mt8885an1 Zarlink Semiconductor, mt8885an1 Datasheet - Page 6

• Manufacturer Part Number: mt8885an1
• Description: Integrated Dtmf Transceiver With Power-down And Adaptive Micro Interface
• Manufacturer: Zarlink Semiconductor

1.5
The simple steering circuit shown in Figure 5 is adequate for most applications. Component values are chosen
according to the following inequalities (see Figure 7):
The value of t
to be recognized by the receiver. A value for C1 of 0.1 µF is recommended for most applications, leaving R1 to be
selected by the designer. Different steering arrangements may be used to select independent tone present (t
and tone absent (t
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 t
maintain a valid signal condition long enough to be registered. Alternatively, a relatively short t
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.
Guard Time Adjustment
REC
DP
improves talk-off performance since it reduces the probability that tones simulated by speech will
is a device parameter (see AC Electrical Characteristics) and t
GTA
) guard times. This may be necessary to meet system specifications which place both accept
V
MT8885
DD
St/GT
V
ESt
DD
Figure 5 - Basic Steering Circuit
t
t
REC
REC
t
t
DO
ID
≥ t
Zarlink Semiconductor Inc.
≥ t
≤ t
≤ t
DAmax
DPmax
DAmin
DPmin
t
t
GTP
MT8885
GTA
R1
= (R1C1) In [V
+ t
= (R1C1) In (V
+ t
+ t
+ t
6
GTAmax
GTAmin
GTPmin
GTPmax
Vc
C1
- t
- t
- t
- t
DD
DPmin
DD
DPmax
DAmax
DAmin
/ (V
/ V
TSt
DD
-V
)
TSt
)]
REC
is the minimum signal duration
REC
with a long t
Data Sheet
GTP
DO
)