The Marvelous Disappearing Capacitor: A Clever Trick to Improve Photodiode Amplifier Performance
This article introduces a clever technique to improve the performance of photodiode amplifiers: bootstrapping. The parasitic capacitance of a photodiode limits its ability to amplify rapidly changing signals. In a traditional transimpedance amplifier (TIA), this capacitance reduces bandwidth. The article analyzes the working principle of a TIA, explaining how the photodiode's parasitic capacitance affects circuit performance. The author presents a bootstrapped circuit using an op-amp and JFET, which effectively eliminates the parasitic capacitance by keeping the voltage across the photodiode terminals virtually the same, significantly improving bandwidth. The article also discusses a variant AC-coupled bootstrapped circuit and provides relevant formulas.