Prototype of a digitizer module based on multicycle-encoding FPGA ADC for a small animal PET

Current research in small animal positron emission tomography (PET) scanners focus on obtaining better spatial resolution and higher sensitivity. These enhancements of scanner performance result in a corresponding increase in the complexity of the electronics, which usually manifests through an increase in the number of electronics channels. Analog-to-digital converters (ADCs) implemented in field programmable gate arrays (FPGAs) are an effective way to simplify electronics complexity. In this paper, a resource-saving multicycle-encoding structure of an FPGA-based ADC with automated calibration is proposed, which achieves a sampling rate of 250 Msps. A digitizer module prototype containing 64 charge measurement channels based on the FPGA ADC is designed using a Kintex-7 FPGA. The effective number of bits (ENOB) achieved using the FPGA ADC is 4.26 bits under a 10.0555 MHz sine wave input. The charge measurement resolution of each channel is better than 5 parts per thousand full width half maximum under a 0.8 V signal input and 3% under inputs in the range 0.1 V to 1.2 V. The integral nonlinearity of each channel is within +/- 1%.