A Mixed-Signal TIA with Input Restoring ADC

Transimpedance amplifiers (TIAs) are used in a wide variety of low noise current sensing frontends. A recently proposed mixed-signal TIA (MS-TIA) is an extension of the integrator-differentiator TIA but including digitization and digital differentiation. However, the MS-TIA requires a high resolution analog-to-digital converter (ADC) in order to maintain good sensitivity. Capacitive digital-to-analog converter (C-DAC) based successive approximation register (SAR) ADCs achieve high resolution at medium bandwidth with good power efficiency, however require a power hungry ADC input driver. In this paper, a combination of the MS-TIA and a modified C-DAC reset scheme is presented, which eliminates the need for a high performance ADC input driver, resulting in major improvements regarding power consumption and linearity. The results are verified by transistor level simulations in a standard 180nm CMOS technology.