Digital linearization and cancellation of capacitive coupling for a scanning tunneling microscope

Abstract

This article describes the development and test of a digital control loop, to control the tip-to-specimen distance in a scanning tunneling microscope. This digital controller performs a frequency-independent linearization of the gap-to-current relationship, as well as the compensation of the undesirable capacitive coupling between the electrodes of the scan tube and the input of the current-to-voltage converter, two difficulties normally associated with analog controllers. In the described work, the control loop is implemented on an inexpensive fixed-point DSP, processing the signals at a 25 kHz sampling rate.

High-performance digital control system for scanning tunnelling microscopy

“…The parameter adjustment technique that we propose is based on our previous study [1]. Once the junction is established, weak control parameters are used to insure the stability of the system.…”

“…To avoid this problem, the approach proposed here is based on a previous study [1]. It allows the precise identification and compensation of the capacitive coupling at the digital level on the DSP.…”

“…The instrument presented in this document is based on a preliminary study by Paillard et al [1]. The objective of the previous work was to evaluate the use of a fixed-point DSP to lower the cost and enhance the performance of a previous analogue instrument.…”