Design of high-linear CMOS circuit using a constant transconductance method for gamma-ray spectroscopy system

We propose a novel circuit to be applied to the front-end integrated circuits of gamma-ray spectroscopy systems. Our circuit is designed as a type of current conveyor (ICON) employing a constant-gm (transconductance) method which can significantly improve the linearity in the amplified signals by using a large time constant and the time-invariant characteristics of an amplifier. The constant-gm method is obtained by a feedback control which keeps the transconductance of the input transistor constant. To verify the performance of the propose circuit, the time constant variations for the channel resistances are simulated with the TSMC 0.18μm transistor parameters using HSPICE, and then compared with those of a conventional ICON. As a result, the proposed ICON shows only 0.02% output linearity variation and 0.19% time constant variation for the input amplitude up to 100 mV. These are significantly small values compared to a conventional ICON's 1.39% and 19.43%, respectively, for the same conditions.