Comparative Study of Trans-linear and Trans-impedance Readout Circuits for Optical Beam Deflection Sensors in Atomic Force Microscopy
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The optical beam deflection sensor remains the most popular force detection method used in atomic force microscopy. With the recent development of short cantilevers, a means for measuring small deflections at high frequencies has become a challenge. Minimizing the noise level of the readout electronics without significantly limiting the detection bandwidth still remains a challenge. In this work, a recently proposed trans-linear readout circuit-based technique, in which necessary analog arithmetics are done in the current domain instead of the voltage domain, is compared to a more traditional trans-impedance readout circuit-based topology. Our developed trans-impedance readout circuit recorded a noise floor of 9.48 × 10−13 V2 Hz−1 compared to 1.41 × 10−11 V2 Hz−1 for the trans-linear readout circuit. Also, the measured −3 dB bandwidth of 11 MHz for the transimpedance readout circuit was slightly higher than the 10 MHz for the trans-linear readout circuit. Trans-impedance readout circuits, with proper circuit design considerations and careful selection of electronic parts, still remain competitive for use in high-speed operations in atomic force microscopy.
KeywordsAtomic force microscopy Cantilever Optical beam deflection Thermal noise
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