Working life is an essential performance index for battery-powered portable radiation detectors. In these applications, an energy-efficient front-end electronic is of great importance. According to the comparison of mostly used amplifiers, an inverter amplifier, which can achieve the highest energy efficiency, is proven to be a good candidate for the analog front-ends. However, such amplifier suffers from low gain which should be improved in the real applications. In addition, the optimum W/L ratios of both PMOS and NMOS transistors in this topology requires careful consideration in the step of noise optimization of the inverter amplifier.

In our group, an energy-efficient front-end readout application-specific integrated circuit (ASIC) based on gain-boost inverter amplifiers for Si-PIN detectors. A tradeoff between noise and power dissipation is performed in the first part. Next, an ASIC prototype including eight-channel analog front-ends is designed in CMOS 0.35 μm mixed-signal 3.3 V process. Each channel mainly includes a charge sensitive amplifier, a slow pulse shaper, an output buffer, a fast shaper and a discriminator. In these blocks excluding the output buffer, all core amplifiers are implemented by the inverter-based amplifier. The die size is 2.1 mm × 2.4 mm.

The simulation results are obtained. The input charge range is 0.2 ~ 24 fC. The equivalent noise charge is 126 e- + 11 e- / pF. The power dissipation is about 0.6 mW/channel. The fabrication of the chip has been finished.

For future work, the ASIC will be measured for performance evaluation. Moreover, the energy efficiency will be improved to satisfy the requirements of portable nuclear instrumentation such as electronic personal dosimeters and energy-spectrum analyzer.

（Authors: B. Wang, Reviewer: W. Gao）