A 1.5-V direct digital synthesizer with tunable delta-sigma modulator in 0.13-μm CMOS

In direct digital synthesizer (DDS) applications, the drawback of the conventional delta sigma (ΔΣ) modulator structure is that its signal band is fixed. In the new architecture presented in this paper, the signal band of the ΔΣ modulator is tuned according to the DDS output frequency. We use a hardware-efficient phase-to-sine amplitude converter in the DDS that approximates the first quadrant of the sine function with 16 equal-length piecewise second-degree polynomial segments. The DDS is capable of frequency, phase, and quadrature amplitude modulation. The die area of the chip is 2.02 mm² (0.13 μm CMOS technology). The total power consumption is 138 mW at 1.5 V with an output frequency of 63.33 MHz at a clock frequency of 200 MHz (D/A converter full-scale output current: 11.5 mA).