基于ToT的PET成像前端读出ASIC设计与实现

Design and Implementation of a Low Noise Front-End Readout ASIC for PET Imaging Based on ToT

To T(Time-over-Threshold)读出策略是在PET成像中利用信号的时间宽度同时获取能量和时间信息的方法。基于To T的前端读出电路具有简单、高效、功耗低、面积小的优点。采用0.35μm CMOS工艺,设计并实现了基于To T的低噪声16通道PET成像前端读出ASIC芯片。为了实现低噪声,在电荷灵敏放大器中采用了输入管尺寸匹配技术,在成形器中采用了低噪声放大器。为了提高响应速度,在电压甄别器中采用了预放大和箝位推挽输出结构。芯片的测试结果表明,能量输入范围为3.5~56 f C,等效噪声电荷为211.4 e^-+16.0 e^-/p F,能量与输入电荷之间的非线性误差小于2%,单通道功耗为1.82 m W。与现有电路相比,该芯片的噪声降低了56.4%,在PET成像系统中具有广阔的应用前景。

To T（ time-over-threshold） readout method,applied in the front-end readout circuits for PET imaging,can obtain both the energy and time information simultaneously by measuring the time width of signal. The front-end readout circuit using To T readout method has the advantages of simple circuit structure,high efficiency,low power consumption and small chip size. A low noise 16-channel front-end readout ASIC using To T readout method was designed and fabricated in a0. 35 μm CMOS process for PET imaging application. In order to reduce the noise,the size matching technique of input transistors was used in the design of charge sensitive amplifier,and a low noise amplifier was adopted in the CR-RC shaper.The discriminator was composed of a pre-amplifier and a clamp push-pull output circuit for increasing the output speed. The chip tested results showed that a typical channel provided an equivalent noise charge（ ENC） of 211. 4 e^-＋ 16. 0 e^-/p F with a power consumption of 1. 82 m W and had achieved an energy information nonlinearity of 2% in the input energy range of 3. 5 f C to 56 f C. Compared with that of the existed approaches using the same To T readout method,the noise of this ASIC was reduced by 56. 4% at least. It could be an alternative approach in the front-end readout circuits for PET imaging system.