nw6003 Integrated Device Technology, nw6003 Datasheet - Page 6

• Manufacturer Part Number: nw6003
• Description: Type Ii Caller Id Decoder
• Manufacturer: Integrated Device Technology

NW6003 TYPE II CALLER ID DECODER
DUAL TONE ALERT SIGNAL DETECTION
and loop (off-hook) state, while Bellcore specifies a similar Dual Tone
Alert Signal called CPE Alerting Signal (CAS) in off-hook state. The
low and high tone frequencies of two different systems are as follows:
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 Dual Tone Alert Signal. 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 and BT (a minimum duration for valid signals). STD is the
guard time qualified CAS/Dual Tone Alert Signal detection output, it
indicates the correct detection.
Figure 7. Guard Time Circuit of Dual Tone Alert Signal Detection
ST/GT
High Tone Frequency
Switch
Switch
Low Tone Frequency
BT specifies a Dual Tone Alert Signal in both idle (on-hook) state
The incoming Alert Signal goes through anti-alias filter and then is
STD
Ring
EST
Q1
Q2
Tip/
Dual tone detected
ON
t
Comparator
DP
Figure 8. Guard Time Waveform
t
GP
t
REC
NW6003
+
-
V
2130 Hz ± 1.1%
2750 Hz ± 1.1%
TGT
Alerting Signal
V
TGT
BT
ON
VCC
P
N
Q1
Q2
ST/GT
EST
STD
V
2130 Hz ± 0.5%
2750 Hz ± 0.5%
TGT
t
ABS
Bellcore
VCC
t
DA
t
GA
ON
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 Figure 9 to provide different RC time constant (varying resistance
value) during charging and discharging.
DA
Figure 7 shows the operation of the guard time circuit and Figure 8
+ t
GA
Figure 9. Guard Time Circuits with Unequal Present
ST/GT
ST/GT
, where t
GP
VCC
VCC
EST
EST
is the tone present guard time. The total absent time is t
DA
REC
is the tone absent detection time and t
R 1
R 1
C
C
= t
DP
and Absent Times
R 2
R 2
+ t
INDUSTRIAL TEMPERATURE RANGE
GP
, 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
TGT
=R1R2/(R1+R2)
=R1R2/(R1+R2)
=R1CIn(VCC/(VCC-V
=R
DP
=R
=R1CIn(VCC/V
> t
t
-Vd(R
is the tone present detection
P
GA
P
GA
CIn((VCC-Vd(R
CIn((VCC-Vd(R
TGT
-Vd(R
P
/R2)))
P
/R2)))
TGT
)
P
GA
P
/R2))/
/R2))/
TGT
is the tone
))
ABS