78A207
MFR1 Receiver
April 2000
DESCRIPTION
The 78A207 is a single-chip, Multi-Frequency (MF)
receiver that can detect all 15 tone-pairs, including
ST and KP framing tones. This receiver is intended
for use in equal access applications and thus meets
both Bell and CCITT R1 central office register
signaling specifications.
The 78A207 employs state-of-the-art switched
capacitor filters in CMOS technology. The receiver
consists of a bank of channel-separation bandpass
filters followed by zero-crossing detectors and
frequency-measurement bandpass filters, an
amplitude check circuit, a timer and decoder circuit,
and a clock generator. The device does not attempt
to identify strings of digits by the KP (key pulse) and
ST (stop) tone pairs.
No anti-alias filtering is needed if the input signal is
band-limited to 26 KHz. The only external
component required is an inexpensive television
“color burst” 3.58 MHz crystal.
The outputs interface directly with standard CMOS
or TTL circuitry and are three-state enabled to
facilitate bus-oriented architecture.
FEATURES
• Meets Bell and CCITT R1 specifications
• 20-pin plastic DIP
• Single low-tolerance 5V supply
• Detects all 15 tone-pairs including ST and KP
• Long KP capability
• Built-in amplitude discrimination
• Excellent noise tolerance
• Outputs in either “n of 6” or hexadecimal code
• Three-state outputs, CMOS-compatible and
TTL-compatible
BLOCK DIAGRAM
PRE-FILTER
ZERO
CROSSING
DETECTORS
VIN
BANDPASS
FILTER
THRESHOLD
DETECTOR
TONE DETECTOR
VOLTAGE
REF
VDD AGN DGND
CSTR
DV
DE
LKP
HEX
D5
D4
D3
D2
D1
D0
EN
X1
X2
CHIP CLOCKS
XOUT
CLOCK
GENERATOR
VOLTAGE DIVIDER
700 700
1500
1700
900
1100
1300
900
1100
1300
1500
1700
R
S
Q
R
S Q
QUAL
LOGIC
QUAL