參數(shù)資料
型號(hào)： KSZ8997
廠商： Micrel Inc
文件頁數(shù)： 7/39頁
文件大小： 0K
描述： IC SWITCH 10/100 8PORT 128PQFP
標(biāo)準(zhǔn)包裝： 66
系列： *
類型： *
應(yīng)用： *
安裝類型： 表面貼裝
封裝/外殼： 128-BFQFP
供應(yīng)商設(shè)備封裝： 128-PQFP（14x20）
包裝： 托盤
產(chǎn)品目錄頁面： 1081 (CN2011-ZH PDF)
其它名稱： 576-1043
Micrel, Inc.
KS8997/KSZ8997
February 2007
15
M9999-022807-1.1
Functional Overview: Physical Layer Transceiver
100BaseTX Transmit
The 100BaseTX transmit function performs parallel-to-serial conversion, 4B/5B coding, scrambling, NRZ to NRZI
conversion, MLT3 encoding and transmission. The circuit starts with a parallel to serial conversion, which converts
the MII data from the MAC into a 125MHz serial bit stream. The data and control stream is then converted into 4B/5B
coding followed by a scrambler.
The serialized data is further converted from NRZ to NRZI format, and then transmitted in MLT3 current output. The
output current is set by an external 1% 3.01k resistor for the 1:1 transformer ratio. It has a typical rise/fall time of
4ns and complies with the ANSI TP-PMD standard regarding amplitude balance, overshoot and timing jitter. The
wave-shaped 10BaseT output is also incorporated into the 100BaseTX transmitter.
100BaseTX Receive
The 100BaseTX receiver function performs adaptive equalization, DC restoration, MLT3 to NRZI conversion, data
and clock recovery, NRZI to NRZ conversion, de-scrambling, 4B/5B decoding and serial to parallel conversion. The
receiving side starts with the equalization filter to compensate for inter-symbol interference (ISI) over the twisted pair
cable. Since the amplitude loss and phase distortion is a function of the length of the cable, the equalizer has to
adjust its characteristics to optimize the performance. In this design, the variable equalizer will make an initial
estimation based on comparisons of incoming signal strength against some known cable characteristics, then it tunes
itself for optimization. This is an ongoing process and can self adjust against environmental changes such as
temperature variations.
The equalized signal then goes through a DC restoration and data conversion block. The DC restoration circuit is
used to compensate for the effect of base line wander and improve the dynamic range. The differential data
conversion circuit converts the MLT3 format back to NRZI. The slicing threshold is also adaptive.
The clock recovery circuit extracts the 125MHz clock from the edges of the NRZI signal. This recovered clock is then
used to convert the NRZI signal into the NRZ format. The signal is then sent through the de-scrambler followed by
the 4B/5B decoder.
Finally, the NRZ serial data is converted to the MII format and provided as the input data to the MAC.
PLL Clock Synthesizer
The KS8997 generates 125MHz, 62MHz, 25MHz and 10MHz clocks for system timing. Internal clocks are generated
from an external 25MHz crystal.
Scrambler/De-Scrambler (100BaseTX only)
The purpose of the scrambler is to spread the power spectrum of the signal in order to reduce EMI and baseline
wander. The data is scrambled through the use of an 11-bit wide linear feedback shift register (LFSR). This can
generate a 2047-bit non-repetitive sequence. The receiver will then de-scramble the incoming data stream with the
same sequence at the transmitter.
10BaseT Transmit
The output 10BaseT driver is incorporated into the 100BaseT driver to allow transmission with the same magnetics.
They are internally wave-shaped and pre-emphasized into outputs with a typical 2.3V amplitude.
10BaseT Receive
On the receive side, input buffer and level detecting squelch circuits are employed. A differential input receiver circuit
and a PLL perform the decoding function. The Manchester-encoded data stream is separated into clock signal and
NRZ data. A squelch circuit rejects signals with levels less than 400mV or with short pulse widths in order to prevent
noises at the RXP or RXM input from falsely triggering the decoder. When the input exceeds the squelch limit, the
PLL locks onto the incoming signal and the KS8997 decodes a data frame. The receiver clock is maintained active
during idle periods in between data reception.
Power Management
Power-Save Mode
The KS8997 will turn off everything except for the Energy Detect and PLL circuits when the cable is not installed on
an individual port basis. In other words, the KS8997 will shutdown most of the internal circuits to save power if there
is no link.
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