Adjustable Amplifier and Time-Based Digitizer with Fast Timing for SiPM- and APD-based PET Photodetectors

Applications

• Positron Emission Tomography (PET) systems:
• PET systems with silicon photomultiplier (SiPM) or avalanche photodiode (APD) photodetectors
• Time-of-Flight Positron Emission Tomography (PET) systems which require time resolution of at least 100-300ps
• High resolution (about 1mm) PET systems which require tens-of-thousands of electronics channels
• Data acquisition for prototype and research systems where it is necessary to easily adjust the circuit parameters for use with various silicon photodetectors

Advantages

• Efficient and simple digitization scheme which achieves excellent time resolution and provides pulse energy information while consuming low power and capturing a small number of samples
• Digitized pulse waveform facilitates pulse processing algorithms to achieve better time and energy resolution and to resolve pulse pile-up
• Fully digital output is robust against amplitude and pulse-width noise
• Adjustable input impedance and gain allows the integrated circuit to be used with a variety of silicon photodetectors

Claim 1 of Issued Patent

1. An integrated circuit in a PET imaging system with a plurality of photodetectors, wherein the plurality of photodetectors are optically coupled to scintillation crystals for a PET scanner, comprising: a plurality of differential transimpedance amplifiers with differential inputs and differential outputs, wherein differential inputs for each differential transimpedance amplifier of the plurality of differential transimpedance amplifiers are electrically connected to a photodetector of the plurality of photodetectors; a plurality of level crossing analog-to-digital converters wherein differential inputs for each level crossing analog-to-digital converter of the plurality of level crossing analog-to-digital converters are electrically connected to differential outputs of a differential transimpedance amplifier of the plurality of differential transimpedance amplifiers, wherein each level crossing analog-to-digital converter of the plurality of level crossing analog-to-digital converters, comprises: a plurality of differential comparators with differential inputs and differential threshold inputs, wherein the differential inputs are electrically connected to the output of the differential outputs of the differential transimpedance amplifier of the plurality of differential transimpedance amplifiers electrically connected to the level crossing analog-to-digital converter; and a clock for providing a time stamp, wherein each level crossing analog-to-digital converter of the plurality of level crossing analog-to-digital converters, further comprises a plurality of flip flops, wherein each flip flop receives input from a differential comparator of the plurality of differential comparators and the clock, wherein clock output is provided to a D input of each flip flop and differential comparator output is provided as input to a clock terminal of each flip flop, wherein output of each flip flop provides a digital representation of a shape of a current pulse waveform from a photodetector of the plurality of photodetectors.

Related Links

• Molecular Imaging Instrumentation Lab
• Front-end IC with Fast Timing Project

Patents

• Published Application: WO2013085923
• Published Application: 20150001404
• Issued: 9,244,179 (USA)