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參數(shù)資料
| 型號： | T7256A |
| 英文描述： | Compliance with the New ETSI PSD Requirement |
| 中文描述： | 符合新的ETSI PSD的要求 |
| 文件頁數(shù)： | 86/116頁 |
| 文件大?。?/td> | 1056K |
| 代理商： | T7256A |
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Data Sheet
January 1998
T7256 Single-Chip NT1 (SCNT1) Transceiver
82
Lucent Technologies Inc.
Questions and Answers
(continued)
U-Interface
(continued)
Q12:
I am planning on using a Raychem PTC (p/n
TR600-150) on the U-interface of the T7256
as shown in Figure 20. The device is rated at
6
—12
. I am concerned about the loose toler-
ance on the PTC resistance. Will I be able to pass
the return loss requirements in ANSI T1.601 Sec-
tion 7.1
A12:
The NT1 impedance limits looking into tip/ring are
derived from the T1.601 return loss requirements
(Figure 17 in T1.601). At the narrowest point in
the templates, the permissible range is between
111
to 165
. The tolerance on the PTC will
reduce the impedance margin somewhat, but
should still be acceptable.
Figure 32 is derived from the return loss template
in ANSI T1.601. Return loss is a measure of the
match between two impedances on either side of
a junction point. The following equation is an
expression of return loss in terms of the complex
impedances of the two halves of the circuit Z
1
, Z
2.
RL (dB) = 20 log
When the impedances are not matched, the junc-
tion becomes a reflection point. For a perfectly
matched load, the return loss is infinite, whereas
for an open or short circuit, the return loss is zero.
The return loss expresses the ratio of incident to
reflected signal power and should consequently
be fairly high.
Z
Z
1
Z
2
Z
2
+
–
-------------------
5-4056 (C)
Figure 32. Transceiver Impedance Limits
10000
1000
100
10
1
1.0
1.4
2.0
2.8
4.0
5.6
7.9
11.2
15.8
22.4
31.6
44.7
63.1
89.1
125.9 177.8 251.2
I
)
FREQUENCY (kHz)
UPPER BOUND > 165
LOWER BOUND < 110.4
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