MT8889C 데이터 시트보기 (PDF) - Zarlink Semiconductor Inc

부품명

상세내역

제조사

MT8889C

Integrated DTMFTransceiver with Adaptive Micro Interface

Zarlink Semiconductor Inc 

MT8889C

applications, leaving R1 to be selected by the

designer. Different steering arrangements may be

used to select independent tone present (tGTP) and

tone absent (tGTA) guard times. This may be

necessary to meet system specifications which place

both accept and reject limits on tone duration and

interdigital pause. Guard time adjustment also allows

the designer to tailor system parameters such as talk

off and noise immunity.

Increasing tREC improves talk-off performance since

it reduces the probability that tones simulated by

speech will maintain a valid signal condition long

enough to be registered. Alternatively, a relatively

short tREC with a long tDO would be appropriate for

extremely noisy environments where fast acquisition

time and immunity to tone drop-outs are required.

Design information for guard time adjustment is

shown in Figure 6. The receiver timing is shown in

Figure 7 with a description of the events in Figure 9.

Call Progress Filter

A call progress mode, using the MT8889C, can be

selected allowing the detection of various tones,

which identify the progress of a telephone call on the

network. The call progress tone input and DTMF

input are common, however, call progress tones can

only be detected when CP mode has been selected.

DTMF signals cannot be detected if CP mode has

been selected (see Table 7). Figure 8 indicates the

useful detect bandwidth of the call progress filter.

Frequencies presented to the input, which are within

the ‘accept’ bandwidth limits of the filter, are hard-

limited by a high gain comparator with the IRQ/CP

pin serving as the output. The squarewave output

obtained from the schmitt trigger can be analyzed by

a microprocessor or counter arrangement to

determine the nature of the call progress tone being

detected. Frequencies which are in the ‘reject’ area

will not be detected and consequently the IRQ/CP

pin will remain low.

LEVEL

(dBm)

-25

0

250

500

750

= Reject

FREQUENCY (Hz)

= May Accept

= Accept

Figure 8 - Call Progress Response

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 7 - Receiver Timing Diagram

5

Share Link: