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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 mVpp. 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.
Date of Conference: 2002