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전자부품 데이터시트 검색엔진 |
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전자부품 데이터시트 검색엔진 |
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LAN9117 데이터시트(HTML) 53 Page - Microchip Technology |
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LAN9117 데이터시트(HTML) 53 Page - Microchip Technology |
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2005-2016 Microchip Technology Inc. DS00002267A-page 53 LAN9117 4.2.3 NRZI AND MLT3 ENCODING The scrambler block passes the 5-bit wide parallel data to the NRZI converter where it becomes a serial 125MHz NRZI data stream. The NRZI is encoded to MLT-3. MLT3 is a tri-level code where a change in the logic level represents a code bit “1” and the logic output remaining at the same level represents a code bit “0”. 4.2.4 100M TRANSMIT DRIVER The MLT3 data is then passed to the analog transmitter, which launches the differential MLT-3 signal, on outputs TXP and TXN, to the twisted pair media via a 1:1 ratio isolation transformer. The 10Base-T and 100Base-TX signals pass through the same transformer so that common “magnetics” can be used for both. The transmitter drives into the 100 impedance of the CAT-5 cable. Cable termination and impedance matching require external components. 4.2.5 100M PHASE LOCK LOOP (PLL) The 100M PLL locks onto reference clock and generates the 125MHz clock used to drive the 125 MHz logic and the 100Base-Tx Transmitter. 4.3 100Base-TX Receive The receive data path is shown in Figure 4-2. Detailed descriptions are given below. 4.3.1 100M RECEIVE INPUT The MLT-3 from the cable is fed into the PHY (on inputs RXP and RXN) via a 1:1 ratio transformer. The ADC samples the incoming differential signal at a rate of 125M samples per second. Using a 64-level quanitizer it generates 6 digital bits to represent each sample. The DSP adjusts the gain of the ADC according to the observed signal levels such that the full dynamic range of the ADC can be used. FIGURE 4-2: RECEIVE DATA PATH MAC A/D Converter MLT-3 Converter NRZI Converter 4B/5B Decoder Magnetics CAT-5 RJ45 100M PLL Internal MII 25MHz by 4 bits RX_CLK 25MHz by 5 bits NRZI MLT-3 MLT-3 MLT-3 6 bit Data Descrambler and SIPO 125 Mbps Serial DSP: Timing recovery, Equalizer and BLW Correction MLT-3 MII 25MHz by 4 bits |
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