Fully digitally controller for cantilever-based instruments
View Patent ↗A controller for cantilever-based instruments, including atomic force microscopes, molecular force probe instruments, high-resolution profilometers and chemical or biological sensing probes. The controller samples the output of the photo-detector commonly used to detect cantilever deflection in these instruments with a very fast analog/digital converter (ADC). The resulting digitized representation of the output signal is then processed with field programmable gate arrays and digital signal processors without making use of analog electronics. Analog signal processing is inherently noisy while digital calculations are inherently “perfect” in that they do not add any random noise to the measured signal. Processing by field programmable gate arrays and digital signal processors maximizes the flexibility of the controller because it can be varied through programming means, without modification of the controller hardware.
1. An apparatus, comprising:
a connection to receive at least one signal indicative of a movement of a cantilever in an atomic force microscope;
a digital circuit, coupled to receive said at least one signal indicative of movement of said cantilever, and carrying out at least one digital operation in said digital circuit on said signal, where said digital circuit includes both a digital signal processor (DSP), and a field programmable gate array, each of said digital signal processor and said field programmable gate array carrying out digital operations on the signal from the cantilever;
said digital circuit carrying out a first set of digital tasks to process the signal from the cantilever in the digital signal processor DSP, which first set of digital tasks include reprogramming the digital signal processor at specified intervals;
said digital circuit carrying out a second set of digital tasks to process the signal from the cantilever in the field programmable gate array, which second set of digital tasks, which do not require re-programming; and
said digital circuit outputting a position correcting signal.
2. The apparatus as in claim 1 , wherein said digital circuit operates at a first time, carrying out a first digital operation on the signal from the cantilever in the digital signal processor (DSP), and operates at least a second digital operation on the signal from the cantilever in the field programmable gate array; and
at a second time, reprogramming operations carried out by the digital signal processor (DSP), so that at said second time, carrying out said second digital operation on the signal from the cantilever in the digital signal processor (DSP), and carrying out at least said first digital operation on the signal from the cantilever in the field programmable gate array.
3. The apparatus as in claim 1 , wherein said digital circuit determines in phase and quadrature components of the signal from the cantilever, and determines magnitude and phase of the in phase and quadrature components, and uses only the magnitude in a digital feedback computation that creates said position correcting signal.
4. The apparatus as in claim 1 , further comprising an external controller, sending communication to the digital circuit, said communication including at least a communication which controls said reprogramming.
5. The apparatus as in claim 4 , further comprising a USB interface, and wherein said communication is over said USB interface.
6. The apparatus as in claim 1 , wherein said first and second digital operations includes a direct digital synthesis.
7. The apparatus as in claim 1 , wherein said first and second digital operation includes a digital low pass filter operation.
8. The apparatus as in claim 1 , wherein said first and second digital operation includes a digital dual phase lock-in mixer.
9. The apparatus as in claim 1 , further comprising a cross point switch, receiving said at least one signal, and enabling said at least one signal to be switched to a plurality of different outputs.
10. The apparatus as in claim 9 , wherein said outputs include a first output comprising said field programmable gate array, and a second output comprising said digital signal processor.
11. The apparatus as in claim 1 , further comprising at least one analog filter, filtering said at least one signal in a location in a signal path prior to said field programmable gate array and said digital signal processor.