Design and analysis of high-speed split-segmented switched-capacitor DACs

Abstract

In order to achieve high speed and high resolution for switched-capacitor (SC) digital-to-analog converters (DACs), an architecture of split-segmented SC DAC is proposed. The detailed design considerations of kT/C noise, capacitor mismatch, settling time and simultaneous switching noise are mathematically analyzed and modelled. The design area W---Cu is defined based on that analysis. It is used not only to identify the maximum speed and resolution but also to find the design point (W, Cu) for certain speed and resolution of SC DAC topology. The segmentation effects are also considered. An implementation example of this type of DACs is a 12-bit 6-6 split-segmented SC DAC designed in 65 nm CMOS. The linear open-loop output driver utilizing derivation superposition technique for nonlinear cancellation is used to drive off-chip load for the SC array without compromising its performance. The measured results show that the SC DAC achieves a 44 dB spurious free dynamic range within a 1 GHz bandwidth of input signal at 5 GS/s while consuming 50 mW from 1 V digital and 1.2 V analog supplies. The overall performance that was achieved from measurement is poorer than expected due to lower power supply rejection ratio in fabricated chip. This DAC can be used in transmitter baseband for wideband wireless communications.