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參數(shù)資料
| 型號： | AM79C874VC |
| 廠商： | ADVANCED MICRO DEVICES INC |
| 元件分類： | 網(wǎng)絡(luò)接口 |
| 英文描述： | NetPHY-1LP Low Power 10/100-TX/FX Ethernet Transceiver |
| 中文描述： | DATACOM, ETHERNET TRANSCEIVER, PQFP80 |
| 封裝： | 12 X 12 MM, PLASTIC, MO-136BAM, TQFP-80 |
| 文件頁數(shù)： | 20/60頁 |
| 文件大小： | 869K |
| 代理商： | AM79C874VC |
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Am79C874
P R E L I M I N A R Y
MLT-3
This block is responsible for converting the NRZI data
stream from the PDX block to the MLT-3 encoded data
stream. The effect of MLT-3 is the reduction of energy
on the copper media (TX or FX cable) in the critical fre-
quency range of 1 MHz to 100 MHz. The receive sec-
tion of this block is responsible for equalizing and
amplifying the received data stream and link detection.
The adaptive equalizer compensates for the amplitude
and phase distortion due to the cable.
MLT-3 is a tri-level signal. All transitions are between
0 V and +1 V or 0 V and -1 V. A transition has a logical
value of 1 and a lack of a transition has a logical value
of 0. The benefit of MLT-3 is that it reduces the maxi-
mum frequency over the data line. The bit rate of TX
data is 125 Mbps. The maximum frequency (using
NRZI) is half of 62.5 MHz. MLT-3 reduces the maximum
frequency to 31.25 MHz.
A data signal stream following MLT-3 rules is illustrated
in Figure 2. The data stream is 1010101.
Figure 2.
MLT-3 Waveform
The TX± drivers convert the NRZI serial output to
MLT-3 format. The RX± receivers convert the received
MLT-3 signals to NRZI. The transmit and receive sig-
nals will be compliant with IEEE 802.3u, Section 25.
The required signals (MLT-3) are described in detail in
ANSI X3.263:1995 TP-PMD Revision 2.2 (1995).
The NetPHY-1LP device provides on-chip filtering. Ex-
ternal filters are not required for either the transmit or
receive signals. The traces from the transformer to the
NetPHY-1LP device should have a controlled imped-
ance as a differential pair of 100 ohms. The same is
true between the transformer and the RJ-45 connector.
The TX pins can be connected to the media via either
a 1:1 transformer or a 1.25:1 transformer. The 1.25:1
ratio provides a 20% transmit power savings over the
1:1 ratio. Refer to Figure 3.
Adaptive Equalizer
The NetPHY-1LP device is designed to accommodate
a maximum cable length of 140 meters UTP CAT-5 ca-
ble. 140 meters of UTP CAT-5 cable has an attenuation
of 31 dB at 100 MHz. The typical attenuation of a 100
meter cable is 21 dB. The worst case attenuation is
around 24-26 dB defined by TP-PMD.
The amplitude and phase distortion from the cable will
cause intersymbol interference (ISI) which makes clock
and data recovery impossible. The adaptive equalizer
is made by closely matching the inverse transfer func-
tion of the twist-pair cable. This is a variable equalizer
that changes its equalizer frequency response in ac-
cordance to cable length. The cable length is estimated
based on comparisons of incoming signal strength
against some of the known cable characteristics. The
equalizer has a monotonical frequency response, and
tunes itself automatically for any cable length to com-
pensate for the amplitude and phase distortion incurred
from the cable.
Baseline Wander Compensation
The 100BASE-TX data stream is not always DC bal-
anced. The transformer blocks the DC component of
the incoming signal, thus the DC offset of the differen-
tial receive inputs can wander. The shift in the signal
levels, coupled with non-zero rise and fall times of the
serial stream can cause pulse-width distortion. This
creates jitter and a possible increase in error rates.
Therefore, a DC restoration circuit is needed to com-
pensate for the attenuation of the DC component.
The NetPHY-1LP device implements a patent-
pending DC restoration circuit. Unlike the traditional im-
plementation, it does not need the feedback informa-
tion from the slicer and clock recovery circuit. This not
only simplifies the system/circuit design, but also elim-
inates any random/systematic offset on the receive
path. In 10BASE-T and 100Base-FX modes, the base-
line wander correction circuit is not required and there-
fore will be bypassed.
MLT-3
1
0
1
0
1
0
1
8 ns
22235I-4
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| AM79C874VD | 制造商:Advanced Micro Devices 功能描述:PHY 1-CH 10Mbps/100Mbps 80-Pin TQFP 制造商:AMD (Advanced Micro Devices) 功能描述:PHY 1-CH 10Mbps/100Mbps 80-Pin TQFP |
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