The implementation of dual-truncation ΣΔ D/A converters

A novel D/A (digital-to-analog) conversion technique is introduced which achieves high linearity and high resolution D/A conversion by using two D/A converters (DACs): one with high linearity but low bit resolution and the other with low linearity but relatively high bit resolution. The key subsystems in this technique are the analog differentiators, which can have relatively large gain error but only very small phase error. The authors examine the issues concerning the implementation of these differentiators with switched-capacitor circuits. Simulation results indicate that using a 3-level and a 33-level DAC, the system achieves a 114 dB peak SNR (signal-to-noise ratio) value when the oversampling ratio is 128. In addition to increasing the SNR, the use of a multibit DAC also reduces the swing of the input signal to the analog smoothing filter, and thus reduces the nonlinear effects of this filter