Design Of Analog Equalizer For 10/100M Ethernet Transceive

As 10Base-T/100Base-TX uses low-cost Category 5 Unshielded Twist Pairs as its transmission medium and can provide a high-speed and wide-bandwidth network, it has been the first choice in Local Area Network (LAN). Due to the nonideal characters of this medium, the data signals will suffer from the DC gain attenuation, high frequency attenuation and Baseline Wander, which induces the inter-symbol interference (ISI). To achieve the objective that symbol error rate (BER) is less than 10-10, it's necessary to use appropriate equalization technology to compensate the channel response, thus the effects produced by the nonideal characters can be eliminated effectively. Moreover, the equalizer should implement different equalization according to the different length of the twisted pair, this is namely self-adaptive equalization.In this paper, the reasons for signal distortion are analyzed, the transmission model of twisted pair is deduced, and the theory of equalizer and the common LMS adaptive arithmetic is introduced. In real CMOS circuit implementation, Baseline Wander Canceller is designed to repair the low-frequency energy lost in transformer; Auto Gain Control (AGC) is designed to compensate DC gain attenuation; High Pass Filter (HPF) is dedigned to compensate high-frequency attenuation. A Current adder and V/I converter realizes the analog addition, which makes up an analog equalizer with AGC and HPF. In addition, some accessorial circuits have been proposed to assist the equalizer, such as bias circuit, dual to single circuit and common-mode feedback circuit. To improve the stability of the system, a bandgap reference with low-temperature coefficient and high power supply restrain ratio has also been proposed.All of the circuits are implemented by Cadence tools and based on SMIC 0.35μm mixed signal 2P3M CMOS process.