A CMOS Gm-C Analog Pre-Equalizer for 1000BASE-T Analog Receive Filters

This paper presents a CMOS implementation of an analog pre-equalizer used in 1000BASE-T analog front ends. The purpose of this filter is to simplify the overall receiver complexity by providing partial equalization before the analog-to-digital converter. The filter architecture is decided in conjunction with the design of 1000BASE-T receivers and the constraints of process and power supply. The proposed filter, which has one zero and two poles, is implemented by a G_m -C filter in a 0.25mum 1-poly 5-metal digital CMOS process. A new linearization circuit is used in the transconductance cells to meet the linearity requirement even with a low power-supply voltage. System-level simulations indicate that the filter can reduce the overall receiver power and area without sacrificing performance. Measurements show that the filter response can be programmed for cable lengths from 10m to 150m, the total harmonic distortion is -47.5dB with a 1V_PP input at 13.4MHz, and the input dynamic range is 51dB. The total power dissipation is 25mW from a single 2.5V power supply, and the active area is 0.5mm²