MT88L85 데이터 시트보기 (PDF) - Mitel Networks
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MT88L85 Datasheet PDF : 20 Pages
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Advance Information
MT88L85
signal duration to be recognized by the receiver. A
value for C1 of 0.1 µF is recommended for most
VDD
St/GT
tGTP = (RPC1) In [VDD / (VDD-VTSt)]
tGTA = (R1C1) In (VDD/VTSt)
RP = (R1R2) / (R1 + R2)
C1
R1
ESt
VDD
St/GT
R2
a) decreasing tGTP; (tGTP < tGTA)
tGTP = (R1C1) In [VDD / (VDD-VTSt)]
tGTA = (RpC1) In (VDD/VTSt)
RP = (R1R2) / (R1 + R2)
C1
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
R1
R2
ESt
b) decreasing tGTA; (tGTP > tGTA)
Figure 6 - Guard Time Adjustment
A call progress mode, using the MT88L85, 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.
EVENTS
Vin
ESt
St/GT
RX0-RX3
b3
A
tREC
B
tREC
TONE #n
tDP
tGTP
C
D
tID
TONE
#n + 1
tDA
E
tDO
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
4-75
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