A 13-b 1.1-MHz oversampled DAC with semidigital reconstruction filtering

A digital-to-analog converter (DAC) composed of a cascaded digital /spl Sigma//spl Delta/ modulator and the combination of a semidigital/digital finite-impulse response (FIR) and an infinite-impulse response (IIR)-SC/RC filter is described. The architecture enables the analog linear reconstruction of 16/spl times/ oversampled digital signals. With the analog section implemented in CMOS 0.18-/spl mu/m and the digital part programmed into a field-programmable gate array (FPGA), the modulator plus reconstruction filter achieves a peak SNR of 78 dB. The spurious-free dynamic range reaches 80 dB and stays better than 73 dB within the 1.104-MHz signal band. A missing-tone-power ratio of 70 dB, demonstrated for a signal with 15-dB peak-to-average ratio, proves that the solution is suitable for ADSL-CO transmitters.

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