MT88L70 Datasheet, PDF (12/16 Pages) Mitel Networks Corporation – 3 Volt Integrated DTMF Receiver

MT88L70
Data Sheet
EVENTS
V_in
ESt
St/GT
Q₁-Q₄
StD
TOE
A
t_REC
B
t_REC
TONE #n
t_DP
t_GTP
D
C
E
F
G
t_ID
t_DO
TONE
#n + 1
t_DA
TONE
#n + 1
t_GTA
t_PQ
DECODED TONE # (n-1)
t_PSrD
t_QStD
#n
HIGH IMPEDANCE
# (n + 1)
t_PTD
t_PTE
V_TSt
EXPLANATION OF EVENTS
A)
TONE BURSTS DETECTED, TONE DURATION INVALID, OUTPUTS NOT UPDATED.
B)
TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS.
C)
END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMAIN LATCHED UNTIL NEXT VALID
TONE.
D)
OUTPUTS SWITCHED TO HIGH IMPEDANCE STATE.
E)
TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN OUTPUTS (CURRENTLY
HIGH IMPEDANCE).
F)
ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, OUTPUTS REMAIN LATCHED.
G)
END OF TONE #n+1 DETECTED, TONE ABSENT DURATION VALID, OUTPUTS REMAIN LATCHED UNTIL NEXT
VALID TONE.
EXPLANATION OF SYMBOLS
V_in
DTMF COMPOSITE INPUT SIGNAL.
ESt
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
St/GT STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
Q₁-Q₄
StD
4-BIT DECODED TONE OUTPUT.
DELAYED STEERING OUTPUT. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE
REQUIRED GUARD TIME THUS CONSTITUTING A VALID SIGNAL.
TOE
t_REC
t_REC
t_ID
t_DO
t_DP
t_DA
t_GTP
t_GTA
TONE OUTPUT ENABLE (INPUT). A LOW LEVEL SHIFTS Q₁-Q₄ TO ITS HIGH IMPEDANCE STATE.
MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID.
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION.
MINIMUM TIME BETWEEN VALID DTMF SIGNALS.
MAXIMUM ALLOWABLE DROP OUT DURING VALID DTMF SIGNAL.
TIME TO DETECT THE PRESENCE OF VALID DTMF SIGNALS.
TIME TO DETECT THE ABSENCE OF VALID DTMF SIGNALS.
GUARD TIME, TONE PRESENT.
GUARD TIME, TONE ABSENT.
Figure 7 - Timing Diagram
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