A novel output baseline holder circuit for CMOS front-end analog channels

We propose a novel CMOS baseline holder circuit, able to keep at a specified value the dc output voltage of typical integrated front-end analog channels coupled to silicon detectors, for both high energy physics and medical imaging applications. The circuit, together with the shaping filter, forms a slow feedback loop. A very low frequency pole is obtained in the feedback path, without using large capacitance values, by exploiting a circuit technique based on the properties of operational transconductance amplifiers. The huge time constant achievable with the proposed technique makes this solution suitable to be applied to high-gain front-end circuits, since the stability conditions can be easily fulfilled. Two different non-linearity effects are exploited to limit the baseline shift which occurs at high signal rates. The circuit has been designed in a standard CMOS 0.35μm technology and the first experimental results obtained from different prototypes show the effectiveness of the proposed solution.