®
MT3170B/71B, MT3270B/71B, MT3370B/71B
Wide Dynamic Range DTMF Receiver
Features
•
•
•
•
•
•
•
•
•
Wide dynamic range (50dB) DTMF Receiver
Call progress (CP) detection via cadence
indication
4-bit synchronous serial data output
Software controlled guard time for MT3x70B
Internal guard time circuitry for MT3x71B
Powerdown option (MT317xB & MT337xB)
4.194304MHz crystal or ceramic resonator
(MT337xB and MT327xB)
External clock input (MT317xB)
Guarantees non-detection of spurious tones
ISSUE 2
May 1995
Ordering Information
MT3170/71BE
8 Pin Plastic DIP
MT3270/71BE
8 Pin Plastic DIP
MT3370/71BS
18 Pin SOIC
MT3370/71BN
20 Pin SSOP
-40 °C to +85 °C
Applications
•
•
•
Integrated telephone answering machine
End-to-end signalling
Fax Machines
Description
The MT3x7xB 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 MT3x70B provides an early steering
(ESt) logic output to indicate the detection of a DTMF
signal and requires external software guard time to
validate the DTMF digit. The MT3x71B, 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 detector circuit indicates the cadence
(i.e., envelope) of the tone burst. The cadence
information can then be processed by an external
microcontroller to identify specific call progress
signals. The MT327xB and MT337xB can be used
with a crystal or a ceramic resonator without
additional components. A power-down option is
provided for the MT317xB and MT337xB.
PWDN
VDD
VSS
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
Parallel to
Serial
Converter
& Latch
ESt
or
DStD
ACK
INPUT
AGC
Mux
SD
OSC2
OSC1
(CLK)
Oscillator
and
Clock
Circuit
To All Chip Clocks
Energy
Detection
MT3170B/71B and MT337xB only.
MT3270B/71B and MT337xB only.
MT3x71B only.
Figure 1 - Functional Block Diagram
4-3
MITEL [ MITEL NETWORKS CORPORATION ]
