Dark current reduction by an adaptive CTIA photocircuit for room temperature SWIR sensing

We report an adaptive capacitive transimpedance amplifier circuit for room temperature sensing of short wave infrared (SWIR) radiation. The photocircuit reduces junction leakage current by measuring the current across a photodiode held at zero bias. This is critical to enable room temperature SWIR detection using materials with smaller bandgaps (and higher leakage current) such as InGaAs, which are typically operated at cooled temperatures. The transimpedance amplifier incorporates a floating gate current mirror in order to precisely cancel offset using nonvolatile analog storage. We experimentally verify that we are able to precisely tune the input offset and demonstrate a reduction in dark current of an InGaAs photodiode by two orders of magnitude, from 700pA to 2.25pA, when comparing similar adaptive and non-adaptive circuits. These circuits have been fabricated in a standard 0.6μm CMOS process.