Design of digital-intensive wireless RF receiver using VCO-based ADC

Abstract

From the immense growth of wireless connectivity, the necessity for software-defined radio (SDR) receiver has been increased. However, a baseband low-pass filter (LPF) and a variable gain ampilfier (VGA) in the conventional receiver become a bottleneck to achieve low-power and low-cost SDR receiver. That is because they uses passive components which occupy large area and are difficult to be programmable, and analog op-amp suffering from the lower supply voltage in the deep-submicron CMOS process. In order to solve this problem, this work proposes a digital-intensive receiver architecture which removes analog baseband LPF and VGA by connecting analog-to-digital converter (ADC) to the downconversion mixer. The proposed architecture performs channel filtering in the digital domain and it guarantees easier programmability and lower area and power consumption than the analog channel filter in the conventional receiver architectures. Instead of beneficial digital channel filtering, the proposed receiver requires high performance ADC which achieves high signal-to-noise ratio (SNR) and embedded anti-aliasing filtering. In this work, we exploits the voltage-controlled oscillator (VCO)-based ADC which is composed of ring VCO and digital counter. Despite of simple architecture, it provides very special properties, first-order noise shaping and embedded Sinc anti-aliasing filtering which are the requirement of ADC in the proposed digital-intensive receiver. As the limitation of sampling frequency comes from the digital circuits, the sampling frequency can be multi-GHz which provides high OSR and hence high SNR. The embedded Sinc filter in the VCO-based ADC is highly appropriate for the narrowband receiver because nulls are generated in the integer times sampling frequency where the aliased channel lies. In this work, the nonidealities of VCO-based ADC such as VCO phase noise, delay cell mismatch, VCO nonlinearity, sampling jitter are mathematically analyzed. Form this anal...