Title :
A CMOS oversampled DAC with multi-bit semi-digital filtering and boosted subcarrier SNR for ADSL central office modems
Author :
Lin, Andrew C Y ; Su, David K. ; Hester, Richard K. ; Wooley, Bruce A.
Author_Institution :
Center for Integrated Syst., Stanford Univ., CA, USA
fDate :
4/1/2006 12:00:00 AM
Abstract :
An oversampled digital-to-analog converter for use in ADSL central office modems has been integrated in 0.18-μm CMOS technology. The converter features a multi-bit semi-digital filter for reconstruction and a digital pre-emphasis filter that boosts the SNR of subcarriers affected by noise shaping and flattens the overall in-band magnitude response. A resampled impulse response is employed to simplify the implementation of the semi-digital filter. The combination of digital and semi-digital filtering allows the design to meet all ADSL performance requirements with only 180 current cells and a third-order analog low-pass reconstruction filter. When sampling at 200 MSample/s, the converter achieves 86-dB dynamic range for a 1.1-MHz bandwidth, with an average MTPR of 65 dB.
Keywords :
CMOS integrated circuits; digital filters; digital subscriber lines; digital-analogue conversion; low-pass filters; modems; transient response; 0.18 micron; 1.1 MHz; ADSL; CMOS technology; asymmetric digital subscriber line; boosted subcarrier SNR; central office modems; digital pre-emphasis filter; impulse response; in-band magnitude response; low-pass reconstruction filter; multibit semi-digital filter; noise shaping; oversampled DAC; oversampled digital-analog converter; third-order analog filter; CMOS technology; Central office; Digital filters; Digital-analog conversion; Filtering; Low pass filters; Modems; Noise shaping; Sampling methods; Signal to noise ratio; ADSL; D/A conversion; oversampled DAC; pre-emphasis; semi-digital filtering; sigma-delta modulation;
Journal_Title :
Solid-State Circuits, IEEE Journal of
DOI :
10.1109/JSSC.2006.870919
