this lock in is analogous to that described above with the description of the analog two phase lock in amplifier fig3 here however the unreliable analog multipliers 24 of fig3 are replaced by digital mixers or multipliers 40 which are immune to effects of temperature frequency and bleed through present in analog multipliers eliminating these as error sources and providing a high fidelity output signal also note that as mentioned above because the entire lock in is digital and is described by software any aspect of it can be upgraded or changed by simply reprogramming the fpga this includes changing the detection scheme entirely for example experiments which require the amplitude of the cantilever to be calculated on a cycle by cycle basis such as a fast ac or intermittent contact mode the lock in programmed into the fpga can be replaced instead with a peak detector program all without the need for modifications or additions to the controller hardware all aspects of all of the signal chains in the disclosed controller involve the fpga accordingly any modifications bug fixes new features etc that might need to be made to any of the signal processing hardware during the normal course of the controller 39 s life can now be made by a simple program change digital signal processor the dsp 32 forming part of the disclosed controller is located inside the controller itself rather than inside the interface computer as has been the case with other.