MT8880C
Data Sheet
Equation 1, which is the ratio of the total power of all the extraneous frequencies to the power of the fundamental
frequency expressed as a percentage. The Fourier components of the tone output correspond to V2f.... Vnf as
measured on the output waveform. The total harmonic distortion for a dual tone can be calculated using Equation 2.
VL and VH correspond to the low group amplitude and high group amplitude, respectively, and V2IMD is the sum of all the
intermodulation components. The internal switched-capacitor filter following the D/A converter keeps distortion products
down to a very low level as shown in Figure 10.
EXPLANATION OF EVENTS
A)
B)
C)
TONE BURSTS DETECTED, TONE DURATION INVALID, RX DATA REGISTER NOT UPDATED.
TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER RETAINED
UNTIL NEXT VALID TONE PAIR.
D)
E)
F)
TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.
ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, DATA REMAINS UNCHANGED.
END OF TONE #n+1 DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER
RETAINED UNTIL NEXT VALID TONE PAIR.
EXPLANATION OF SYMBOLS
Vin
DTMF COMPOSITE INPUT SIGNAL.
ESt
EARLY STEERING OUTPUT. INDICATES DETECTION OF VALID TONE FREQUENCIES.
STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.
4-BIT DECODED DATA IN RECEIVE DATA REGISTER
St/GT
RX0-RX3
b3
DELAYED STEERING. INDICATES THAT VALID FREQUENCIES HAVE BEEN PRESENT/ABSENT FOR THE REQUIRED
GUARD TIME THUS CONSTITUTING A VALID SIGNAL. ACTIVE LOW FOR THE DURATION OF A VALID DTMF
SIGNAL.
b2
INDICATES THAT VALID DATA IS IN THE RECEIVE DATA REGISTER. THE BIT IS CLEARED AFTER THE STATUS
REGISTER IS READ.
IRQ/CP
INTERRUPT IS ACTIVE INDICATING THAT NEW DATA IS IN THE RX DATA REGISTER. THE INTERRUPT IS CLEARED
AFTER THE STATUS REGISTER IS READ.
tREC
tREC
tID
tDO
tDP
MAXIMUM DTMF SIGNAL DURATION NOT DETECTED AS VALID.
MINIMUM DTMF SIGNAL DURATION REQUIRED FOR VALID RECOGNITION.
MINIMUM TIME BETWEEN VALID SEQUENTIAL DTMF SIGNALS.
MAXIMUM ALLOWABLE DROPOUT DURING VALID DTMF SIGNAL.
TIME TO DETECT VALID FREQUENCIES PRESENT.
tDA
tGTP
tGTA
TIME TO DETECT VALID FREQUENCIES ABSENT.
GUARD TIME, TONE PRESENT.
GUARD TIME, TONE ABSENT.
Figure 11 - Description of Timing Events
V22f + V23f + V24f + .... V2
nf
THD(%) = 100
Vfundamental
Equation 1. THD (%) For a Single Tone
10
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
