Abstract
This paper compares two complementary-metal-oxide semiconductor front-end transimpedance amplifiers (TIA) intended for use in optical biosensors. They are the shunt-feedback and current-mode circuits, the most widely used topologies for wideband operation. The former consists of a three-stage nested-Miller-compensated amplifier in noninverting mode with a photodiode bootstrapping and a controlled voltage gain; the latter comprises a wideband common-gate feedback current mirror coupled to a current-to-voltage conversion stage and two common-source gain stages. The post-layout simulation results show that the shunt-feedback TIA achieves a maximal gain of 112 dBΩ over a 2-MHz bandwidth, whereas the current-mode TIA has a flat gain of roughly 83 dBΩ over a 115-MHz bandwidth. The overall input rms noise of each circuit was 185 pA/√Hz and 53 nA/√Hz, respectively, with power consumptions of 0.5 and 28.6 mW. We find that the shunt-feedback TIA is a better choice for high-resolution low- to mid-frequency applications.
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