MT8880C Просмотр технического описания (PDF) - Zarlink Semiconductor Inc

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MT8880C

ISO²-CMOS Integrated DTMF Transceiver

Zarlink Semiconductor Inc 

ISO2-CMOS MT8880C

Burst Mode

In certain telephony applications it is required that

DTMF signals being generated are of a specific

duration determined either by the particular

application or by any one of the exchange transmitter

specifications currently existing. Standard DTMF

signal timing can be accomplished by making use of

the Burst Mode. The transmitter is capable of issuing

symmetric bursts/pauses of predetermined duration.

This burst/pause duration is 51 ms±1 ms which is a

standard interval for autodialer and central office

applications. After the burst/pause has been issued,

the appropriate bit is set in the Status Register

indicating that the transmitter is ready for more data.

The timing described above is available when DTMF

mode has been selected. However, when CP mode

(Call Progress mode) is selected, a second burst/

pause time of 102 ms ±2 ms is available. This

extended interval is useful when precise tone bursts

of longer than 51 ms duration and 51 ms pause are

desired. Note that when CP mode and Burst mode

have been selected, DTMF tones may be transmitted

only and not received.

In applications where a non-standard burst/pause

duration is required, burst mode must be disabled

and the transmitter gated on and off by an external

hardware or software timer.

Single Tone Generation

A single tone mode is available whereby individual

tones from the low group or high group can be

generated. This mode can be used for DTMF test

equipment applications, acknowledgment tone

generation and distortion measurements. Refer to

Control Register B description for details.

Distortion Calculations

The MT8880C is capable of producing precise tone

bursts with minimal error in frequency (see Table 1).

The internal summing amplifier is followed by a first-

order lowpass switched capacitor filter to minimize

harmonic components and intermodulation products.

The total harmonic distortion for a single tone can be

calculated using 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

EXPLANATION OF EVENTS

A)

TONE BURSTS DETECTED, TONE DURATION INVALID, RX DATA REGISTER NOT UPDATED.

B)

TONE #n DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.

C)

END OF TONE #n DETECTED, TONE ABSENT DURATION VALID, INFORMATION IN RX DATA REGISTER

RETAINED UNTIL NEXT VALID TONE PAIR.

D)

TONE #n+1 DETECTED, TONE DURATION VALID, TONE DECODED AND LATCHED IN RX DATA REGISTER.

E)

ACCEPTABLE DROPOUT OF TONE #n+1, TONE ABSENT DURATION INVALID, DATA REMAINS UNCHANGED.

F)

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.

St/GT

STEERING INPUT/GUARD TIME OUTPUT. DRIVES EXTERNAL RC TIMING CIRCUIT.

RX0-RX3

b3

4-BIT DECODED DATA IN RECEIVE DATA REGISTER

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

tDA

tGTP

tGTA

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.

TIME TO DETECT VALID FREQUENCIES ABSENT.

GUARD TIME, TONE PRESENT.

GUARD TIME, TONE ABSENT.

Figure 11 - Description of Timing Events

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