A hybrid analog-digital phase-locked loop for frequency mode non-contact scanning probe microscopy
Abstract
Non-contact scanning probe microscopy (SPM) has developed into a powerful technique to image many different properties of samples. The conventional method involves monitoring the amplitude, phase, or frequency of a cantilever oscillating at or near its resonant frequency as it is scanned across the surface of a sample. For high Q factor cantilevers, monitoring the resonant frequency is the preferred method in order to obtain reasonable scan times. This can be done by using a phase-locked-loop (PLL). PLLs can be obtained as commercial integrated circuits, but these do not have the frequency resolution required for SPM. To increase the resolution, all-digital PLLs requiring sophisticated digital signal processors or field programmable gate arrays have also been implemented. We describe here a hybrid analog/digital PLL where most of the components are implemented using discrete analog integrated circuits, but the frequency resolution is provided by a direct digital synthesis chip controlled by a simple peripheral interface controller (PIC) microcontroller. The PLL has excellent frequency resolution and noise, and can be controlled and read by a computer via a universal serial bus connection.
- Publication:
-
Review of Scientific Instruments
- Pub Date:
- January 2014
- DOI:
- 10.1063/1.4862818
- arXiv:
- arXiv:1307.7775
- Bibcode:
- 2014RScI...85a3707M
- Keywords:
-
- Condensed Matter - Mesoscale and Nanoscale Physics;
- Condensed Matter - Other Condensed Matter;
- Physics - Instrumentation and Detectors
- E-Print:
- 7 pages, 5 figures Version 2 contains the full circuit schematic at the end of the article