Mathematical Lock-in Detector

The lock-detectors let you modulate and demodulate any of the input and output signals available in the Nanonis controller with frequencies up to 40 kHz. Up to 8 lock-in detector modules can be used independently from each other or synchronized in a phase coherent manner when the generation of multiple frequencies is required. With the multi-frequency option a single module can demodulate up to 8 harmonics of the same signal or independent input signals. The advantage of an internal lock-in detector over an external device is 

• Higher resolution and dynamic range
• Multifrequency and multi-input operation
• Over 120 dB linearity
• Over 100 dB dynamic reserve
• No need for gain and attenuation switching
• Steeper filters (up to 8. order) 
• Up to 8 lock-ins, which can also be synchronized for phase-coherent operation
• Lock-in can be synchronized with OC4. Measure STM current at the exact oscillation frequency of the probe
• Synchronization with data acquisition when using Sync filtering
• Integration avoids errors due to insufficient settling time with slow filter responses 
• no additional noise source through external cabling
• no potential grounding problems
• flexible and simple setup
• Guided filter set-up utility
• Ability to turn on and off the excitation through software during the experiment
• Ability to turn on and off the excitation for different bias ranges through software during the experiment

Applications range from regular dI/dV, CITS, inelastic electron tunneling spectroscopy (IETS), transport experiments, Hall measurements, multi-frequency and multi-demodulator measurements of open and closed loop transfer functions and every type of phase sensitive measurements.

Figure: Spectroscopy with 20 uV AC modulation 100 uV stepsize on 9V output signal (+-10 V output and input range).

Figure: Dynamic reserve measured with a 100 uV input signal. The frequency of the signal is swept from 1 Hz to 10 kHz, while a 10 V, 1 kHz signal is applied on the same input. 100 dB dynamic reserve are easily achieved even very close to the frequency of the interfering signal demonstrating the excellent signal recovery capability of the lock-in module. Harmonics are due to distortion components and not to lock-in filtering.

Figure: Lock-in filter configuration utility. The user specifies a settling time of 1 ms and a maximum error of 5% (The signal reaches at least 95% of the final value after a step). The utility calculates a set of filter cut-offs (time constants) and filter orders which fulfill these requirements