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AM/FM Modulation

The HF2LI-MOD is an option for the HF2LI and allows for the direct analysis of sidebands in dynamic AM (amplitude modulation) and FM (frequency modulation) schemes. This option helps the user to precisely measure period variations in the frequency or the amplitude of the application signal. Such schemes are typically applied in oscillator and resonator related setups.

Key Features

* Dual-input and dual-output configuration
* Support for bimodal / multi-modal modulation for AFM
* Amplitude modulation and demodulation of
periodic changing signals (simultaneous)
* Frequency modulation (narrow and wide-band) and
demodulation (narrow-band only) of periodic changing signals
* Harmonic analysis
* Sideband separation (single-sided modulation)
* Option upgradeable in the field

Compatibility to Other Options

* Requires HF2LI-MF Multi-frequency option
* Compatible to HF2LI-PLL Phase-locked Loop option

Amplitude Modulation

For AM, the amplitude of a carrier signal is changing periodically (modulation). In most applications this modulation is small and will thus be subject to noise. The purpose of recovering an AM signal is in measuring the sidebands of the carrier signal. Using a lock-in amplifier improves the signal-to-noise ratio as a result of time integration. The HF2LI-MOD supports simultaneous amplitude modulation and demodulation and can be fully controlled from the graphical user interface of the HF2LI. The generation of AM signals is useful for stimulus generation in the application, but is also handy for system testing purposes.
Frequency Modulation

For FM, the frequency of a carrier signal is changing periodically (modulation). In most applications the modulation is small and thus narrow-band frequency demodulation with a corresponding integration scheme is a suitable signal recovery method. The peak frequency deviation and the modulation frequency must satisfy fp < 0.2 * fm. The HF2LI-MOD also supports FM signal generation without the bandwidth limitations of the demodulation.
User Benefits

* Single-box solution for bimodal, multi-modal measurement challenges
* Tandem demodulation implemented using 1 lock-in amplifier (instead of 2)
* Allows to measure the phase of the demodulated signal (not possible with tandem demodulation)
* Compatibility to HF2LI-PLL allows that fc or fm can be derived from a PLL (exclusive choice)
* Single-sided demodulation allows to account for system asymmetries
* Easy to use: no tandem demodulation, no intermediate signal conversions

Applications

* Atomic Force Microscopy (AFM)
* Kelvin Probe Force Microscopy (KPFM)
* Micro & Nano Electro Mechanical Systems (MEMS, NEMS)
* Laser Spectroscopy

Functional Diagram


Specifications









fc: carrier frequency (Hz) 0.7 µHz - 50 MHz
fm: modulation frequency (Hz) 0.7 µHz - 50 MHz
fs: sideband frequency (Hz) fs = m * fc ± n * fm
fp: peak frequency deviation (FM narrow-band) in Hz fp < 20% * fm
fp: peak frequency deviation (FM wide-band) in Hz fp < 100'000 * fm
fi: modulation index fi = (fc + fm) / fc
Ac: amplitude of carrier (AM and FM) in V Ac < Vrange
Am: amplitude of modulation (AM only) in V Ac + Am < Vrange
m,n: harmonic analysis m,n = 1 - 32

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