10.6 A 12b 16GS/s RF-Sampling Capacitive DAC for Multi-Band Soft-Radio Base-Station Applications with On-Chip Transmission-Line Matching Network in 16nm FinFET

Abstract

Future multi-band software-defined-radio base-stations for digital beamforming and massive MIMO applications depend heavily on the availability of highly linear and compact data converters with good power efficiency, while at the same time offering multi-GHz signal-bandwidth at sampling rates well in excess of 10GS/s. Wideband RF-sampling D/A-converters have traditionally been implemented in current-steering architectures, mostly with extensive calibration infrastructure [1] –[3]. The transistor stack required to achieve the necessary static and dynamic output impedance for the code-steered current sources leads to limited supply voltage scalability, while the capacitive self-loading by the current-source array makes true wideband matching at the RF-output inherently difficult. Capacitive digital-to-analog converters (C-DAC) have been widely used as RF DAC or switched-capacitor power amplifiers. Up to now digital transmitters have used C-DACs with inherent mixing functionality in polar or IQ systems for synthesis of high-power RF signals of moderate bandwidth of up to 160MHz [4] –[6]. This work uses a capacitive DAC as a direct RF-sampling DAC with moderate output power level for direct signal synthesis over a bandwidth from 0.5GHz up to at least 8GHz.