bias Circuit
Steering
Circuit
High
Group
Filter
Anti-
alias
Filter
Dial
Tone
Filter
Low
Group
Filter
Digital
Detector
Algorithm
Code
Converter
and
Latch
Digital
Guard
Time
3
Parallel to
Serial
Converter
& Latch
ESt
or
DStD
ACK
AGC
Mux
SD
2
OSC2
OSC1
(CLK)
Oscillator
and
Clock
Circuit
To All Chip Clocks
Energy
Detection
1.
ZL49010/1 and ZL49030/1 only.
2.
ZL49020/1 and ZL49030/1 only.
3.
ZL490x1 only.
Figure 1 - Functional Block Diagram
1
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