A low-power 18-bit sigma-delta digital-to-analog converter with low-temperature-drift reference

An 18-bit Σ-Δ digital-to-analog converter (DAC) with precision-trimmed bandgap reference is proposed for industrial transmitters. A bandgap reference with an 8-bit trimming DAC and a high-order compensation circuit for reducing the temperature coefficient (TC) affected by process and voltage variation was utilized, which effectively guarantees the robustness of the Σ-Δ DAC. Compared with the conventional Σ-Δ DAC, the proposed DAC replaces the on-chip digital interpolation filter (IF) by providing oversampled input digital codes, and a low-pass configurable off-chip passive RC filter is utilized for power reduction. A quantization noise randomization scheme was employed by adding pseudo-random sequences in the Σ-Δ modulator, achieving 27.22 dB improvement in signal-to-noise and distortion ratio (SNDR) with 0.045 mW increase in power consumption. The proposed Σ-Δ DAC is designed with 180 nm CMOS technology with a supply voltage of 3.3 V. Benefiting from the optimization of the filtering mode and the precision trimming technique of the bandgap reference, an SNDR of 108.01 dB was achieved with a power consumption of 0.257 mW. In the temperature range of -40–105 °C, the temperature coefficient of the DAC output was less than 25.83 ppm/°C, under different process conditions.