A programmable filter with self-tuning for DMT VDSL receiver

This paper presents a programmable filter with a self-tuning mechanism. Conformed with the DMT-VDSL (discrete multi-tone very-high-speed digital subscriber loop) system, the filter is configured as a 4-th order Chebyshev low-pass filter with programmable bandwidth in which the ripple is set to 0.5 dB. The cut-off frequencies are 1.104×2ⁿ MHz, where n is 0, 1, 2, 3, 4, corresponding to different transmission rates. The filter is self-tuned by the proposed tuning mechanism that is based on the relation between DC and fundamental components of a filtered clock signal. Peak-and-valley detection is employed to observe the two frequency components in the time domain. Implemented in 0.35 μm 1P4M digital CMOS technology, the circuit occupies an active area of 1.3×1.4 mm². According to the post-layout simulation, it achieves 55 dB THD using 2 V supply voltage while the output swing is 120 mV_pp. The power consumption for the core filter is 2.8 mW, whereas the overall system, including the filter, the output buffer, and the tuning circuits, consumes 28 mW power.