nw6005 Integrated Device Technology, nw6005 Datasheet - Page 6

• Manufacturer Part Number: nw6005
• Description: Enhanced Type Ii Caller Id Decoder
• Manufacturer: Integrated Device Technology

DUAL TONE ALERT SIGNAL DETECTION
Bellcore system and ETSI system, but in BT system it is used in both
on and off-hook signalling. The low and high tone frequencies of three
different systems are as follows:
pin DR/STD is STD. STD goes low when DT-AS has been detected
and return high after DT-AS has ended.
separated into high band and low band by two bandpass filters. The
tone detection algorithm examines the filter outputs to validate the
arrival of the DT-AS. The EST pin becomes active when both tones
are detected. The EST is only the preliminary indication, it must be
qualified by the “guard time” as required by Bellcore, BT and ETSI (a
minimum duration for valid signals). STD is the guard time qualified
DT-AS detection output, it indicates the correct detection.
NW6005 ENHANCED TYPE II CALLER ID DECODER
Frequency
High Tone
Frequency
Low Tone
The Dual Tone Alert Signal is used only in off-hook signalling in
When the device selects DT-AS detection, the bi-purpose output
The incoming Alert Signal goes through anti-alias filter and then is
Figure 5. Guard Time Circuit of Dual Tone Alert Signal
Dual tone detected
2130 Hz
2750 Hz
2130 Hz
2750 Hz
NW6005
Comparator
± 1.1% (on-hook)
± 0.6% (off-hook)
± 1.1% (on-hook)
± 0.6% (off-hook)
Detection
BT
V
TGT
VCC
P
N
Q1
Q2
Bellcore & ETSI
2130 Hz
2750 Hz
EST
STD
ST/GT
± 0.5%
± 0.5%
VCC
C3
R5
6
shows the waveform of the EST, ST/GT and STD pins. The total
recognition time is t
time and t
= t
absent guard time. The guard time is the RC time constant for the
capacitor charge to VCC or discharge to GND. To get the unequal
present and absent guard time, a diode can be connected as shown
in Fig. 7 to provide different RC time constant (varying resistance
value) during charging and discharging.
DA
Fig. 5 shows the operation of the guard time circuit and Fig. 6
+ t
DT-AS
ST/GT
Switch
Switch
Figure 7. Guard Time Circuits with Unequal Present and
STD
EST
Q1
Q2
GA
ST/GT
ST/GT
, where t
VCC
VCC
GP
EST
EST
is the tone present guard time. The total absent time is t
ON
DA
t
Figure 6. Guard Time Waveform
DP
REC
t
is the tone absent detection time and t
GP
R1
R1
C
C
= t
t
REC
DP
+ t
INDUSTRIAL TEMPERATURE RANGE
R2
R2
Absent Times
V
GP
TGT
Alerting Signal
, where t
t
t
t
(V
R
Vd=diode forward voltage
t
t
(VCC-V
t
R
Vd=diode forward voltage
GP
GP
GA
GP <
GP
GA
P
P
ON
TGT
=R1R2/(R1+R2)
=R1R2/(R1+R2)
=R1CIn(VCC/(VCC-V
=R
=R
=R1CIn(VCC/V
> t
DP
t
-Vd(R
P
GA
GA
P
is the tone present detection
CIn((VCC-Vd(R
CIn((VCC-Vd(R
TGT
-Vd(R
P
/R2)))
V
TGT
t
ABS
P
/R2)))
TGT
t
DA
)
t
P
GA
P
GA
/R2))/
ON
TGT
/R2))/
is the tone
))
ABS