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最近100Mbps的100Base—T Fast Ethernet的应用表明,Category—3的非屏蔽双绞线电缆配以常规的双电平信号不可能实现可靠的100Mbps数据传输。为了利用多电平信号在多对双绞线上传输,从而使已经安装的Category-3电缆能传输10倍的数据流量,就必须采用某种形式的均衡技术。 最简单的可用均衡技术是可编程模拟高通滤波器。在接收信号通路中接入这种均衡器,就可以弥补双绞线通道的低通频率响应特性的影响。接收器电路首先测量信号的衰减程度以粗略估计环路的长度,然后在信号通路中接入合适的高通模拟均衡器电路。
The recent application of 100Mbps 100Base-T Fast Ethernet shows that Category-3 unshielded twisted-pair cable with conventional two-level signals is not possible to achieve reliable 100Mbps data transmission. In order to utilize multi-level signals transmitted over multiple pairs of twisted-pair cables, allowing Category-3 cables already installed to transmit 10 times the data traffic, some form of equalization must be used. The simplest available equalization technique is a programmable analog high-pass filter. Access to this equalizer in the receive signal path can compensate for the effects of the low-pass frequency response of the twisted pair channel. The receiver circuit first measures the attenuation of the signal to roughly estimate the length of the loop and then accesses the appropriate high-pass analog equalizer circuit in the signal path.