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MT88E45BS1 参数 Datasheet PDF下载

MT88E45BS1图片预览
型号: MT88E45BS1
PDF下载: 下载PDF文件 查看货源
内容描述: [Telephone Calling No Identification Circuit, CMOS, PDSO20, 0.300 INCH, LEAD FREE, SOIC-20]
分类和应用: 光电二极管
文件页数/大小: 30 页 / 1003 K
品牌: ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
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MT88E45
MT88E45B
Data Sheet
Vdd
Both Tones Present
P Q1
+
-
Comparator
R1
N Q2
= Vss
VTGt
C
ST/GT
V
diode
R2
Rp=R1 || R2
EST
DR
/
STD
Indicates STD in CAS
detection mode
CAS
t
DP
EST
t
GP
ST/GT
t
REC
t
GA
t
DA
t
ABS
t
GP
=R1C ln [Vdd / (Vdd-VTGt)]
t
GA
=RpC ln
Rp=R1 || R2
t
GA
=0 if R2=0
STD
Vdd - Vdiode (Rp/R2)
VTGt - Vdiode (Rp/R2)
Figure 5 - CAS Guard Time Circuit Operation
Tone present guard time (t
GP
) operation: In Figure 5 5 initially there is no CAS, EST is low so Q1 is off. C has been
fully charged applying 0 V to ST/GT so Q2 is on. When both tones are detected EST goes high and turns off Q2.
Because C has been fully charged (ST/GT=0V), the comparator output is low and Q1 stays off. With both Q1 and
Q2 off the high at EST discharges C through R1 and the ST/GT voltage increases from 0 V. When the voltage
exceeds the comparator threshold VTGt, which is typically 0.5 Vdd, the comparator output goes high; Q1 turns on
and accelerates the discharge of C (ST/GT goes quickly to Vdd); STD goes low to indicate that a valid CAS has
been received. If one or both tones disappeared before t
GP
has been reached (i.e. when ST/GT voltage is still below
VTGt), Q2 turns back on and charges C quickly to bring the ST/GT voltage back to 0 V. Then if EST goes high again
the t
GP
duration must start over.
Tone absent guard time (t
GA
) operation: In Figure 5 5 initially both tones have been detected for t
GP
so C is fully
discharged and ST/GT is at Vdd. While both tones continue to be detected EST stays high; ST/GT is at Vdd (the
comparator output is high); so Q1 is on and Q2 is off. When one or both tones stop EST goes low and turns off Q1.
Because C is fully discharged (ST/GT=Vdd), the comparator output is high and Q2 stays off. With both Q1 and Q2
off the low at EST charges C through Rp=(R1 || R2) and the ST/GT voltage falls towards 0V. When the voltage has
fallen below VTGt, the comparator output goes low. Since EST is also low Q2 turns on and accelerates the
charging of C so that ST/GT goes quickly to 0V. STD goes high to indicate that the CAS has ended. If EST goes
back to high before t
GA
has been reached (i.e. when ST/GT voltage is still above V
TGt
), Q1 turns back on and
discharges C quickly to bring the ST/GT voltage back to Vdd. Then if EST goes low again the t
GA
duration must start
over. To set t
GA
=0, set R2 to 0.
10
Zarlink Semiconductor Inc.