MT8880CS-1 데이터 시트보기 (PDF) - Mitel Networks

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MT8880CS-1

ISO²-CMOS Integrated DTMF Transceiver

Mitel Networks 

MT8880C/MT8880C-1 ISO2-CMOS

EVENTS

Vin

ESt

St/GT

RX0-RX3

b3

A

tREC

B

tREC

TONE #n

tDP

tGTP

C

D

E

tID

tDO

TONE

#n + 1

tDA

TONE

#n + 1

tGTA

DECODED TONE # (n-1)

tPStRX

#n

tPStb3

# (n + 1)

F

VTSt

b2

Read

Status

Register

IRQ/CP

Figure 9 - Receiver Timing Diagram

of time segments is fixed at 32, however, by varying

the segment length as described above the tone

output signal frequency will be varied. The divider

output clocks another counter which addresses the

sinewave lookup ROM.

The lookup table contains codes which are used by

the switched capacitor D/A converter to obtain

discrete and highly accurate DC voltage levels. Two

identical circuits are employed to produce row and

column tones which are then mixed using a low

noise summing amplifier. The oscillator described

needs no “start-up” time as in other DTMF

generators since the crystal oscillator is running

continuously thus providing a high degree of tone

burst accuracy. A bandwidth limiting filter is

incorporated and serves to attenuate distortion

products above 8 kHz. It can be seen from Figure 10

that the distortion products are very low in amplitude.

Scaling Information

10 dB/Div

Start Frequency = 0 Hz

Stop Frequency = 3400 Hz

Marker Frequency = 697 Hz and

1209 Hz

Figure 10 - Spectrum Plot

4-38

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