A novel baseline holder circuit for nuclear imaging front-end electronics

A novel baseline holder circuit (BLH) is proposed here, able to produce a stable baseline level at the output of a typical analog front-end channel for particle detectors, both at dc and at high rate operation. The circuit is suitable to be used in modern high-sensitivity gamma-ray medical imaging systems, where high gain shapers are required. A very low frequency pole, which is fundamental for the stability of the shaper-BLH loop, is realized by means of operational transconductance amplifiers (OTA), which allow to save area, making the circuit suitable for the integration in a standard CMOS technology. Non-linearity effects have been exploited to reduce the baseline shift at high input signal rates, due to the low dc gain of the shaper+BLH system. The circuit has been designed in a standard 0.35 mum CMOS technology, and extensive simulations prove the effectiveness of the adopted solutions. A baseline drift of less than 1.8 mV has been observed for a 30 KHz input rate.