mt88l85anr1 Zarlink Semiconductor, mt88l85anr1 Datasheet - Page 6

• Manufacturer Part Number: mt88l85anr1
• Description: 3 V Integrated Dtmf Transceiver With Power-down And Adaptive Micro Interface
• Manufacturer: Zarlink Semiconductor

receiver will tolerate signal interruptions (drop out) too short to be considered a valid pause. This facility, together
with the capability of selecting the steering time constants externally, allows the designer to tailor performance to
meet a wide variety of system requirements.
Guard Time Adjustment
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
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 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 8.
GTP
) and tone absent (t
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
V
MT88L85
DD
St/GT
V
ESt
DD
Figure 5 - Basic Steering Circuit
t
t
REC
t
t
REC
ID
DO
Zarlink Semiconductor Inc.
≥ t
≥ t
≤ t
≤ t
DAmax
DAmin
DPmax
MT88L85
DPmin
t
t
GTP
GTA
R1
= (R1C1) In [V
= (R1C1) In (V
+ t
+ t
+ t
+ t
6
GTAmax
GTPmax
GTPmin
GTAmin
Vc
C1
- t
- t
- t
- t
DD
DD
DPmin
DAmax
DPmax
DAmin
/ (V
/ V
TSt
DD
)
-V
TSt
)]
REC
is the minimum signal duration
REC
with a long t
Data Sheet
DO