5222-DS02-R datasheet(15/76 Pages) BOARDCOM

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Preliminary Data Sheet

BCM5222

7/20/04

Broadcom Corporation

Document 5222-DS02-405-R

Digital Adaptive Equalizer

Page 3

DIGITAL ADAPTIVE EQUALIZER

The digital adaptive equalizer removes Intersymbol Interference (ISI) created by the transmission channel media. The

equalizer accepts sampled unequalized data from the ADC on each channel and produces equalized data. The BCM5222

achieves an optimum signal-to-noise ratio by using a combination of feed forward equalization and decision feedback

equalization. This powerful technique achieves a 100BASE-TX BER of less than 1 x 10-12 for transmission up to 100 meters

on CAT 5 twisted pair cable, even in harsh noise environments. The digital adaptive equalizers in the BCM5222 achieve

performance close to theoretical limits. The all-digital nature of the design makes the performance very tolerant to on-chip

noise. The filter coefficients are self-adapting to any quality of cable or cable length. Due to transmit pre-equalization in

10BASE-T mode, the adaptive equalizer is bypassed in these two modes of operation.

ADC

The receive channel has a 6-bit, 125-MHz analog-to-digital converter (ADC). The ADC samples the incoming data on the

receive channel and produces a 6-bit output. The ADC output is fed to the digital adaptive equalizer. Advanced analog circuit

techniques achieve low-offset, high-power-supply noise rejection, fast-settling time, and low-bit error rate.

DIGITAL CLOCK RECOVERY/GENERATOR

The all-digital clock recovery and generator block creates all internal transmit and receive clocks. The transmit clock is locked

to the 25-MHz clock input, while the receive clock is locked to the incoming data stream. Clock recovery circuits optimized

to MLT3 and Manchester encoding schemes are included for use with the different operating modes. The input data stream

is sampled by the recovered clock, and fed synchronously to the digital adaptive equalizer.

BASELINE WANDER CORRECTION

A 100BASE-TX data stream is not always DC balanced. Because the receive signal must pass through a transformer, the

DC offset of the differential receive input can wander. This effect, known as baseline wander, can greatly reduce the noise

immunity of the receiver. The BCM5222 automatically compensates for baseline wander by removing the DC offset from the

input signal, and thereby significantly reduces the chance of a receive symbol error.

The baseline wander correction circuit is not required, and therefore is bypassed, in 10BASE-T operating mode.

MULTIMODE TRANSMIT DAC

The multimode transmit digital-to-analog converter (DAC) transmits MLT3-coded symbols in 100BASE-TX mode and

Manchester-coded symbols in 10BASE-T mode. It allows programmable edge-rate control in TX mode, which decreases

unwanted high frequency signal components, thereby reducing EMI. High-frequency pre-emphasis is performed in

10BASE-T mode. The transmit DAC utilizes a current drive output, which is well balanced, and produces very low noise

transmit signals.

5222-DS02-R 数据表(PDF) 15 Page - Broadcom Corporation.

5222-DS02-R 数据表(HTML) 15 Page - Broadcom Corporation.

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