A 12-bit 2.5MS/s multi-channel ramp Analog-to-Digital Converter for Imaging detectors

This paper presents a 12-bit multi-channel ramp Analog-to-Digital Converter (ADC) for Imaging detectors dedicated to high-energy physics and biomedical imaging applications. A two-level conversion scheme is employed to reduce the conversion time. The conventional Wilkinson-type architecture with a 5-bit Gray counter is used for coarse conversion while a multiphase sampling technique is proposed for fine conversion. An array of delay-locked loop is designed to generate 140-phase clocks so as to achieve a fine resolution of 7-bit. A one-channel prototype chip is designed in 0.35 mum CMOS technology. The maximum conversion time is measured as about 400 ns, which corresponds to a sample rate of about 2.5 MS/s. The power dissipation is about 3 mW/channel.