參數(shù)資料
型號(hào)： T7264
英文描述： T7264 U-Interface 2B1Q Transceiver
中文描述： T7264 U型接口2B1Q收發(fā)器
文件頁(yè)數(shù)： 45/54頁(yè)
文件大?。?/td> 876K
代理商： T7264
Lucent Technologies Inc.
45
Data Sheet
April 1998
T7264 U-Interface 2B1Q Transceiver
Appendix A. Questions and Answers
(continued)
A23:
(continued)
With no impairments, the T7264 SNR is typically
32 dB on the 18 kft 26 AWG loop. When all ANSI-
specified impairments are added, the SNR is
about 22.7 dB, still leaving adequate margin to
guarantee error-free operation over all ANSI
loops.
Finally, to estimate range over straight 24 AWG
cable, the 18 kft loop loss can be used as a limit
(since the T7264 can operate successfully with
that amount of loss), and the following calcula-
tions can be made:
= 24 kft
Therefore, the operating range over 24 AWG
cable is expected to be about 24 kft.
Q24
: What cable simulator is used for evaluating the
T7264
A24
: The original version of the transceiver was tested
using real cable for ANSI loop performance mea-
surements. However, currently, the Lucent Tech-
nologies Microelectronics Group laboratory uses
the TAS2200A* Cable Emulator for evaluation
purposes.
Q25
: The data sheet states that the T7264 meets the
ANSI T1.601-1992 standard. Is there detailed
evaluation data available on loops 1 and 4
A25
: The results shown in the following table for some
typical devices have been obtained in laboratory
testing. Loops 1 and 4 are the most difficult
cases.
Q26
: What does the energy spectrum of a 2B1Q signal
look like
A26
: Figure A1 (curve P1) in the ANSI T1.601
standard gives a good idea of what this spectrum
looks like.
Q27
: Does the return loss measurement described in
ANSI T1.601, Section 7, require that the T7264
terminate a metallic cable with 135
during
powerdown
A27
: No. ANSI and ETSI specifications do not require
this. They require that the device be placed in an
active mode with the transmitter producing 0 V
(same as quiet mode) while performing the return
loss measurements. The T7264 is placed in this
mode by pulling the
RESET
pin low.
Q28
: How is the T7264 set to quiet mode
A28
: The device is placed in the quiet mode by pulling
the
RESET
pin low. In this mode, the transmitter is
on, but is producing 0 V.
Q29
: Please clarify the meaning of ANSI Standard
T1.601, Section 7.4.2, Jitter Requirement #3.
A29
: The intent of this requirement is to ensure that
after a deactivation and subsequent activation
attempt (warm start), the phase of the receive
and transmit signals at the NT will be within the
specified limits relative to what they were prior to
deactivation. This is needed so that the LT, upon
a warm-start attempt, can make an accurate
assumption about the phase of the incoming NT
signal with respect to its transmit signal. Note that
the T7264 meets this requirement by design
because the NT phase offset from transmit to
receive is always fixed.
Q30
: How can proprietary messages be passed across
the U-interface
A30
: The embedded operations channel (eoc)
provides one way of doing this. ANSI defines 64
8-bit messages which can be used for non-
standard applications. They range in value from
binary 00010000 to 01000000.
There is also a provision for sending bulk data
over the eoc. Setting the data/message indicator
bit to 0 indicates the current 8-bit eoc word con-
tains data that is to be passed transparently with-
out being acted on. Note that there is no
response time requirement placed on the NT in
this case (i.e., the NT does not have to echo the
message back to the LT). Also note that as of
1993 this is only an ANSI provision and is not an
ANSI requirement. The T7264 does support this
provision.
* TAS2200A is a trademark of Telecom Analysis Systems Incorpo-
rated.
Loss of 18 kft 26 AWG loop @ 20 kHz
Loss per kft of 24 AWG cable @ 20 kHz 1.6 dB
38.7 dB
ANSI
Loop #
Configuration
1992 ANSI
XTALK Margin
(dB)
1.9
7.6
1
4
LT
LT
---------------------------
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