Delta-Sigma Modulation for Direct Digital Frequency Synthesis

This paper compares different $DeltaSigma$ modulation techniques for direct digital frequency synthesis (DDS). $DeltaSigma$ modulators such as MASH, feedforward, feedback, and error feedback have been implemented in both the phase and frequency domains in a CMOS DDS prototype IC fabricated in a 0.35-$mu$m CMOS technology with core area of $1.7times 2.1 {hbox {mm}}^{2}$ and total current consumption of 75 mA. Measured DDS performance demonstrates that the frequency domain $DeltaSigma$ modulation technique achieves better output spectrum purity than the phase domain method. Moreover, a programmable feedforward $DeltaSigma$ modulator is proposed to achieve different in-band and out-band noise shaping effects for DDS applications.