A compact, fast, and low-noise current-to-voltage amplifier is built for scanning tunneling microscopy. The amplifier consists of two amplification stages. The first stage performs low-noise transimpedance amplification by using a high performance FET operational amplifier together with a high-ohm feedback resistor of 1GΩ and a parallel trimming capacitor. The ac boosting amplifier in the second stage recovers the higher frequency above the 3dB cutoff of the first stage to extend the maximum bandwidth up to 100kHz. This two-stage current-to-voltage amplifier shows a low current noise below sub-pA rms when tuned to have the bandwidth of around 1kHz. It also guarantees stable frequency response in the presence of 1000pF input capacitance.
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Kim et al. (2005) studied this question.
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